Infrared investigation of ionic hydration in ion-exchange membranes. Part 1.—Alkaline salts of grafted polystyrene sulphonic acid membranes

Abstract

Infrared spectroscopic measurements have been performed on thin ion-exhange membranes which consist of alkaline salts of polystyrene sulphonic acid grafted on a Teflon FEP matrix. The membranes under investigation were placed in isopiestic equilibrium with water vapour in the sampling cell. The water content of these FEP–PSSA systems has been determined at 25°C by measuring the integrated absorbance of the sorbed-water bending vibration as a function of the nature of the cation. The dependence of the position of the water stretching and bending vibration bands and of the symmetric vibration of the SO₃^– groups with the nature of the cation and the water content has led to various conclusions concerning the ionic interaction and hydration in the membrane. The peculiar behaviour of Li⁺ is due to its ability to interact strongly with the anion. A model of ion clustering has been proposed to explain the spectra of water in the presence of large alkali ions.