Selective Swelling of Polystyrene (PS)/Poly(dimethylsiloxane) (PDMS) Block Copolymers in Alkanes

Block copolymers (BCPs) containing poly(dimethylsiloxane) (PDMS) blocks have been extensively used as precursors to prepare nanoporous materials with a diversity of compositions and morphologies. However, it remains desirable to facilely and efficiently transform the precursors into porous structures under mild conditions. Herein, we investigate the swelling behaviors of thin films of polystyrene-block-poly(dimethylsiloxane)-block-polystyrene (PS-b-PDMS-b-PS, SDS) in linear alkanes and produce well-defined nanoporosities in the SDS films following the mechanism of selective swelling-induced pore generation. Alkanes strongly swell PDMS blocks while slightly swell PS blocks, triggering the cavitation of the PDMS minority phases. The pore sizes as well as the porosities are determined by the interaction between the alkanes and the constituent blocks. Alkanes with lower carbon numbers exhibit a stronger affinity to the copolymer, leading to larger pores. Interestingly, we find that n-hexane is able to produce a porosity >30% at room temperature within a duration as short as 1 min. We demonstrate that PDMS, which has a lower surface energy, is enriched on the film surface, thus rendering a strong hydrophobicity to the produced porous SDS films. Ethanol permeation tests demonstrate the interconnected and accessible porosities and tunable flux as well as excellent pressure resistance of the porous SDS films, implying their potential applications as selective membranes in the filtration of organic solvents and oil/water separation.