Energy-saving, responsive membranes with sharp selectivity assembled from micellar nanofibers of amphiphilic block copolymers

Abstract

Membrane technology contributes significantly in a large number of energy- and environment-related fields in a clean and efficient way. It remains a challenge to develop advanced membranes with simultaneous high flux and sharp selectivity. Such membranes require a thin selective layer, high porosity, and strong hydrophilicity. A promising strategy to fabricate such membranes is to build an integral selective layer of nanofibers on a macroporous support. We report an extremely simple method to produce uniform nanofibers with diameters of <30 nm by directly dissolving block copolymers of polystyrene-block-poly(4-pyridine) (PS-b-P4VP) with long, glassy PS blocks in a polar solvent. The fibers were cylindrical micelles with PS cores covered by P4VP coronae, formed through a heating-enabled micellization process. We deposited the fibers on the surface of macroporous supports by vacuum filtration to fabricate composite membranes. The gaps between the fibers served as mesh pores, with effective sizes down to several nanometers. Distinct from other types of nanofibers, the micellar fibers had a P4VP-covered surface, which not only enhanced the adhesion between fibers, but also endowed the membrane with a stimuli-responsive function. The fiber layers could be made very thin, with a thickness of ∼270 nm or even thinner, but were mechanically stable and exhibited a water flux as high as 940 L m⁻² h⁻¹ bar⁻¹ at ∼100% rejection to bovine serum albumin. The fiber membrane displays an energy-saving characteristic as it provides high flux under low pressures compared with commercial ultrafiltration (UF) membranes. For example, it produces a flux over 10 times larger than that of commercial UF membranes. The membranes are promising for the removal of particulate contaminants from water as demonstrated by their excellent concentration capability for 5 nm gold colloidal nanoparticles.