A facile process to prepare fouling-resistant ultrafiltration membranes: Spray coating of water-containing block copolymer solutions on macroporous substrates

Ultrafiltration membranes derived from block copolymers (BCPs) are gaining much attention for their superiority in tunable pore structures and intrinsic surface functions. In terms of the practical applications of BCP membranes, simple and efficient manufacturing processes are essential and remain highly demanded. Herein, we propose a facile process to prepare BCP composite membranes by spray-coating polysulfone/poly(ethylene glycol) (PSF-b-PEG) solutions onto macroporous substrates. A small amount of nonsolvent (water) is added into the BCP solutions to act as the pore-forming agent. During spray coating, the evaporation of solvent and the rising water content lead to phase separation of BCP solutions in the atomized droplets. Subsequent drying removes water, and the volumes occupied by water are transformed into nanoscale pores, thus producing bi-layered composite membranes with the nanoporous BCP coatings as the selective layers atop the macroporous substrates. Water-affinitive PEG chains in PSF-b-PEG are crucial to adsorb and stabilize water droplets during pore formation. The thickness of the BCP selective layers is predominantly determined by the dosage of the sprayed BCP solutions, enabling tunable separation properties of the BCP membranes. In spite of the extremely simple preparation process, thus produced membranes exhibit good ultrafiltration performances, comparable or better than that of membranes prepared by much more complicated processes. Furthermore, PEG chains are enriched on pore walls, endowing the membranes an intrinsic fouling resistance.