An infrared study of water in perfluorosulfonate (Nafion) membranes

Abstract

We have studied the infrared spectra of H 2 O, D 2 O, and HDO in hydrated Nafion membranes in the sodium form. The spectrum of isotopically isolated HDO exhibits two distinct absorption bands in the OH stretching region and similarly in the OD stretching region. These bands have been taken to correspond to two distinct environments of the OH groups in Nafion, identified as [Formula: see text] and[Formula: see text]. It appears that a substantial proportion of water molecules have an OH group (or occasionally both OH groups) exposed to the fluorocarbon environment. This implies that the hydrated ion clusters are either much smaller than previously estimated or, more likely, are non-spherical in shape with frequent local intrusions of the fluorocarbon phase. Water in Nafion is much less strongly hydrogen-bonded than water in aqueous salt solutions at the same temperature and may be expected to have distinct physical properties.