(520a) Random Polyampholyte Amphiphilic Copolymers As Fouling-Resistant Membrane Selective Layers with Controlled Pore Size and Chemistry

Membranes offer a highly energy-efficient, simple to operate, scalable and portable separation method for many applications, from water treatment to oil and gas processing to pharmaceutical manufacturing. Yet, their broader use is often limited by insufficient selectivity and/or fouling with complex feeds. Self-assembly of functional polymeric materials is a powerful platform for designing membranes capable of new and more efficient separations. Here, we present a new class of self-assembled random amphiphilic copolymers that, when used as selective layers of thin film composite (TFC) membranes, result in membranes with broadly tunable selectivity in the ultrafiltration-nanofiltration range along with excellent fouling resistance. These polymers, amphiphilic polyampholytes (APAs), are water-insoluble random/statistical terpolymers that comprise hydrophobic, anionic, and cationic monomers that is insoluble in water. When APAs are rod-coated onto a porous support to form a TFC membrane, it self-assembles to crate disordered bicontinuous domains as narrow as 1.3 nm whose size is controlled by monomer chemistry and the ratio of anionic and cationic monomers. The salt and small organic molecule selectivity can be tuned by controlling the ratio of positive and negative monomer subunits of our copolymers, through a combination of changes in pore size and surface charge. For instance, it is possible to prepare membranes whose rejection of sodium sulfate from 5% to 93% with no significant change in effective pore size. Furthermore, these membranes are extremely fouling-resistant to a wide variety of feeds, especially when the molar ratio of anionic and cationic groups is 1:1. This approach allows access to a very broad array of functional groups lining the effective nanopores of these membranes, opening the door for complex separations while maintaining scalability and reliability.