(342d) Self-Assembly of Zwitterionic and Charged Random Copolymers for Membranes with Exceptional Performance

Membranes offer a highly energy-efficient, simple to operate, scalable and portable separation method for applications that range from water treatment to oil and gas processing to pharmaceutical manufacturing. Yet, their broader use is typically limited by their limited selectivity and/or fouling in the presence of complex feeds. Polymer self-assembly is a powerful tool for developing new membranes with controlled nanostructure and pore chemistry. Many efforts in this field have focused on block copolymers, resulting in membranes with impressive features and performance. This presentation will instead focus on the self-assembly of random copolymers that combine hydrophobic repeat units with zwitterionic or charged monomers. Due to the very high incompatibility between these units, self-assembly occurs despite the very short segment lengths. The resultant materials feature a bicontinuous network of hydrophilic domains through which water and solutes permeate, held together by the hydrophobic regions. The random architecture, coupled with post-treatment steps such as cross-linking, enable membranes with extremely small effective pore sizes, from ~1.5 nm pores that separate dyes and salts, down to 0.9 nm pores the perform ion separations. Using cross-linkable zwitterionic amphiphilic copolymers (ZACs), we have developed membranes that can separate not only based on ion size and charge, but also based on the favorability of ion-zwitterion interactions, leading to unprecedented selectivity between like-sized anions. More recently, we have also shown that amphiphilic polyampholytes, defined as terpolymers that combine hydrophobic, anionic, and cationic monomers, can behave similar performance to ZACs, exhibiting tunable, controlled pore size, excellent fouling resistance, and high permeance. Importantly, this new material family offers us broader freedom to design the chemical environment in the nanopores, addressing new precision separations.