Surface Forces Apparatus Conference 2014 Cancun, Mexico • August 24-29 International Workshop in
Colloidal and Interfacial Science, Technology, Engineering and Mathematics (CAI-STEM) Fiesta Americana Condesa Hotel • Cancun, Mexico
1
The organizers would like to gratefully acknowledge the support from:
National Science Foundation
Office of Naval Research Global
The world leader in the development of instruments for studying surface forces and other interfacial phenomena
University of California Santa Barbara
The College of Engineering at the University of South Florida
The ACS Journal of Surfaces and Colloids
2
International Workshop in
Colloidal and Interfacial Science, Technology, Engineering and Mathematics (CAI-STEM) Fiesta Americana Condesa Hotel • Cancun, Mexico
3
Topics of the Workshop include:
Session 1: Materials and Processes Chair: Professor Yuval Golan Ben-Gurion University of the Negev
Session 8: Frontiers in Science Inspired by CAI STEM Chair: Professor Norma Alcantar University of South Florida
Session 2: Innovation in CAI-STEM Chair: Professor Noshir Pesika Tulane University
Session 3: Colloidal Systems Chair: Professor Jacob Israelachvili University of California-Santa Barbara
Session 4: Biomedical Applications I Chair: Professor William Ducker Virginia Tech Co-Chair: Professor Deborah Leckband University of Illinois, Urbana-Champaign
Session 5: Biomedical Applications II Chair: Professor Deborah Leckband
Session 9: Structures and Characterization Techniques in CAI-STEM Chair: Professor Tonya Kuhl University of California-Davis
Session 10: Intermolecular Forces I Chair: Professor Suzanne Giasson University of Montreal
Session 11: Nano-Macro / Catalysis Chair: Professor Sylvia Thomas University of South Florida Co-Chair: Professor José Campos Terán Universidad Autonoma Metropolitana / Cuajimalpa
University of Illinois, Urbana-Champaign Co-Chair: Professor William Ducker
Session 12: Intermolecular Forces II
Virginia Tech
Chair: Professor Sylvia Thomas
Session 6: Novel Instrumentation to Characterize Surface Forces, Colloidal Systems and Interfaces Chair: Jarek Majewski Los Alamos National Lab and UC-Davis
Session 7: Distance and Time Regimes in CAI-STEM
4
University of South Florida Co-Chair: Professor Suzanne Giasson University of Montreal
Session 13: Intermolecular Forces III Chair: Professor José Campos Terán Universidad Autonoma Metropolitana / Cuajimalpa
Chair: Professor Marina Ruths
Co-Chair: Professor Suzanne Giasson
University of Massachusetts-Lowell
University of Montreal
Oganizing Committee:
Jacob Israelachvili
Sylvia Thomas
Univesity of California-Santa Barbara
University of South Florida
Noshir Pesika
Tonya Kuhl
Tulane University
University of California-Davis
Marina Ruths University of Massachusetts-Lowell
Phaedra Silva National Autonomous University of Mexico
JosĂŠ Campos TerĂĄn Universidad Autonoma
Deborah Leckband University of Illinois, UrbanaChampaign
William Ducker Virginia Tech
Suzanne Giasson University of Montreal
Metropolitana
Norma Alcantar Yuval Golan
University of South Florida
Ben-Gurion University of the Negev
Jarek Majewski Los Alamos National Lab and UC-Davis 5
Jacob N. Israelachvili “[Water], It’s so small and simple and common, and yet it’s very complicated.” - Jacob Israelachvili, 2006
P
rofessor Israelachvili’s work has focused on understanding the intermolecular and surface forces
and interactions of physical and chemical systems that determine the structure and properties (both static and dynamic) of complex fluid and soft matter systems, i.e., colloids, interfacial phenomena and separations systems in general, and in particular, polymers, selfassembling systems, biomolecules, membranes, in both aqueous electrolyte and nonaqueous liquids. His work has led to new fundamental insights as well as practical advances in technological/industrial areas of engineering and bioengineering such as personal care products (e.g., cosmetics, detergents), paints and coatings, adhesives and lubricants, pharmaceuticals, food emulsions, green processing, composites, solvents, oil and perfume extractions, absorptive materials, etc. His work as also contributed to the understanding and creation of new materials with large length scales from the super-macro (crustal plates and earthquakes) to the sub-nano regime (atomic lattice commensurability effects on adhesion and friction), and time scales, for example, clarifying continuous transitions between solids and liquids. In particular, his recent research into dynamic (non-equilibrium, transient, hysteretic, rate-, time- and history-dependent interactions and phenomena) have opened the way for studying non-equilibrium phenomena that are central to many technological, such as, ‘directed-assembly’ versus ‘self-assembly’, processes and, of course,
6
biological systems and mechanisms. Within this broad area, Professor Israelachvili’s research contributions have had a profound effect on our understanding of the basic underlying molecular forces that control the physics of an enormous class of colloidbased and biological materials. His contributions to the scientific underpinnings of understanding adhesion and bioadhesion phenomena have been enormous. He truly stands out as a modern day giant of the field. In 1971, Israelachvili and Adams published a landmark paper describing the design of an apparatus in which two solid surfaces could be brought in a controlled way to within a few angstroms of one another in order to measure precise force vs distance relationships between the surfaces in vapor or liquid. There are several features of this invention that persist in their power and novelty 40 years later. This surface forces apparatus (SFA) is the only method that can make accurate force-surface separation measurements between two macroscopic surfaces (on which controlled surface chemistries can be constructed), in contrast to atomic force microscopy which uses small, generally uncharacterized, probes. The SFA is also the only method that can directly measure absolute distances (surface separations) directly since the contact position, contact area and surface profiles (e.g., deformed shapes) can be unambiguously and accurately determined. There are major classes of problems in intersurface, colloidal,
biological and frictional interaction that can only be
later of other groups trained by him or inspired by
studied effectively with the SFA. For example, structural
his work, these SFAs have been used to investigate
or lubrication forces in liquids confined between two
interactions between surfaces, molecules, polymers
solids are entirely different from those between a probe
and biological molecules and surfaces, and to shed
and a surface. Only SFA measurements are sufficiently
light on the microscopic mechanisms underlying
well-defined to be compared quantitatively with
them. More recently, the SFA was shown to be able
theory. Israelachvili’s use of his SFA allowed for the
to measure electrochemical reactions (and directly
first direct test of existing theories of interaction forces
visualize adsorption or dissolution in real time) at
—as in the case of the Derjaguin-Landau-Verwey-
the same time as the forces between the surfaces
Overbeek (DLVO) theory of the repulsive electrostatic
were being measured – thus combining simultaneous
and attractive van der Waals forces between particle
measurements of physical forces with chemical
surfaces in aqueous solutions).
reactions. The SFA is now used in many university and industrial research laboratories where it has become
Israelachvili demonstrated the unique and quantitative
a standard tool for measuring adhesion, friction, long-
capabilities of the SFA in a series of papers in the
range colloidal interactions and many other surface
1980’s. His work on structural forces in organic solvents
phenomena.
and water is an excellent example. The existence of oscillatory forces had been predicted by theory before
It is also worth mentioning that Professor Israelachvili
they were first observed by Israelachvili and his team.
is the author of a textbook entitled “Intermolecular
After his careful quantitative measurements, not only
and Surface Forces” (1st and 2nd eds, Academic Press,
were they readily analyzed but compared in detail
1985, 1991; 3rd ed. Elsevier, 2011) that has become
with theory and computation. A more recent example
a classic of modern understanding of such forces, and
has been his recent work on the connection between
a ‘bible’ for the community of surface, colloid and
friction and adhesion hysteresis.
complex fluid scientists. It is widely used as a graduate textbook and in university and industrial research
The capability of the apparatus to study a range
laboratories.
of interesting surface chemistries was shown by Israelachvili’s long series of investigations of supported
Professor Israelachvili has become the leading figure
membranes. He was the first to measure physical
in the area of intermolecular and surface forces, and
forces of membrane fusion and between surface-
enjoys wide recognition among physicists, chemists,
tethered biological ligand-receptor interactions. It
engineers and biologists. His studies and discoveries
has also allowed for the establishment of the limits
using the SFA have revolutionized our conceptual
of applicability of some fundamental interactions
thinking about many aspects of the liquid state and of
(as in the case of tests of the limits of applicability
surface and interfacial forces and dynamics.
of the Kelvin and Laplace Equations of capillary condensation). Finally, as mentioned above, the
It is our pleasure to once again bring the SFA scientific
SFA was used by Professor Israelachvili and his
community together and organize this workshop on his
coworkers to discover completely new types of
honor.
interactions (such as oscillatory solvation forces or the long-range hydrophobic interaction). In the hands of Professor Israelachvili and his colleagues, and
Sincerely,
SFAC2014 Organizing Committee
7
Workshop Administration Nancy Emerson
Chemical Engineering Department University of California, Santa Barbara Santa Barbara, CA 93106 Phone: 805-893-7870 e-mail: emerson@engineering.ucsb.edu
Janet Gillis
College of Engineering Communications & Marketing Dept. University of South Florida Tampa, FL 33620 Phone: 813-785-9359 cell e-mail: janetgillis@usf.edu
Ryan Wakefield
College of Engineering Communications & Marketing Dept. University of South Florida Tampa, FL 33620 Phone: 727-412-2705 cell e-mail: rwakefield1@usf.edu
Marcy Kornfeld
College of Engineering Communications & Marketing Dept. University of South Florida Tampa, FL 33620 Phone: 727-974-1601 e-mail: mkornfeld@usf.edu
8
SFA Conference Schedule
At a Glance: Presentation Schedule-SFA Conference 2014 Time
Sunday August 24 Registration & Tours
8:30- 8:50 8:50- 9:10 9:10- 9:30 9:30- 9:50
Hotel pick up @ 8:00 Coach Tour to Coba OR Tulum
9:50-10:10
Monday August 25
Tuesday August 26
Wednesday August 27
Thursday August 28
Friday August 29
All Talks in Condesa 3
All Talks in Condesa 3
All Talks in Condesa 3
All Talks in Condesa 3
All Talks in Condesa 3
Materials & Processes
Biomedical Applications I
Distance & Time Regimes
Intermolecular Forces I
Intermolecular Forces II
Yuval Golan Raymond Tu Alejandro Gil-Villegas Hugo Christenson
Deborah Leckband Jarek Majewski Delphine Gourdon Bruno Zappone
Carlos Drummond Joelle Frechette Boxin Zhao Derek Chan
Roger Horn Christiane Helm Mark Robbins Shinji Yamada
Anja Royne PatriciaMcGuigan Yu Tian Juan Valentin Escobar
Kazue Kurihara
Noshir Pesika
Dusan Bratko
Magdaleno Medina-Noyola
Jose Luis Arauz-Lara
10:10-10:40
Registration Begins @ 10:00 in Hotel Main
Coffee Break Innovation in CAI-STEM
Coffee Break Biomedical Applications II
Coffee Break Frontiers in Science
Coffee Break Nano-Macro / Catalysis
Coffee Break Intermolecular Forces III
10:40-11:00 11:00-11:20
Reception Area
Manfred Heuberger Venkat Bhethanabotla
William Ducker Roe-Hoan Yoon
Norma Alcantar Herbert Waite
Suzanne Giasson Marina Ruths
Antonio Topete-Camacho Michael Rapp
11:20-11:40
Markus Biesalski
Edgar Vazquez-Contreras
Sylvia Thomas
Hongbo Zeng
Rafael Tadmor
11:40-12:00
Ryan Toomey
George Wren Greene
Matthew Tirrell
Xavier Banquy
Closing Remarks Private Coach Trip to Tulum – Box lunch included
12:00-12:20
Dong Soo Hwang
Dong Woog Lee
Jacob Israelachvili
Jose Campos-Teran
Lunch / Afternoon Activities Welcome Reception
Lunch / Afternoon Activities Dinner
Lunch / Afternoon Activities Dinner
Lunch / Afternoon Activities
Lunch / Afternoon Activities
17:30-18:30
Colloidal Systems
Novel Instrumentation
Structure & Characterization
18:00-18:20
Upper Pool Deck*
Alenka Luzar
Kai Kristiansen
Tonya Kuhl
18:20-18:40
Dinner 18:30 to 19:30
Ilona Kretzschmar
Roe-Hoan Yoon
Joseph Zasadzinski
Drinks and Appetizers
18:40-19:00
Hotel Restaurant of
Miguel Costas
Yong-Jian Wang/Eric Perez
Zhenghe Xu
Upper Pool Deck Conference Banquet
12:20-17:00 17:00-18:00
Dinner
19:00-19:30
Your Choice
Coffee Break
Coffee Break
Coffee Break
19:30-19:50
Meet the Participants
Markus Valtiner
Poster Session I
Poster Session II
19:50-20:10
Exercise
Rolando Castillo
Upper Deck Pool*
Upper Deck Pool*
20:10-20:30
Located in
Victor Breedveld
20:30-20:50
Condesa 3
Stephen Donaldson
21:00-23:00
Networking
Networking
Round Table Discussions
Keynote Speakers Matthew Tirrell Roger Horne
Networking
Networking
Upper Pool Deck* Networking
*In the event of rain events scheduled for the Upper Pool Deck will be held in Condesa 3.
9
Surface Forces Apparatus Conference 2014 Program International Workshop in Colloidal and Interfacial Science, Technology, Engineering & Mathematics (CAI-STEM)
Saturday, August 23, 2014 10:00 10:00
17:00 17:00
Arrival and Registration - Main Reception Area Hospitality Desk and Tour Registration – Foyer Condesa 3
Sunday, August 24, 2014 7:00 8:00 8:00 10:00 10:00 17:30 18:30 19:30 21:00
8:00 17:00 17:00 17:00 17:00 18:30 19:30 21:00 23:00
Breakfast Private coach tour to Chichen Itza buffet lunch included Private coach tour to Coba buffet lunch included Arrival and Registration – Main Reception Area Hospitality Desk and Tour Registration - Foyer Condesa 3 Welcome Reception – Upper Pool Deck (rain venue Condesa 1A) Dinner at the Fiestamericana restaurant of your choice Meet the participants exercise - Condesa 3 / Refreshments - Foyer Condesa Networking
EARLY MORNING SESSION Monday, August 25, 2014, 8:30-10:10 Condesa 3 Session 1: Materials and Processes Chair: Professor Yuval Golan, Ben-Gurion University of the Negev
10
8:30
8:50
8:50
9:10
9:10 9:30 9:50 10:10
9:30 9:50 10:10 10:40
Yuval Golan – “New insights on wet chemical synthesis of functional nanomaterials” Raymond Tu – “Periodically Sequenced Peptides: A New Tool for Nanoscale Materials Synthesis” Alejandro Gil-Villegas - Primitive models of rodlike colloidal particles” Hugo Christenson – “Crystal Nucleation from Vapour on Mica” Kazue Kurihara – “Novel Instrumentation in Surface Forces Measurement” Coffee Break – Foyer Condesa 3
LATE MORNING SESSION Monday, August 25, 2014, 10:40-12:20 Condesa 3 Session 2: Innovation in CAI-STEM Chair: Professor Noshir Pesika, Tulane University 10:40
11:00
11:00
11:20
11:20
11:40
11:40
12:00
12:00
12:20
12:20 17:00
17:00 18:00
Manfred Heuberger – “Confined density fluctuations and surface forces in supercritical CO2” Venkat Bhethanabotla – “Biomarker Quantification at Clinically Relevant Concentrations using Plasmonic Enhancement of Fluoroscence Combined with Surface Acoustic Waves” Markus Biesalski – “Functional Paper-based Materials - from Microcrofluidics to Sensing” Ryan Toomey – “Probing the adhesion of particles to responsive polymer coatings with hydrodynamic shear stresses” Dong Soo Hwang – “Cation-pi Interaction: New Insight for Underwater Adhesion” Lunch and afternoon activities of your choice Dinner at the Fiestamericana restaurant of your choice
EVENING SESSION Monday, August 25, 2014, 18:00-20:50 Condesa 3 Session 3: Colloidal Systems Chair: Professor Jacob Israelachvili, University of California-Santa Barbara 18:00 18:20
18:20 18:40
18:40
19:00
19:00 19:30
19:30 19:50
19:50
20:10
20:10
20:30
20:30
20:50
21:00
23:00
Alenka Luzar – “Metastable Vapor in Janus Nanoconfinement” Ilona Kretzschmar – “Surface Force Measurements: Investigating Packing Order in Janus” Miguel Costas – “Cyclodextrin-SDS Self-Assembled Viscoelastic Films at the Liquid/Air Interface” Coffee Break – Foyer Condesa Markus Valtiner – “AFM and SFA – two complementary techniques: Recent advances and exciting synergies” Rolando Castillo – “Particle dynamics in concentrated suspensions of thread-like supramolecular structures” Victor Breedveld – “Diffusion of Hard and Soft Colloids Confined Between Parallel Walls” Stephen Donaldson – “Development of a general interaction potential for hydrophobic and hydrophilic interactions” Networking
11
EARLY MORNING SESSION Tuesday, August 26, 2014, 8:30-10:10 Condesa 3 Session 4: Biomedical Applications I Chair: Professor William Ducker, Virginia Tech Co-Chair: Professor Deborah Leckband, University of Illinois, Urbana-Champaign 8:30 8:50
8:50 9:10
9:10
9:30
9:30
9:50
9:50
10:10
10:10
10:40
Deborah Leckband – “Biomolecular adhesion in confined geometries” Jarek Majewski – “Endothelial Cells Response to Mechanical Shear Forces Studied by Neutron Scattering” Delphine Gourdon – “Relationship between structure and mechanics in the tumor extracellular matrix and effect on cancer progression” Bruno Zappone- “Contact lubrication of biological surfaces: the role of mucinous glycoproteins” Noshir Pesika – “Load-induced hydrodynamic lubrication of porous polymer films” Coffee Break – Foyer Condesa 3
LATE MORNING SESSION Tuesday, August 26, 2014, 10:40-12:20 Condesa 3 Session 5: Biomedical Applications II Chair: Professor Deborah Leckband, University of Illinois, Urbana-Champaign Co-Chair: Professor William Ducker, Virginia Tech
12
10:40 11:00
11:00 11:20
11:20
11:40
11:40
12:00
12:00
12:20
12:20 17:00
17:00 18:00
William Ducker – “Preventing Bacterial Colonization Using Colloidal Crystals” Roe-Hoan Yoon – “Thermodynamics or Solvophobic Interaction between Hydrophobic Surfaces in Ethanol” Edgar Vazquez-Contreras – “The biological interface of a homodimeric protein” George Wren Greene – “Lubricin protein: a biological, universal anti-adhesive with properties comparable to polyethylene glycol” Dong Woog Lee – “The role of lipid domains in membrane protein adsorption and inter-membrane adhesion between myelin sheaths” Lunch and afternoon activities of your choice Dinner at the Fiestamericana restaurant of your choice
EVENING SESSION Tuesday, August 26, 2014, 18:00-19:00 Condesa 3 Session 6: Novel Instrumentation to Characterize Surface Forces, Colloidal Systems and Interfaces Chair: Jarek Majewski, Staff Scientist, Los Alamos National Laboratory / Adjunct Professor, University of California-Davis 18:00
18:20
18:20 18:40
18:40 19:00
19:00 19:30 21:00
19:30 21:00 23:00
Kai Kristiansen – “The Electrochemical and the 3D Actuator-Sensor attachments of the SFA” Roe-Hoan Yoon – “Direct Force Measurement Involving Deformable Surfaces” Yong-Jian Wang / Eric Perez – “Combining SFA and FRET to monitor the progressive zippering of two biomolecules during force measurements” Coffee Break –Foyer Condesa Poster Session I - Upper Pool Deck (rain venue Condesa 3) Networking
EARLY MORNING SESSION Wednesday, August 27, 2014, 8:30-10:10 Condesa 3 Session 7: Distance and Time Regimes in CAI-STEM Chair: Professor Marina Ruths, University of Massachusetts-Lowell 8:30 8:50
8:50 9:10
9:10
9:30
9:30 9:50 10:10
9:50 10:10 10:40
Carlos Drummond – “Modes of Action in Water-Based Lubricants” Joelle Frechette – “Characterization of the interplay between topography and elasticity on hydrodynamic interactions” Boxin Zhao – “Contact Dynamics of Bio-inspired Polydopamine and Its Nanocomposites Thin Films” Derek Chan – “The coalescence dynamics between oil drops in water” Dusan Bratko – “Surface patterning with ionic functionalization” Coffee Break – Foyer Condesa 3
LATE MORNING SESSION Wednesday, August 27, 2014, 10:40-12:20 Condesa 3 Session 8: Frontiers in Science Inspired by CAI STEM Chair: Professor Norma Alcantar, University of South Florida 10:40
11:00
11:00 11:20
11:20 11:40
11:40
12:00
12:00
12:20
12:20 17:00
17:00 18:00
Norma Alcantar – “Frontiers on dispersant technology: The use of natural materials in oil spill cleanups” Herbert Waite – “An Energy-dispersive Biocoating Made by Mussels” Sylvia Thomas – “Scanning Electron Microscopy and Contact Angle Characterization of Opuntia Ficus-Indica [Mucilage] Nanofibers” Matthew Tirrell “Reversible adhesion with polyelectrolyte brushes tailored via the uptake and release of multi-valent ions” Jacob Israelachvili – “A brief history of concepts and measurements of intermolecular and surface forces” Lunch and afternoon activities of your choice Dinner at the Fiestamericana restaurant of your choice
13
EVENING SESSION Wednesday, August 27, 2014, 18:00-19:00 Condesa 3 Session 9: Structures and Characterization Techniques in CAI-STEM Chair: Professor Tonya Kuhl, University of California-Davis 18:00
18:20
18:20
18:40
18:40
19:00
19:00 19:30 21:00
19:30 21:00 23:00
Tonya Kuhl – “Novel Scattering Methods Reveal Structure of Single Supported Lipid Membranes” Joseph Zasadzinski - “Confocal Imaging of Monolayer Phase Behavior and the Double Layer” Zhenge Xu – “Drainage and forces in thin liquid films between approaching air bubbles and hydrophobic surfaces” Coffee Break- Foyer Condesa Poster Session II - Upper Pool Deck (rain venue Condesa 3) Networking
EARLY MORNING SESSION Thursday, August 28, 2014, 8:30-10:10 Condesa 3 Session 10: Intermolecular Forces I Chair: Professor Suzanne Giasson, University of Montreal 8:30
8:50
8:50
9:10
9:10 9:30
9:30 9:50
9:50
10:10
10:10
10:40
Roger Horn – “Dynamic behavior of the air water interface revealed in bubble-mica collisions studied using the SFA” Christiane Helm – “Measurement of long-ranged steric forces between polyelectrolyte layers physisorbed from 1M NaCl” Mark Robbins – “Contact and Friction of Rough Adhesive Surfaces” Shinji Yamada – “Aging and Stiction of Molecularly Confined Liquid Lubricants” Magdaleno Medina-Noyola – “A Molecular Theory of Equilibriation and Aging” Coffee Break – Foyer Condesa 3
LATE MORNING SESSION Thursday, August 28, 2014, 10:40-12:20 Condesa 3 Room Session 11: Nano-Macro / Catalysis Chair: Professor Sylvia Thomas, University of South Florida Co-Chair: Professor Jose Campos-Teran, Universidad Autonoma / Cuajimalpa
14
10:40
11:00
11:00 11:20
11:20 11:40
11:40 12:00
12:00 12:20
12:20
17:00
Suzanne Giasson – “Adhesion and Friction Between Supported Core Shell pH Sensitive Polymeric Nanoparticles” Marina Ruths – “Nanoscale friction of uniaxially stretched polymer films” Hongbo Zheng – “Understanding Hydrophobic Interactions of Polymer Surfaces” Xavier Banquy – “Interaction forces mediated by structured polymers” Jose Campos-Teran – “Enhanced Catalytic Functionality of Peroxidases – Nanoparticles Complexes by its Surface Immobilization” Lunch and afternoon activities of your choice
EVENING SESSION Thursday, August 28, 2014, 17:00-21:00 Upper Pool Deck (rain venue Condesa 3) 17:00 19:00 21:00
19:00 21:00 23:00
Round Table with drinks and appetizers Banquet / Keynote Speakers Networking
EARLY MORNING SESSION Friday, August 29, 2014, 8:30-10:10 Condesa 3 Session 12: Intermolecular Forces II Chair: Professor Sylvia Thomas, University of South Florida Co-Chair: Professor Suzanne Giasson, University of Montreal 8:30
8:50
8:50
9:10
9:10 9:30 9:50
9:30 9:50 10:10
10:10
10:40
Anja Royne – “The role of surface forces in the slow propagation of brittle fractures” Patricia McGuigan – “Wetting Measurements of Microspheres and Macroscopic Droplets using the AFM” Yu Tian - “Gecko adhesion and its attachment/detachment control” Juan Valentin Escobar – “Force of adhesion on super-solvophovic surfaces” Jose Luis Arauz-Lara – “Dynamic version of Lindemann’s criterion: cage melting in liquids” Coffee Break – Foyer Condesa 3
LATE MORNING SESSION Friday, August 29, 2014, 10:40-12:00 Condesa 3 Room Session 13: Intermolecular Forces III Chair: Professor Jose Campos Teran, Universidad Autonoma / Cuajimalpa Co-Chair: Professor Suzanne Giasson, University of Montreal 10:40
11:00
11:00
11:20
11:20
11:40
11:40 12:00
12:00 17:00
Antonio Topete-Camacho – “Hybrid Nanoplatforms for Multimodal Therapy Diagnosis and of Cancer” Michael Rapp – “Hydrophobic, electrostatic, and dynamic polymer forces at surfactant-modified silicone surfaces” Rafael Tadmor – “Lateral and Normal Adhesion Forces at the Interface between a Liquid Drop and a Substrate” Closing Remarks Private coach tour to Tulum Box Lunch Included
15
Keynote Speakers Banquet Dinner • Thursday, August 28 • 7:00 pm
Matthew Tirrell
Pritzker Director and Professor • Institute for Molecular Engineering • University of Chicago Professor Tirrell received a BS degree in Chemical Engineering from Northwestern University and a PhD in Polymer Science and Engineering from the University of Massachusettes. He began his academic career as an Assistant Professor in the Department of Chemical and Materials Engineering at the University of Minnesota where he later served as Head of the Department. He then moved to the University of California at Santa Barbara where he served as Dean of Engineering. Jacob and Matt have worked together for many years and have many collaborative publications.
