Interplay between 'alfa'-relaxation and morphology transition of perfluorosulfonate ionomer membranes

Abstract

Nafion a-relaxation is the subject of intense investigations as it regulates the performance of electric actuators and polymer electrolyte fuel cells. Dielectric spectroscopy and atomic force microscopy measurements of Nafion membranes allow identifying the conformation transition of the polymeric aggregates as the process underlying the a-transition. The dielectric permittivity curves of Nafion membranes show that for relative humidity higher than ~60% and for temperatures higher than ~120 C, the arelaxation displaces to lower frequencies. Such unusual behavior is attributed to an elongation of Nafion polymeric aggregates occurring at high temperatures (T > 120 C) and is in perfect agreement with morphological changes inferred from atomic force microscopy analyses.