Controlling the zwitterionization degree of alternate copolymers for minimizing biofouling on PVDF membranes

This study sheds light on the effect of the zwitterionization degree (ZD) of alternate copolymers on the antifouling properties of coated polyvinylidene fluoride (PVDF) membranes. A series of copolymers was formed from poly (maleic anhydride-alt-1-octadecene) which underwent a ring opening reaction leading to zwitterionization, and used as coating materials for PVDF membranes. A complete surface analysis (FT-IR, XPS, SEM) of the membranes served at controlling that the membranes were efficiently modified. Then, bacterial attachment and HT1080 cell adhesion biofouling tests revealed that Z55.5 membrane, modified with a copolymer having a 55.5% ZD, resisted to biofouling better than membranes modified with copolymers having a lower or a higher ZD. Stability tests, surface free energy calculations, and FT-IR mapping results showed that the modification using Z55.5 was the most stable and homogeneous. Therefore, there is an optimal ZD ensuring a compromise between high stability and low-biofouling. As the ZD increases, the hydrophobic interactions stabilizing the coating are challenged by strong dipole interactions between the zwitterionic moieties and the surrounding environment, which destabilizes the zwitterionic coating. Practically, the optimized Z55.5 membrane was used to harvest Microalgae, and outperformed a commercial hydrophilic membrane (FRR_Z55.5 = 61% vs. FRR_com = 15%), consistent with reduced adhesion of the algae on the surface as evidenced by SEM, and measured by the irreversible flux decline ratio (DR_{ir, Z55.5} = 39% vs. DR_{ir, com} = 85%).