α-Relaxation and Morphology Transition of Perfluorosulfonate Ionomer Membranes

Nafion α-relaxation has been the subject of intense investigations as it regulates the performance of electric actuators and polymer electrolyte fuel cells (PEMFC). Dielectric spectroscopy and atomic force microscopy (AFM) measurements of Nafion membranes allowed identifying the conformation transition of the polymeric aggregates as the process underlying the α-transition. The dielectric permittivity curves of Nafion showed that for temperatures T > 120 °C, the α-relaxation displaces to lower frequencies. Such unusual behavior was attributed to an elongation of Nafion polymeric aggregates occurring at T ∼ 120 °C and is in agreement with both water uptake measurements and morphological changes inferred from AFM analyses.