Surface modification of polyimide and polysulfone membranes by ion beam for gas separation

The surface carbonization of polyimide (PI) and polysulfone (PSf) by ion be am has been performed to adapt the carbon molecular sieve properties on the skin of the polymeric membranes without the deformation of the membrane st ructure. In order to control the structure of membrane skin and to improve gas transport properties, the irradiation conditions, such as the dosage an d the source of ion beams, have been varied. The ideal separation factor of CO2 over N-2 through the surface-modified PI and PSf membranes increased t hreefold compared to those of the untreated, pristine membranes, whereas th e permeability decreased with almost two orders of magnitude. This appears to be due to the fact that the structure of membrane skin has been changed to a barrier layer. The formation of barrier layer was confirmed by compari ng the calculated values of a simple resistance model with the experimental results, and the estimated permeability of this barrier was 10(-4) barrer. It was concluded that ion beam irradiation could provide a useful tool for improving selectivity for gas separation membranes. (C) 2000 John Wiley & Sons. Inc.