After serving as Dean for 10 years, Professor Tirrell moved to the University of California at Berkeley where he served as Chair for the Department of Bioengineering. In 2011 he accepted the position of Founding Pritzker Director of the Institute for Molecular Engineering at the University of Chicago. Matthew Tirrell is a pioneering researcher in the fields of biomolecular engineering and nanotechnology, specializing in manipulation and measurement of the surface properties of polymers, materials that consist of long, flexible chain molecules. His work combines microscopic measurements of intermolecular forces with the creation of new structures. His work has provided new insight into polymer properties, especially surface phenomena, such as adhesion, friction, and biocompatibility, and new materials based on self-assembly of synthetic and bioinspired materials.
Roger Horn Dean of Research Training • Deakin University Professor Roger Horn graduated with BSc (Hons) in physics from Monash University (Australia) followed by a PhD on the physics of liquid crystals from Cambridge University (1977). After a post-doctoral fellowship at the Université de Paris Sud, he joined the Australian National University in 1978 where he worked with Jacob on pioneering surface force measurements. In 1988 Roger moved to the US National Institute of Standards and Technology in Gaithersburg, Maryland, before returning to Australia and joining the University of South Australia in Adelaide in 1992. He established surface force laboratories in both places, modifying the SFA technique for use with silica surfaces at NIST, and a different modification to investigate fluid drop – solid interactions at UniSA. Roger was Deputy Director of the Ian Wark Research Institute at UniSA from the time of its foundation in 1994 until mid-2009. He is now the Dean of Research Training at Deakin University in Melbourne, where he has oversight of research students from across the university. While that role keeps him busy, he still dabbles in research with a small team under his supervision.
16
Abstracts for Oral Presentations: Session 1: Materials and Processes Chair: Professor Yuval Golan, Ben-Gurion University of the Negev
1. New insights on wet chemical synthesis of functional nanomaterials By: Yuval Golan Director, Ilse Katz Institute for Nanoscale Science and Technology Ben-Gurion University of the Negev | Beer Sheva 84105, Israel ygolan@bgu.ac.il The synthesis of anisotropic semiconductor nanoparticles of uniform shape and size, and their assembly into well-defined and useful structures or assemblies is a current major challenge. Ordered arrays of zinc sulfide nanorods and nanowires were synthesized using a single precursor in molten primary alkylamines. The conditions for obtaining distinct morphologies of nanowires and nanorods were identified, depending on the reaction temperature and time, the chain length and the headgroup composition of the surfactant. New insights on the role of different surfactants in determining shape, size and assembly, by means of their distinct interactions with different crystallographic facets of the inorganic nanocrystals will be discussed. More recently, we have studied the effect of various short chain surfactant additives on the formation of semiconductor thin films (e.g., lead sulfide). While addition of most surfactants resulted in the well expected effect of growth inhibition and grain size refinement, other molecules interestingly lead to significant acceleration of the reaction rate and to thick, monocrystalline films.
17
2. Periodically Sequenced Peptides: A New Tool for Nanoscale Materials Synthesis By: Lorraine Leon, Matthew Kubilius and Raymond Tu The City College of The City University of New York New York, New York 10031 tu@ccny.cuny.edu
Periodically sequenced peptides can be confined to interfaces and assembled into patterns that present chemical functionalities with exceptional spatial precision. These rationally designed peptides and polypeptides are rapidly becoming useful components in nanostructured materials for applications ranging from drug delivery to energy storage. This presentation will examine several fundamental aspects of self-assembly and pattern formation of well-defined sheet forming peptides confined at interfaces (see figure). Our approach involves three steps. (1) We design and synthesize simple periodic peptide sequences, yielding surface-active b-strands that self-organize into aggregates to form patterns as a function of the peptide sequence. Rational peptide design allows us to systematically explore the role of hydrophobicity, electrostatics and molecular size on materials properties. (2) We use a set of interfacial characterization tools to examine in intermolecular assembly and supramolecular mechanics of the self-assembled structures. (3) We apply two-dimensional equations of state that define both the phase behavior and the critical surface cvvoncentrations of nascent aggregates at the interface. Subsequently, we can apply these parameters to predict the dimensions of pattern formation and to determine the potential of the peptide assemblies as biomimetic materials.
Figure. A periodically sequenced peptide confines a b-strand structure to the air-water interface, hydrophobic (yellow) and hydrophilic (blue) amino acids.
18
3. Primitive models of rodlike colloidal particles By: Alejandro Gil-Villegas Physical Engineering Department, Sciences and Engineering Division University of Guanajuato, Mexico gil@fisica.ugto.mxt Our understanding of the thermodynamic and structural properties of rodlike colloidal particles can be accomplished by using primitive models that take into account the competing effects between charge and shape of the particles. In this talk we present results obtained by computer simulation for the phase diagrams of systems of charged hard spherocylinders (CHSC) under different conditions, like variations in the location of the charge within particles, presence of a second substance or the effect of gravity. In all the cases, CHSC systems exhibit liquid crystalline (LC) phases that can be controlled or modulated by varying the shape and the charge of the particles, and that can be evidenced obtaining different structural properties, like the structure factor.
19
4. Crystal Nucleation from Vapour on Mica By: James Campbell,1 Fiona Meldrum2 and Hugo Christenson*1 1
School of Physics and Astronomy, 2School of Chemistry
University of Leeds, Leeds LS2 9JT, United Kingdom *h.k.christenson@leeds.ac.uk We have recently experimentally demonstrated with the SFA how heterogeneous crystal nucleation from vapours of organic compounds occurs without the need for any supersaturation.1,2 In a two-step process, supercooled liquid first condenses in the annular wedge formed by the mica surfaces in contact, and is then followed by crystal nucleation in the condensate. In a parallel study we have revealed the frequent presence of acute, pocket-like openings at the base of cleavage steps on the mica surface.3 These pockets have wedge angles of a few degrees and are ideal sites for capillary condensation from vapour. In our most recent work we have dispensed entirely with the SFA and used optical microscopy to study crystal nucleation in the pockets, which turn out to be the preferred nucleation sites on a mica surface. With simple organic compounds the condensation of supercooled liquid (or amorphous solid) can unambiguously be detected from intensity changes in the interference fringes visible in reflected light (see Figure 1), up to 160 K below the melting point. Crystals then nucleate in these condensates and grow out of the pockets if the supersaturation is high enough. Ice deposition on mica from vapour most likely also occurs by nucleation in supercooled water condensates at -41±4 °C. To our knowledge this is the first hint of experimental evidence for a model of ice nucleation proposed nearly 50 years ago by Fukuta [4], and these results are of obvious significance to atmospheric nucleation on aerosol particles, many of which are layered aluminosilicates like mica, e.g., kaolinite, montmorillonite and illite. Figure 1. An open pocket at the base of a step on a mica surface is revealed by interference fringes in reflected light. The bottom edge of the pocket becomes serrated when T < -38 °C due to ice formation in an atmosphere of water vapour. A “snowflake” grows out of the corner of the pocket upon further cooling.
20
[1] T. Kovacs, F.C. Meldrum and H. K. Christenson, J. Phys. Chem. Lett. 2012, 3, 1602-1606. [2] T. Kovacs and H. K. Christenson, Faraday Discuss. 2012, 159, 123-138. [3] J. M. Campbell, F. C. Meldrum and H. K. Christenson, Cryst. Growth Des. 2013, 13, 1915-1925. [4] N. Fukuta, J. Atmos. Sci. 1966, 23, 741-750
5. Novel Instrumentation in Surface Forces Measurement By: Kazue Kurihara Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Japan; Institute for Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Sendai, Japan kurihara@tagen.rohoku.ac.jp
Surface forces measurement is a powerful tool for studying origins of forces operating between molecules and/or surfaces of interest. It also offers a unique, novel surface characterization method, which “monitors surface properties changing from the surface to the bulk (depth profiles)” and provides new insights into surface phenomena. We have recently developed a novel SFA, which is called a twin-path SFA1 and can study opaque samples such as metals. The small displacement of a surface, the bottom one in this study, was measured by the two-beam (twin path) interferometry technique using the phase difference between the laser light reflected by the fixed mirror and that by the mirror on the back of the bottom surface unit. It is possible to determine the distance with a resolution of 0.2 nm in the working range of 5 μm. This apparatus can be used to measure the interactions between opaque samples, and also to extend the scope of the surface forces measurement. We have constructed a spectroscopic SFA2,3 and an electrochemical SFA4,5. This lecture describes these recent developments. We also developed the resonance shear measurement (RSM) for studying confined liquids. Recent application of RSM will be described too.
References 1) H. Kawai, H. Sakuma, M. Mizukami, T. Abe, Y. F kao, H. Tajima, K. Kurihara, Rev. Sci. Instrum., 79, 043701 (2008). 2) D. Fukushi, M. Kasuya, H. Sakuma, K. Kurihara, Chem. Lett. 40, 776 (2011). 3) Y. Saito, M. Kasuya, and K. Kurihara, Chem. Lett., 41, 1282¬1284 (2012). 4) T. Kamijo, M. Kasuya, M. Mizukami, K. Kurihara, Chem. Lett. 40, 674-675 (2011). 5) M. Kasuya, K. Kurihara, Langmuir, 30, 7093-7097 (2014). 6) S. Nakano, M. Mizukami and K. Kurihara, Soft Matter, 10, 2110 (2014) 21
Session 2: Innovation in CAI-STEM Chair: Professor Noshir Pesika, Tulane University
1. Confined density fluctuations and surface forces in supercritical CO2 By: Erich Schurtenberger and Manfred Heuberger Advanced Fibers, Swiss Federal Laboratories for Materials Science and Technology Supercritical CO2 is an interesting solvent because it is non-flammable, chemically inert and nontoxic. At elevated pressures it exhibits liquid-like density, gas-like diffusivity and its surface tension is very small. Supercritical CO2 (scCO2) is already applied in a range of industrial applications as environmentally friendly solvent, as plasticizer in polymer processing or as low surface energy reaction medium. We present the first direct measurement of surface forces across supercritical carbon dioxide; the forces are particularly sensitive to the exact locus in the phase diagram around the critical point; long-range attractive surface forces are detected not just near the critical point, but also along the supercritical extension of the coexistence line, which is arguably called the â&#x20AC;&#x153;supercritical ridgeâ&#x20AC;?. Using a precisely adjustable model slit pore confining a stratum of CO2, our experiment can measure the change of thermodynamic potential and also detect changes in refractive index (mass density) across the confined CO2. The model slit pore is realized between two atomically smooth mica surfaces in a highpressure extended surface forces apparatus eSFA. Our data suggest that upon increasing confinement thermal fluctuations of higher density are selectively depleted, which leads to the observation of a timeand space- averaged density reduction in the confined film. Experimental evidence of this confinement effect has consequences for the theoretical understanding as well as technological applications of CO2 in porous materials. We would like to make use of such surface forces in polymer pores to change the foaming behavior of polymer melts processed under supercritical CO2. Ideally this could allow us to reduce foaming upon melt expansion and use CO2 as plasticizer for synthetic fiber melt spinning. 1. Schurtenberger, E. and M. Heuberger, The extended surface forces apparatus. Part IV: Precision Static Pressure Control. Review of Scientific Instruments, 2011. 82(103902): p. 8. 2. Schurtenberger, E. and M. Heuberger, Supercritical Casimir Effect in Carbon Dioxide. Journal of Supercritical Fluids, 2012. 71: p. 120-126. 22
2. Biomarker Quantification at Clinically Relevant Concentrations using Plasmonic Enhancement of Fluoroscence Combined with Surface Acoustic Waves By: Samuel Morrill1, Mandek Richardson1, Subramanian Sankaranarayanan2 and Venkat Bhethanabotla1 1
Department of Chemical & Biomedical Engineering
University of South Florida, 4202 E. Fowler Avenue, Tampa, Florida 33620 2
Center for Nanoscale Materials
Argonne National Laboratories, 9700 S Cass Avenue, Argonne Illinois 60439
Immunofluorescence assays are commonly used for the detection of proteins and antigens. For biomarker quantification at clinically relevant levels, these assays suffer from weak fluorescence signals causing poor detection limits, background signals causing noise and false-positives, and slow attachment times of antigens to antibodies. In this work, plasmonic enhancement of fluorescence is used to strengthen the optical signal intensity by a factor as large as 1000, and surface acoustic waves are used to remove interfering signals from non-specifically bound proteins and to speed up the rate of attachment. A biosensor device which combines both phenomena was realized to demonstrate a rapid and reliable immunofluorescence assay at clinically relevant concentrations. Plasmonic enhancement of fluorescence was understood and optimized within finite difference time domain (FDTD) calculations. A multi-scale model coupling a continuum scale fluid-solid interaction finite element model with atomistic simulations is used to understand the influence of acoustic streaming forces and the removal mechanism of the non-specifically bound proteins at the solid-fluid interface of the surface acoustic wave biosensor device.
23
3. Functional Paper-based Materials - from Microcrofluidics to Sensing By: Markus Biesalski1,2 Technische Universit채t Darmstadt, Department of Chemistry, Laboratory of Macromolecular Chemistry & Paper Chemistry, Darmstadt, Germany 1
Technische Universit채t Darmstadt, DFG-Excellence Center of Smart Interfaces (CSI), Darmstadt, Germany 2
Throughout the last decade, we have witnessed an increasing amount of studies, addressing the use of the low-cost material paper in high-tech applications, progressing from substrates for blood-typing, to enzymatic reaction engineering, low-cost DNA-sensors and purification of antibodies. Paper is a particularly attractive substrate for such applications due to interesting advantageous properties: (i) no external pumps are needed for the fluid transport due to capillary forces, (ii) paper can be considered as low-cost material consisting of the earths most abundant material: cellulose, and (iii) the lignocellulosic fiber surface can be chemically modified by various chemical means. In this talk, I will give an overview about how functional copolymers can be used to tailor paper substrates in a fashion suitable for different applications from paper based microfluidics to sensors and actuators. In addition I will show that by using simple and established papermaking technologies, it is possible to design fluidic timers for microfluidic applications. In brief, lab-sheets consisting of different fiber sources (eucalyptus sulfate and cotton linters pulp) and varying porosities are being designed and further modified with small millimeter-scaled channels using hydrophobic barriers consisting of fiber-attached, hydrophobic polymers. Parameters that influence fluid flow in such papers such as fiber source, paper grammage, and channel width on the flow rates through the channel were studied. I will show that our results suggest that accurate control of fluid transport processes with standard filter papers is complex, however, by controlling the paper sheet porosity through varying the density of the fibers in the sheet, affords the fabrication of chemically identical sheets whereby capillary flow can be modulated over a broad range of technically important flow rates.
24
4. Probing the adhesion of particles to responsive polymer coatings with hydrodynamic shear stresses By: Ryan Toomey and Gulnur Sanden 1
Department of Chemical & Biomedical Engineering
University of South Florida, 4202 E. Fowler Avenue ENB 118, Tampa, Florida 33620 Toomey@usf.edu
Lower critical solution temperature (LCST) polymers in confined geometries have found success in applications that benefit from reversible modulation of surface properties, including drug delivery, separations, tissue cultures, and chromatography. Fundamental studies of adhesion to LCST surfaces have been carried out with both the surface forces apparatus and colloidal probe AFM, often with contradictory results. In this talk, I will discuss the adhesion of polystyrene microspheres to cross-linked poly(N-isopropylacrylamide), or poly(NIPAAm) coatings, as studied with a spinning disk method. This method applies a linear range of hydrodynamic shear forces to physically adsorbed microspheres along the radius of a coated disk. Quantification of detachment is accomplished by optical microscopy to evaluate the minimum shear stress to remove adherent particles. Experiments were performed to assess the relationship between the surface chemistry of the microsphere, the thickness and cross-link density of the poly(NIPAAm) coating, the adsorption (or incubation) time, and the temperature on the detachment profiles of the microspheres. Results suggest that slow dynamic processes in the poly(NIPAAm) films strongly influence the detachment shear stresses. Moreover, whether an adsorbed microsphere can be released (through a modulation in the swelling of the poly(NIPAAm) coating by temperature) depends on both the surface chemistry of the microsphere and the extent of the adsorption time. Finally, the results show that the structure of the poly(NIPAAm) coating can significantly affect performance, which may explain several of the conflicting findings that have been reported in the literature.
25
5. Cation-pi Interaction: New Insight for Underwater Adhesion By: Dong Soo Hwang1, Hongbo Zeng2 1
School of Environmental Science and Engineering & School of Interdisciplinary Bioscience and
Bioengineering, Pohang University of Science and Technology (POSTECH), Pohang, S. Korea 790-784 Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 2V4, Canada
2
hongbo.zeng@ualberta.ca Cation-pi Interactions are one of the most important noncovalent interactions in biological systems. Cation-pi Interaction that is widely present between an electron-rich system (e.g., Phe, Tyr, Trp) and adjacent cations (e.g., Na+, K+) or species containing positive charges (e.g., Lys, Arg) in the physiological conditions of the living organisms. Recent studies on adhesion mechanism of mussel adhesive proteins by using an Surface forces apparatus (SFA) suggest Cation--Interaction as an important underwater adhesion mechanism. In this presentation, the mechanical nature of Cation-pi Interactions in aqueous media was probed directly using a surface forces apparatus (SFA) for the first time. Strong and reversible underwater cohesions between two opposing mfp-1 films which do not have any positively charged amino acid residues in testing pH were measured even with passivation of DOPA. Cation--pi? interaction, which act between an electron-rich system (egs. Tyr, Dopa, Phe, Trp) and adjacent cations (egs.,n-terminus amine, Lys, Arg, His), was suggested as a main contributor to the cohesive nature of two opposed mfp-1 layers. SFA measurements and theoretical simulations also confirm that Cation-pi Interactions in aqueous media depend on the type and concentration of positively charged ions (Lys, NH4+, K+, Li+, Na+) and type of aromatic side groups (indole, phenol, benzene) present in solution. Therefore, deployment of cation-interactions can be a complementary strategy for the successful underwater adhesion of mussels.
References 1. Lu, Q, Oh DX, Lee Y, Jho YS, Hwang DSZeng HB . Nanomechanics of cation-pi interactions in
3. Hwang DS, Zeng H, Lu Q, Israelachvili JN, Waite JH. Adhesion mechanism in dopa-deficient foot
aqueous solution. Angewandte Chemie.Int. Eds., 2013, 52, 3944-8 2. Lu Q, Hwang DS, Yan L, Zeng H. Molecular interactions of mussel protective coating protein, mcfp-1, from Mytilus californianus. Biomaterials, 2012, 33,1903-.
protein from green mussels. Soft Matter, 2012, 8, 5640-5648. 26
Session 3: Colloidal Systems in CAI-STEM Chair: Professor Jacob Israelachvili, University of California-Santa Barbara University
1. Metastable Vapor in Janus Nanoconfinement By: Alenka Luzar Department of Chemistry, Virginia Commonwealth University aluzar@vcu.edu We study competition between liquid and vapor states of water confined between diametrically different surfaces, one hydrophilic and the other strongly hydrophobic (Janus interface). Using a mean field model and Molecular Dynamics simulations, we demonstrate that vapor bubbles can persist in the confinement in a long-lived metastable state. In contrast to well-known metastability of the liquid with respect to capillary evaporation, metastable confined vapor has so far not been anticipated, as infiltration does not involve the formation of new liquid-vapor interfaces. In the case of a Janus interface, however, we show that the liquid-vapor area passes through a maximum during infiltration. This counterintuitive phenomenon provides a new mechanism for water mediated (Laplace) attraction between solutes with contrasting polarities that can play an important role by enabling adhesion between polar and nonpolar particles in both biophysical systems and heterogeneous nanomaterials.
Work supported by NSF; Collaborators: Joshua Driskill, Davide Vanzo and Dusan Bratko.
27
2. Surface Force Measurements: Investigating Packing Order in Janus Particle Monolayers By: Ilona Kretzschmar Department of Chemical Engineering, the City College of New York, City University of New York, 140th ST. and Convent Ave., New York, NY 10031
Close-packed particle monolayers have shown promise as substrates for surface-enhanced Raman spectroscopy and other optically active coatings.[1] Hexagonal close packing is the favorable structure, when particles of the same size, shape, and surface charge are convectively assembled into monolayers. In contrast, polystyrene sulfonate (sPS) spheres with a hemispherical gold cap, so-called Janus particles, are found to form randomly packed monolayers.[2] Understanding the cause of this observed phenomenon may lead to an engineering parameter that controls the degree of randomness in the monolayer potentially leading to monolayers with tunable optical properties. It is hypothesize that the packing order observed in the Janus particle monolayer is a function of the interaction forces between adjacent particles and the substrate. We will report on the surface forces measured between solid gold and solid sPS particles of 2.4 micrometer diameter and a glass substrate in the presence of electrolyte solutions with varying ionic strengths using colloidal atomic force microscopy. In addition, sPS and Janus particle monolayers have been convectively assembled under ionic and non-ionic conditions using drop casting of sPS and Janus particle solutions onto a silicon wafer. Scanning electron microscopy is used to determine the particle packing and orientation.
[1] Two-Dimensional Array of Silica Particles as a SERS Substrate D. Christie, J. Lombardi, and I. Kretzschmar J. Phys. Chem. C, 2014, 118, 9114-9118 [2] Surface Force Measurements: Investigating Packing Order in Janus Particle Monolayers F. Guzman, E. Cranston, M. Rutland and I. Kretzschmar IRES 2009 Summer Program report.
28
3. Cyclodextrin-SDS Self-Assembled Viscoelastic Films at the Liquid/Air Interface By: Jorge Hernández,1 José Campos,2 Ángel Piñeiro,3 Richard Campbell,4 Miguel Costas1 Laboratorio de Biofisicoquímica. Departamento de Fisicoquímica. Facultad de Química. Universidad Nacional Autónoma de México. Cd. Universitaria. México D.F. 04510, México. 1
Departamento de Procesos y Tecnología, Universidad Autónoma Metropolitana, Unidad Cuajimalpa, México D.F. 05348, México. 2
Departamento de Física Aplicada, Facultad de Física, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain. 3
4
Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France.
Native α-cyclodextrin (α-CD) and sodium dodecyl sulfate (SDS) are found to spontaneously form
viscoelastic films at aqueous solution/air interfaces. Temperature and the relative amounts of α-CD and SDS strongly modify the viscoelastic properties of such films. Using isothermal titration calorimetry the distribution of species in the bulk solution were determined. A large number of surface techniques have been used to characterize the films, namely shape-response measurements to volume perturbations on drop hanging from a capilary, neutron reflectivity, Brewster angle microscopy, dynamic surface tension, ellipsometry and the continious injection and oscillating drop methods to quantify the viscoeslastic behavior. It was found that the films are mainly formed by α-CD2-SDS1 inclusion complexes, reflecting the bulk solution distribution of species.
29
4. AFM and SFA – two complementary techniques: Recent advances and exciting synergies By: Markus Valtiner Max-Planck-Institut für Eisenforschung GmbH Max-Planck-Straße1 D-40237 Düsseldorf
In this contribution I will discuss recent exciting experimental advances towards probing reactive interfaces and non-equilibrium processes in real time combining the electrochemical Surface Forces Apparatus (EC-SFA) and Atomic Force Microscopy (AFM) as two complementary techniques. The presentation will try to give an overarching comparison of AFM and SFA experiments, in particular with respect to differences, similarities as well as synergistic aspects. First, we will discuss how equilibrium SFA and non-equilibrium AFM force probe experiments compare for similar systems. Here, experiments in high salt concentrations (> 100 mM up to pure salts) will be discussed, with a focus on electric double layers, and in particular the structuring in the inner Helmholtz-plane (structural forces). Second, recent experiments of non-equilibrium i.e. actively progressing electrochemical processes such as oxidation/ reduction of noble metal interfaces in EC-SFA will be discussed. EC-SFA can be used as a complementary tool to spectroscopic ellipsometry, providing detailed information about growing/ dissolving thin (below 1nm) films. In addition, charge generation or depletion during active processes leads to non-equilibrated electric double layers, which can be much different from equilibrated double layers. Effective decay lengths of non-equilibrated double layers can be 1-2 orders of magnitude larger compared to equilibrium situations. Finally, we will discuss and compare adhesion measurement with SFA, and surface-surface as well as surface-to-molecule bond breaking under non-equilibrium conditions using AFM experiments.
