A perfluorosulfonic acid Nation membrane has been studied with infrared spectroscopy. Infrared spectra of the membrane in acid form at the different degree of hydration were analysed in details and the conclusions about the state of sulfonic groups within clusters were drawn. The results indicate that in swollen samples in acid form hydrate structures involving dissociated sulfonic groups and water molecules are formed. These structures are analogous to those found in polystyrenesulfonic acid. With progressive drying of the Nation membrane the network of hydrate structures breaks up and functional groups are transformed into their undissociated forms.

Abstract:The state of sulfonic acid groups in a thoroughly dried and slightly hydrated Nation membrane has been analysed applying infrared spectroscopy. IR spectra in the vOH stretching vibration region were analysed in detail. A computer-curve resolution technique was used to determine band parameters of each OH band. The results of this analysis indicate a rather complex process of association of sulfonic groups in the Nation membrane. The association of these groups in the Nation membrane differs in several respects from that in the polystyrenesulfonic acid membrane which results from the differencies in membrane structures, both on molecular and supermolecular level.