Effect of methanol on plasticization and transport properties of a perfluorosulfonic ion-exchange membrane

The transport properties of a perfluorosulfonic acid membrane swollen in different concentrations of aqueous methanol mixtures are investigated. Solvent uptake, proton conductivity and methanol permeability of a commercial Nafion® 117 membrane are evaluated at different methanol concentrations. Small-angle X-ray scattering analysis is performed to study the morphological effects on the formation of ionic clusters created by aqueous methanol mixtures. It is concluded that the observed decrease in proton conductivity and increase in methanol permeability are associated with morphological transitions as well as with the size of the ion cluster, as determined by the concentration of methanol in the test mixture. Wide-angle X-ray scattering studies indicate that the crystalline region is deformed by absorbed methanol; the size of crystalline domains and the crystallinity change with methanol concentration due to plasticization. Absorbed methanol also degrades the mechanical properties, as witnessed by tensile strength measurements.