METHANOL AND WATER-UPTAKE, DENSITIES, EQUIVALENTAL VOLUMES AND THICKNESSES OF SEVERAL UNIVALENT AND DIVALENT IONIC PERFLUOROSULFONATE EXCHANGE MEMBRANES (NAFION-117) AND THEIR METHANOL WATER FRACTIONATION BEHAVIOR AT 298-K

Maximum methanol and water uptake by H+, Li+, Na+, K+, Rb+, Mg2+, Ca2+, Sr2+, and Ba2+ forms of perfluorosulphonate ion-exchange (Nafion-117) membranes, as well as their densities, equivalent volumes and thicknesses in their dry and methanol-swollen and water-swollen states have been determined and the extent of solvent electrostriction evaluated. Compared with a water sorption of 6-20 wt.%, the membranes show an expanded range of 6-40 wt.% methanol sorption, the corresponding volume changes being 14-40% (water) and 19-132% (methanol). The swollen-membrane densities exhibited a linear relationship with solvent uptake. Membrane thicknesses, found to be independent of the cationic form in the dry state and showing a small increase on water sorption, showed significant variations on methanol-wetting. Solvent fractionation studies carried out in 50 mol% methanol-water revealed a larger solvent sorption and selective enrichment of water in the membrane phase. Unusually large swelling of the H+, Li+ and Na+ form membranes in methanol and other observations have been interpreted in terms of cluster sizes computed from the data, free energies of hydration of the counter ions involved, solvent-matrix and solvent-sulphonate ion interaction, molar volumes of solvents, swelling pressures in the membranes and the known hydration/solvation effects in polystyrene divinylbenzene sulphonate type of exchangers.