30
5. Particle dynamics in concentrated suspensions of thread-like supramolecular structures By: Rolando Castillo Institute of Physics, UNAM. P. O. Box 20-364, Mexico D. F. 01000 We study the Brownian motion of probe particles embedded in three systems embedded with threadlike supramolecular structures: wormlike micelles (zwitterionic TDPS/SDS/brine, CTAB/NaSal/water), bacteriophages (fd), and slightly interconnected polymers (acrylamide-bisacrylamide/water). The motion of the probe particles was tracked with diffusing wave spectroscopy, and the mean square displacement of these particles as a function of time was obtained. This allowed us to obtain the long-time diffusion coefficient for microspheres moving in the threadlike network, and the cage size. The bulk mechanical susceptibility of the fluid determines the response of the probe particles excited by the thermal stochastic forces. As a consequence, the mean square displacement curves allowed us to calculate the elastic (storage) and the viscous (loss) moduli as a function of the frequency. The results reflect the structural differences among these relatively similar systems. In addition, for the micelle system we estimated the characteristic lengths of the network as the mesh size, the entanglement length, the persistence length, and the contour length. In the fd suspension, a comparison was made between measured and calculated relaxation moduli. Calculations were made employing a theory for highly-entangled isotropic solutions of semiflexible polymers using a tube model, where various ways of calculating the needed parameters were used. Although some features are captured by the model, it is far from the experimental results, mainly at high frequencies. In the polymeric system, the particle mean square displacement was analyzed in terms of a model developed by us to understand the particle motion in a polymeric network that constrains the particle movement based on a Fokker-Planck equation. The model reproduces well the observed experimental features. We also present that the colloidal dynamics in complex fluids with absorption using diffusing wave spectroscopy seem to be slower producing incorrect results, if corrections are not considered. We propose an expression for the time-averaged light intensity auto-correlation function that correctly describes the time fluctuations, where the diffusion approximation accurately describes the light propagation within the sample. The time fluctuations of the scattered light were related to the mean square displacement of the embedded particles. The correct colloidal dynamics in the turbid media can be evaluated and experimentally assessed. It opens the possibility of doing micro-rheology with optical methods in systems where absorption cannot be avoided. 31
6. Diffusion of Hard and Soft Colloids Confined Between Parallel Walls By: Sricharan Yarlagadda, Jae Kyu Cho & Victor Breedveld School of Chemical & Biomolecular Engineering Georgia Institute of Technology Atlanta, GA 30332-0100 The presence of solid walls imposes constraints on the flow field and thus affects the hydrodynamic mobility of a nearby moving particle. As a result, Brownian diffusion of colloids in suspension is suppressed significantly near walls. For hard, spherical colloids, this effect has previously been studied both experimentally and theoretically. The mobility of soft colloidal systems, which in contrast are characterized by being deformable, compressible and/or porous, has remained relatively unexplored, in spite of their abundance and relevance for various applications. Examples of such systems include droplets in microfluidic devices, cells and nanoparticles in microvascular environments, and multiphase flow in porous media for enhanced oil recovery. We will present experimental studies of Brownian diffusion of hard and soft colloids in a quiescent fluid under varying degrees of confinement between parallel walls. To this end, uniform, quasi-2D suspensions were created in a confinement cell by using monodisperse hard silica particles as spacers between glass slides. Polystyrene beads were used as model hard colloids, while microgel particles (porous, compressible and deformable) and toluene-swollen polystyrene beads (deformable) were used as two relevant examples of model soft colloids. By varying the sizes of spacers and colloids, a wide range of degree of confinement could be explored, which sets this study apart from prior work. Our experiments show that the hard sphere hindrance effects are in excellent agreement with analytical predictions from literature, across a much wider range of confinement than previously explored experimentally. In addition, the behavior of soft colloids under confinement, both microgels and droplets, differs significantly from their hard colloidal counterparts, even at relatively low degrees of confinement. Soft colloids exhibit unusually high mobility under confinement, even when the wall spacing is strikingly close to or even exceeds the particle diameter in unconfined flow. We will discuss the mechanisms that are responsible for the enhanced mobility of the microgels and droplets, which have fundamentally different softness characteristics.
32
7. Development of a general interaction potential for hydrophobic and hydrophilic interactions By: Stephen Donaldson, Anja Røyne, Kai Kristiansen, Michael Rapp, Matthew Gebbie, Saurabh Das, Bradley Chmelka, Markus Valtiner, and Jacob Israelachvili University of California Santa Barbara, Department of Chemical Engineering
By performing direct surface force measurements, we have derived an interaction potential for the contribution of the attractive hydrophobic interaction as two surfactant bilayers approach, stress (causing the bilayers to thin and expose hydrophobic area), rupture, fuse, and are then separated from adhesive contact. The model quantitatively describes the complex interaction potential during bilayer hemifusion, including the long range forces, short range forces, hydrophobic breakthrough point, and final hydrophobic adhesion at contact. Between the bilayers, the hydrophobic interaction potential depends on the amount of exposed hydrophobic area, which progressively increases as the bilayers are further stressed. Generalization of the interaction potential results in a non-dimensional number, the “Hydra parameter” with symbol Hy, which can account for the amount of hydrophobicity at a given interface. Hy = 1 for a fully hydrophobic interaction (corresponding to an interfacial energy of 50 mJ/m2 for a hydrocarbon surface in water), and Hy = 0 for no hydrophobic contribution. For Hy < 0, the equation also naturally accounts for hydrophilic interactions, i.e., the repulsive steric-hydration force between hydrophilic surfaces, where now the magnitude of the repulsion depends on the degree of hydration. An exponential decay length of ~1 nm is proposed for both the attractive (hydrophobic) and repulsive (hydration) forces. The interaction potential is tested for a variety of surfaces and parameters: surfactant bilayers and monolayers and self-assembled hydrophobic polymer surfaces will be discussed. A new picture is emerging that suggests that both hydrophobic and hydrophilic interactions can be described by a single unifying equation, suggesting a similar mechanism for both interactions, for example, a depleted water density (and/or decrease of the hydrogen bonding order parameter) near hydrophobic surfaces.
33
Session 4: Biomedical Applications 1 Chair: William Ducker, Virginia Tech University Co-Chair: Deborah Leckband, University of Illinois, Urbana-Champaign
1. Biomolecular adhesion in confined geometries By: Deborah Leckband Cell adhesion proteins function in narrow gaps between cell membranes and adhesive substrates, and recent findings suggest that the resulting reduction in configurational entropy in these confined spaces can enhance protein interactions that are not detected in measurements of protein binding in solution. Surface force measurements appear to provide direct evidence for confinement-enhanced protein interactions that have demonstrable impact on the formation of cell-cell adhesions. Force measurements of cell adhesion proteins, cadherins, detected multiple protein-protein binding interactions. Two of three interactions detected with the SFA are also measured in solution binding measurements. However, a third interaction, which is not detected in solution or by crystallography, contributes to cell-cell binding and appears to be important for the formation of tight intercellular junctions. These findings demonstrate that the unique force sensitivity, distance resolution, and geometry of SFA measurements reveal unique biophysical mechanisms adhesion protein function that are not detected by tradition solution based methods, but are physiologically significant.
34
2. Endothelial Cells Response to Mechanical Shear Forces Studied by Neutron Scattering. By: J. Majewski1, A. Junghans1, L. Pocivavsek3, MJ Waltman1, N. Zebda2, K. Birukov2 1 Lujan Neutron Scattering Center, (LANSCE-LC), Los Alamos National Laboratory 2 University of Chicago, +University of Pittsburgh 3 Bioenergy & Environmental Science, B-8, Los Alamos National Laboratory We report on the first-ever successfully completed neutron reflectometry experiments on living human endothelial cells under fluid mechanical shear stress that provide valuable insight on the boundary layer dynamics of complex bio-medical systems, which could lead to advances in the treatment of atherosclerosis and other disorders associated with the cardiovascular system. Key in controlling the two functions of the vascular system - selective vascular resistance and antithrombotic properties - is a monolayer of cells termed endothelium that covers the inner surface of blood vessels. Given that the vascular system is under constant fluid mechanical stress due to its nature as a fluid conduction system, it is not surprising that mechanical forces influence endothelial cell function and response. It has been shown that endothelial cell monolayers grown on solid substrates and exposed to shear rates activate a cascade of biochemical pathways that restructure the internal cytoskeleton of the cell and cell-substrate anchoring points called focal adhesions. Shear induces the cells to undergo a symmetrybreaking transition whereby the entire cell monolayer aligns along the direction of shear. Another highly studied area involving endothelial cells and fluid mechanical shear stress involves pathologic buildup of lipids in arterial walls: atherosclerosis. Previous worked could show that the distribution of atherosclerotic lesions in the vascular network corresponded to areas of turbulent blood flow occurring at bifurcation points in the arterial tree. Most existing work in endothelial mechano-biology has focused on single cells and even single molecules and protein complexes. Yet the collective behavior of the monolayer of cells has been less well explored. It is clear however that endothelial cells makes strong lateral connections between each other and that these connections change as a function of mechanical stress. Neutron reflectometry is able to reveal information that is inaccessible to other techniques, e.g. the structure and composition of the boundary layer between the endothelial cells and the supporting substrate. The thickness of such a layer, its composition (protein rich vs. fluid rich), and most importantly how its composition and structure changes as a function of shear, is of high significance for the understanding of the fluid mechanical shear stress on endothelial cells and the effects this has on overall blood vessel health. 35
3. Relationship between structure and mechanics in the tumor extracellular matrix and effect on cancer progression By: Delphine Gourdon Cornell University The extracellular matrix protein fibronectin (Fn) forms a fibrillar network that tightly controls not only physiological cell behavior such as early tissue development and wound healing but also the progression of numerous diseases such as cancer. In particular, it has been recently shown that breast cancer-associated stromal cells up-regulate the quantity of deposited Fn and modify its conformation by increasing Fn fiber stretching and unfolding [1]. However, (i) the correlation between structural and mechanical properties of tumor-associated Fn and (ii) their effect on tumor vascularization (angiogenesis) are still undefined. Here we first used the Surface Forces Apparatus to measure the Young’s modulus of the initial (24 hours) Fn matrix deposited by 3T3-L1 pre-adipocytes preconditioned with tumor soluble factors derived from an aggressive breast cancer cells line (MDA-MB-231). Our results (obtained on decellularized matrices) reveal that tumor soluble factors promote matrix stiffening (62%) and thickening (38%) with respect to control matrices. The stiffening of these tumor-associated Fn matrices (no other extracellular matrix component such as collagen was detected) was then shown to correlate with increased molecular unfolding of Fn within matrix fibers, as determined by Förster Resonance Energy Transfer. Finally, changes in cell adhesion and proangiogenic capability were tested by reseeding new (untreated) 3T3L1s on these tumor-associated matrices and assessed via cell counting and quantification of vascular endothelial growth factor (VEGF) secretion, respectively; and αv and β1 integrin-blocking antibodies were utilized to examine altered integrin specificity as a potential mechanism of altered cell-matrix signaling. Our findings indicate that stiff and unfolded tumor-associated Fn matrices decrease adhesion while enhancing VEGF secretion by breast cancer-associated adipogenic stromal cells, and that altered integrin specificity is likely responsible for such changes. Therefore, our findings suggest that both the mechanical and conformational properties of tumor-associated Fn significantly alter cell adhesion and further dysregulate the downstream proangiogenic behavior of surrounding cells. These results not only have important implications for our understanding of tumor angiogenesis but also enhance our knowledge of cell-matrix biomechanical interactions that may be harnessed for other applications including advanced tissue engineering approaches.
[1] E.M. Chandler, M.P. Saunders, C.J. Yoon, D. Gourdon, and C. Fischbach Adipose progenitor cells increase fibronectin matrix strain and unfolding in breast tumors. Phys. Biol. 8(1), 015008 (2011). 36
4. Contact lubrication of biological surfaces: the role of mucinous glycoproteins By: Bruno Zappone,1* Jacob N. Israelachvili 2 1 2
Consiglio Nazionale delle Ricerche, CNR-IPCF, Università della Calabria, Rende 87036, Italy
Department of Chemical Engineering and Materials Department, University of California, Santa Barbara, CA 93106, USA
*Presenting author: Bruno Zappone, email: bruno.zappone@cnr.it, Phone: +39 0984 496120, Fax: +39 0984 494401.
Wet tissues of the human body such as articular cartilage, cornea, digestive tracts and reproductive organs show much better lubrication in aqueous fluids than most artificial materials. Effective contact lubrication originates from the complex interplay between water and specialized surface-active molecules, among which mucinous glycoproteins and hyaluronic acid (HA) play a prominent role. Using a Surface Force Apparatus, we have measured the normal and friction forces acting between two solid surfaces bearing monolayers of adsorbed HA and lubricin mucin, the two most abundant lubricating macromolecules at the cartilage surface. Lubricin has a ABC triblock structure with a long, unstructured, strongly hydrophilic and negatively charged B block. When B is not adsorbed on the substrate, but anchored via the globular end blocks A and C in the form of a dense ‘brush-like’ monolayer, lubricin completely removes adhesion and reduces substrate wear, drastically reducing the friction coefficient to µ ≈ 0.03 between two solid hydrophilic surfaces [1]. Lubricin binds to HA and reduces friction and wear between adsorbed HA layers, suggesting a synergistic interaction in lubricating the contact between cartilage
(a) Schematic representation of a mucin molecule showing the sugar moieties of lubricin. (b) AFM image of a lubricin dimer.
surfaces [2]. Ongoing SFA nanotribology studies on oral and gastric mucins are expected to deepen our understanding of the molecular scale mechanisms of boundary bio-lubrication and guide the development of bio-inspired artificial lubricants and coatings for water-based applications. [1] B. Zappone et al., Biophys J 92 (2007) 1693; Langmuir 24 (2008) 1495. [2] S. Das et al., Biomacromolecules 14 (2013) 1669
37
5. Load-induced hydrodynamic lubrication of porous polymer films By: Noshir Pesika and Tushar Khosla Department of Chemical Engineering, Tulane University In this study, we explore the mechanisms involved in the lubrication of porous polymer-based surfaces or coatings with ultra-low coefficients of friction arising from the partial hydrodynamic repulsive forces acting between shearing solid yet compliant surfaces. Through tribological experiments, using a universal materials tester, we show how it is possible to shift the lubrication regime from boundary lubrication to hydrodynamic lubrication even at relatively low shearing velocities. We hypothesize that the extruding liquid from the pores provides a repulsive hydrodynamic force, which aids in minimizing contact between the shearing surfaces. Conventional phololithography and molding techniques are used to fabricate the porous polydimethyl siloxane (PDMS) surfaces. Specifically, the effect of the pore density and pore size on the lubrication properties will be elucidated. Potential applications for these low friction biocompatible surfaces include their use in the fabrication of joint implants.
38
Session 5: Biomedical Applications 2 Chair: Deborah Leckband, University of Illinois, Urbana-Champaign Co-Chair: William Ducker, Virginia Tech University
1. Preventing Bacterial Colonization Using Colloidal Crystals By: Mehdi Kargar,1 Amy Pruden,2 and William A. Ducker3 1
Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA, USA.
2
Via Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, USA.
3
Department of Chemical Engineering, Virginia Tech, Blacksburg, VA, USA.
Bacterial infections are one of the leading causes of human misery, and hospital acquired infections alone are the fourth most common cause of death in the US. The most common medical treatment of device and implant infections is long-term systemic treatment with antibiotics; an alternative strategy for reducing the incidence of these infections is to alter the properties of medical surfaces to delay colonization by bacteria. Here we investigate the use of topography to prevent bacterial colonization. The hypothesis is that a highly curved surface will be less favorable for bacterial adhesion and colony formation. We investigated the adhesion and colony formation of Pseudomonas aeruginosa PAO1 on a solid coated in close-packed spheres of polystyrene. Solids were pretreated with serum and then exposed to bacteria under low shear for one day in a center for disease control biofilm reactor. Whereas flat sheets are covered in large colonies after one day, a close-packed layer of 630â&#x20AC;&#x201C;1550 nm monodisperse spheres prevents colony formation. Moreover, the film of spheres reduces the density of P. aeruginosa adhered to the solid by an average of 80%. Our data show that when P. aeruginosa adheres to the spheres, the distribution is not random. For 630 nm and larger particles, P. aeruginosa tends to position its body in a 2-fold site. We rationalize the selectivity on the basis of energy minimization for adhesion: sites differ in the deformation needed to achieve a given contact area. We rationalize the inhibition of colonization by the 630â&#x20AC;&#x201C;1550 nm spheres in terms of the lack of adjacent favorable positions for bacteria. A closepacked layer of polystyrene spheres also delays colony formation on a medical-grade stainless-steel needle over a period of one day. This suggests that a colloidal crystal approach to biofilm inhibition might be applicable to a variety of materials and geometries. 39
2. Thermodynamics of Solvophobic Interaction between Hydrophobic Surfaces in Ethanol By: Zuoli Li and Roe-Hoan Yoon* Center for Advanced Separation Technologies Virginia Tech Blacksburg, Virginia 24061 AFM surface force measurements have been conducted in pure ethanol using gold surfaces hydrophobized with alkanethiols (CnSH) with n = 2-16. The results show that the measured forces are net attractive and become stronger with decreasing thickness of the thin liquid films (TLFs) of ethanol confined between hydrophobic surfaces. The measured forces increase with increasing chain lengths, increasing surface hydrophobicity, and decreasing temperature. A thermodynamic analysis of the surface forces measured at 5 to 35 oC show that the solvophobic interactions entail decreases in both excess film enthalpy and entropy with decreasing film thickness. It has been found also that the changes in the excess film enthalpy (DHf) are larger in magnitude than the corresponding changes in the TDSf term, indicating that the solvophobic interactions are enthalpic. Despite the high degrees of enthalpyentropy compensations observed, the Gibbs free energy changes remained negative, suggesting that the structural changes associated with significant entropy decreases may aid the solvophobic interactions. The structural changes may involve small changes in the number densities and/or the strengths of hydrogen bonds across the film thickness as well as the possible changes in ethanol conformation.
40
3. The biological interface of a homodimeric protein By: Edgar Vázquez Contreras1* and María Elena Chánez Cárdenas2. 1
Departamento de Ciencias Naturales, DCNI, Universidad Autónoma Metropolitana Unidad Cuajimalpa.
Av. Vasco de Quiroga N° 4871 Esq. Carlos Graef, Col. Santa Fe Cuajimalpa, Del. Cuajimalpa de Morelos. C.P. 05348, México, D. F. Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía, México, DF, México 2
* evazquez@correo.cua.uam.mx In general, the inner region of the protein three-dimensional structure is maintained by mainly hydrophobic interactions. Conversely their exterior consists primarily of hydrophilic amino acids residues; they are the ones that maintain direct contact with water, the main component of the medium for soluble proteins. Only on this condition the proteins can generate the function for which they were created by nature, i.e. forming an interface with the environment. This interface is formed naturally between the amino acids residues of the exterior of the protein and the medium in which they are located, this is a biological interface. When this interface is disturbed, such as when environmental conditions favor the exposition of the hydrophobic region - that is hidden in the interior of proteins - to the environment, the macromolecule function disappears. The three-dimensional array that allows function is only maintained when the interface between the residues of the protein and the medium containing it, is appropriate. Indeed, the stability of the structure of proteins is only marginal and is disturbed by small changes in the ambient (by varying the temperature, pH or the concentration of specific molecules), then the biological interface that allows the existence of the function it is very delicate. In all proteins studied to date, the threedimensional structure is mainly formed by perfectly ordered interactions between their amino acid residues. These interactions are of non-covalent nature and include hydrogen bonds and hydrophobic interactions, but some can also be ionic. Among the variety of classifications that exist to sort proteins, there is a category of macromolecules which are formed by more than one subunit or monomer, that are generically known as oligomers being the homodimers the simplest because they are composed by only two identical subunits. The complexity at this level is very large because exist oligomeric proteins that have dozens of different types of subunits. In general, when the region that joins the subunits involved in this type of proteins was studied, it was found that is mainly a hydrophobic area; means that the amino acid residues that structured this region are mostly nonpolar. Within the oligomers there are some for which the function or stability of its subunits exist even when they are not forming the aggregate, these
41
are called non-forced oligomers. But there are others for whom the isolated subunits are unstable or they lack of function, they are called forced oligomers. Among the latter is triosephosphate isomerase, which is the enzyme that catalyzes step 5 of glycolysis, the biological process of energy production under anaerobic conditions. In this study we present our results about the nature of the interface formed between the subunits of a forced homodimeric protein. It will be show results of function, structure and stability, and the use of site-directed mutagenesis to construct a protein that allows us to understand the factors involved in the correct formation of the interface between the subunits and how this is involved in the forced nature displayed by the function of this protein. This work was supported by CONACyT MĂŠxico (47310308)
42
4. Lubricin protein: a biological, universal anti-adhesive with properties comparable to polyethylene glycol By: George W. Greene1,*Lisandra L. Martin2, Agnes Michalczyk2, Leigh Acklandc, Roger Horn1 1
Institute of Frontier Materials, Deakin University, Burwood, Australia 3125
2
School of Chemistry, Monash University, Clayton, Australia 3800
3
School of Life and Environmental Science, Deakin University, Burwood, Australia 3125
Lubricinis a glycoprotein found in articular joints which has been recognized as being an important biological boundary lubricant molecule. Besides providing lubrication, we demonstrate, using a Quartz crystal microbalance, that lubricin protein also exhibits anti-adhesive properties and is highly effective at preventing the non-specific adsorption of globular proteins,constituents of blood plasma, and cells. This impressive anti-adhesive property combined with lubricinâ&#x20AC;&#x2122;s ability to readily self-assemble to form dense, telechelic polymer brush layers on a wide variety of substrates and its innate biocompatibility makes it an attractive candidate for anti-adhesive and anti-fouling coatings. In addition, lubricinâ&#x20AC;&#x2122;s strong, anionic charge, a property that is atypical among anti-adhesive molecules, enables its use in electrohydrodynamic applications such as capillary electrophoresis and electroosmotically controlled microfluidic chips where the non-specific adsorption of proteins to surfaces is detrimental to the device performance.We show that coatings of lubricin protein are as effective as, or better than self-assembled monolayers of polyethylene glycol over a wide range of pHs and provide a simple, versatile, and highly effective method of controlling unwanted adhesion to surfaces.
43
5. The role of lipid domains in membrane protein adsorption and intermembrane adhesion between myelin sheaths By: Dong Woog Lee, Xavier Banquy, Kai Kristiansen, Yair Kaufman, Joan Boggs, and Jacob Israelachvili The myelin sheath is a multilamellar membrane which concentrically wraps around the axons of neurons. It forms a compact structure allowing the nerve axons to transmit fast and accurate electric signals via saltatory propagation. Myelin basic protein (MBP) is one of the essential proteins determining myelin structure, strongly holding the cytoplasmic leaflet side (major dense line) together by electrostatic and hydrophobic interactions. Defects or disruptions in the myelin bilayers increase the capacitance, which could lead to changes in nerve signal conduction, resulting in sensory and motor disabilities. Multiple sclerosis (MS) is the most common progressive neurological disorder and is characterized by the appearance of the lesions in myelin, reflecting loss of bilayer adhesion, swelling across the water gaps, vacuolization, vesiculation, and eventual disintegration of the myelin sheath.
Using a surface forces apparatus (SFA), we studied the effect of lipid composition (which effects lipid domain size and distribution) on the MBP adsorption which essentially effects inter-membrane separation (water gap thickness) and adhesion. We found that a slight change in lipid composition from healthy to EAE (experimental autoimmune encephalomyelitis: a disease model of multiple sclerosis) caused abnormal adsorption of MBP between myelin bilayers, eventually leading to significant swelling, i.e., an increase in membrane separation and also a decrease in inter-membrane adhesion. Using Atomic force microscopy (AFM), we also found that MBP specifically binds to the liquid disordered (Ld) phase of the bilayers, which implies an important role of lipid domains on MBP adsorption.
44
Session 6: Novel Instrumentation to Characterize Surface Forces, Colloidal Systems and Interfaces Chair: Jarek Majewski, Los Alamos National Lab and UC-Davis
1. The Electrochemical and the 3D Actuator-Sensor attachments of the SFA By: Kai Kristiansen1, Markus Valtiner2, Xavier Banquy3, Hongbo Zheng4, Jacob Israelachvili1 1
Department of Chemical Engineering, University of California Santa Barbara, USA
2
Max-Planck-Institute for iron research, Dusseldorf, Germany
3
Faculty of Pharmacy, Universite de Montreal, Canada
4
Department of Chemical and Materials Engineering, University of Alberta, Canada
The capabilities of the Surface Forces Apparatus (SFA) are rapidly evolving with implementations of various attachments. These attachments allow the SFA to be used in research in a wide variety of areas, from biological and soft condensed matter physics to chemical engineering, tribology, geophysics, and electrochemistry. Here I want to review two recently developed attachments in our lab: the Electrochemical [1-3] and the 3D actuator-sensor [4] attachments to the SFA, and discuss key results achieved with these attachments. Some results are (a) dissolution of silica and other mineral surfaces in the presence of electric potential and its implications to geological, corrosion and related processes, (b) in-situ monitoring of oxide growth of gold surface, (c) behavior of liquid crystals in electric fields, and (d) off-axis friction forces and non-zero velocity path. References: [1] Kristiansen K, Valtiner M, Greene GW, Boles JR, and Israelachvili J, Pressure solution â&#x20AC;&#x201C; the importance of the electrochemical surface potentials, Geochimica et Cosmochimica Acta, 75 (2011) 6882-6892. [2] Valtiner M, Banquy X, Kristiansen K, Greene GW, Israelachvili J. The electrochemical surface forces apparatus: The effect of surface roughness, electrostatic surface potential and anodic oxide growth on interaction forces and friction between dissimilar surfaces in aqueous solutions, Langmuir 28 (2012) 13080-13093. [3] Israelachvili J, Kristiansen K, Gebbie M, Lee D W, Donaldson S H, Das S, Rapp M V, Banquy X, Valtiner M, Yu J. The Intersection of Interfacial Forces and Electrochemical Reactions, Journal of Physical Chemistry B, 117 (2013) 16369-16387. [4] Kristiansen K, Banquy X, Zeng H, Charrault E, Giasson S, Israelachvili J. Measurements of anisotropic (off-axis) friction-induced motion, Advanced Materials 24 (2012) 5236-5241.
