(740b) Fouling Resistant, High Flux Membranes with ~1nm Effective Pore Size By Zwitterionic Copolymer Self-Assembly

Membranes with permeate size cut-offs in the nanometer range have numerous applications in the biochemical, pharmaceutical and food industries, as well as in specialized wastewater treatment processes. To be commercially viable, membranes for molecular-size-based separations need to exhibit high flux and fouling resistance, and be readily synthesized and fabricated into large-area membranes. Zwitterionic groups strongly resist biomacromolecular fouling due to their high degree of hydration, which makes them promising materials for membrane applications. Zwitterions are also documented to self-assemble into channel-type clusters 0.6-2 nm in size. Within certain composition ranges, random copolymers of zwitterionic and hydrophobic monomers self-assemble to form bicontinuous networks of nanochannels. We introduce a new class of high flux, fouling resistant, size-selective nanofiltration membranes whose selective layers are made of this family of copolymers. We have synthesized such copolymers and formed thin film composite membranes by coating them onto commercial ultrafiltration membrane supports. These membranes exhibit fluxes as high as 21 L/m².h.bar, which can be further improved by better coating methods. Based on the rejection of anionic dyes of varying sizes, they show size-based selectivity with a cut-off around 1 nm. This pore size closely matches the size of the zwitterionic nanochannels, measured to be ~1.1-1.4 nm in diameter by transmission electron microscopy (TEM). These are the first examples of membranes that gain their selectivity from the microphase separation of zwitterionic groups, in addition to exploiting this functionality for fouling resistance. We expect these membranes to be promising candidates for various applications including the purification of pharmaceuticals, antioxidants, and textile wastewater treatment.