Block copolymer ultrafiltration membranes by spray coating coupled with selective swelling

Abstract

Block copolymers (BCPs) have been demonstrated to be promising precursors in the fabrication of ultrafiltration membranes with well-defined porosities. To maximize the separation performance, BCPs are usually used in the forms of thin-film composite membranes with nanoporous BCP separation layers on the top of macroporous substrates. However, it remains a challenge to prepare such composite structures in an efficient and controllable way. Herein, we demonstrate that spray coating of BCP solutions on macroporous substrates followed by selective swelling is a facile and highly controllable strategy to produce BCP composite membranes. First, the BCP solution was spray-coated on a macroporous nylon support. By changing polymer concentrations as well as various spray conditions, a defect-free and uniform dense BCP layer was obtained. The thickness of the BCP layer can be controlled within the scope of a few micrometers simply by altering the step width of spray coating. Neither pre-filling of the macroporous supports to prevent solution permeation nor post-treatment to strengthen the adhesion of the two layers is required during the spray coating process. The BCP-coated support was then soaked in hot ethanol to create nanoporosity in the BCP layer following the mechanism of selective swelling-induced pore generation. Thus-produced composite membranes exhibit excellent ultrafiltration performances. Meanwhile, the pore sizes, surface hydrophilicity and consequently separation performances of the membranes can be conveniently tuned by changing swelling conditions. We expect this spray coating coupled with selective swelling to produce BCP-based composite membranes at large scale for industrial production.