45
2. Direct Force Measurement Involving Deformable Surfaces By: Lei Pan and Roe-Hoan Yoon* Center for Advanced Separation Technologies 146 Holden Hall Department of Mining and Minerals Engineering Virginia Tech, 24061 U.S.A. Phone: (540) 231-7056 ryoon@vt.edu
Direct force measurement for bubble-surface interactions has been a challenge due to bubble deformation, which makes it difficult to determine separation distances between two macroscopic surfaces. It is also necessary to accurately determine contributions from the capillary force which varies with curvature. In the present work, we have developed a new force apparatus that can be used to determine both hydrodynamic and surface forces involving deformable surfaces. The apparatus, named Force Apparatus for Deformable Surfaces (FADS), is capable of recording the optical interference fringes generated from fast-evolving wetting films by means of a high-speed camera, while directly measuring the interaction forces at the same time. The recorded fringes are used to obtain spatiotemporal film profiles, which are then analyzed to determine the hydrodynamic forces using the lubrication theory. From the hydrodynamic forces determined in this manner and the overall forces measured directly, one can determine the disjoining pressure (or surface force) in wetting films. The film profiles obtained using FADS show that the wetting films of water formed on hydrophilic surfaces are flat at equilibrium due to the presence of the repulsive surface forces resisting film thinning. The films formed on hydrophobic surfaces thin faster and form â&#x20AC;&#x2DC;pimpledâ&#x20AC;&#x2122; films before rupture possibly due to the presence of long-range attractive forces. The results obtained in the present work have been analyzed using the Frumkin-Derjaguin isotherm to better understand the role of different surface forces in bubble-surface interactions. The new force apparatus developed in the present work may also be used for the force measurement involving other deformable surfaces such as biological membranes, oils, liquid CO2, etc.
46
3. Combining SFA and FRET to monitor the progressive zippering of two biomolecules during force measurements By: Yong Jian Wang1*, Feng Li2, Nicolas Rodriguez1, Eric Perez1, Frederic Pincet1 1
Laboratoire de Physique Statistique, Ecole Normale SupĂŠrieure Paris, France
2
School of Medicine, University of Yale, United States
yjwang@lps.ens.fr Naturally stable membranes separate the inside from the outside of cells, and require specialized molecules in order to fuse. SNAREs are the proteins inducing fusion between membranes in the cell. Their detailed mode of action remains unknown. When a v-SNARE on one membrane binds to a t-SNARE on another membrane, both membranes fuse. The most well-known SNAREs are the neuronal SNAREs. Their zippering releases enough energy to bring the membranes together, curve them and nucleate a fusion pore. The Surface Force Apparatus (SFA) enables the measurement of assembling energy of biomolecules. It was used to measure the energy released by the assembly of the SNARE complex [1]. In order to fully understand this assembling process that is critical to efficient neurotransmission, there is a need to follow the binding state of two SNAREs during the assembling process. Although the SFA technique has a distance resolution of 0.2nm, it does not allow following the binding state of two SNAREs during the assembling process. To achieve this, it is possible to use FĂśrster Resonance Energy Transfer (FRET). We have improved the SFA to allow the detection of FRET along with the force measurements. Thus, with fluorophore labeled SNARE proteins, we can detect FRET between SNARE proteins along with force-distance profiles. This allows the investigation of the structural information on SNARE complex assembly at the sub-molecular level in the narrow space between the membranes. The setup will be described and the first measurements will be presented.
[1]. Li F., Pincet F., Perez E., Eng W.S., Melia T.J., Rothman J.E., Tareste D., Nat Struct Mol Biol., 14 890 (2007)
47
4. Lateral and Normal Adhesion Forces at the Interface between a Liquid Drop and a Substrate By: Rafael Tadmor Lamar University rafael.tadmor@lamar.edu Naturally stable membranes separate the inside from the outside of cells, and require specialized molecules in order to fuse. SNAREs are the proteins inducing fusion between membranes in the cell. Their detailed mode of action remains unknown. When a v-SNARE on one membrane binds to a t-SNARE on another membrane, both membranes fuse. The most well-known SNAREs are the neuronal SNAREs. Their zippering releases enough energy to bring the membranes together, curve them and nucleate a fusion pore. The Surface Force Apparatus (SFA) enables the measurement of assembling energy of biomolecules. It was used to measure the energy released by the assembly of the SNARE complex [1]. In order to fully understand this assembling process that is critical to efficient neurotransmission, there is a need to follow the binding state of two SNAREs during the assembling process. Although the SFA technique has a distance resolution of 0.2nm, it does not allow following the binding state of two SNAREs during the assembling process. To achieve this, it is possible to use Fรถrster Resonance Energy Transfer (FRET). We have improved the SFA to allow the detection of FRET along with the force measurements. Thus, with fluorophore labeled SNARE proteins, we can detect FRET between SNARE proteins along with force-distance profiles. This allows the investigation of the structural information on SNARE complex assembly at the sub-molecular level in the narrow space between the membranes. The setup will be described and the first measurements will be presented.
[1]. Li F., Pincet F., Perez E., Eng W.S., Melia T.J., Rothman J.E., Tareste D., Nat Struct Mol Biol., 14 890 (2007)
48
Session 7: Distance and Time Regimes in CAI-STEM Chair: Professor Marina Ruths, University of Massachusetts-Lowell
1. Modes of Action in Water-Based Lubricants By: Carlos Drummond UniversitĂŠ de Bordeaux drummond@crpp-bordeaux.cnrs.fr Water films oppose a small resistance to shear because of its low viscosity. However, it is apparent that its load-bearing capabilities are rather poor. For this reason, additives are typically added to water to improve its lubrication properties; salts, surfactant and polymer are regularly used as friction modifiers. They facilitate the sliding of proximate surfaces through a variety of mechanisms including steric or electrostatic repulsion and surface hydration, usually as a result of the adsorption of a lubricant boundary layer. In this work few examples of boundary lubricants of increasing complexity based on self-assembled surfactant and polymers will be described. It will be discussed how the morphology of the films has important implications on its lubricant properties. A complex velocity dependence of the friction is often observed, with a maximum value at intermediate velocities. The measured friction also depends on the recent history of the sliding surfaces. We discuss the complex behavior of the friction observed in terms of a model that takes into account the adhesion and the hysteretic deformation of the sheared boundary layer, and the elastohydrodynamic effects resulting of its low elastic modulus. These examples illustrate the complexity of the subject and suggest pathways for the smart design of multicomponent water-based boundary lubricants.
49
2. Characterization of the interplay between topography and elasticity on hydrodynamic interactions. By: Rohini Gupta, Yumo Wang, and Joelle Frechette Chemical and Biomolecular Engineering Department, Johns Hopkins University, Baltimore MD 21218
Using the SFA we measure the hydrodynamic interactions between smooth and structured surfaces. The structured surfaces consist of hexagonal arrays of cylindrical post with different aspect ratios and spacing. We contrast rigid surfaces where the posts are made from SU-8 (E â&#x2030;&#x2C6; 1GPa) and soft or compliant surfaces using different PDMS (E < 1MPa). Using multiple beam interferometry we characterize the out of contact elastohydrodynamic deformation and hydrodynamic forces of the structured surface for different approach velocities and fluid viscosities. We compare the forces measured to Reynolds equation with corrections for deformation based on the work of Davies et al (JFM 1986). Our results highlight the competition between radial fluid drainage and drainage through the surface structure.
50
3. Contact Dynamics of Bio-inspired Polydopamine and Its Nanocomposites Thin Films By: Boxin Zhao, Kuo Yang, Wei Zhang, Aleksander Cholewinski Department of Chemical Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1 Dopamine is one of the simplest catecholamines, which is water-soluble and has a high affinity to surfaces and can self-polymerize to form a nanoscale polydopamine (PDA) film on surfaces in water. The similar catechol functional groups have been found in the adhesive proteins of marine mussels. Even though dopamine is well known as a neurotransmitter in human body, its “sticky’ nature and self-polymerization ability when adsorbed on surface have been exploited by material scientists for surface modification and functionalizations. However, the surface forces, adhesion and micro-mechanical properties of polydopamine are still less understood, limiting its transfer to practical applications where external stress and strain may damage or crack the film. In recent years, we have started to investigate the surface and tribological properties of polydopamine thin films in both dry and wet conditions. First, the effective elastic modulus of the PDA nanoscopic film has been analyzed in the framework of JKR contact mechanics by incorporating the classical plate theory; it was estimated to be about 10GPa. Thus, the PDA film is prone to crack when coated onto a substrate whose elastic modulus is less than 10GPa. We have performed a series of contact dynamic studies to characterize the PDA thin film coated on glass, epoxy, silicone rubber, and verify that PDA film coated on a soft substrate are subject to cracking in dry conditions. Second, we studied the adhesion and tribological behaviors of PDA film by indenting and sliding a hemispherical probe in air and in water. It has been found that the adhesion properties of the PDA coated different surfaces are almost identical, indicating that the nanoscale PDA film ( ~10nm thick) can mask the surface chemistry of the substrates even though the surface energy of the coated substrates are different. In air, the measured works of adhesion on PDA coated different surfaces are close to those of the calculated thermodynamic work of adhesion. In water, the measured works of adhesion were significantly lower than the calculated thermodynamic work of adhesion, showing a more pronounced detrimental effect of water on adhesion than expected. In addition, the effective adhesion was found to increase with contact time, showing the time-dependent dynamic nature of the surface interactions. The friction measurements revealed a reduction of friction force in water by 20% to 200% in comparison to the friction force in air, indicating the PDA coating are highly hydrated and might serve as a lubrication coating when used in water. These observations also suggested that the polydopamine is not as “sticky” as the monomer dopamine. Furthermore, we have found that the “sticky” nature of dopamine can be preserved when added in the synthesis of polymer nanocomposite (e.g. electrical conductive polypyrrole) and even some physical hydrogels so as to improve film adhesion of these functional nanocomposites.
51
4. The coalescence dynamics between oil drops in water By: Derek Y. C. Chan Particulate Fluids Processing Centre, University of Melbourne, Parkville VIC 3010, Australia D.Chan@unimelb.edu.au The hydrophobic attraction describes the well-known tendency for nonpolar molecules and surfaces to agglomerate in water, controlled by the reorganization of intervening water molecules to minimize disruption to their hydrogen bonding network. Past measurements of such attraction between extended non-polar surfaces with dimensions in the micrometre to centimetre scale, had been made between chemically hydrophobised solid mica or silica surfaces. The reported range of the attraction between these engineered surfaces varied from tens to hundreds of nanometres and has magnitudes larger than conventional colloidal forces. This additional attraction has been attributed to arise from adsorbed mobile molecular layers rearranging to form charged patches on the surfaces, with further subtleties arising if species within the hydrophobic layer can change conformation during interaction. Capillary bridging by nanobubbles formed on hydrophobic surfaces provides another source of strong, long-range attraction and degassing the water affects the range and magnitude Therefore where solid surfaces have been rendered hydrophobic by surface modification, different mechanisms, perhaps not directly related to the molecular properties of water, seem to be responsible for the additional attraction between such hydrophobised solid surfaces. Here, we use coalescence studies to probe the interaction between two hydrophobic oil drops in water by controlling the electrical double layer repulsion through adjusting the solution pH and ionic strength, the van der Waals attraction or repulsion by refractive index adjustments and the hydrodynamic repulsion or attraction by varying the relative velocity of the two drops [1, 2]. The oil/water interfaces are molecularly smooth but their ability to deform during interaction require additional theoretical analysis to interpretation experimental observations.
Moderating the van der Waals interaction with mixtures of perfluorooctane and perfluorobenzene and electrical double interaction with salt concentration and pH. The range of the hydrophobic force between fluorinated oil drops.
[1] Tabor, R. F.; Wu, C; Grieser, F.; Dagastine, R. R.; Chan, D. Y. C., J Phys Chem Letts 2013, 4, 3872-3877.
[2] Li, E. Q; Vakarelski, I. U.; Chan, D. Y. C.; Thoroddsen, S. T., Langmuir 2014, 30, 5162-5169.
52
5. Surface patterning with ionic functionalization By: Dusan Bratko Virginia Commonwealth University
Introduction of ionic moieties can lead to dramatic changes in nanoparticle wetting by, and solubility in water. The magnitude of the effect strongly depends not only on the amount but also on the distribution pattern of planted ionic groups. We explore the influence of the overall area density, and the lengthscale of ionic heterogeneities on the wetting free energy of alkyl-functionalized graphane with sporadic ionic groups. Computer simulations reveal two contrasting dependences of wetting enhancement on the extent of ionic surface functionalization; quadratic, or linear due to non-cooperative charge hydration. Depending on the extent of surface segregation, we observe up to four-fold change in solid/ solution surface tension at constant overall density of the charges. Understanding the prevalent scaling and surface patterning is essential for the design of nano-patterned materials whose wettability can be tailored at minimal chemical modification.
Supported by DOE. Collaborators D. Vanzo and A. Luzar.
53
Session 8: Frontiers in Science Inspired by CAI STEM Chair: Professor Norma Alcantar, University of South Florida
1. Frontiers on dispersant technology: The use of natural materials in oil spill cleanups By: Fei Guo1, Daniela Stebbins1,3, Tunan Peng1, Sylvia Thomas2, Ryan Toomey1 and Norma Alcantar1 1
Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, FL, USA
2
Department of Electrical Engineering, University of South Florida, Tampa, FL, USA
3
Water Treatment Plant at City of Tampa, Florida, USA
norma@usf.edu
A dispersant is a surface active media that will optimize the separation of two or more phases to prevent clumping or to enhance dissipation of the phases. The characteristics for an exceptional dispersant include small particle size, high stability, long shelf life, low cost of production, ease of application, and low concentrations. For instance, the use of chemical-based dispersants for oil spill cleanup operations has been led by Corexit® (EC9500A, produced by Nalco Environmental Solutions LLC) and JD-2000™ (manufactured by GlobeMark resources Ltd.). Both dispersants are listed in the U.S. Environmental Protection Agency’s (EPA) Product Schedule, have been used to disperse crude oil spills, and are considered less toxic than oil alone. Functional surfactants from natural materials have the advantage of being biodegradable and can be obtained through sustainable agriculture. We studied the properties of functional natural surfactants obtained from the Opuntia ficus-indica cactus as dispersants of crude oil droplets in water (O/W emulsions) in both fresh and seawater and the effect of oil concentration and surfactant concentration on droplet size and stability, as well as on the critical micelle concentration. Since emulsification is caused by the stirring of an oil/surfactant/water system, the dynamic equilibrium of the droplets inducing their rupture and coalescence depends on the formulation and composition variables, mixing characteristics, and preparation conditions. Three extracts of this cactus plant were studied for their effectiveness as dispersants and were compared with those from Corexit®. Results indicated that these natural surfactants effectively dissipate heavy and light crude oil from the air-water interface of a water column for rapid biodegradation. It was determined that the amount of natural surfactants needed to obtain optimal dispersion stability is lower than that needed of Corexit®. This project has been funded by the Gulf of Mexico Research Initiative via C-MEDS 54
2. An Energy-dispersive Biocoating Made by Mussels By: J. Herbert Waite1*, Dusty R. Miller1, Saurabh Das2, Jacob N. Israelachvili2 Marine Science Institute Department of Chemical Engineering University of California Santa Barbara, CA 93106, USA jacob@engineering.ucsb.edu
Mussel byssal threads are coated by an inconspicuous cuticle that is 5 Âľm-thick. This cuticle provides resistance to wear and abrasion in the high-energy intertidal zone. Nanomechanical analyses have determined that the hydrated cuticle combines the stiffness of a hard epoxy (2 GPa) with the extensibility of a rubber (120%). The scarcity of fabricated materials exhibiting both high stiffness and high extensibility has motivated us to investigate cuticle as a model of an energy dispersive biomaterial. Byssal cuticle is a polymer composite in which spherical particles (200-500 nm) are dispersed in a continuous matrix. The particles consist of a repeat protein, mfp-1, condensed by extensive coordination with Fe3+, whereas the continuous matrix is a double network of mfp-1 and another acidic protein that awaits more complete characterization. We have proposed that the double network forms from a complex coacervate of the two proteins prior to undergoing differential cross-linking. With this in mind, we have prepared coacervates of mfp-1 and hyaluronic acid and investigated the frictional and damage mitigating properties of these using the SFA. Coacervates of mfp-1 and hyaluronate protect mica surfaces from damage at even the highest normal compression of 350 mN.
* presenting author Funded by the Institute of Collaborative Biotechnologies through grant W911NF-09-0001 from the Army Research Office and the MRSEC Program of the National Science Foundation under award No. DMR 1121053
55
3. Scanning Electron Microscopy and Contact Angle Characterization of Opuntia ficus-indica [Mucilage] Nanofibers By: Sylvia W. Thomas(a), Norma A. Alcantar(b), Fei Guo(b), Daniela Stebbins(b), Manopriya Devisetty Subramanyam(a), Hruday Chand Katakam (a), Sam Perez(a), and Rasudha Muppaneni(a) University of South Florida, Department of Electrical Engineering
(a)
SFA
University of South Florida, Department of Chemical & Biomedical Engineering
4202 E. Fowler Ave., ENB118, Tampa, FL 33620, U.S.A. sylvia@eng.usf.edu Nanofiber membranes are currently being investigated as effective devices for the treatment of water contaminated by toxic metal ions, organic and inorganic solutes, and microorganisms. The characteristics which make these nanofiber membranes prevalent for water treatment are the high surface area and nano-scale pore size of the nanostructures. A cost effective process used to fabricate these nanofiber membranes is electrospinning. A natural, biocompatible material, opuntia ficus-indica [cactus mucilage] has been used to electrospin micro-to-nano scaled fibers when miscible with poly vinyl alcohol (PVA):water and polystyrene (PS):D-Limonene polymer solutions. Ratios of 70:30 and 50:50 of polymer to mucilage solutions are electrospun to produce novel nanofiber membranes. These electrospun cactus nanofiber membranes have been characterized using scanning electron microscopy to show fibers ranging from 4 microns to 7 nanometers in diameter. Typically, polymers demonstrate hydrophobic surfaces, but with the incorporation of the natural material, mucilage, various levels of hydrophilicty are observed using contact angle measurements. A sample solution is coated onto a glass slide, and a water droplet is used to test the wetting phenomena and the union of these low surface energy materials. By adjusting various microscopic parameters, a tangent is drawn at the intersection of water and polymeric solution to measure the contact angle. We demonstrate the versatility of the Opuntia ficus-indica [cactus mucilage] nanofiber membrane to form hydro surfaces that can be effective for filtration devices. Utilizing Atomic Fluorescence Spectrometry (AFS), relative tests have been performed using different filtration layers: 1) coated and non-coated GVWP 0.22 Âľm and 0.45 Âľm filters from Millipore, and 2) 1 g of pre-washed sand from Fisher Scientific and a layer of mucilage nanofibers. The final results show that mucilage nanofiber membranes are capable of removing arsenic from sample solutions. By these data, it can be interpreted that mucilage nanofiber membranes have the potential to serve as the basis for the next generation of sustainable filters that make use of natural materials.
56
4. Reversible adhesion with polyelectrolyte brushes tailored via the uptake and release of multi-valent ions By: Matthew Tirrell and Robert Farina Institute for Molecular Engineering, University of Chicago 5747 South Ellis Avenue; Jones Laboratory 222, Chicago, IL 60637 mtirrell@uchicago.edu Applications of end-tethered polyelectrolyte ‘brushes’ once primarily revolved around their colloidal stabilization and high lubrication properties. However, current efforts with polymer brushes have taken a general shift towards biological realms and stimuli-responsive materials. Our work explores responsive and reversible aspects of polyelectrolyte brush behavior when polyelectrolyte chains interact with oppositely charged multi-valent ions and complexes. Other studies with responsive polyelectrolyte materials have mostly centered investigations on temperature, pH, or mono-valent salt effects. However, previous work has also left an important void in the stimuli-responsive polyelectrolyte literature regarding polyelectrolyte interactions with multi-valent entities; which as described throughout this paper produce tremendous physical property changes. When polyelectrolyte brushes contain trivalent lanthanum counterions, for example, adhesion measured upon separating two brushes has been measured at as high as 30 mN/m (almost half the surface tension of water with respect to air, 72 mN/m). Furthermore, this adhesion has been observed to reversibly appear and disappear upon the uptake and release, respectively, of multi-valent counter ions.
The collapse of two polyelectrolyte brushes and their subsequent adhesion is facilitated by the addition of tri-valent La3+ to the bulk solution. Here, the normalized force between two surfaces coated with selfassembled NaPSS brushes (F/R) is plotted as a function of distance. This experiment was performed in a fixed overall ionic strength solution of I0 = 0.003 M. Bulk lanthanum concentrations were sequentially increased from the lowest concentration (0.1 x 10-6 M) to the highest (3.0 x 10-6 M), as can been seen in the legend.
57
5. A brief history of concepts and measurements of intermolecular and surface forces By: Jacob Israelachvili Department of Chemical Engineering, and Materials Department, University of California, Santa Barbara, CA 93016 jacob@engineering.ucsb.edu
A brief review will be given of the developments of ideas, concepts and theories of intermolecular and inter-surface forces, and how these were influenced (or ignored) by observations of nature and, later, systematic experimental measurements. It is educational to see how things gradually changed over the last 2000 years[1]: experimentation replaced rhetoric, measurement and quantification replaced hand waving, energy replaced force in calculations, discrete atoms replaced the (continuum) aether, thermodynamics replaced caloric and mechanistic models, randomness and probability replaced certainty, and delicate experiments at the sub-nano scale revealed fascinating self-assembling structures and complex behavior of even the simplest systems. Today’s systems of interest are highly complex, multicomponent, and ‘dynamic’ – especially living biological systems. Such systems or – more correctly – ‘processes’ are not static but evolve in both space and time, with the relevant space and time (or rate) scales typically varying over more than 7 orders of magnitude. They are often far from equilibrium, and even when they receive a continuous supply of energy, they may not even be in some steady-state. It is questionable whether such processes could ever be described by simple pair-potentials or force functions. The review will end by discussing today’s challenges, for example, how can dynamic complex fluid systems be studied, both theoretically and in the laboratory.
[1]
A brief history of intermolecular and surface forces in complex fluid systems. Marina Ruths, Jacob
Israelachvili, Langmuir (2013) 29, 9605–9619.
58
Session 9: Structures and Characterization Techniques in CAI-STEM Chair: Professor Tonya Kuhl, University of California-Davis
1. Novel Scattering Methods Reveal Structure of Single Supported Lipid Membranes By: Tonya L. Kuhl Department of Chemical Engineering and Materials Science, University of California at Davis tlkuhl@ucdavis.edu
Over the past several decades, supported lipid membranes have been used as model systems of cellular membranes, to investigate various membrane interactions, and as platforms for development of biosensors. Precise structural characterization by x-ray reflectivity and grazing incidence diffraction at the solid-liquid interface offers a wealth of insight into membrane organization, self-assembly, and domain formation as well as how membranes respond to changes in their environment. In this talk, I will discuss some recent advances in our understanding of supported membranes including (1) high resolution details regarding the inorganic-organic interface; (2) changes in the membrane structure with fabrication method, temperature, and solution conditions; and (3) a novel, â&#x20AC;&#x153;texturedâ&#x20AC;? lipid phase induced by specific-multivalent protein binding to membrane embedded receptors. The talk will particularly highlight the importance of x-ray scattering techniques for single, lipid bilayer structural characterization.
59
2. Confocal Imaging of Monolayer Phase Behavior and the Double Layer By: Ian C. Shieh, Department of Chemical Engineering, University of California, Santa Barbara, CA 93106 Joseph A. Zasadzinski, Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 zasad008@umn.edu General acceptance of complex monolayer and bilayer phase behavior, especially phase coexistence and critical phenomena, has relied on the visualization of fluorescently tagged lipids preferentially segregated between phases. This segregation, which is due to differences in local molecular organization, provides the contrast necessary to visualize even subtle differences in packing density, molecular tilt, and short and long-range order. Visualization of the distribution of labeled lipids has settled numerous debates over the molecular scale organization of monolayers and bilayers. However, fluorescently tagged lipids are effectively insoluble in the aqueous subphase and are trapped in the monolayer. As a result, expelling the fluorescent lipid from one phase means concentrating the fluorescent lipid in another phase, which can result in fluorescence quenching, alterations in domain structures, or perturbations of the mechanical properties of the monolayer. These unknown concentration and quenching effects limits analysis to qualitative assessment of the fluorescence intensity distributions. An alternative to fluorescently labeled lipids is Brewster Angle Microscopy (BAM); however, resolution limitations, ease of use, and the cost of the specialized instrumentation have limited the acceptance of BAM. We show that the selective adsorption of a water-soluble fluorescent dye from the subphase to the monolayer provides similar contrast to insoluble lipid dyes in conventional confocal microscope images of gas, liquid-expanded (LE) and liquid condensed (LC) phases. The water-soluble dyes also provide contrast between liquid ordered (lo) and liquid disordered (ld) phases in the vicinity of critical points. Isotherms, domain sizes and shapes are the same as those visualized with low concentrations of fluorescently tagged lipids. Unlike insoluble lipid dyes, the water-soluble dye concentration is set by a dynamic equilibrium between the monolayer and subphase; the dye is not concentrated in the LE (or ld) phase as the fraction of LC (or lo) phase increases. The optical sectioning of the confocal microscope allows the interfacial fluorescence of the monolayer-adsorbed dye to be visualized and rejects the fluorescence from the subphase, which is not possible with conventional wide-field microscopy. The absolute fluorescence intensity determined by optical sectioning through a fluorescently labeled monolayer provides the experimental microscope point-spread function. This allows for de-convolution 60
of the confocal image so that the total adsorption and the adsorption/desorption rates of the dye can be quantified. The rate of dye adsorption can be described with classic Langmuir adsorption kinetics and saturates in a few minutes. In addition to visualizing the lateral features of the interface, optical sectioning can determine the distribution of labeled species distributed between the subphase and the monolayer. This allow us to determine the surface potential and fractional ionization of an anionic dipalmitoylphosphatidylglycerol (DPPG) monolayer by quantifying the excess cationic dye within the electric double layer using the Guoy-Chapman theory combined with a mass-action model for the dissociation equilibrium of DPPG. We find excellent agreement between theory and experiment at low surface potentials with no adjustable parameters (high ionic strength), but theory over-predicts the ion concentration, surface potential and dissociation at higher surface potentials (low ionic strength) where the mean field Guoy-Chapman model breaks down due to ion correlation and finite ion size effects. There are few measurements of the counterion concentration in the vicinity of a fluid-fluid interface; the distribution of ions at an organic liquid/water interface required the use of synchrotron X-ray reflectivity and extensive modeling. Conventional monolayer surface potential measurements using the Kelvin vibrating capacitive probe measures the surface potential of both the monolayer-water and monolayerair interfaces and requires certain assumptions to separate the two potentials, which can only be done semi-quantitatively. Scanning Kelvin Force microscopy has also been used to map the surface potential distribution at the nanoscale, but is not compatible with freely floating monolayers at the air-water interface. We expect that these methods might be extended to quantify the distribution of a variety of labeled proteins, polymers, and other materials of interest in the vicinity of monolayers at the air-water interface using conventional confocal microscopy. The method may also be amenable to determining local fluorophore concentrations near liquid-liquid interfaces and liquid-solid interfaces to further address issues of ion distributions in systems at high potential or high concentration.
