Surface modification of thin film composite polyamide membranes by electrostatic self deposition of polycations for improved fouling resistance

Interfacially polymerized polyamide thin film composite membrane was modified by electrostatic self-assembly of polyethyleneimine on the membrane surface, and the modified membrane showed significantly improved antifouling properties. The charge reversal on the membrane surface due to the application of the polyethyleneimine layer was shown to increase the fouling resistance of the membrane to cationic foulants because of the enhanced electrostatic repulsion, and the increased surface hydrophilicity would help minimize the flux reduction. The effects of parameters involved in the membrane surface modification (e.g., polyethyleneimine concentration and deposition time) on the membrane performance were investigated in terms of water permeation flux and salt rejection. The membrane modification was found to increase salt rejections when MgCl2 and NaCl were tested. The fouling behavior of the membranes was also studied with and without the presence of dodecyltrimethylammonium bromide (which is a common cationic surfactant present in waste water). It was shown that while the deposited polyethyleneimine surface layer tended to offer additional resistance to permeation, the improved fouling resistance and the increased surface hydrophilicity compensated for the reduction in membrane permeability due to the deposition of the polyethyleneimine layer.