Engineering Polymer Forest on Membranes: Tuning Density, Thickness, and Architecture for Biofouling Control

Applying membrane technology for alleviating the water crisis calls for the investigation of green, low-cost, and stable antibiofouling membranes. In this study, a forest-like polymer layer consisting of a homopolymer or dual-functional block copolymer with fouling resistant and antimicrobial properties was grafted onto graphene oxide-coated polyamide (PA) membranes to control biofouling. Activators regenerated by the electron transfer-atom transfer radical polymerization technique were utilized to controllably grow a polymer on the membrane with a desired density, thickness, and architecture. With a higher density, the polymer forest protects the membrane from bacteria attachment more effectively. Surface hydrophilicity significantly improves the bacteria resistance of the membrane. Block copolymer brushes with different architectures mitigate biofouling caused by Gram-positive (G(+)) and Gram-negative (G(−)) bacteria via different strategies. With a bacteria-“attacking” moiety on top, the membrane is found to reduce biofouling caused by Bacillus subtilis via a bacteria-“defending” and bacteria-“attacking” synergistic effect. However, in controlling biofouling caused by Escherichia coli, the bacteria-“defending” function plays a critical role. The block copolymer-modified membrane exhibits a lower flux decrease (27%) associated with E. coli proliferation compared to that for a control PA membrane (80%), and it also achieves a 100% flux recovery after two cycles of “fouling–cleaning” operation. The results from this study elucidates the structure–property–performance relationship for polymer forest-grafted membranes and exemplifies engineering design for a polymer brush used for developing the next generation of functional membranes.