(195d) Ion Exchange Membranes from Sulfonated Polysulfone through Phase Inversion: Influence of Ion Exchange Capacity on Membrane Morphology

Many theories and experimental data have been developed and confirmed for the relationship between membrane morphology and the difference in solubility parameter for the formation of non-charged membranes. However, this relationship between membrane morphology and solubility parameter difference is not well established and clear for the formation of charged membranes. In this paper, polysulfone and sulfonated polysulfone (SPSf) with different ion exchange capacities (IEC) were used as the starting materials for membrane preparation through a wet phase inversion process, while different non-solvents, i.e., water and isopropanol were employed as coagulants. The resultant charge membranes have diverse membrane morphology that includes finger-like, sponge-like, and dense-like structures. Efforts were given to understand the thermodynamic and dynamic driving forces for the inversion processes and to correlate with membrane morphology with them. It was found that as the IEC value of SPSf increases, the phase inversion process in isopropanol becomes slow. Such phenomenon is in contrary to the predication by the Hildebrand solubility parameter theory. In other words, as the calculated Hildebrand solubility parameter of SPSf increases with increasing IEC value, the difference in Hildebrand solubility parameters between SPSf with IPA would also increase and favor a rapid phase inversion. Calculations suggest that the Hansen solubility parameter (dd , dp , dh) theory gives a consistent relationship with experimental observation between membrane morphology and solubility parameter difference for the formation of charged membranes.