Sequential coating of nanopores with charged polymers: A general approach for controlling pore properties of self-assembled block copolymer membranes

A general approach is developed for controlling the pore size and pore chemistry of integral isoporous membranes derived from the assembly of polystyrene-b-poly-4-vinyl pyridine (PS-b-P4VP) diblock copolymer. In this approach, initially, the sub-50 nm pore surface, decorated with poly-4-vinyl pyridine (P4VP) polymer brush, is coated with polyacrylic acid (PAA). PAA offers a majority of anionic and a minority of neutral acid functionalities. The neutral acid groups adhere to the P4VP segments of the pore wall through hydrogen bonding interactions and the anionic sites remain free. The availability of the anionic sites sets the stage for a layer-by-layer deposition of cationic and anionic polymers, in a sequential manner, on the pore-wall surface through a continuous flow of a dilute polyelectrolyte solution through the nanoporous membrane. In this way, multiple layers, stabilized through electrostatic interactions, can be deposited leading to a continuous decrease in the pore size and a known surface charge. Due to the known facile nature of the large area isoporous asymmetric membrane formation and modular nature of the polyelectrolyte assembly, the present approach is anticipated to yield new block copolymer membranes with tailored separation, sensing, and catalytic properties.