(747g) Boosting the Performance of Random Zwitterionic Copolymers Using Ionic Liquids during Membrane Formation

Polymer self-assembly is a promising tool for scalable manufacture of membranes while maintaining high permeability and controlled pore size. Tuning copolymer composition (monomers, additives) and processing methods can change copolymer behavior which can dramatically affect the self-assembly and hence the membrane performance (permeability, selectivity, fouling resistance). Studies based on block copolymers demonstrate the influence of additives (solvent, homopolymer etc.) on the copolymer self-assembly and membrane performance. But studies on additives in casting solutions of random copolymers and how they affect membrane performance have not been reported to our knowledge. Recently, we have introduced a new class of membranes with ~ 1 nm effective pore size whose selective layers are made of self-assembling zwitterionic amphiphilic random copolymers. These membranes derive not only their excellent fouling resistance but also their permeability and selectivity from this self-assembled nanostructure. These membranes have numerous applications in the biochemical and pharmaceutical industries, as well as wastewater treatment processes. These membranes are prepared simply by coating random copolymers of hydrophobic and zwitterionic monomers onto a porous support membrane. In this study, we have used ionic liquids and other additives in the coating solutions to boost and alter the performance of these membranes. Membranes prepared by coating copolymer solutions with sufficient amounts of selected additives on commercial ultrafiltration membrane supports exhibit permeances as high as 50 L/m².hr.bar, up to 10 times higher than membranes formed without additives. These membranes also exhibit a narrow pore size distribution, retaining the same size-based selectivity with a ~1 nm size cut-off demonstrated by filtering negatively charged dyes. Performance of these membranes depends on the amount of additive as well as the membrane manufacturing method (non-solvent, drying time etc.). This is attributed to phase separation and solvent diffusion kinetics that are in play during membrane formation by SNIPS (self-assembly and non-solvent induced phase separation) mechanism. These structure-property relationships serve as a guideline to develop new materials with high fluxes and sharp selectivity for various applications such as textile wastewater treatment, pharmaceutical purification and bioseparation applications.