Modification of aromatic polyamide thin-film composite reverse osmosis membranes by surface coating of thermo-responsive copolymers P(NIPAM-co-Am). I: Preparation and characterization

This study focuses on the surface modification of the commercial aromatic polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membranes with thermo-responsive copolymers poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am)) for improved membrane properties. Firstly, thermo-responsive copolymers P(NIPAM-co-Am) with certain lower critical solution temperature (LCST) were synthesized by free radical copolymerization in aqueous solution. The resultant copolymers were then used to modify the commercial TFC RO membranes through surface coating technique under different conditions, and the surface properties of the resulting modified membranes were characterized by ATR-FTIR, XPS, SEM, AFM, and contact angle measurement. Finally, the reverse osmosis performance of the modified RO membranes was evaluated by permeation experiment with salt aqueous solution. The experimental results revealed that thermo-responsive copolymer P(NIPAM-co-Am) could be successfully deposited on the surface of the commercial aromatic polyamide TFC RO membrane by dip-coating method under certain conditions and the surface hydrophilicity of the modified membrane would change with the environmental temperature; that while the deposited copolymer P(NIPAM-co-Am) surface layer tended to offer additional resistance to permeation, the increased surface hydrophilicity would compensate for the reduction in membrane permeability; and that the surface coating layer of copolymer P(PNIAM-co-Am) had little influence on the salt rejection of the modified TFC membrane.