Selective Swelling Induced Pore Modification in Thin Films of Block Copolymer Active Water Purification Membranes

The self-assembling characteristics of block copolymers (BCPs) provide a promising pathway in developing ultrafiltration membranes with continuous nanoporous channels. Such uniquely defined morphologies can be further tuned by selectively partitioning an active species into the pore-forming domain of BCP. In this report, we present an asymmetric etch-generated membrane possessing a high density of pores when cast using a poly(styrene)-b-poly(4-vinlypyridine) (PS-b-P4VP) BCP. The porous structure in the ~120 nm thick selective BCP film has been optimized for a less tortuous path by controlling the choice of solvent mixtures and later placed on polyethersulfone support layer. This membrane assembly exhibits water flowrates above 1000 Lm^-2h^-1bar^-1 while maintaining the uniform distribution of nanopores. Furthermore, the pores in the membrane have been altered by adding homopolymer and solvent blends and later using quaternization process. The effect on pore properties with increasing etching time and blend concentrations has been studied using Atomic Force Microscopy which showed an increasing trend from 30-70 nm in pore diameter. These results indicate related enhancement of properties for high-performance membranes.