61
3. Drainage and forces in thin liquid films between approaching air bubbles and hydrophobic surfaces By: Zhenghe Xu, Xurui Zhang, Plamen Tchoukov, Louxiang Wang, Mansoureh Shahalami, Qingxia Liu, Jacob Masliyah Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6. Understanding colloidal forces and hydrodynamic resistance between air bubbles and solid surfaces in an aqueous medium is of special interests because of their significant role in important applications such as flotation and lubrication. In 1939, Derjaguin and Kussakov showed complex deformation, known as dimples of the liquid-air interface before the formation of a flat thin liquid film during the impact of an air bubble on a mica surface. Thin film technique using Scheludko cell with optical interferometry allows for accurate measurement of film thickness profile [1] but colloidal forces are not measured directly at controllable dynamic conditions. Dynamic interactions between air bubbles and solid surfaces have been measured recently using atomic force microscopy (AFM) - colloidal probe method . In AFM experiments the film thickness and profile are not measured, instead modeling is used to
[2]
extract this information [3]. Furthermore, the above mentioned techniques are limited to hydrodynamic conditions of relatively low Reynolds numbers. Recently an integrated thin film drainage apparatus (ITFDA) employing a bimorph force sensor for accurate measurement of overall forces and a computerinterfaced video system to track the bubble deformation during the bubble/solid impact was developed, allowing the measurement of colloidal forces between bubbles/droplets and solid surfaces over a wide range of hydrodynamic conditions up to an approach velocity of 50 mm/s [4]. To measure the film thickness and profile, the ITFDA was further integrated with optical interferometry, leading to a new thin film force apparatus (TFFA) that combines the force and film thickness measurements in a single instrument as shown in Figure 1.
With this new TFFA, the effect of surface hydrophobicity and approach velocity on hydrodynamic resistance, film thickness profile and film lifetime is studied. For an air bubble of diameter 1.5-2.4 mm interacting in aqueous media with either a glass sphere of diameter 1.5 mm or flat fused silica glass window, the results show that the film rupture is mainly controlled by hydrophobicity of the solid interface, while bubble approach velocity has a small effect. While the films were stable in the case of hydrophilic surface, the films ruptured when the surface was rendered hydrophobic. Hydrodynamic resistance of the film decreased linearly with increasing the hydrophobicity of the solid surface at 62
constant bubble approach velocity. Bubble approach velocity and hydrophobicity of the solid controlled the temporal spatial evolution of the film. Dimple formation was suppressed at low approach velocities and for hydrophobic surfaces. In conclusion, the new TFFA can be a very useful tool in studying the colloidal forces and role of different hydrodynamic conditions that govern bubbles-solids attachment process.
Figure 1. Schematics of TFFA.
References [1] Sheludko, A. Thin liquid films. Adv. Colloid Interf. Sci. 1967, 1, 391-464. [2] Ducker W., Senden T., Pashley R., Nature 1991, 353, 239−241. [3] Chan D., Klaseboer E., Manica R., Adv. Colloid Interface Sci. 2011, 165, 70−90. [4] Wang L., Sharp D., Masliyah J.; Xu Z., Langmuir 2013, 29, 3594−3603.
63
Session 10: Intermolecular Forces I Chair: Suzanne Giasson, University of Montreal
1. Dynamic behavior of the air water interface revealed in bubble-mica collisions studied using the SFA By: Lorena A. Del Castillo(1), Satomi Ohnishi(1), Steven L. Carnie(2), and Roger G. Horn(1,3) 1. Ian Wark Research Institute, University of South Australia, Adelaide, Australia 2. Department of Mathematics and Statistics, University of Melbourne, Australia 3. Institute for Frontier Materials, Deakin University, Melbourne, Australia roger.horn@deakin.edu.au
An adaptation of the surface force apparatus has been used to investigate the approach of a mm-scale air bubble in aqueous electrolyte solution to a flat mica surface. Fringes of equal chromatic order that result from optical interference between the air/water interface and a thin layer of silver on the outer surface of the mica are observed in reflection and used to obtain accurate measurements of the bubbleâ&#x20AC;&#x2122;s deformation that results from surface and hydrodynamic forces [1,2,3]. The same method was used previously to investigate deformation of a mercury drop as it approached mica, with electrical control of the mercuryâ&#x20AC;&#x2122;s potential allowing the predominant surface force, a double-layer interaction, to be varied at will [4,5]. A model based on the Poisson-Boltzmann theory of double-layer forces, StefanReynolds theory of thin film hydrodynamics, and the Young-Laplace equation for the local curvature of a fluid-fluid interface, provided an excellent fit to the mercury data [6]. The close fit suggests that all of the assumptions in the model are well founded, including a no-slip hydrodynamic boundary condition at the mercury/water interface, constant and homogeneous interfacial tension, constant and homogenous surface potential (as expected for a conducting material), and constant Newtonian viscosity in the thin aqueous film that separates the mercury and mica. In contrast, the data for the air bubble interacting with mica cannot be fitted by the standard model, which suggests that one of more of the above assumptions is invalid. There are strong indications from the data that the bubble surface properties are inhomogeneous in space and dynamic in time, with variations in local surface charge and surface tension occurring near the region of closest approach 64
to the mica. These variations result from the bubbleâ&#x20AC;&#x2122;s interaction with mica, through one or both of the double-layer interaction and liquid flow in the thin aqueous film. One consequence is that the hydrodynamic boundary condition at the air/water interface is neither uniform and constant slip or no-slip.
References: [1] Connor, J.N. PhD thesis, University of South Australia 2001; [2] Pushkarova, R.A.; Horn, R.G. Langmuir 2008, 24, 8726-8734; [3] Del Castillo, L.A. PhD thesis, University of South Australia 2011; [4] Connor, J.N.; Horn, R.G. Langmuir 2001, 17, 7194-7197 [5] Connor, J.N.; Horn, R.G. Faraday Discuss. 2003, 123, 193-206. [6] Manica, R; Connor, J.N.; Carnie, S.L.; Horn, R.G.; Chan, D.Y.C. Langmuir 2007, 23, 626-637.
65
2. Measurement of long-ranged steric forces between polyelectrolyte layers physisorbed from 1M NaCl By: Christiane Helm Ernst Moritz Arndt University of Greifswald The colloidal probe technique (CPT) is used to measure distance-dependent interaction forces between polyelectrolyte layers physisorbed from 1M NaCl solution in salt solutions between 0.1mM and 1M. Both linear polycations (poly(allylamine)hydrochloride, poly-l-lysine) and linear polyanions (poly(styrenesulfonate), PSS) are used. The repulsive interaction energies in the range between 10-7 and 10-4 J/m2 are described by the theory of Alexander and de Gennes for surfaces covered with neutral anchored polymers. However, the brush thickness scales with molecular area and salt concentration with a power of â&#x2C6;&#x2019;1/3 as known from a salted brush and reaches approximately 50% of the contour length in diluted solutions. The findings are confirmed by CPT images using a gold layer as height reference. The degree of polymerization N of PSS is varied. For low N, domains of PSS brushes coexist with flatly adsorbed PSS. For N = 380, the brush area fraction is 6%. With increasing degree of polymerization, brush area fraction and domain size increase, whereby the domain radii vary between 50 nm and 1.5 Îźm. Lateral homogeneous brush layers are found for a degree of polymerization exceeding 1100. CPT reveals that the surface forces are a superposition of steric and electrostatic forces; their respective contribution is determined by the brush area fraction.
66
3. Contact and Friction of Rough Adhesive Surfaces By: Lars Pastewka1,2, Tristan A. Sharp1 and Mark O. Robbins1 1
Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA MikroTribologie Centrum μTC, Fraunhofer-Institut für Werkstoffmechanik IWM, 79108 Freiburg, Germany
2
Experimental surfaces typically have roughness on a wide range of length scales. In many cases they can be described as self-affine fractals with the root mean squared (rms) height change dh over lateral length l scaling as dh~lH over nanometer to micrometer scales. The Hurst exponent H is usually between 0.5 and 0.8. This roughness greatly reduces the fraction of the area Areal that is in intimate molecular contact and thus can contribute to friction and adhesion. The talk will first describe how roughness affects the contact area Areal and interfacial stiffness k between nominally flat nonadhesive surfaces. Both are linearly proportional to load N with prefactors given by scaling theory. Next contact between a rough sphere and flat is studied as a function of sphere radius R. At low loads, roughness dominates and the area is proportional to load. At high loads, the response approaches the Hertz relation for smooth surfaces. The second part of the talk will consider the effect of adhesive forces on rough surface contact. An efficient Greens function approach allows calculations for systems with roughness on nanometer to micrometer scales to be performed with atomic resolution in the contact. Results for a wide range of geometries can be collapsed using simple scaling relations that depend on the root mean squared surface slope, sphere radius, elastic modulus, and work of adhesion. Unless the surfaces are extremely smooth or soft, there is no contact at zero load and Areal ∝ N. A simple scaling relation predicts the change in prefactor with adhesion and the conditions under which a
finite adhesion force is needed to separate the surfaces. The traditional Fuller-Tabor model for adhesion of rough surfaces is shown to be qualitatively inconsistent with the simulations. The talk will conclude by considering how forces in the contact area give rise to friction. Friction shows strong scale effects and the partial slip assumed in many contact models is not found in contacts with dimensions of nanometers to micrometers. Supported by NSF Grant No. DMR-1006805 and CMMI-0923018.
67
4. Aging and Stiction of Molecularly Confined Liquid Lubricants By: Shinji Yamada1, 2 1
New Industry Creation Hatchery Center, Tohoku University
2
Analytical Science Laboratories, Kao Corporation
yamada.s@niche.tohoku.ac.jp When the thickness of a liquid lubricant film between solid surfaces approaches molecular dimensions, the molecular motions in the film are highly restricted and the system shows solid-like responses upon shearing. One of the characteristic features of the solid-like responses is static friction (stiction) at the commencement of sliding. It is well-known that the stiction spike height (difference between static friction force and kinetic friction force) of liquid-lubricated surfaces is strongly dependent on surface stopping (aging) time because confinement-induced solidification of liquids is a time-dependent process (this aging effect is referred to as structural aging). In addition, aging increases the real contact area due to the plastic deformation of surface materials (geometrical aging) that also increases stiction. Therefore, it is important to separate the two aging effects quantitatively to discuss the molecular mechanisms of stiction. The surface forces apparatus (SFA) technique is very suitable for this purpose; the SFA and the FECO optical technique enable us to perform the accurate and simultaneous measurements of the stiction spike height, liquid film thickness, and the real contact area as a function of aging time. This means that the stiction spike height normalized by the contact area can be obtained; we can exclude the effect of geometrical aging and evaluate the effect of structural aging on stiction qualitatively and quantitatively. Taking the advantage of the above potential of the SFA, stiction behaviors of a variety of confined lubricant systems (low-molecular-weight oils and polymer melts) were investigated by stop-start friction experiments.1-3 The results show that the freezing on stopping and melting on starting involve complex molecular mechanisms depending on the chemical structures of liquid lubricants. Comparison with the stiction measurements for liquid-lubricated macroscopic rough surfaces will be also described.
References: (1) S. Yamada, J. Chem. Phys. 131, 184708 (2009). (2) S. Yamada, J. Chem. Phys. 137, 194702 (2012). (3) S. Yamada, K. Inomata, T. Tanabe, and K. Kurihara, manuscript in preparation.
68
5. A Molecular Theory of Equilibration and Aging By: M. Medina-Noyola Instituto de Física “Manuel Sandoval Vallarta”, Universidad Autónoma de San Luis Potosí, Álvaro Obregón 64 Zona Centro, San Luis Potosí, S.L.P., México. medina@ifisica.uaslp.mx
The phenomenology of the glass transition in “thermally-driven” molecular glass formers and in “density-driven” hard-sphere colloidal systems are widely believed to share a common underlying universal origin. For this expectation to have a more fundamental basis, however, one has to understand why and how undercooling and overcompressing may lead to analogous glassy behavior. One manner to advance in this understanding is to describe these phenomenologies within the same theoretical framework, which exhibits their analogy as one of its main predictions. In this work we apply the recently-developed non-equilibrium extension of the self-consistent generalized Langevin equation theory of irreversible relaxation [Phys. Rev. E (2010) 82, 061503; id. 061504; ibid. (2013) 87, 052306] to describe the isochoric irreversible processes (equilibration or aging) of a glass-forming soft-sphere liquid constrained to remain spatially uniform, after it was subjected to either a sudden crunch to a higher density or a sudden quench to a lower temperature. The theory describes the non-equilibrium evolution of the static structure factor S(k;t) and of the dynamic properties, such as the self-intermediate scattering function FS(k,t;t), where t is the correlation time and t is the evolution or waiting time after the crunch (or quench). The scenario of the irreversible evolution is predicted to be basically the same, with the volume fraction and the inverse temperature playing an analogous role. The predicted evolution of the a-relaxation time ta(t,f) as a function of t after a crunch to a final volume fraction f, allows us to define an equilibration time teq(f), as the time after which ta(t) has attained its equilibrium value taeq (f). It is predicted that both, teq(f) and taeq (f) diverge as f approaches f(a), where f(a) (=0.582) is the hard-sphere dynamic-arrest volume fraction. The theory also predicts that for finite waiting times t the plot of ta(t; f) as a function of f exhibits two regimes, corresponding to samples that have fully equilibrated within this waiting time, f< f(c)(t), and to samples for which equilibration is not yet complete, f > f(c)(t). The crossover volume fraction f(c)(t) increases with t but saturates to the value f(a). This two-regime scenario is observed in molecular dynamics simulations of incompletely equilibrated hard-sphere. The same scenario, changing f to 1/T as a control parameter, is also predicted for the quench processes, and is semi-quantitatively confirmed by the corresponding simulations.
69
Session 11: Nano-Macro / Catalysis Chair: Sylvia Thomas, University of South Florida Co-Chair: José Campos, Universidad Autonoma de Metropolitana/ Cuajimalpa
1 . Adhesion and Friction Between Supported Core Shell pH Sensitive Polymeric Nanoparticles By: L. Giraud1, S. Giasson1,2 1
Faculty of Pharmacy, Université de Montréal, lucie.giraud@umontreal.ca
2
Department of Chemystry, Université de Montréal, suzanne.giasson@umontreal.ca
C.P. 6128, succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7 suzanne.giasson@umontreal.ca Static and dynamic interaction forces between two pH-sensitive polymeric nanoparticle monolayers irreversibly attached onto mica surfaces and immersed in water were investigated using the Surface Forces Apparatus. The NPs were core-shell made of a polystyrene (PS) core covered with a polyacrylic acid (PAA) shell. The weakly charged polyelectrolyte shell (PAA) can undergo changes in the degree of ionization upon changes in pH or ionic strength allowing physico-chemical properties such as volume, surface potential and structure to be modulated. Such NPs are promising materials for designing smart materials whose surface properties (adhesion, permeability) and interactions with the surrounding environment can be modulated in response to an external stimulus or signal. Surface force measurements were carried out to assess the adhesion, friction and resistance to the compression and shear of the nanoparticles (NPs) under different pH. The normal and friction forces between two opposing NPs monolayers were strongly dependant on the pH. The range of the normal forces increased with pH suggesting an increase in the swelling of the immobilized NPs associated with an increase in the degree of ionization of the PAA. The normal forces were purely repulsive regardless of pH indicating the absence of adhesion. The friction forces significantly decreased with increasing the swelling of the NPs. Comparison with other studies on friction between different polymer-coated surfaces will be presented in order to elucidate the role of the polymer structure in controlling friction.
70
2. Nanoscale friction of uniaxially stretched polymer films By: Marina Ruths, Xin Xu, Yutao Yang, Emmanuelle Reynaud, Daniel F. Schmidt Department of Chemistry, Department of Mechanical Engineering, and Department of Plastics Engineering, University of Massachusetts Lowell, Lowell, MA 01854, USA marina_ruths@uml.edu Polymer substrates with a built-in capability for alignment of nanometer-sized objects are of interest for the development, performance, and large-scale production of robust, flexible devices. We have used atomic force microscopy (AFM) in friction mode to investigate the effects of uniaxial stretching on the nanoscale adhesion and friction of glassy polymer substrates. Examples will be shown of the different friction responses of semi-crystalline and amorphous polymers along and across the stretching direction, and how this friction response is altered as the strength of adhesion between the polymer and the AFM tip is deliberately changed.
71
3. Understanding Hydrophobic Interactions of Polymer Surfaces By: Hongbo Zeng Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 2V4, Canada *Phone: +1-780-492-1044, Fax: +1-780-492-2881, hongbo.zeng@ualberta.ca
Characterization of adhesion properties and molecular interaction mechanisms of polymers has attracted much research interest for many years. In this presentation, the recent advances in understanding the hydrophobic interactions of polymer surfaces will be presented. The interactions between two hydrophobic polymer surfaces and between a hydrophobic polymer surface and a hydrophilic substrate were directly measured using a surface forces apparatus (SFA) in different electrolyte solutions, in which polystyrene was used a model hydrophobic polymer. We found that the long-range hydrophobic interaction measured is due to bridging of microscopic and sub-microscopic bubbles on polystyrene surfaces. The range of the hydrophobic interaction decreases with increasing the electrolyte concentration for NaCl and CaCl2, but shows no significant change for HCl and CH3COOH, which is related to the formation and stability of bubbles on hydrophobic surfaces due to the ion specificity. The range of the hydrophobic interactions was reduced to about 10-20 nm by degassing the aqueous solutions, but gradually recovered when re-exposing the degassed solution to air. Moreover, spontaneous cavitation of water between two interacting polystyrene surfaces was directly observed in degassed aqueous solution at a separation of <20 nm. The interaction between an air bubble used as a probe attached to the cantilever of an atomic force microscope (AFM) and partially hydrophobized mica surfaces was further measured to investigate the role of the additional attraction at partially hydrophobized surfaces and hydrodynamic conditions in bubble attachment to substrate surfaces. Our results indicate that dissolved gasses in solutions play an important role in the interactions of polymer surfaces, and support a three-regime â&#x20AC;&#x153;hydrophobicâ&#x20AC;? interaction model proposed.
72
4. Interaction forces mediated by structured polymers By: Xavier Banquy University of Montreal xavier.banquy@umontreal.ca Macroscopic phenomena such as adhesion and lubrication involve, at the nanoscopic level, interaction forces between surfaces mediated by (macro)molecules. In the case of macromolecules promoting adhesion or lubrication, the vast range of interaction mechanisms identified so far has been mostly related to the conformation of the polymer at the surfaces. The role of the polymer architecture itself on the interactions is much less explored. In this context we will present some recent advances using water soluble polymers whose architecture has been carefully designed to either promote lubrication or adhesion. We will show in a few examples using structured multiblock polymers, how architecture can exquisitely control polymer conformation at the solid-liquid interface and give rise to surprising new molecular interaction mechanisms.
73
5. Enhanced Catalytic Functionality of Peroxidases – Nanoparticles Complexes by its Surface Immobilization By: Iker Iñarritu1, Jorge. Aburto2, Eduardo Torres3, José Campos-Terán1* 1
Departamento de Procesos y Tecnología, DCNI, Universidad Autónoma Metropolitana-Cuajimalpa,
Artificios 40-sexto piso, Col. Hidalgo, México, D. F., 01120. jcampos@correo.cua.uam.mx 2
Coordinación de Procesos de Transformación, Instituto Mexicano del Petróleo, Eje Central Lázaro
Cárdenas Norte 152, Col. San Bartolo Atepehuacan, México, D. F., 07730. 3Centro de Química-ICUAP, Benemérita Universidad Autónoma de Puebla, Edificio 103G, Ciudad Universitaria. Peroxidases are versatile enzymes that catalyze the oxidation of a wide variety of compounds of commercial and environmental interest. They have been used for green chemistry and asymmetric synthesis such as the enantioselective oxidations of sulfides, enantioselective epoxidation of disubstituted alkenes, and enantioselective oxidation of racemic epoxyalcohols. As well as, the oxidations of pollutans like dyes, pesticides and polycyclic aromatic hydrocarbons. In spite of the attractive characteristics of biotransformations catalyzed by peroxidases with high selectivity and conversion at ambient temperature and pressure, their industrial applications are still negligible because of their low operational stability. Several strategies have been reported for improving peroxidases biocatalytic functionality. Among them, immobilization on mesoporous materials and nanoparticles has drawn the attention because of the interesting characteristics of the resulting biocatalyst. Immobilization of peroxidases within a pore or on a surface with special physical chemistry characteristics has allowed enhancement of the biocatalytic performance of these enzymes and produce more robust biocatalysts, which are more adapted to industrial conditions. In this work, results in the generation of biocatalysts with peroxidases, CdS nanoparticles and mesoporous materials are presented, detailing the methodology and the parameters that affect enzyme adsorption on the material such as the pore size, surface and enzyme electrical charge, chemistry of the material, enzyme concentration, enzyme structure, etc. Keywords: peroxidases, nanoparticles, mesoporous materials
References: Gandubert, V. J, Torres, E., Niemeyer, C. M., J. Mater. Chem., 2008, 18, 3824–3830; Longoria, A., Tinoco, R., Torres, E., Enzyme Technology of Peroxidases: Immobilization, Chemical and 74
Genetic Modification. In Biocatalysis based on heme peroxidases, E. Torres and M. Ayala (Eds). Springerverlag, 2010. 1st Edition, Germany. ISBN 978-3-642-12626-0 José Campos-Terán, Iker Iñarritu, Jorge Aburto, Eduardo Torres.“Enhanced functionality of peroxidases by its immobilization at the solid –liquid interface of mesoporous materials and nanoparticles”, Chapter 16, 335-352,”Proteins in solution and at interfaces: Methods and Applications in Biotechnology and Materials Science”, Juan M. Ruso Beiras y Ángel Piñeiro Guillén (Eds). John Wiley & Sons, Inc. ISBN: 9780470952511
75
Session 12: Intermolecular Forces II Co-Chair:Chair: Sylvia Thomas, University of South Florida Co-Chair: Suzanne Giasson, University of Montreal
1. The role of surface forces in the slow propagation of brittle fractures By : Anja Røyne* Department of Physics, University of Oslo anja.royne@fys.uio.no
Slow fracture propagation, also referred to as subcritical fracturing or stress corrosion cracking, plays an important role in the fatigue and long term failure of brittle materials such as rocks, ceramics, glass and metals. It has also been postulated to be the underlying mechanism for slow earthquakes and aftershocks of major earthquakes. The fracture propagation threshold and the velocity of these slowly moving fractures are highly dependent on the presence and nature of chemical species inside the aperture of the fracture. In some materials, such as glasses and metals, stress enhanced dissolution or weakening reactions at the crack tip are thought to be the primary driving mechanism. However, observations indicate that subcritical fracture propagation in crystalline rocks and ceramics is to a large extent controlled by the effects of confined fluids on the interfacial forces acting behind the crack tip. I will discuss how surface forces may influence fracture propagation in these materials, and show how surface force measurements may provide new insight on the mechanical stability of rocks and ceramics.
76
2. Wetting Measurements of Microspheres and Macroscopic Droplets using the AFM By: Patricia M. McGuiggan, Jun Ma, Samuel Rosenthal, Shengfeng Cheng*, and Mark Robbins Johns Hopkins University Baltimore, Maryland 21218, USA Virginia Polytechnic Institute & State University patricia.mcguiggan@jhu.edu Measuring the contact angle that a liquid makes with a small solid probe is more difficult than measuring the contact angle of a liquid on a macroscopic surface. In this talk, I will discuss AFM measurements of the wetting force of a liquid against a single spherical probe (radius, r â&#x2C6;ź 20 - 30 Îźm).
The measured force-distance curves are in excellent agreement with macroscopic wetting theory. From these measurements, the contact angle, contact angle hysteresis, and surface tension are simultaneously determined. In addition, when the microsphere attached to an AFM cantilever is brought into contact with a sessile water drop, the meniscus rises onto it because of capillary forces. Immediately after the initial rise of the meniscus, the microsphere oscillates about a fixed average position while partially immersed in the liquid. Because of the constant average deflection of the AFM cantilever, we can assume that the microsphere/water contact line is pinned and the measured oscillation reflects the motion of the sessile drop interface. The small (<100 nm) oscillations of the interface are readily measured with AFM. The oscillations correspond to the resonance oscillation of the entire droplet. Although the microsphere volume is 6 orders of magnitude smaller than the drop, it excites the normal resonance modes of the liquid interface. Resonance oscillation frequencies were measured for drop volumes between 5 and 200 ÎźL. The results for the two lowest normal modes are quantitatively consistent with continuum calculations for the natural frequency of hemispherical drops with no adjustable parameters. The droplet can also be driven into resonance and the resonance frequency measured by AFM. The method may enable sensitive measurements of volume, surface tension, and viscosity of small drops.
