BLOCK COPOLYMER INTEGRAL ASYMMETRIC MEMBRANES USING SNIPS PROCESS

Abstract

Over the last decade, membranes prepared using block copolymer self-assembly and non-solvent induced phase separation (SNIPS) process have become increasingly desirable candidates for water purification and protein separation applications due to their excellent permselectivity. However, biofouling is a major problem encountered in the filtration process as it may lead to a reduction in effective pore size, pore blockage and formation of a biofilm on the membrane surface. Thus, there is a pressing need to design new systems that incorporate an anti-fouling property while retaining the high performance capabilities of SNIPS membranes. Poly(ethylene oxide) (PEO) is a promising candidate to reduce membrane fouling due to its hydrophilic nature. To date it has remained challenging to extend the SNIPS process to new polymers with PEO end block, including poly(isoprene-b-styrene-b-ethylene oxide) (ISO), which involves optimizing a multitude of parameters to obtain desired membrane structure and performance. To overcome this impediment, two chemically distinct triblock terpolymers, poly(isoprene-b-styrene-b-(4-vinyl) pyridine) (ISV) and ISO were blended in the dope solution in order to fabricate membranes using the SNIPS process. The weight ratio of ISV to ISO in the blended solutions was varied. Scanning Electron Microscopy (SEM) images of both the pure ISV and blended membranes reveal a mesoporous skin layer atop a macroporous substructure. The asymmetric membranes from 9:1 and 7:3 blends retained their pH-responsive permeability behavior characteristic to pure ISV membranes. Additionally, about a three-fold decrease in protein adsorption was observed in 5:5 blended membranes compared to pure ISV, likely due to the antifouling property of PEO. Thus, the blended membranes exhibit properties characteristic of the chemistries present in both the parent block copolymers. This study corroborates the ability and ease of the SNIPS process combined with a facile “mix and match” approach to access and tailor unique chemical functionalities in a single membrane opening doors to previously challenging property combinations.