Out-of-phase thermo-mechanical coupling behavior of proton exchange membranes

The thermal effects and mechanical effects on the durability of proton exchange membranes (PEMs) have been studied extensively in the literatures. However researches on the thermo-mechanical coupling behavior of PEMs are very limited. In this study, the interaction of mechanical and thermal effects in Nafion^® NRE-212 was investigated using experimental methods. The thermo-mechanical coupling experiments were conducted following the in-phase proportional loading path, where the maximum/minimum mechanical loads and temperatures occur simultaneously and out-of-phase non-proportional rectangular loading paths where a phase difference of 90° existed between thermal and mechanical loads. During the creep processes under a variable temperature in out-phase profiles, the creep strain was found to be history-dependent in the membrane. The effect of initial temperature on the creep was significant in the first cycle. Moreover, temperature cycles were applied as thermal loading conditions and the history-dependence was also observed for thermal stresses. The maximum thermal stress did not occur at the lowest temperature.