Swelling-induced mesoporous block copolymer membranes with intrinsically active surfaces for size-selective separation

Block copolymers (BCPs) are receiving growing interest in the preparation of advanced membranes with regular pores due to their capability to form highly ordered, mesoscopic structures via microphase separation. We report on the fabrication of composite membranes with mesoporous amphiphilic BCPs as the size-selective layer and a macroporous membrane as the supporting layer by coating BCPs onto the supporting membrane. Mesopores were generated in the BCP layer by a selective swelling-induced pore-formation process. The composite membranes showed high pore regularity, strong mechanical robustness, and a separating property that can be tuned simply by changing the swelling time. Furthermore, the polyelectrolyte-natured blocks were exclusively relocated on the pore surface of the BCP layer during the swelling process, rendering an intrinsically active surface on the membrane. As a result, the hydrophilicity and fouling resistance of the membranes were significantly enhanced, and the membranes possessed a reversible pH-sensitive water flux. The membranes were used to separate nanoparticles of similar sizes and it was observed that the membrane subjected to 24 h of swelling was able to discriminate 10 nm gold particles from a mixture containing 2 nm gold particles with ∼100% yield, demonstrating its superior size selectivity.