77
3. Gecko adhesion and its attachment/detachment control By: Yu Tian State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China Tel: +86-10-6278-2981, Fax: +86-10-6278-1379, E-mail: tianyu@mail.tsinghua.edu.cn tianyu@mail.tsinghua.edu.cn Geckos have extraordinary capabilities of climbing vertical walls and upside down ceilings, with strong attachment strength and easy removal. The mechanism of dry adhesion of gecko hairs with hierarchical structures down to nanometer scale and rapid switching between attachment and detachment has been the focus of scientific study for over a century. The rapid switching between gecko foot attachment and detachment is analyzed theoretically based on a tape peel model that incorporates the adhesion and friction forces originating from the van der Waals forces between the submicronsized spatulae and the substrates. The role of the soft lamellar skin in gecko toe adhesion has been experimentally revealed. The lamellar skin acting as a soft spring sustains most of the normal deformation during preloading and maintains a wide range of adhesive state rather than a repulsive state. The sequential engagement and peeling off of setal array are responsible for the reliable gecko adhesion and friction control. This soft spring supported pillar structure should be adopted in future bio-inspired adhesives design. It indicates the importance of integration and optimization of nanoscale structures as well as the incorporation of their unique, sizedependent properties into functional macroscale devices.
Keywords: Friction, Adhesion, Lamellar, Spatulae
78
4. Force of adhesion on super-solvophovic surfaces By: Juan Valentin Escobar Departamento de Física, Universidad Autónoma Metropolitana, Mexico City, Mexico escobarjuanvalentin@gmail.com
Liquids and solids are in general expected to behave very differently in their contact with a solid surface. While we know from experience that the mechanical deformation of an elastic solid sphere is perfectly reversible, a liquid drop normally deforms in an irreversible way. Nevertheless, a liquid drop in contact with a perfectly-solvophobic surface should also deform reversibly, giving rise to a loss of contact angle hysteresis. In this talk [1] I will show how thermal oxidation of a microcrystalline boron-doped diamond film creates pyramids decorated with sub-micron protrusions that turn its naturally mercuryphobic surface into perfectly-mercuryphobic. We measure the pull-up force of a macroscopic Hg drop on this surface, using a specially designed force microscope, and find it to be ~0.55μN, independent of contact pressure or area of contact, just as in the case of an elastic solid sphere and a plane. This allows us to estimate the surface energy for a flat surface (45mJ/m2) and compare with theoretical models [3]. Our force of adhesion results match the predictions of a theoretical model similar to the one put forward by Johnson Kendall and Roberts [2] in in which the surface tension of the liquid plays the role of the Young’s modulus of the elastic solid. Finally, I will demonstrate potential uses of our force microscope to study DeGenne’s pinning points and out of equilibrium wetting systems.
Keywords: Force of adhesion, Contact Angle Hysteresis, Mercury
References: [1] Force of Adhesion Upon Loss of Contact Angle Hysteresis: When a Liquid Behaves Like a Solid, Physical Review Letters, 111, 22, 226102, (2013) [2] Raul Esquivel and Juan V Escobar, in progress. [3] Surface energy and the contact of elastic Solids, K. L. Johnson, K. Kendall, and A. D. Roberts, Proceedings of the Royal Society A, 324, 301 (1971). 79
5. Dynamic version of Lindemann’s criterion: cage melting in liquids By: Jose Luis Arauz-Lara Instituto de Física Universidad Autónoma de San Luis Potosí, Alvaro Obregón 64, 78000 San Luis Potosí, S.L.P., Mexico
In this work we report experimental and theoretical results suggesting that the basic notion of Lindemann’s criterion for melting of crystalline solids also manifest itself in the dynamics of colloidal liquids. We study the motion of single colloidal particles embedded in different complex fluids, and we find that the escape of the colloidal particles from the instantaneous cage formed by neighboring particles occurs when the square root of its mean squared displacement is in the order of 1 tenth of the neighbors interparticle distance, thus following a dynamic version of Lindemann’s criterion.
80
Session 13: Intermolecular Forces III Chair: José Campos, Universidad Autonoma de Metropolitana / Cuajimalpa Co-Chair: Suzanne Giasson, University of Montreal
1. Hybrid Nanoplatforms for Multimodal Therapy Diagnosis and of Cancer By : A. Topete1, 3,*, P. Iglesias2, Iker Iñarritu3, José Campos-Terán3, J. A. Costoya2, S. Barbosa1, P. Taboada1, V. Mosquera1 1
Grupo de Física de Coloides y Polímeros, Facultad de Física
Grupo de Oncología Molecular, Facultad de Medicina, Universidad de Santiago de Compostela, 15782-Santiago de Compostela, Spain. 2
Universidad Autónoma Metropolitana-Unidad Cuajimalpa, 05348-México D.F. *topete.antonio@ gmail.com 3
Nanomedicine is an emerging field in which several disciplines such as colloid technology, biology and medicine meet. The main goal of this new area is the development of new intelligent materials at the nanoscale with multiple abilities combined in one individual system. Simultaneous multimodal therapy and diagnosis (theranosis)1 of diseases could lead to a new personalized treatment, reducing painful secondary effects and costs. In this work we present the synthesis, characterization and application of a hybrid nanostructure, called nanoshells2, made of a polymeric core (loaded with anticancer drug doxorubicin, DOXO) and a porous gold shell, which were functionalized with a complex composed by a NIR fluorophore and photodynamic therapy agent3, indocyanine green (ICG), human serum albumin (HSA), and folic acid (FA), a cancer-targeting agent. The hybrid nanostructure has a surface plasmon resonance peak at the Near Infrared window (700-1000 nm)4, which makes it an ideal nanosystem for multimodal therapy and imaging. References: 1. T. Lammers, et al., Mol. Pharm. (2010), 7: 1899-1902.
3. J. Rao, A. et al., Curr. Opin. Biotechnol. (2007), 18: 17.
2. Oldenburg, S.J. et al., Chem Phys Lett, (1998), 288: 243-247.
4. Shenkman, K. A. Crit. Care Med. (2002), 30:267.
81
2. Hydrophobic, electrostatic, and dynamic polymer forces at surfactant-modified silicone surfaces By: Michael V. Rapp1, Stephen H. Donaldson Jr.1, Matthew A. Gebbie2, Saurabh Das2, Yair Kaufman1, and Jacob Israelachvili1,2 1
Department of Chemical Engineering, University of California-Santa Barbara, CA 93106, USA
2
Materials Department, University of California-Santa Barbara, CA 93106, USA
Surfactant self-assembly is an effective way to tailor the complex forces at hydrophobic interfaces. To investigate surfactant behavior at hydrophobic surfaces, we have synthesized covalently grafted polydimethylsiloxane (PDMS) thin films on extended gold surfaces that behave as collapsed polymer brush surfaces in solution, with uniform thickness, surface coverage, and surface chemistry. The Surface Forces Apparatus (SFA) was used to measure the surface forces due to the adsorption and self-assembly of surfactants at these silicone interfaces. We find that short-chain aliphatic surfactants will adsorb to PDMS and behave as a layer of smeared-out charges, and their interaction with mica can be described by traditional double layer theory. We also show that certain polymeric surfactantsâ&#x20AC;&#x201D;containing a PDMS mid-block domain and cationic quarternary ammonium end-groupsâ&#x20AC;&#x201D;adsorb onto the PDMS surface and form unique fluctuating nanostructures. These soft nanostructures display polymer-like exploration behavior at the silicone surface and give rise to a long-ranged, rate-dependent, and temperaturedependent attractive force on approach to mica. These same polymer surfactants will mediate strong adhesion in water between silicone and mineral surfaces; specific Coulombic interactions between the cationic surfactant end-groups and mica results in a rate-dependent polymer bridging force during separation as the surfactants are pulled from the PDMS interface. Thus, we highlight the versatile array of surfactant structures that may form at hydrophobic surfaces, we emphasize the need to consider interaction dynamics at self-assembled polymer layers, and we promote the use of polymer surfactants as adhesives in wet environments.
82
SFAC 2014 Poster Presentation Listing Poster 1 - Page 85 Arenas-Gomez, Brisa brisa@fisica.unam.mx Worm-like micelles in water solutions of 1, 4 poly(1, 3-butadiene)-polyethylene oxide diblock copolymer Poster 2 - Page 86 Zhao, Wen wen@mail.usf.edu Removal of methyl orange in aquaculture water by spray-coated TiO2 photocatalysis
Poster 7 - Page 92 Cheng, Hsiu Wei cheng@mpie.de Complementary SFA and AFM Study of Room Temperature Ionic Liquid Structuring on Electrode Surfaces: Symmetric and Asymmetric System Poster 8 - Page 93 Cremaldi, Joseph jcremald@tulane.edu Oil drop interactions with surfaces varying in energy and topography
Poster 3 - Page 87 Cadirov, Nicholas ncadirov@umail.ucsb.edu Stick-slip friction of gecko-mimetic patterned surfaces on smooth and rough surfaces
Poster 9 - Page 94 Das, Saurabh saurabh@engineering.ucsb.edu Tough Coating Proteins: Subtle Sequence Variation Modulates Cohesion
Poster 4 - Page 88 Campos-Terán, José jcampos@correo.cua.uam.mx Conformational and Disorder to Order Transitions in Proteins: the role of Apolipoproteins Structure in their Function
Poster 10 - Page 95 Dobbs, Howard A. howarddobbs@umail.ucsb.edu Creation of reusable, synthetic surfaces with tunable roughness for the SFA
Poster 5 - Page 90 Cardenas-Valencia A. M. Evaluation of novel membrane interface for underwater mas spectrometers Dissolved methane separation and detection as a case study Poster 6 - Page 91 Cheemalapati, Surya cheemalapati@mail.usf.edu Design of On-Chip Blood Coagulation Sensor
Poster 11 - Page 96 Dobbs, Howard A. “Differential double-layer dissolution” of aluminosilicate materials Poster 12 - Page 97 Ducker, William A. wducker@vt.edu Preventing Bacterial Colonization Using Colloidal Crystals Poster 13 - Page 98 Gebbie, Matthew A. magebbie@engineering.ucsb.edu Ionic liquids and dilute electrolytes: the surprising connection
Poster 14 - Page 99 Giraud, Lucie luciegiraud30@gmail.com Adhesion and Friction Between Supported Core Shell pH Sensitive Polymeric Nanoparticles Poster 15 - Page 100 Guo, Fei feiguo@mail.usf.edu Effect of a natural cactus based-mucilage dispersant on the surface tension and droplet size of dispersed crude oil Poster 16 - Page 101 Iñarritu , Iker iker.inarritu@gmail.com Optimizing peroxidase and nanoparticle immobilization for enhanced enzymatic functionality in biosensors Poster 17 - Page 103 Kaufman, Yair yairkauf@icloud.com A Unified Predictive Model for Wetting of Rough Surfaces Poster 18 - Page 104 Khosla, Tushar tkhosla@tulane.edu Load Induced Hydrodynamic Lubrication of Porous Polymer Films Poster 19 - Page 105 Kienle, Daniel dfkienle@ucdavis.edu Measuring refractive index profiles of confined fluids Poster 20 - Page 106 Kurniawan, James jkurn@ucdavis.edu Structure, Charge, and Interaction Forces between Solid Supported Membranes
83
Poster 21 - Page 108 Martinez Rodriquez, Nadine Nrodriguez@lifesci.ucsb.edu Tropocollagen type-1 chain increases cohesion between mussel foot protein films
Poster 28 - Page 115 Sanden, Gulnur gefe@mail.usf.edu Probing Adhesion to Poly(N-isopropylacrylamide) Coatings Using a Spinning Disk Method
Poster 35 - Page 125 Yoon, Roe Hoan ryoon@vt.edu Thermodynamics of Solvophobic Interaction between Hydrophobic Surfaces in Ethanol
Poster 22 - Page 109 Muppaneni, Rasudha rmuppaneni@mail.usf.edu Effect of Viscosity on Fiber Formation
Poster 29 - Page 117 Sarmiento Gómez, Erick esarmiento@ifisica.uaslp.mx The Brownian motion of anisotropic colloidal particles
Poster 23 - Page 110 Oak, Shreyas soak@tulane.edu Production of Hard Carbon Spheres and surface modification to stabilize an emulsion
Poster 30 - Page 118 Schrader, Alex M. schrader@umail.ucsb.edu The Role of Interfacial Water in Short-Range Interactions between Bilayers
Poster 36 - Page 126 Zhang, Xiaoxun xx.zhang.cn@gmail.com Adhesion of monocrystal surfaces: mimicking grain boundaries in the surface forces apparatus (SFA)
Poster 24 - Page 111 Peng, Tunan tpeng@mail.usf.edu Alternative water treatment using Cactus mucilage from Opuntia spp: Application on bacteria removal
Poster 31 - Page 119 Stewart, Justin jwstewar@mail.usf.edu Micro-flow cytometry using Photonic Crystals
Poster 25 - Page 112 Pyayt, Anna cheemalapati@mail.usf.edu Lensless Diffraction Imaging of Bacteria Poster 26 - Page 113 Pyayt, Anna pyayt@usf.edu Design of optofluidic sensor for point-of-care hemolysis diagnostics Poster 27 - Page 114 Raman, Sangeetha raman@mpie.de Deciphering the scaling of single molecule interactions using Jarzynski’s equality
84
Poster 32 - Page 120 Su, Rongxin surx@tju.edu.cn Design of a Surface Plasmon Resonance Attachment for the Surface Forces Apparatus Poster 33 - Page 122 Utzig, Thomas utzig@mpie.de Investigating the specific adhesion between amine-functionalized polymers and gold surfaces: Electrochemical influences and scaling relations Poster 34 - Page 123 Vázquez Contreras, Edgar evazquezc@gmail.com The biological interface of a homodimeric protein
Poster 1
Worm-like micelles in water solutions of 1, 4 poly(1, 3-butadiene) polyethylene oxide diblock copolymer Brisa Arenas-Gomez, Marko Vincekovic, Cristina Garza, and Rolando Castillo. (IF-UNAM,CINVESTAV-IPN) The main purpose of this study is to determine for the first time the structure of the selfassembled aggregates in the system made of 1,4 poly(1,3-butadiene)-polyethylene oxide diblock copolymer (IUPAC name: poly(but-2-ene-1,4-diyl)-block-polyoxyethylene) and water, and the rheological behavior of the solution. The degree of polymerization of the polybutadiene and polyethylene oxide blocks is 37 and 45, respectively. The diblock copolymer concentration was limited to be 2.5 wt% to avoid phase separation. Small X-ray scattering revealed that the diblock copolymer self-assembles in worm-like micelles with a diameter of 12 nm. This system does not closely follow the rheological behavior of worm-like micelle solutions made of typical surfactants. The system steadily shear thins reaching very low viscosity values at large shear rates, however there are not shear-thickening peaks. In thixotropic loops, the micellar solution does not present hysteresis. The viscoelastic spectra do not follow the Maxwell model at low and intermediate frequencies. This uncommon behavior for a worm-like micellar system is explained by the slow dynamics of the self-assembly. The extremely high hydrophobicity of the polybutadiene block does not allow any micellar rearrangement.
85
Poster 2
Removal of methyl orange in aquaculture water by spray-coated TiO2 photocatalysis Wen Zhao1, Yangyang Zhang1, Laura R. Gonzalez2, Fei Zhong3, Daniela Stebbins1, Sandra Pettit1, Sarina Ergas2, Norma Alcantar1 1. Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, FL, U.S.A 2. Department of Civil and Environmental Engineering, University of South Florida, Tampa, FL, U.S.A 3. Marine Fisheries Research Institute of Jiangsu Province, Nantong, Jiangsu, P.R. China
Aquaculture is one of Floridaâ&#x20AC;&#x2122;s major profitable industries. Although it brings considerable income, the negative environmental impact of aquaculture include high energy and freshwater consumption, release of nitrogen containing wastewaters, and off-flavor compound generation. Geosmin and 2-methylisoborneol (MIB) are two kinds of representative off-flavor componds, which will reduce the quality and marketability of the fish products. Photocatalysis is a very effective technology, which has a high potential to remove many organic pollutants, including off-flavor compounds. Titanium dioxide is the most widely used photocatalyst, which has been shown to have a relatively high activity. In this project, methyl orange was used as a surrogate compound for off-flavor compounds. TiO2 particles were immobilized onto glass plates by a spray-coating method. Several experiments were applied to optimize the photocatalyst reactor performance. Adhesion of TiO2 nanoparticles to the surfaces of the glass plates was verified. Removal of TiO2 was insignificant, even after one week of flushing deionized water through the reactor. A photocatalysis reactor was designed, constructed and tested for methyl orange removal. Optimal conditions for reactor operation included a catalyst loading rate 0.25 mg/ cm2, water depth of 2 mm and liquid flow rate of 2.5 mL/s. Methyl orange removal rate was compared in both aquaculture water and DI water. Due to the presence of natural organic matter (NOM) in the aquaculture water, the methyl orange degradation rate decreased from 0.73 hr-1 to 0.44 hr-1.
86
Poster 3
Stick-slip friction of gecko-mimetic patterned surfaces on smooth and rough surfaces Nicholas Cadirov, Saurabh Das, Sathya Chary, Jack Hogan, Kimberly L. Turner, and Jacob N. Israelachvili, University of California Santa Barbara
The discovery and understanding of geckoâ&#x20AC;&#x2122;s frictional-adhesion adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. However, few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, especially considering the frictional forces. This work utilizes a modified Surface Forces Apparatus (SFA) to measure frictional forces between a micro-array of tilted polydimethylsiloxane (PDMS) gecko-mimicking flaps against smooth and rough glass surfaces. Interesting phenomena occur on smooth and rough surfaces including stick-slip friction where the surfaces undergo constant attachments and detachments during shearing, as well as interlocking mechanisms between gecko-like structured adhesives and rough surfaces. Friction forces also tend to be stronger when shearing along the direction of the tilt of the flaps compared to shearing against the tilt. The results demonstrate the significance of preload, shearing velocity, and commensurability of the two surfaces in order to ensure a secure attachment.
87
Poster 4
Conformational and Disorder to Order Transitions in Proteins: the role of Apolipoproteins Structure in their Function José Campos-Terán1, Paola Mendoza-Espinosa2, Rolando Castillo3 and Jaime Mas-Oliva2 1
Departamento de Procesos y Tecnología, DCNI, Universidad Autónoma Metropolitana-Cuajimalpa, D.
F., México; 2Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, D. F., México; 3
Instituto de Física, Universidad Nacional Autónoma de México, D. F., México.
A great number of biological processes occurring at the cell membrane level are induced by interactions of proteins with the lipidic membrane. In general, most of these active biological components are amphiphilic and bear positive net charge at pH 7, two features favoring their insertion into lipid membranes. In addition, their biological activity is often related to their high propensity to form alpha helices structures. However, in contrast to the notion established for many years that protein function depends on rigid 3D structures, nowadays there is important evidence suggesting that non-structured segments of proteins play important roles in protein function. Therefore, disorder-to-order dynamic conformational transitions have been proposed as an attractive mechanism involved in protein–protein recognition. The case of apolipoproteins (apos) is an example where a good knowledge of the role of the secondary structure in protein activity seems essential. Apos combine with lipids in order to form different classes of lipoprotein particles, which are involved in the plasma transport and mobilization of molecules such as cholesterol, triglycerides and phospholipids from and to cell membranes. Apos apparently give lipoproteins directionality and the ability to interact with receptors at the surface of cells. Apos such as apo A-I, apo A-II, apo C-I and apo E3 are known as exchangeable apos because of their ability to move and exchange between different lipoprotein particles. This exchange is driven by protein-protein and protein-lipid interactions. Although these apos present no similarities in their primary structure, important similarities appear at the secondary level, mainly due to the presence of amphipathic alpha helices as their main structural motif. In this work, adsorption and surface interaction studies with apo C-I (a monomer) and apo A-II (a dimer) at different interfaces (air-water, solid-water, lipid monolayers) are reviewed, detailing how the protein interactions could give way to a mechanism where disorder to order transitions result in how apos modulate their function, namely protein/enzyme activity and self exchangeability between lipoprotein particles.
88
References: “Forces between Hydrophilic Surfaces Adsorbed with Apolipoprotein AII Alpha Helices”, Salvador Ramos, José Campos-Terán, Jaime Mas-Oliva, Tommy Nylander and Rolando Castillo. Langmuir, 24 (2008), 85688575. http://dx.doi.org/10.1021/la800348y “Conformational and Disorder to Order Transitions in Proteins: Structure/Function Correlation in Apolipoproteins” José Campos-Terán, Paola Mendoza-Espinosa, Rolando Castillo, Jaime Mas-Oliva. Chapter 17, Pags. 331-358. “Protein-Protein Interactions: Computational and Experimental Tools”, Weibo Cai and Hao Hong (Eds). Intech, Rijeka, Croacia. ISBN 978-953-51-0397-4. http://dx.doi.org/10.5772/37217
89
Poster 5
Evaluation of novel membrane interface for underwater mas spectrometers Dissolved methane separation and detection as a case study A. M. Cardenas-Valencia1, T. Gentz2, M. Schlueter2, R. T. Short1 1
Marine and Space Sensing Program, SRI International, U.S.A,2 Alfred Wagener Institute for Polar and
Marine Research (AWI), Bremerhaven, Germany A component that has enabled the development of underwater mass spectrometers is a mechanically supported membrane interface probe. Our two research groups have used metallic porous frits that support polydimethyl siloxane (PDMS) membranes embedded in a heated membrane probe assembly, allowing the deployment of the underwater membrane introduction mass spectrometer (MIMS) instruments to ocean depths of 2000 meters. The fabrication of such frits has consisted of shaping larger Hastalloy C porous materials to the size required to support a PDMS capillary of 0.64 mm ID and 1.19 mm OD using a diamond-coated wheel and Dremel tool. This procedure is time-consuming and cumbersome, and the porosity of the final frits is likely not reproducible. To facilitate the fabrication of the membrane assembly, we report on the use of new porous metallic structures. Frits with diameters of approximately 3.0 mm (1/8â&#x20AC;?) and known porosities (48.3 % and 32.5%) were produced by the Fraunhofer Institute in Dresden, Germany, using powder metallurgical processes. We used these frits to fabricate new membrane interface assemblies. Using a new custom-heated membrane probe with the new porous frits, we performed calibrations relating dissolved methane concentrations to mass spectrometer response (m/z 15) using linear least-squares fitting procedures. Both the limit of detection (methane concentration in the tens of nanomolars) and the sensitivity (on the order of 10-1 pico-amps/nanomole of methane) were found to be comparable with those obtained with the previously fabricated Hastelloy C frits. The calibration parameters for the new assembly were also found to be a function of the flow rate (reveling the flux inlet dependence on the interface boundary layer), temperature, and sample hydrostatic pressure.
90
Poster 6
Design of On-Chip Blood Coagulation Sensor Surya Cheemalapati, Harry Tuazon, Anna Pyayt University of South Florida, Department of Chemical and Biomedical Engineering
Here we propose a new design of an on chip continuous blood coagulation sensor measuring the change in refractive index of blood which increases with coagulation. The main sensor component is an optical wave guide, therefore it can be made very small and be integrated on a chip. The change in reflected power from the waveguide-blood interface is monitored as blood coagulates. Fresnelâ&#x20AC;&#x2122;s equation is used for extracting the information about the refractive index. The system is analyzed using three-dimensional FDTD simulations for optimization of the sensor design for potential work with the whole blood samples. At first, the noise due to the presence of cell is calculated. Next, the design of a waveguide cladding-based filtering structure for elimination of the noise from cells is proposed and significantly decreased noise level is demonstrated using simulations
91
Poster 7
Complementary SFA and AFM Study of Room Temperature Ionic Liquid Structuring on Electrode Surfaces: Symmetric and Asymmetric System Hsiu Wei Cheng*, Theodoros Baimpos, Philip Stock and Markus Valtiner Department of Interface Chemistry and Surface Engineering, Max-Planck Institut für Eisenforschung GmbH, Max-Planck-Straße 1, D-40237, Düsseldorf, Germany.
In the last few years room temperature ionic liquids (RTILs) have gained ample interest not only due to their unique solvent properties, RTILs are interesting solvents for electrochemistry and energy conversion. RTILs provide a wide solvent-stability window over large potential regimes, compared to aqueous and conventional organic solvents. Any energy conversion is an interface process, and as such the solvent structuring at an electro active interface determines electrochemical reaction mechanisms as well as kinetics. Force probe experiments are an ideal tool to study solvent structuring at interfaces in great detail. Yet, there are considerable disagreements in the recent literature between experiments using atomic force microscopy (AFM) and surface force apparatus (SFA). Here, we measure and compare RTILs layering at various electrode interfaces (Mica, Pt, Au …) measured by both SFA and AFM. We focus on two different RTILs (EMIM BTI and EMIM TFMS) and discuss mica-mica (symmetric) and mica-platinum (asymmetric) systems. Further, X-ray Photo Spectroscopy (XPS) was also used to study the surface chemical composition (anion to cation ratio) of surfaces covered by thin layers of RTILs. We have discovered very pronouns liquid layering events only near mica surfaces using both SFA and AFM analysis. The comparisons of symmetric and asymmetric, as well as metallic/non-metallic systems clearly indicate the solvent structuring behaviors are strongly affected by surface geometry, charge distribution as well as system symmetry.
92
Poster 8
Oil drop interactions with surfaces varying in energy and topography Joseph C. Cremaldi, Tushar Khosla, David Cutting, Kristen Wollman, Noshir Pesika Department of Chemical and Biomolecular Engineering, Tulane University During an oil spill, oil droplets have the potential to spread on a variety of marine surfaces which may be harmful to living organisms. Biological surfaces represent a range of surface structures and chemistries, both of which affect their interactions with oil droplets. Contact angle measurement represents a method of taking both of these factors into account through measurement of the overall surface activity, and the Cassie-Baxter approximation allows one to model them. In this study, we aim to quantify the interaction of oil with various surfaces, first on flat surfaces of varying wetting properties and then with the added contribution from surface structure. By understanding the type and magnitude of these interactions, our aim is to develop novel oil dispersants (which can be used during an oil spill) that prevent oil droplets from adhering to or contaminating marine life.
