Zwitterionic polymers, comprising anionic and cationic groups on the same repeat unit, display many intriguing properties: They are extremely resistant to fouling, exhibit high degrees of hydration, show complex interactions with ionic groups, and are responsive to ionic strength as well as specific ions. Zwitterionic amphiphilic materials, such as surfactants, have a strong tendency to self-assemble. Recent work has shown that Zwitterionic Amphiphilic Copolymers (ZACs), statistical copolymers that combine zwitterionic and hydrophobic repeat units, self-assemble to create disordered bicontinuous domains as small as 1-2 nm over a broad composition range. These materials can create extremely fouling-resistant membrane selective layers whose properties and selectivity can be tuned by controlling their chemistry. However, the narrow range of commercially available zwitterionic monomers and difficulties in dissolving and processing resultant polymers limit their utility. This presentation will focus on how amphiphilic terpolymers that incorporate a combination of anionic, cationic, and hydrophobic repeat units, termed Amphiphilic PolyAmpholytes (APAs), can behave similarly to ZACs in terms of self-assembly, fouling resistance, and membrane performance, particularly when the equimolar amounts of anionic and cationic monomers are incorporated into the polymer. Resultant membranes, prepared using scalable approaches, exhibit excellent fouling resistance, coupled with selectivity in roughly the nanofiltration range, prepared using scalable approaches. The self-assembled structure and membrane selectivity can be further tuned by changing the ratio of anionic and cationic monomers, as well as changing the chemical structure of charged groups. This approach can significantly broaden the range of chemical functional groups that can be incorporated into these membranes, opening the door for better control over selectivity and interactions for future applications.
