Room-temperature swelling of block copolymers for nanoporous membranes with well-defined porosities

Abstract

Selective swelling of block copolymers (BCPs) has been an efficient way to produce nanoporous materials with well-defined porosities. Currently, the cavitation of bulk BCP films by selective swelling needs to be performed at elevated temperatures (typically 50–70 °C), which is not only tedious in operation but also energy extensive. Herein, we develop the room-temperature (RT) swelling strategy to enable pore formation in BCP films with no need of heating. Simply introducing a solvent selective to the majority blocks of BCPs into the swelling bath allows the initiation of selective swelling-induced pore generation at room temperature because of plasticizing effect on BCP matrix. The swelling degrees and porosities of BCP films can be flexibly tuned by changing the compositions of the swelling bath and the swelling durations. The universality of this RT swelling strategy is also demonstrated by its applicability to both polystyrene (PS)-based BCPs and polysulfone-based BCPs with high glass transition temperatures. We prepare composite membranes with nanoporous polystyrene-block-poly (2-vinyl pyridine) (PS-b-P2VP) selective layers on top of macroporous substrates by using this RT swelling approach. Interestingly, thus-produced membranes exhibit more uniform pores with narrow pore size distributions, resulting in better selectivity. RT swelling is featured as convenient and energy-saving, and is desired in large-scale manufacturing of nanoporous BCP materials for various applications.