93
Poster 9
Tough Coating Proteins: Subtle Sequence Variation Modulates Cohesion Saurabh Dasa, Dusty R. Millerb, Yair Kaufmana, Nadine R. Martinez Rodriguezc, Alessia Pallaorod, Matthew J. Harringtonf, Maryte Gylysd, Jacob N. Israelachvilia, e, 1, J. Herbert Waiteb, c, d, e, 1 a
Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA, bBio-
molecular Science and Engineering, University of California, Santa Barbara, California 93106, USA; cDepartment of Molecular, Cell & Developmental Biology, University of California, Santa Barbara, California 93106, USA; dDepartment of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA; eMaterials Research Laboratory, University of California, Santa Barbara, California 93106, USA. fDepartment of Biomaterials, Max Planck Institute for Colloids and Interfaces, 14424 Potsdam-Golm, Germany Mussel foot protein-1(mfp-1) is a coating protein that forms the major constituent of the protective cuticle covering all exposed portions of the byssus that anchors the marine mussels to mineral surfaces in harsh intertidal zone. The reversible interaction between the Dopa side-chains in the protein and Fe3+ in the cuticle is thought to be responsible for its ability to accommodate core strains of up to 120% in M. californianus while simultaneously contributing to its disparate stiffness. We have investigated the interactions between mfp-1 from two mussel species, M. californianus (Mc) and M. edulis (Me), and Fe3+ using both surface sensitive and solution phase techniques. Our results show that although both mfp-1 (Mc) and its homologue, mfp-1 (Me), bind iron, mfp-1 (Mc) forms intramolecular bonds whereas mfp-1(Me) forms intermolecular bonds. We also show that the cohesive force of interaction between the organic films of mfp-1 (Mc) is maximum for protein deposited at 50 Îźg/ml. Increasing the deposition concentration decreased the interaction energy significantly showing that increasing the amount of protein does not always increase cohesion. Addition of Fe3+ did not change the cohesion energy between the mfp-1 (Mc) films significantly at pH 5.5. However, iron mediates the bridging between the mfp-1 (Mc) films at the physiologically relevant pH of 7.5, when most of the mussel foot proteins lose their ability to adhere reversibly. This preservation of cohesion between the protein films at high pH is through the formation of multivalent bonds between Fe3+ and Dopa which prevents the oxidation of Dopa to Dopa-quinone. Given that the cuticle of M. californianus withstands twice the strain of M. edulis cuticle bolsters the argument that the innate attraction found in mfp-1 (Mc) films may be important for the engineering of strain tolerant composite coatings for biomedical applications.
94
Poster 10
Creation of reusable, synthetic surfaces with tunable roughness for the SFA Howard A. Dobbs, Yair Kaufman, Jeffrey S. Scott, Jacob N. Israelachvili University of California Santa Barbara
One of the main challenges in using the Surfaces Forces Apparatus (SFA) to measure the physical forces between surfaces is the requirement of molecularly smooth surfaces. Currently, muscovite mica is used as the basic substrate surface because of its ability to cleave macroscopic, molecularly smooth surfaces, chemical inertness and transparency; however, surface preparation is a delicate process where mistakes in the cleaving of ultra-thin mica sheets, back-silvering of a reflective coating layer, or gluing procedures can lead to unusable surfaces. Furthermore, mica surfaces are only usable for a limited amount of time before the surfaces are damaged or dirtied, preventing further or repeated use. With a biased sputtering deposition, we have successfully created silica surfaces with a root mean squared (RMS) roughness comparable to that of mica, 0.1 nm, that are also robust and reusable with a standardized cleaning process. Moreover, the nature of the deposition technique allows for fine-tuning of the surface roughness of the prefabricated disks. An initial investigation into the effects of surface roughness on adhesion and friction using the SFA is reported and compared with the predictions of the JKR theory, which describes the contact mechanics of two flat surfaces.
95
Poster 11
“Differential double-layer dissolution” of aluminosilicate materials Howard A. Dobbs, Kai Kristiansen, Jacob N. Israelachvili, Bradley F. Chmelka University of California Santa Barbara In geological systems, local removal of material between different rock grain contacts under high compressive stress in aqueous environments has been repeatedly observed and traditionally described as a “pressure solution” effect wherein the driving force of dissolution is due to the higher solubility of materials under lithostatic stress which create large chemical potential gradients near the grain contact. Previous work by the Israelachvili group using a Surface Forces Apparatus (SFA) has shown that changes in the electrical potential difference between quartz and mica surfaces correlate with the changing quartz dissolution rate, even at relatively low applied pressures (effective lithostatic stresses),1 suggesting that the driving force may be electrochemical rather than purely mechanical in nature. Using an SFA, we have measured the dissolution rates of silica and alumina nanoparticles trapped between two mica surfaces at room temperature as a function of the salt solution chemistry, applied voltage, and applied pressure. Our results show that the dissolution rate is strongly affected by the cation concentration and applied voltage in basic solutions, pH 10 to 13, indicating that enhancement of the dissolution is due to an induced electrochemical stress between two asymmetric materials when their electronic double layers overlap, which is appropriately termed “differential double-layer dissolution.” A fundamental understanding of the enhanced dissolution mechanism provides new insight into the behavior of geological systems while also driving future applications in industry. By controlling the difference between the electronic double layer potentials, dissolution can be enhanced at relatively benign solution conditions for aluminosilicate materials, making industrial application of aluminosilicate binder systems, e.g. cement, more feasible. 1
96
Greene, G.W., et al., Geochimica et Cosmochimica Acta, 73, 2862–2874 (2009).
Poster 12
Preventing Bacterial Colonization Using Colloidal Crystals Mehdi Kargar,a Amy Pruden,b and William A. Duckerc a. Department of Mechanical Engineering,Virginia Tech, Blacksburg, VA, USA. b. Via Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, USA. c. Department of Chemical Engineering, Virginia Tech, Blacksburg, VA, USA.
Bacterial infections are one of the leading causes of human misery, and hospital acquired infections alone are the fourth most common cause of death in the US. The most common medical treatment of device and implant infections is long-term systemic treatment with antibiotics; an alternative strategy for reducing the incidence of these infections is to alter the properties of medical surfaces to delay colonization by bacteria. Here we investigate the use of topography to prevent bacterial colonization. The hypothesis is that a highly curved surface will be less favorable for bacterial adhesion and colony formation. We investigated the adhesion and colony formation of Pseudomonas aeruginosa PAO1 on a solid coated in close-packed spheres of polystyrene. Solids were pretreated with serum and then exposed to bacteria under low shear for one day in a center for disease control biofilm reactor. Whereas flat sheets are covered in large colonies after one day, a close-packed layer of 630â&#x20AC;&#x201C;1550 nm monodisperse spheres prevents colony formation. Moreover, the film of spheres reduces the density of P. aeruginosa adhered to the solid by an average of 80%. Our data show that when P. aeruginosa adheres to the spheres, the distribution is not random. For 630 nm and larger particles, P. aeruginosa tends to position its body in a 2-fold site. We rationalize the selectivity on the basis of energy minimization for adhesion: sites differ in the deformation needed to achieve a given contact area. We rationalize the inhibition of colonization by the 630â&#x20AC;&#x201C;1550 nm spheres in terms of the lack of adjacent favorable positions for bacteria. A closepacked layer of polystyrene spheres also delays colony formation on a medical-grade stainless-steel needle over a period of one day. This suggests that a colloidal crystal approach to biofilm inhibition might be applicable to a variety of materials and geometries. 97
Poster 13
Ionic liquids and dilute electrolytes: the surprising connection Matthew A. Gebbie1, Howard A. Dobbs2, Markus Valtiner2, Xavier Banquy2, Eric T. Fox3, Wesley A. Henderson3, Jacob N. Israelachvili1,2 1
Materials Department, 2Department of Chemical Engineering,
University of California, Santa Barbara, CA 93016 3
Department of Chemical and Biomolecular Engineering,
North Carolina State University, Raleigh, NC 27695
Since ionic liquids are composed solely of ions, dilute electrolyte theory is typically presumed to be inapplicable for modeling their electrostatic screening properties. We performed equilibrium forcedistance measurements across the common ionic liquid [C4mim][NTf2] using a surface forces apparatus with in situ electrochemical control. Our results show an exponentially decaying force consistent with the formation of a diffuse electric double layer, where the characteristic decay length (the effective Debye length) is in quantitative agreement with a simple thermodynamic model where only a small fraction of the ionic liquid ions are thermally dissociating to behave as effectively free ions. The remaining ions behave as a highly correlated ionic medium, analogous to electrically charged thermal excitations in semiconductor materials. Thus, outside of strongly surface bound, non-mean field ion layers, ionic liquids can be conceptualized as dilute electrolyte solutions in confined interfaces, which is likely valid in bulk solution as well. These results resolve several scientific paradoxes and may also suggest new molecular mechanisms of ionic transport in ionic liquids.
98
Poster 14
Adhesion and Friction Between Supported Core Shell pH Sensitive Polymeric Nanoparticles L. Giraud1, S.Giasson1,2 1
Faculty of Pharmacy, Université de Montréal, lucie.giraud@umontreal.ca
2
Department of Chemystry, Université de Montréal, suzanne.giasson@umontreal.ca
C.P. 6128, succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7
Static and dynamic interaction forces between two pH-sensitive polymeric nanoparticle monolayers irreversibly attached onto mica surfaces and immersed in water were investigated using the Surface Forces Apparatus. The NPs were core-shell made of a polystyrene (PS) core covered with a polyacrylic acid (PAA) shell. The weakly charged polyelectrolyte shell (PAA) can undergo changes in the degree of ionization upon changes in pH or ionic strength allowing physico-chemical properties such as volume, surface potential and structure to be modulated. Such NPs are promising materials for designing smart materials whose surface properties (adhesion, permeability) and interactions with the surrounding environment can be modulated in response to an external stimulus or signal. Surface force measurements were carried out to assess the adhesion, friction and resistance to the compression and shear of the nanoparticles (NPs) under different pH. The normal and friction forces between two opposing NPs monolayers were strongly dependant on the pH. The range of the normal forces increased with pH suggesting an increase in the swelling of the immobilized NPs associated with an increase in the degree of ionization of the PAA. The normal forces were purely repulsive regardless of pH indicating the absence of adhesion. The friction forces significantly decreased with increasing the swelling of the NPs. Comparison with other studies on friction between different polymer-coated surfaces will be presented in order to elucidate the role of the polymer structure in controlling friction.
99
Poster 15
Effect of a natural cactus-based mucilage dispersant on surface tension and droplet size of dispersed crude oil Fei Guo1, Daniela Stebbins1,3, Tunan Peng1, Sylvia Thomas2, Ryan Toomey1 and Norma Alcantar1 1
Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, FL, USA
2
Department of Electrical Engineering, University of South Florida, Tampa, FL, USA
3
Water Treatment Plant at City of Tampa, Florida, USA
Cactus mucilage is extracted from the cactus plant Opuntia ficus-indica, commonly known as Nopal or Prickly pear. The extraction process yields two types of mucilage: a non-gelling extract (NE) and a gelling extract (GE). These two mucilage extracts have been used to stimulate the dispersion process of the oil phase into the water phase in common oil-in-water (O/W) emulsions and to aid the stabilization of the oil/mucilage droplets into the system by lowering the surface tension and maintaining the interfacial forces differential close to zero. We evaluated the effect of the cactus plant-based mucilage on the surface tension and droplet size of dispersed crude oil in O/W emulsions. Cactus mucilage extracts and conventional dispersants were evaluated under different conditions and concentrations, including two concentrations of oil (3, 6% v/v) and several dispersant-to-oil ratios (1:1,1:3, 1:20, 1:40) at room temperature. Synthetic seawater and surrogate oil (crude oil from BP with properties similar to the Macondo rig) were used. The results of the dispersion obtained using mucilage extracts were compared with results using conventional dispersants (Corexit® EC9500A). The average droplet size in systems treated with 1.5% w/v of NE cactus mucilage was 5 µm/droplet; where as the average droplet size in systems treated with 1.5% w/v of Corexit® EC9500A was 6.2 µm/droplet. In addition, Corexit® EC9500A and cactus mucilage dispersions showed similar long-term stability of droplet formation. The surface tensions of oil/water emulsion dropped from 60 mN/m to 40 mN/m. Although the mucilage is known as a non-toxic substance and is digestable, the toxicity of the two mucilage extracts was assessed in cold-blooded animals. A standard EPA toxicity test using Daphnia magna colonies exposed to both NE and GE mucilage extracts in concentrations ranging from 0 to 2000 mg/L showed that mucilage can be considered as non-toxic to the evaluated species with a median lethal concentration (LC50) above 2000 mg/L. Cactus mucilage is an alternative technology to mitigate the damage that oil may cause to the aquatic ecosystem and can minimize undesired effects associated with the use of synthetic dispersants in oil spills. 100
Poster 16
Optimizing peroxidase and nanoparticle for enhanced enzymatic functionality in biosensors immobilization 1
1
2
1
Iker Iñarritu , Antonio Topete , Eduardo Torres , José Campos-Terán . 1
Departamento de Procesos y Tecnología, DCNI, Universidad Autónoma Metropolitana Unidad Cuajimalpa.
2
Centro de Química ICUAP, Benemérita Universidad Autónoma de Puebla.
iker.inarritu@gmail.com
Introduction. Biosensors use a sensing biological molecule connected to a transducer, which translates a physical or chemical change to a measurable signal; this makes biosensors very specific and easy to use. However, their low stability can make them expensive, so an increase in operational and storage stability as well as maintaining enzymatic activity stable are needed for their practical use (1). It is therefore necessary to find and evaluate the physicochemical factors that determine the activity of peroxidases – nanoparticles systems to generate a robust biosensor. Peroxidases and CdS nanoparticles (QDs, synthesized by reverse micelles method (2)) have been successfully immobilized by our research group on solid surfaces to improve their operational stability and functionality as biosensors. However, the immobilized system detaches from the support after triggering enzymatic activity. This limitation can be overcome by confinement of the system, since enzymatic activity has been shown to maintain (3) or even increase its level (4). This system has been created on silica surfaces silanized with vaporized 3 – aminopropyltriethoxysilane (APTES), followed by adsorption of QDs on these surfaces, and finally by chloroperoxidase (CPO) or horseradish peroxidase (HRP) immobilization. Methods. Adsorption kinetics were measured with a Quartz Crystal Microbalance (QCM-D), using the Sauerbrey equation to correlate changes in oscillation frequency of a piezoelectric silica crystal with the adsorbed mass on its surface. The components are then rinsed with buffer to verify correct adsorption. The bulk concentrations required for achieving a monolayer were determined for each component. After immobilization, enzymatic activity was triggered by irradiating the system with 365 nm UV light to create reactive oxygen species (ROS) from the QDs. Amplex Red® was used as substrate and its conversion to Resorufin was measured by UV-Vis spectroscopy at 572 nm. Results. Several immobilization sequences have been tested for enhancing enzymatic functionality (Figure 1): Bulk: Enzymatic activity measured in solution.
Monolayer: A monolayer of QDs followed by a monolayer of HRP were immobilized. Layer by layer: Immobilization of the equivalent to half of a QDs monolayer followed by a HRP monolayer; and finally another half of a QDs monolayer. 5x QDs monolayer: The equivalent of 5 QDs monolayers followed by a monolayer of HRP.
101
Figure.1 Normalized enzymatic activity for HRP-QDs system with different immobilization sequences.
The normalized activity of all immobilized systems was enhanced compared to the bulk. This work explores and analyzes the differences in enzymatic activity between immobilized systems.
Acknowledgements. UAM-PCNI, ICyTDF (ICYTDF-FFUTPICTGDF-2008) and CONACYT (Becario No. 234651).
References. 1. Niemeyer, C.M; Mirkin, C.A. (2004). Nanobiotechnology. Wiley Interscience:; p 469. 2. Gandubert V.J; Torres E, Niemeyer C.M. (2008). J Mater Chem.18: 3824 – 3830. 3. Soni S, Desai J.D; Devi S (2001). J. Appl. Polym. Sci. 82:1299 – 1305. 4. Sato S, Murakata T, Ochifuji M, Fukushima M, Suzuki T. (1994). J. Chem. Eng. Jpn; 27: 732 – 736.
102
Poster 17
A Unified Predictive Model for Wetting of Rough Surfaces Yair Kaufman, Himanshu Mishra and Jacob Israelachvili
Thermodynamic equilibria at solid-liquid-gas interfaces, which involve interplay of intermolecular and surface forces, manifest as contact angles, θr. On flat and (atomically) smooth surfaces, the equilibrium contact angles, θo, can be accurately predicted by the Young-Dupré equation (if the interfacial tensions are known). However, predicting contact angles on irregular rough surfaces, θr, when the asperities are not completely filled by the liquid is not straightforward. When a liquid comes into contact with a rough surface it can partially (wetting state 1) or completely (wetting state 2, also known as the Wenzel’s state) fill the pores on the surface (see figure). Both the states render different θr , which can be quasi-stable or thermodynamically stable depending on the pore geometry. The Cassie-Baxter’s model for wetting is often used to estimate the wet (liquid-solid) and dry (liquid-vapor) area fractions on a rough surface after the contact angles θr have been measured. However, there is no model that could be employed to predict θr for a liquid-solid-gas interface apriori, given the θo. During the talk, a unified model for wetting of smooth and rough surfaces, especially with reentrant features, will be presented. This model predicts θr apriori by considering the following geometrical features of a surface (via electron- and atomic force microscopy): (1) typical slopes (αmin), (2) typical distances between the asperities (L), (3) typical sizes of the cavities (R), and (4) the intrinsic/ thermodynamic contact angle on the flat surface θ0. Furthermore, the model analyzes the stability of the apparent contact angle, θr, for a given pore geometry via an energy minimization approach. These insights should be helpful towards designing stable omniphobic and omniphilic surfaces via engineering specific surface topographies.
103
Poster 18
Load Induced Hydrodynamic Lubrication of Porous Polymer Films Khosla Tushar, Cremaldi Joseph, Pesika Noshir Department of Chemical and Biomolecular Engineering, Tulane University In our project, we study the tribological properties of porous polymer based surfaces under induced loads in aqueous conditions. Using a universal materials tester, we show how it is possible to change the lubrication regime from boundary lubrication to hydrodynamic lubrication even at relatively low shearing velocities. We hypothesize that the compressed liquid under pressure produces a repulsive hydrodynamic force as it is extruded from the pores. This reduces the effective area of contact between two shearing surfaces resulting in low coefficient of friction. The porous polymer samples are prepared from poly methyl siloxane (PDMS) and polyurethane (PU) using conventional photolithography and molding techniques. Specifically the effect of pore density and the pore depth is studied to optimize the design that offers the least coefficient of friction. The potential applications of such low friction, biocompatible, flexible surfaces could be as a coating in joint replacement implants.
104
Poster 19
Measuring refractive index profiles of confined fluids Daniel F Kienle and Tonya L. Kuhl University of California, Davis Department of chemical engineering and materials science
This work describes a surface force apparatus (SFA) data analysis method for determining the optical thickness of thin films or any variation in the refractive index of a fluid near a surface. The technique does not require contacting or confining the fluid or film. By analyzing data taken at many inter-surface separation distances out to at least 300 nm, the properties of a film can be quantitatively determined. The film can consist of material deposited on the surface, or variation in a fluidâ&#x20AC;&#x2122;s refractive index near a surface resulting from, for example, a concentration gradient, depletion in density, polymer brushes, or surface roughness. The method is demonstrated using aqueous polyethyleneimine (PEI) adsorbed onto mica substrate, which has a large concentration and therefore refractive index gradient near the mica surface. The layer thickness determined using the proposed method is consistent with the compressed thickness measured using conventional SFA methods. Additionally, a thorough investigation of the effects of random and systematic error in the surface force apparatus data analysis and modeling are described in detail.
105
Poster 20
Structure, Charge, and Interaction Forces between Solid Supported Membranes James Kurniawan and Tonya Kuhl Department of Chemical Engineering and Material Science University of California at Davis Solid supported bilayer systems have been used as the platform to study lipid membranes that mimic the fundamental physical properties and the thermodynamics of biological membranes. In this first part of this work, I will describe and compare various techniques that are used to construct these membranes with well-defined composition in order to isolate and study specific properties of biological membranes. Langmuirâ&#x2C6;&#x2019;Blodgett (LB), Langmuirâ&#x2C6;&#x2019;Schaefer (LS), and vesicle fusion technique are frequently used to deposit symmetric, asymmetric, and/or mixed membranes on substrates such as atomically smooth mica and glass. Proper techniques with appropriate deposition parameters are necessary to deposit a wellpacked supported bilayer for subsequent studies. For example, this work demonstrates that drying the inner monolayer after LB deposition can significantly increase the transfer ratio of the outer monolayer to yield a higher packed membrane. In the second part of the work, I will compare SFA measurements of the membrane thickness and interaction forces of mixed lipid systems with other characterization methods such as neutron and x-ray scattering, atomic force microscopy (AFM), zeta potential, and fluorescence microscopy (FM). In particular, a binary mixture of saturated PC lipid with cholesterol, and ternary mixture of unsaturated (both single and double unsaturation) PC lipid, saturated PC lipid, and cholesterol were studied. In all cases, a weak, long-range electrostatic repulsion was found in these supposedly neutral membrane systems. Corroborative AFM and zeta potential measurements indicated that the electrostatic repulsion is due to a small level of charged lipid impurities verses from membrane spanning holes that exposed the underlying mica surface. At contact, the membranes were adhesive. The magnitude of the adhesion was greater than the van der Waals interaction between pure PC membranes without cholesterol. The enhanced adhesion was primarily attributed to hydrophobic attraction due to the presence of 106
nanoscopic membrane defects which exposed the underlying membrane leaflet. The interaction forceâ&#x2C6;&#x2019; distance profiles also demonstrated that the defects enabled membrane restructuring in the contact region.
107
Poster 21
Tropocollagen type-1chain increases cohesion between mussel foot protein films Nadine R. Martinez Rodrigueza, Saurabh Dasb, Yair Kaufmanb, Wei Weic, Herbert Waiteb,c,1 and Jacob Israelachvilib,c,1 a
Department of Molecular, Cell & Developmental Biology,
University of California, Santa Barbara, California 93106, USA. Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA.
b
c
Materials Research Laboratory, University of California, Santa Barbara, California 93106, USA.
Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, USA. d
Marine mussels use a mixture of proteins to form a byssus and adhere to surfaces in a harsh intertidal environment. These proteins have been extensively studied on mineral and metal surfaces; however, there have been no studies on its bonding interactions with another structural protein. Here we report the bridging interaction of Collagen type-1, the most abundant protein found in the human body and mussel foot proteins (mfp) using a surface forces apparatus (SFA). We used a hydrophilic and hydrophobic variant of mfp-3 to assess the nature of interaction between the protein and collagen. We find that collagen intercalates to mfp-3 (both hydrophobic and hydrophilic) layer and is also responsible for bridging two mussel protein films. The bridging interaction is persistent between two oxidized mfp films and the cohesion is maintained. At low pH, collagen increases the cohesive energy of interaction between un-oxidized mfp_ 0.2 mJ m-2 to Wad = 7.2 Ă&#x201A; 0.6 mJ m-2. Oxidation significantly decreased the cohesion 3 from Wad = 5.4 + between mfp-3 (Wad = 3.4 _+ 0.7 mJ m-2), however, collagen recovered the cohesion (W = 7 Ă&#x201A; 0.7 mJ ad
m-2). Our results show that mfp-3 interacts with collagen through electrostatic and hydrogen bondng interactions. These results have important implications on the development of synthetic polymers for medical and dental glue applications.
108
Poster 22
Effect of Viscosity on Fiber Formation Sylvia W. Thomas1, Manopriya Devisetty1, Hruday Chand Katakam1, Samuel Perez1, Erica Wilkes2, Fei Guo3, Norma Alcantar3, Rasudha Muppaneni1 1
University of South Florida, Department of Electrical Engineering
2
Science Department, King High School
3
University of South Florida, Department of Chemical & Biomedical Engineering
4202 E. Fowler Ave., ENB118, Tampa, FL 33620, U.S.A.
Electrospinning is a process in which the surface tension of a polymer solution is influenced by an electric field and then undergoes plastic stretching to form fibers. A polymer cone forms at the tip of a needle and a jet of fibers are collected on a collector plate as a non-woven web. The nanofibers are collected in spiral manner with diameters ranging from nanometers to a few microns. Parameters, which may affect the formation of fibers, are the infusion rate, applied voltage, temperature, and/or distance to the collector, etc. Although there are many operational and material parameters that affect the fiber formation, it has been noted that viscosity has a significant affect when compared to the others. The change in the concentration of the solution changes its viscosity measurements. It is suggested that this change in viscosity will impact the formation of fibers and the reduction of bead formation. This paper mainly focuses on tracking concentration versus viscosity and its effect on fiber formation. Different polymer solutions of natural materials and dopants show changes in viscosity and successful fiber formation. The natural material, cactus mucilage from the Opuntia ficus-indica, is mixed with a polymer solution called polystyrene and a solvent, D-limonene, in different volume ratios of 70:30, 50:50, 30:70. For low concentrations of cactus mucilage:polymer to solvent, fiber formation is low and the solution electrosprays. For higher concentrations, electrospun nanofibers are formed and a fiber membrane is fabricated. Viscosity measurements are collected and mapped to concentration and fiber formation. This cactus nanofiber membrane is used as a water filter to demonstrate functionality of removing arsenic content from water. Atomic Fluorescence Spectrometry (AFS) tests are performed using polystyrene and D-limonene: mucilage nanofibers and results show removal of up to 18.94% of arsenic.
