Tuning pore size in block copolymer thin film for ultrafiltration applications

Porous membranes are commonly utilized in ultrafiltration (UF) applications such as water and biotechnological purification due to their capacity to filter nanometer size molecules. Block copolymers (BCPs) have been recognized as a particularly promising class of materials for membrane applications based on their ability to form films with dense arrays of uniform nanoscale pores by self-assembly. Tuning pore size and chemistry makes it possible to tailor self-assembled membrane functionality for specific applications. In this study, the self-assembled domain size in polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) thin films was controlled by blending P4VP homopolymers that selectively segregate to minority domains; the effect of homopolymer molecular weight and mass fraction on self-assembled domain orientation and pore size after homopolymer removal by selective solvents were investigated. Pore sizes were further reduced by incorporating metal oxides into pore walls via a vapor phase infiltration process achieving sub 10 nm pore diameters.