Statistical mechanics of complex materials and biological systems
PHILLIP GEISSLER ALDO DE BENEDICTIS DISTINGUISHED PROFESSOR OF CHEMISTRY MEMBER, AMERICAN CHEMICAL SOCIETY
WARDED THE DONALD STERLING NOYCE PRIZE FOR EXCELLENCE IN UNDERGRADUATE TEACHING A AND THE UC BERKELEY DISTINGUISHED TEACHING AWARD ALFRED P. SLOAN FELLOWSHIP AND A KAVLI FRONTIERS FELLOW
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Phillip Geissler uses theory and computer simulations to study molecular phenomena at the frontiers of physical chemistry. His work spans a variety of systems ranging from aqueous solutions and interfaces to biomolecular assemblies, to nanoscale materials. These systems share essential motifs of disorder and heterogeneity that are amenable to the tools of modern statistical mechanics. Using those tools, he explores emergent physical principles which govern complex molecular systems. “A characteristic feature of the microscopic world is that nothing stands still. For instance, if you look at a glass of water on a macroscopic scale, it will appear that nothing is happening,” Geissler states. “It looks completely placid. But it is universally true that if you zoom in and focus on what’s going on at the scale of nanometers or angstroms the molecules are in constant motion.” His work with longtime collaborator Richard Saykally, a physical chemist in the department, has clarified many aspects of these molecular motions in liquid water. For example, their combined experimental and theoretical approach resolved a forty year old question about how water molecules arrange themselves in a liquid drop. They demonstrated that nearby molecules in water adopt not just a few intermolecular structures, but instead a whole continuum of arrangements – from strong hydrogen bonds to highly distorted geometries. They later showed how dissolved salts can stick to the interface between liquid water and air, controlled in part by microscopic undulation of the liquid’s surface.
College of Chemistry, UC Berkeley
ON CREATING THEORETICAL SOLUTIONS What are examples of your research in statistical mechanics? PG — In a very recent example, we showed that active particles – self-propelled particles that move in different ways than typical molecules – can crystallize much as common substances do. Like bacteria and flocks of birds, these particles consume energy to power their motion and thus do not follow familiar laws of equilibrium thermodynamics. And yet they can condense and crystallize in close analogy to water. This tantalizing result suggests that we can eventually understand living, nonequilibrium systems with principles and concepts similar to those we currently teach in undergraduate physical chemistry. My young theory colleagues David Limmer and Kranthi Mandadapu are doing important research to discover such new laws. In another example, we worked with Berkeley Lab material scientist Thomas Russell to develop a way to print 3-D structures composed entirely of liquids. The approach uses a modified 3-D printer to inject threads of water into silicone oil, sculpting tubes made of one liquid into another liquid. The key is a special nanoparticle-derived surfactant that locks the water in place, in essence a special soap that prevents the tubes from breaking up into droplets. Our theoretical contribution helped establish a physical basis for the locking mechanism, which gives clues on how to improve these nanoparticles. What kinds of theoretical problems interest you? PG — What fascinates me is how the variability of microscopic structure can dictate the way things work. The kinds of problems that appeal to me are problems where the answer is not a single structure, or not just an average, but the answer really lies in understanding what underpins those variations and what combinations of molecular motions are important to how a particular phenomenon works..
