Unfolding of nafion fibrillar polymeric aggregates as the origin of α‑relaxation

Full text: Nafion α‑relaxation process is reported to arise from the energy dissipated upon the unfolding of the fibrillar polymeric aggregates. The origin of Nafion α‑relaxation has been the subject of intense investigations since it regulates the performance of electric actuators and polymer electrolyte fuel cells. The analysis of dielectric spectroscopy measurements as a function of temperature revealed that an unfolding process imparted by strong electrostatic interactions among sulfonic terminal groups occurs in Nafion membranes. Such conformational transition is irreversible and accounts for the Nafion thermomechanical properties as probed by differential scanning calorimetry and dynamic mechanical analysis. The elongation of the polymeric aggregates upon heating is associated with the Nafion anisotropic morphology as inferred from small angle X-ray scattering and supported by recently reported atomic force microscopy analyses. The combined experimental data provides compelling evidence that the unfolding of the polymeric structure is the underlying process for the nanoscale morphology of Nafion at the α-relaxation temperature. (author)