Enhanced oil-fouling resistance of poly(ether sulfone) membranes by incorporation of novel amphiphilic zwitterionic copolymers

In this study, a novel amphiphilic copolymer, poly(carboxyl betain methyl acrylamide-co-3,3,4,4,5,5, 6,6,7,7,8,8,8-tridecafluorooctyl acrylate) P(CBMA-co-TFOA), with zwitterionic and fluorinated moieties was synthesized by free radical polymerization and a subsequent quaternization reaction. The synthesized copolymers acted as additives and were blended with poly(ether sulfone) (PES) to fabricate low oil-fouling PES membranes through nonsolvent induced phase separation (NIPS). The prominent surface enrichment of hydrophilic zwitterionic (CBMA) and low surface energy (TFOA) segments on the membrane surface was verified by X-ray photoelectron spectroscopy (XPS), water contact angle measurements and surface energy analysis. The excellent oil-fouling resistant capacity of these modified membranes was demonstrated by oil/water emulsion separation tests. In particular, membrane PES/P3, with the optimized hydrophilic and hydrophobic ratio, achieved the highest anti-oil-fouling properties with a total flux decay as low as 17.4% (nearly no irreversible flux-decline) and high flux recovery (99.3%) after simple water flushing. These desirable antifouling properties are believed to originate from the binary-cooperative effect of zwitterionic and low surface energy microdomains. Moreover, three-cycle oil/water separation tests and underwater immersion experiments further revealed that the as-prepared membranes have remarkable antifouling stability. The results of this study provide a new insight into the surface chemical heterogeneity-antifouling property relationships of membranes for efficient oil/water separation.