PROGRAM 3: SUMMARIES New Engineered Biopolymers and Synthetic Polymers

P3.2 Hydrophobic-Hydrophillic Switching of Proteins and Synthetic Polymers

49 Development of stimuli responsive biopolymers for controlling froth stability Leader: Prof Chun-Xia Zhao (UoA)

Key Personnel:

Dr Chris Richie (Monash)

Dr Susana Brito Abreu (UQ)

Prof David Weitz, AI (Harvard)

PhD Student: Yang Li (UQ/UoA)

50 Development of stimuli responsive RAFT polymers Leader: Dr Chris Ritchie (Monash)

Key Personnel:

Prof George Franks (UOM)

Prof Yongjun Peng (UQ)

A/Prof Seher Ata (UNSW)

PhD Student: Samadhi Fernando (Monash)

Yuxi Liu (Monash)

51 Development of stimuli responsive RAFT polymers for controlling froth stability Leader: Prof Yongjun Peng (UQ)

Key Personnel: Prof San H. Thang (Monash)

Chemical Science

Bo Fan, San H. Thang et al., 2022, 13, 4192

A series of stimuli-responsive peptides and proteins have been designed at the UoA for making foams and emulsions. A stimuli-responsive peptide AM1 and a protein DAMP4 have been systematically characterised in terms of their foaming ability, and bubble size, surface tension and bubble stability in comparison with traditional frothers such as MIBC, DPM (di(propylene glycol) methyl ether), and DPG (dipropylene glycol). Furthermore, peptides with smaller molecular weight were designed and synthesised allowing not only stimuli-responsive functions, but also low production cost which are essential for their practical applications. The Monash team has developed novel stimuli-responsive fluorescent unnatural amino acids. Discussions between the two groups will be continued to combine the strength of the two labs.

This project looks to develop a series of novel compounds based on the naturally occurring light, pH and temperature responsive flavylium chromophore via synthetic chemical approaches. The bioavailability of chemical feedstocks to eventually replace novel synthetic reagents is a significant consideration for any new reagent to be feasibly utilised in mineral processing (cost and biodegradability – environmental impact). To this end, the team devised and prepared switchable small molecule surfactants and polymers that can be tuned to have significantly different responses to temperature and light depending on their composition and structure. The differing states have been shown to possess dramatically different frothing properties and affinity for gangue materials such as quartz and a range of clays. Detailed thermo- and photochemical characterisation of these materials is underway to determine rate constants which will be correlated with the performance of the reagents using traditional characterisation of froth stability and flotation performance.

Through a systematic variation of the RAFT block copolymers structures by controlling the number of incorporated poly( n -butyl acrylate) (PBA) units during copolymerisation, a series of block copolymers were generated with different molecular weights and functionalities as characterised using GPC (gel permeation chromatography) and NMR (nuclear magnetic resonance) at Monash. The generated structure features in RAFT copolymers played a significant role in governing the corresponding properties such as quartz mineral collection, and binding affinity to engender surface hydrophobicity as correlated by flotation, contact angle measurements and interfacial behaviour in accordance with foam/frothing studies. The RAFT copolymers presented unique insights and opportunities into the future to impart hydrophobicity on quartz while simultaneously controlling molecular surface activity and unwanted froth stabilisation compared to dodecylamine (DDA).