109
Poster 23
Production of Hard Carbon Spheres and surface modification to stabilize an emulsion. Shreyas Oak, Kate Roberts, Mary Kate Holleran, Noshir Pesika Tulane University, Department of Chemical and Bimolecular Engineering The aim of this research is to create an oil in water emulsion using modified hard carbon spheres. This can be an alternative method for containing and cleaning oil spills. The use of hard carbon spheres possibly achieves both goals through the formation of Pickering emulsions for stabilization and the introduction of steric barriers at the interface for coalescence prevention. Untreated graphitic carbon spheres are oleophilic and thus sit primarily in the oil phase. However creation of an oil in water emulsion requires the particles to be biased towards the water phase. To achieve that, hard carbon spheres are modified by grafting polymer brushes on their surfaces, making them more hydrophilic. This poster mainly focusses on production of hard carbon spheres, modification of their surface chemistry to make them more hydrophilic and contact angle analysis of wafers coated with different polymers.
110
Poster 24
Alternative Water Treatment using Cactus Mucilage from Opuntia SPP: Application on Bacteria Removal Tunan Peng, Fei Guo, Daniela Stebbins, Ryan Toomey and Norma Alcantar Throughout the past decade an increasing amount of attention has been drawn to the water contamination problems that affect the world. As a result, a variety of purification methods targeted at communities in developing countries have surfaced and, although all have contributed to the effort of improving water quality, few have been accepted and sustained for long term usage. Case studies indicate that the most beneficial methods are those which use indigenous resources, as they are both abundant and readily accepted by the communities. Cholera is a rapidly dehydrating, diarrheal can cause disease that kills within hours if no proper treatment can be done in time and it affects millions of people every year (WHO 2011). The cholera outbreak in Haiti that followed a powerful earthquake in 2010 motivated this study. The purpose of this experiment is to investigate an alternative treatment to remove bacteria from water using a natural biomaterial that can be used by communities in need. The mucilage that we are using is from Opuntia ficus-indica specie, commonly known as Nopal or Prickly pear cactus. The Nopal cactus pads are readily available, inexpensive and have been used to clean water by ancient communities in Mexico. Extensive research in our group has shown that the mucilage is efficient at removing turbidity, bacteria (E. coli and Bacillus sp.) and arsenic from contaminated water. We also are investigating the conditions under which cactus mucilage will be able to reduce the levels of a surrogate for Vibrio Cholerae, named Vibrio furnissii. Lyophilized pellets of the surrogate bacteria were purchased from a testing laboratory specialized in environmental and public health threats. Although the higher concentration of the mucilage (10 mg/L) did not decrease the bacteria concentration, the lower concentration of the mucilage (1 mg/L) removed 25% of the original concentration of the bacteria on the top of the water column. The treatment using 1 mg/L of mucilage plus calcium carbonate was determined to remove 40% of the bacteria. These preliminary studies suggest that mucilage from the Opuntia ficusindica is a viable flocculation method for Cholera. Its low cost, accessibility, and current use as a food source in low income communities give mucilage great potential as a water treatment method for areas such as Hati that have had devastating bacterial contaminations.
111
Poster 25
Lensless Diffraction Imaging of Bacteria Karthik raj Konnaiyan1, Edikan Archibong1, Anna Pyayt1 1
Department of Chemical & Biomedical Engineering, University of South Florida
Prompt detection of bacterial contamination of food, drugs and biological fluids is very important. Traditional methods are time consuming and require culturing, gram staining and biochemical analysis, while there is need in technology that can be portable, low cost and requiring minimum time delays. Here, we present a new bacteria detection method based on laser diffraction imaging followed by automatic bacteria detection and classification. The main benefits of this approach are low cost components that can be used for creation of a low cost setup. Diffraction of a laser beam on a sample containing low concentration of bacteria is recorded with a camera and diffraction pattern is analyzed using specialized image processing software. The software is programmed to count bacteria and determine its morphology. This process is accomplished by converting the RGB image into grayscale that is interpreted by particle classifier tool to identify microstructures, the microstructures are then differentiated by comparing the image with the pattern templates that are stored in the database. The results are compared with the images obtained using traditional microscopy to control quality of automatic detection. This method is a simple portable solution without the use of specialized equipment, antibodies or chemicals, which makes it as an attractive pre-screening technology for health and food monitoring.
112
Poster 26
Design of optofluidic sensor for point-of-care hemolysis diagnostics Edikan Archibong1, Justin Stewart1, Harry Tuazon1, Anna Pyayt1 1IBIS Lab, Chemical & Biomedical Engineering, University of South Florida, Tampa, FL. 33260
The risk of women in developing countries dying from pregnancy-related cause is ~25 times higher compared to women living in high income countries. One of the major reasons of maternal and fetal deaths are preeclampsia that can result in a dangerous complication â&#x20AC;&#x201C; HELLP syndrome - characterized by H - hemolysis, EL - elevated liver enzymes, LP - low platelet count. Early diagnosis of the HELLP syndrome is the key to the prevention of the development of the worst symptoms including organ failure followed by death of the mother and the fetus. This requires near patient detection of in-vivo hemolysis. Current methods of hemolysis detection only work for blood plasma, what requires sample preprocessing, use of centrifuges and other expensive equipment and access to trained technicians. Here, we proposed a theoretical design of a point-of-care optofluidic hemolysis sensor that can work with the whole blood and conducted detailed FDTD simulations of optical components, together with the theoretical and computational optimization of the microfluidic sub-system.
113
Poster 27
Deciphering the scaling of single molecule interactions using Jarzynski’s equality Sangeetha Raman*, Thomas Utzig, Theodoros Baimpos, Buddha Ratna Shrestha and Markus Valtiner Department of Interface Chemistry and Surface Engineering, Max-Planck Institut für Eisenforschung GmbH, Max-Planck-Straße 1, D-40237, Düsseldorf, Germany.
Unraveling the complexity of the macroscopic world based on molecular level details relies on understanding the scaling of single molecule interactions towards integral interactions on the macroscopic scale. Here we demonstrate how to decipher the scaling of individual single acid-amine interactions towards the macroscopic level through a synergistic experimental approach combining equilibrium Surface Forces Apparatus (SFA) experiments and non-equilibrium single molecule force spectroscopy (SM-AFM). Combining these two techniques is ideally suited for testing the largely praised Jarzynski’s equality (JE), which relates the work performed under non-equilibrium conditions with the equilibrium free energy. Equilibrium SFA measurements scale linearly with the number density of acidbase bonds at an interface, providing acid-amine interaction energies of 10.9 ± 0.2 kT. Irrespective of how far from equilibrium AFM experiments are performed, the energy calculated using JE converges similarly to 11 ± 1 kT. Our results validate the direct applicability of Jarzynski’s equality to unravel the scaling of non-equilibrium single molecule interactions to scenarios where a large number of molecules simultaneously interact, giving rise to macroscopic equilibrated interaction energies. As such, the developed approach provides a unique strategy for molecular design of novel functional materials through predicting of large-scale properties such as adhesion or cell-substrate interactions based on single molecule or simulation experiments.
114
Poster 28
Probing Adhesion to Poly(N-isopropylacrylamide) Coatings Using a Spinning Disk Method Gulnur Sanden and Ryan Toomey. University of South Florida, Tampa, FL 33620, USA Introduction: The majority of proteins change structure upon adsorption to a solid surface, which has important implications for the regulation of biological functions such as cellular response. It is widely recognized that “switchable” coatings, such as poly(N-isopropylacrylamide), or PNIPAAm, offer the ability to tune protein adsorption. Surface force apparatus (SFA) and atomic force microscopy (AFM) have been used to characterize surface forces and the morphology of proteins adsorbed on switchable surfaces. However, questions remain regarding the relations between the specific architecture of the switchable surface and adhesion of biomolecules. In order to address this, we have implemented a spinning disk method to quickly measure adhesion to cross-linked PNIPAAm coatings. We have also investigated the characteristics of the adsorbed IgG proteins on the coatings with quartz crystal microbalance with dissipation (QCM-D).
Materials and Methods: The spinning disk experiments were performed at 24°C (hydrophilic state) and 42°C (hydrophobic state) for 10 μm sized bare poly(styrene) (PS) microspheres, carboxylated PS microspheres and IgG coated PS microspheres on NIPAAAm photo-cross-linked coatings. To generate the coatings, NIPAAm was copolymerized with the photo-cross-linking monomer, methacroyloxybenzaphenone (MaBP). Solutions of poly(NIPAAm-co-MaBP[0.3 - 3 mol%]) were spin casted on plasma cleaned glass substrates. Cross-linking was accomplished by exposing the film to UV light (365 nm) for 30 minutes. Quantification of the adhesion strength of the PS probes and IgG on PNIPAAm coatings was achieved through obtaining hydrodynamic detachment shear stress profiles of the probes and IgG from the PNIPAAm surfaces.
Results and Discussion: The adhesion of hydrophobic bare PS microspheres scaled linearly with the thickness of the PNIPAAm coating in the hydrophilic state (24°C). The adhesion strength varied from 118 dyne. cm-2 to 142 dyne.cm-2 for a dry thickness between 10 nm and 24 nm. Interestingly, the values of the adhesion strength were greater for the hydrophilic state than the hydrophobic state until the dry film thickness 115
surpassed 24 nm.
In the case of hydrophilic carboxylate PS microspheres, the trend was altered and the adhesion was observed to always be greater on the hydrophilic state compared to the hydrophobic state by a factor of 2.5 between the dry thickness values of 10 nm and 36 nm.
The IgG coated PS spheres showed a similar trend as a function of film thickness for both hydrophilic and hydrophobic PNIPAAm surfaces. The adhesion strength values for the hydrophobic state were higher by approximately factor of 1.7 with respect to hydrophilic state. For a dry thickness of 10 nm the adhesion strength values of hydrophilic and hydrophobic states were 36 dyne.cm-2 and 60 dyne.cm-2, respectively. These results showed a strong agreement with QCM-D measurements. Moreover, by lowering the crosslink density by factor of 10 the adhesion strength value at the hydrophobic surface increased from 74 dyne.cm-2 to 162 dyne.cm-2 between dry thicknesses values of 165-185 nm. The IgG adhesion on PNIPAAm surfaces with 0.3% crosslink density scaled linearly with increasing thickness at both hydrophilic and hydrophobic states. The IgG adhesion exhibited a strong dependence on thickness with approximately a 3-fold increase at the hydrophobic state. Finally, aging studies of carboxylate PS probes on PNIPAAm with 3% crosslink density showed that the adhesion strength at both hydrophilic and hydrophobic states increased linearly as the PS adsorption time was increased from 3hrs to 48 hrs.
Conclusion: The adhesion characteristics of surface attached PNIPAAm coatings have been investigated as a function of coating thickness and structure in correlation with phase transition of the coatings. The adhesion of PS probes and IgG was successfully quantified via spinning disk method. Our findings will help in design of intelligent biomaterial surfaces in respective areas such as tissue engineering.
116
Poster 29
The Brownian motion of anisotropic colloidal particles Erick Sarmiento Gómez1, José Ramón Villanueva Valencia2, Manuel de Jesús Sánchez Miranda1, Edilio Lázaro Lázaro1, Ramón Castañeda Priego2, Magdaleno Medina Noyola1, José Luis Arauz Lara1 1
Instituto de Física, Universidad Autónoma de San Luis Potosí
2
División de Ciencias e Ingenierías, Universidad Autónoma de Guanajuato
One of the main features of colloidal particles is their Brownian motion. Meanwhile detection of translational motion is relatively easy, direct visualization or detection of rotational Brownian motion, as well as production of monodisperse anisotropic colloidal particles has not been an easy task, and fundamental concepts of anisotropic dynamics remain untested. In this work I will present experimental results of the Brownian motion of anisotropic particles under different circumstances. The first system under study is a colloidal mixture of dumbbells and spherical particles confined in a quasi 2D geometry. In this case, hydrodynamic coupling, direct and mediated by the confining walls, plays an important role, thus both translational and rotational motion depends on the total colloidal concentration, however an universality of the ratio of the short time diffusion coefficient of the dumbbell and the monomer was found. In the second system, a mixture of optically anisotropic spherical particles and a nonabsorbing polymer with a radius of gyration similar to the size of the spherical particles was studied, hydrodynamic interactions are negligible, but direct interactions affect both translational and rotational motion in a similar way and experimental results are consistent with theoretical predictions coming from the simplest polymer-colloid interaction, the Asakura-Oosawa mixture. Finally, the case of the motion of a Brownian anisotropic particle in presence of a periodical external field is analyzed, in this case, Brownian motion is hindered because of the interaction of the anisotropic particle with the external field, giving a complex dynamics that depends on the strength of the periodical potential and its periodicity. Our results give an insight of the characteristic features of the coupling between rotational and translational dynamics, on the hydrodynamic interaction between isotropic and anisotropic colloidal particles and of the effects of external periodical fields in the additional degrees of freedom of a anisotropic colloidal particle. 117
Poster 30
The Role of Interfacial Water in Short-Range Interactions between Bilayers Alex M. Schrader, Stephen H. Donaldson Jr., Dong Woog Lee, Songi Han, Jacob N. Israelachvili
Short-range, water-mediated interactions determine the stability of many colloidal suspensions, thin films, and biological assemblies, including materials used in a number of water-based products in the printing, paint, cosmetics, and fuel industries, among others. In many cases, water is thought to give rise to a repulsive and short-range â&#x20AC;&#x2DC;hydration forceâ&#x20AC;&#x2122; (not accounted for by DLVO theory) which prevents particles and surfaces from aggregating or adhering, but the nature of such solvent-structural effects between lipid membranes is disputed. The present work serves to further quantify the magnitude of bilayer hydration interactions through SFA measurements between phospholipid bilayer and mica surfaces in additive-modified solutions. Dimethyl sulfoxide (DMSO) is an additive which displays a number of phenomena attributed to its interactions with lipid membranes and interfacial water, most notably cryoprotection and nonselective membrane permeability enhancement. In this work, SFA measurements between gel-phase dipalmitoylphosphatidylcholine (DPPC) membranes in DMSO/water mixtures show DMSO to increase adhesion and decrease equilibrium separation between the membranes, with the measured separation distances in quantitative agreement with x-ray and neutron scattering results in the literature. The decay length of the exponential repulsion decreased with increasing DMSO concentration, reaching unmeasurably small values by 15 mol% DMSO. An analogous series of experiments between mica surfaces in alkali and tetramethylammonium chloride solutions shows that DMSO decreases the decay length of the repulsion attributed to dehydration of adsorbed cations. In conjunction with EPR and NMR measurements of head group mobility in DPPC vesicles, the SFA measurements infer the ability of DMSO to both dehydrate and suppress thermal fluctuations of head groups. The results further suggest that water structure in the first and second hydration layers of head groups considerably impacts the decay length of the exponential repulsion.
118
Poster 31
Micro-flow cytometry using Photonic Crystals Justin Stewart, Anna Pyayt University of South Florida, 4202 E. Fowler Avenue, Tampa, F.L., 33620 Author e-mail address: pyayt@usf.edu
Photonic crystals serve as powerful building blocks for on-chip photonics. They can be used for a wide range of miniature devices from very compact waveguides to resonators and sensors. Here we present a design of a miniature photonic crystal-based flow cytometer. While traditional large size flow cytometers are very important for analysis and counting of individual cells, they are very expensive, not readily portable and have to be operated in a lab by trained professionals. Use of photonic crystals allows to create miniature device that can be placed on chip, mass produced and be used outside of the lab. The proposed design has been studied using specialized FDTD software, and multiple important flow cytometry functionalities have been demonstrated. Based on spectral and statistical analysis we demonstrated potential for counting individual cells, characterizing their shape, monitoring refractive index of the buffer fluid and the possibility of performing these studies using multiple wavelengths1. Further analysis of transmission signals and use of statistical concepts of central moments allows for simultaneous extraction of information about cell shape, size, and refractive index. [1] J. Stewart and A. Pyayt, â&#x20AC;&#x153;Photonic crystal based microscale flow cytometryâ&#x20AC;?, Optics Express. 22(11), 12853-12860 (2014)
119
Poster 32
Design of a Surface Plasmon Resonance Attachment for the Surface Forces Apparatus Rongxin Su 1,2, Xiaoxun Zhang 2, Kai Kristiansen2, Jeff Scott2, Jacob Israelachvili 2,* 1
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China
2
Chemical Engineering Department, University of California, Santa Barbara, CA 93106, USA
E-mail: surx@tju.edu.cn; jacob@engineering.ucsb.edu
The combination of surface plasmon resonance (SPR) with the surface forces apparatus (SFA) is described (Fig. 1a). The SPR attachment comprises an input white light source, a collimator producing a parallel beam, a polarizer, a glass prism coated with a gold layer (Fig. 1b), an output collimator coupling the light into optical fiber which is connected to the inputs of a spectrometer. This setup will allow simultaneous SFA and SPR measurements to be made in the same experiments (Fig. 2). The upper surface used in the SFA will be a gold nanofilm, which will also serve as the SPR sensor (i) to sensitively study mass transfer between two surfaces after contact, (ii) to real-time monitoring of the kinetic of specific binding as a function of the separation distance, and (iii) to in situ examination of the changes in the conformations of molecules (e.g., polymers) adsorbed on or trapped between the surfaces under normal and shear forces. With the aid of the accurate distance control of the SFA, the effect of distance between the gold nanofilm and the molecules (at the apposing mica surface) on the SPR signal can be directly studied.
Fig. 1. (a) 3D Sketch of the proposed SPR-SFA setup, and (b) glass prism coated with gold layer sitting in the SFA box for the upper surface
120
Fig. 2. Scheme of simultaneous SFA and SPR measurements of intermolecular and surface interactions by SPR-SFA.
121
Poster 33
Investigating the specific adhesion between amine-functionalized polymers and gold surfaces: Electrochemical influences and scaling relations T. Utzig, Düsseldorf/GER, S.H Donaldson Jr., Santa Barbara/USA, M.A. Gebbie, Santa Barbara/USA, S. Raman, Düsseldorf/GER, B.R. Shrestha, Düsseldorf/GER, J.N. Israelachvili, Santa Barbara/USA and M. Valtiner, Düsseldorf/GER Thomas Utzig, Interface Chemistry and Surface Engineering, Max-Planck-Institute for Iron Research GmbH, D-40337 Düsseldorf
Polymers are widely utilized as protective coatings to prevent metal surfaces from wear, corrosion, or bio-fouling. Yet, stability and adhesive properties of polymer to metal bondings are not fully understood at the molecular level. In this poster, we present measurements of the interaction forces between a gold electrode surface and amine-functionalized polymers (PEG) using an electrochemical Surface Forces Apparatus. We examined the potential dependence of specific amine-gold interactions and measured that the binding strength of amine-gold bonds can range from 0.5-40 kbT per binding site, depending on the applied electrochemical potential. Notably, this interaction exhibits a pronounced minimum around the potential of zero charge, where the polymer-gold adhesion is dominated by non-specific interactions between the polymer backbone and electrode surface, consistent with the adhesion of PEG polymers with gold surfaces in the absence of amine functionalization. Further we investigated the scaling of this specific interaction from a single molecular (AFM) level up to a macroscopic (SFA) level, where approximately 107 molecules interact simultaneously. The combination of these two types of experiments provides unique, scale-bridging insight into the complex interplay of adhesive interactions, specific ion adsorption and unspecific background interactions, which potentially impact design and optimization of polymer coatings for numerous applications.
122
Poster 34
The biological interface of a homodimeric protein Edgar Vázquez Contreras1* and María Elena Chánez Cárdenas2. 1.- Departamento de Ciencias Naturales, DCNI, Universidad Autónoma Metropolitana Unidad Cuajimalpa. Av. Vasco de Quiroga N° 4871 Esq. Carlos Graef, Col. Santa Fe Cuajimalpa, Del. Cuajimalpa de Morelos. C.P. 05348, México, D. F. evazquez@correo.cua.uam.mx 2.- Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía, México, DF, México
In general, the inner region of the protein three-dimensional structure is maintained by mainly hydrophobic interactions. Conversely their exterior consists primarily of hydrophilic amino acids residues; they are the ones that maintain direct contact with water, the main component of the medium for soluble proteins. Only on this condition the proteins can generate the function for which they were created by nature, i.e. forming an interface with the environment. This interface is formed naturally between the amino acids residues of the exterior of the protein and the medium in which they are located, this is a biological interface. When this interface is disturbed, such as when environmental conditions favor the exposition of the hydrophobic region - that is hidden in the interior of proteins - to the environment, the macromolecule function disappears. The three-dimensional array that allows function is only maintained when the interface between the residues of the protein and the medium containing it, is appropriate. Indeed, the stability of the structure of proteins is only marginal and is disturbed by small changes in the ambient (by varying the temperature, pH or the concentration of specific molecules), then the biological interface that allows the existence of the function it is very delicate. In all proteins studied to date, the three-dimensional structure is mainly formed by perfectly ordered interactions between their amino acid residues. These interactions are of non-covalent nature and include hydrogen bonds and hydrophobic interactions, but some can also be ionic. Among the variety of classifications that exist to sort proteins, there is a category of macromolecules which are formed by more than one subunit or monomer, that are generically known as oligomers being the homodimers the simplest because they are composed by only two identical subunits. The complexity at this level is very large because exist oligomeric proteins that have dozens of different types of subunits. In general, when the region that joins the subunits involved in this type of proteins was studied, 123
it was found that is mainly a hydrophobic area; means that the amino acid residues that structured this region are mostly nonpolar. Within the oligomers there are some for which the function or stability of its subunits exist even when they are not forming the aggregate, these are called non-forced oligomers. But there are others for whom the isolated subunits are unstable or they lack of function, they are called forced oligomers. Among the latter is triosephosphate isomerase, which is the enzyme that catalyzes step 5 of glycolysis, the biological process of energy production under anaerobic conditions. In this study we present our results about the nature of the interface formed between the subunits of a forced homodimeric protein. It will be show results of function, structure and stability, and the use of site-directed mutagenesis to construct a protein that allows us to understand the factors involved in the correct formation of the interface between the subunits and how this is involved in the forced nature displayed by the function of this protein. This work was supported by CONACyT MĂŠxico (47310308)
124
Poster 35
Thermodynamics of Solvophobic Interaction between Hydrophobic Surfaces in Ethanol Zuoli Li and Roe-Hoan Yoon* Center for Advanced Separation Technologies Virginia Tech Blacksburg, Virginia 24061 AFM surface force measurements have been conducted in pure ethanol using gold surfaces hydrophobized with alkanethiols (CnSH) with n = 2-16. The results show that the measured forces are net attractive and become stronger with decreasing thickness of the thin liquid films (TLFs) of ethanol confined between hydrophobic surfaces. The measured forces increase with increasing chain lengths, increasing surface hydrophobicity, and decreasing temperature. A thermodynamic analysis of the surface forces measured at 5 to 35 oC show that the solvophobic interactions entail decreases in both excess film enthalpy and entropy with decreasing film thickness. It has been found also that the changes in the excess film enthalpy (DHf) are larger in magnitude than the corresponding changes in the TDSf term, indicating that the solvophobic interactions are enthalpic. Despite the high degrees of enthalpyentropy compensations observed, the Gibbs free energy changes remained negative, suggesting that the structural changes associated with significant entropy decreases may aid the solvophobic interactions. The structural changes may involve small changes in the number densities and/or the strengths of hydrogen bonds across the film thickness as well as the possible changes in ethanol conformation. *Corresponding author: Department of Mining and Minerals Engineering Phone: 540-231-7056 Fax: 540-231-3948 e-mail: ryoon@vt.edu
125
Poster 36
Adhesion of Metal Surfaces and Mimicking Grain Boundaries in Surface Forces Apparatus (SFA) Xiaoxun Zhanga,b, Rongxin Suc,b, Kai Kristiansenb, Tobias Brown-Heftb, Mihir Pendharkarb, Saurabh Dasb, Howie Dobbsb, Jeff Scottb, Jacob N. Israelachvilib & Chris Palmstrømb a
School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, China University of California Santa Barbara, Santa Barbara, CA 93106, USA
b c
School of Chemical Engineering, Tanjin University, Tanjin 300072, China
Understanding the nanoscale processes of adhesion, cold welding, and fracture of metals is important in the area of materials science such as the strength of materials, sintering, cracking, and grain boundaries. Using a Surface Forces Apparatus (SFA), we studied the various forces and energies associated phenomena while simultaneously visualizing the changing shapes of the contact (adhesion) junctions at the nanoscale in real time. The surfaces with the same materials (e.g., Au-Au or Pt-Pt) or different materials (e.g., Au-Pt) were brought into contact, with control at the angstrom level, and the interaction force-distance profiles were measured on approach, contact, and separation. We also proposed a novel method to study adhesion and friction of Fe grain boundaries in SFA. The monocrystalline Fe films were grown on mica with a buffer layer of MgO by the molecular beam epitaxy (MBE) technique. The lattice quality and orientations were determined in situ by reflection high-energy electron diffraction (RHEED). The roughness and morphology of the monocrystalline surfaces were observed by an atomic force microscope (AFM). The force-distance relationships between the two monocrystalline surfaces can be obtained using the SFA, and will form basis of calculating the cohesive strength of a grain boundary contact. The methods and results presented in this study have important implications in understanding the thermodynamic and kinetic interaction of metallic surfaces and grain boundaries at the nano-scale.
Keywords: Surface Forces Apparatus (SFA); Metallic adhesion; Grain boundary; Cold-welding; Interfaces.
126
Hotel Map
127
Cancun Region Map
128
Condesa III Presentation Room All talks will be held in the Condesa III room located within the Convention Center.
129
Notes
130
Notes
131
Notes
132
Notes
133
Surface Forces Apparatus Conference 2014 Cancun, Mexico â&#x20AC;˘ August 24-29
978-0-9790189-2-3