Evolution in chemical structure and gas permeation properties of polymides induced by ion beam irradation

Ion beam irradiation can be used to modify the selective layers of polymeric membranes to improve the gas transport properties of the polymeric membrane materials. Through energy transfer from incident ion to polymer backbone, ion beam irradiation can result in degradation of the polymer, which involves crosslink formation between polymer chains, release of small molecules, and formation of the unsaturated bonds. The irradiation induced crosslinking along with the formation of small molecular size defects due to release of small molecules can affect the fractional free volume and the free volume size distribution. Since gas transport properties are determined by the fractional free volume and the free volume size distribution, ion beam irradiation can modify gas transport properties.; This project focused on the investigation of the evolution in chemical structure of three polyimides with different chemical structure (i.e. Matrimid RTM, 6FDA-6FmDA, and (6FDA-6FpDA)1-(6FDA-6FmDA) 1) induced by H+ ion beam irradiation. For three polyimides, while H+ ion beam irradiation at very low ion fluences induced little modification in the chemical structure, ion beam irradiation at relatively high ion fluences could result in significant crosslinking.; The evolution in gas permeation properties of three poly1mides following H+ ion beam irradiation was also investigated. H+ ion beam irradiation of MatrimidRTM at high ion fluences resulted in simultaneous increases in permeabilities and permselectivities, reflecting the increased fractional free volume and a slight shift of the free volume distribution toward small size. For 6FDA-6FmDA, H+ ion beam irradiation increased permeabilities with slight change in permselectivites for most gas pairs, reflecting the increased fractional free volume and a slight shift of the free volume distribution toward large size. For copolymer (6FDA-6FpDA)1-(6FDA-6FmDA)1, H+ ion beam irradiation increased the fractional free volume and greatly shifted the free volume distribution toward large size.; There are two kinds of energy loss mechanisms (i.e., the electronic energy loss and the nuclear energy loss) involving energy transfer, which can contribute to modification at quite different efficiency. Therefore, the investigation was also made on the relative importance of these two energy loss mechanisms for H+ and N+ ion beam modifications of the MatrimidRTM. In the case of N+ ion beam irradiation of MatrimidRTM, the nuclear energy loss is much more important for modification relative to the electronic energy loss although both of energy loss mechanisms contributed to modification. However, in the case of H + ion beam irradiation of MatrimidRTM, only the electronic is predominant.