S. Lounder, P. Kaner, P. Bengani-Lutz, A. Asatekin
Keywords: membrane, filtration, fouling, zwitterion
Summary:Zwitterionic groups, defined as functional groups with equal numbers of positive and negative electrostatic charges, strongly resist biomacromolecular adsorption due to their high degree of hydration. This has led to their incorporation into membranes to prevent fouling by various methods, especially by grafting from and surface functionalization of existing porous membranes. In addition, however, zwitterionic groups have interesting self-assembly capabilities due to their high dipole moments and strong intra- and inter-molecular interactions. Using these important features, we have prepared high flux, fouling resistant, size-selective membranes whose selective layers are made of random and comb-shaped copolymers of zwitterionic and hydrophobic monomers. We have shown that within certain composition ranges, these copolymers self-assemble to form bicontinuous networks of nanochannels that allow water passage, and filter out solutes larger than the channel size. Membranes made using random copolymers exhibit fluxes as high as 50 L/m2.h.bar and size-based selectivity with a cut-off around 1 nm. This pore size closely matches the size of the zwitterionic nanochannels. Depending on the selected zwitterion chemistry, these membranes can be exceptionally fouling resistant, showing little to no flux decline and complete flux recovery with a water rinse upon the filtration of foulants such as protein solutions, oil suspensions, and wastewater streams from oil and textile industries. Well-designed membranes show no flux decline even in week-long fouling experiments with oil suspensions. Furthermore, by modifying the functional groups that segregate into the zwitterionic nanochannels, these membrane chemistries can be adapted to serve as chlorine-resistant nanofiltration membranes. These novel materials are extremely promising for many water treatment applications, from industrial wastewater remediation and reuse to surface water treatment.