Printing zwitterionic self-assembled thin film composite membranes: Tuning thickness leads to remarkable permeability for nanofiltration

Abstract

Abstract Zwitterionic copolymer self-assembled membranes have been shown to have impressive selectivity for nanofiltration applications. Conventional approaches used to fabricate these asymmetric membranes, such as casting followed by phase inversion, typically result in thick selective layers being formed that can limit permeance. In this work, we evaluate the use of electrospray to print thin layers of amphiphilic zwitterionic selective layers onto UF membrane substrates. Dyes are used to probe the rejection of these membranes while their thickness is reduced by orders of magnitude compared to casting methods. As thickness is decreased, water permeance was found to proportionally increase while dye rejection was maintained for some dyes. It was found that a threshold minimum thickness was required to maintain rejection for some dye molecules while the intrinsic permeability of the polymer films changed as a function of thickness. Annealing the membranes was found to increase permeance as well without a significant loss of rejection. Notably, one of our annealed ultra-thin TFC membranes was found to exhibit a water permeance value of 180 LMH/bar and a chlorophyllin rejection at 99.67%. Interestingly, this permeance is indistinguishable from the supporting UF membrane permeance, suggesting that even higher permeance without rejection loss is possible with more permeable support layers.