Selective swelling of block copolymer ultrafiltration membranes for enhanced water permeability and fouling resistance

High permeability is one of the most important pursuits of separation membranes. In this work, high-performance ultrafiltration membranes are prepared by synergetically coupling nonsolvent-induced phase separation (NIPS) and selective swelling of a block copolymer, polysulfone-block-poly (ethylene glycol) (PSF-b-PEG). NIPS is used to prepare PSF-b-PEG membranes with a thin skin layer and a fingerlike sublayer. Subsequent selective swelling generates mesopores in the skin layer and enriches PEG blocks on the surface. Compared to the membranes without swelling, the swelling-treated membranes exhibit simultaneously upgraded permeability, hydrophilicity, and fouling resistance. For instance, the permeability of the membrane swollen in 50% acetic acid at 65 °C for 1 h is doubled compared to the pristine one while the rejection is only modestly reduced. Fouling resistance of the swelling-treated membranes is also improved, which is ascribed to the enrichment of PEG on the membrane surface. We demonstrate that the performances of the membranes can be tuned in a relatively wide range by tailoring the swelling conditions, such as swelling reagents, durations and temperatures. Because of the extreme simplicity and high efficiency, this selective swelling strategy is expected to be applicable in tuning the surface properties and improving performances of many other membranes.