Control of pore size and pore uniformity in films based on self-assembling block copolymers

Blends of self-assembling polystyrene-block-poly(4-vinyl pyridine) (PS-b-P4VP) diblock-copolymers and poly(4-vinyl pyridine) (P4VP) homopolymers were used to fabricate isoporous and nanoporous films. Block copolymers (BCP) self-assembled into a structure where the minority component forms very uniform cylinders, while homopolymers, resided in the core of the cylinders. Selective removal of the homopolymers by ethanol immersion led to the formation of well-ordered pores. In films without added homopolymer, just immersion in ethanol and subsequent swelling of the P4VP blocks was found to be sufficient to create pores. Pore sizes were tuned between 10 and 50 nm by simply varying the homopolymer content and the molecular weight of the block-copolymer. Uniformity was lost when the average pore size exceeded 30 nm because of macrophase separation. However, preparation of films from low MW diblock copolymers showed that it is possible to have excellent pore size control and a high porosity, while retaining a low pore size distribution