Surface-active isoporous membranes nondestructively derived from perpendicularly aligned block copolymers for size-selective separation

Isoporous membranes which have narrow pore size distributions and straight pore profiles promise sharp selectivity at no expense of permeability. However, it remains a challenge to produce isoporous membranes in an affordable and efficient way. In this work, we report on the facile preparation of isoporous membranes based on the nondestructive creation of straight pores in block copolymers of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP). Thin films of PS-b-P2VP are annealed to induce the perpendicular orientation of the P2VP cylinders, and then transferred to macroporous supporting membranes to form mechanically robust composite structures. The copolymer films are treated in hot ethanol to convert the P2VP cylinders into straight pores following the selective swelling-induced pore generation mechanism. The perpendicular alignment of the P2VP cylinders in the PS matrix facilitates the swelling-induced pore generation process, making the membrane highly permeable. Because of its ultrathin thickness, high porosity, and strong hydrophilicity, the membrane exhibits a water flux as high as 1686 L m(-2) h(-1) bar(-1), which is about 10 times higher than that of commerical membranes and also much higher than that of other isoporous membranes with similar effective pore sizes. Furthermore, the membrane has an inherent reversible pH-responsive functionality because of the enrichment of protonizable P2VP chains on the pore wall and membrane surface. (C) 2014 Elsevier B.V. All rights reserved.