Hygrothermal and corrosive effects on mechanical response and fatigue driven cracking behavior of perfluorosulfonic acid ionomer

Perfluorosulfonic acid (PFSA) ionomers is one of the most crucial materials for ion-conductive membrane, however, the fatigue driven failure behavior especially under hygrothermal and corrosive environments remain unclear. Herein, the effects of multiple factors including strain rate, temperature, humidity and chemical attack on the constitutive response and fatigue behavior of PFSA ionomers were investigated using multiple in-situ testing means with monotonic tension and fatigue crack propagation. The results demonstrate that under high hygrothermal conditions, PFSA ionomer exhibit a decrease in strength and stress relaxation resistance accompanied by increased ductility, with enhanced temperature sensitivity, while nonlinear accumulation of damaged side chains and backbone with corrosion time results in increased brittleness and rigidity after chemical corrosion. Increases in both stress ratio and hygrothermal conditions promote crack propagation, whereas higher loading frequencies inhibit it, and following 72 h of corrosion, the crack propagation rate exhibits a two order of magnitude increase. Under high hygrothermal conditions, fracture surface ligaments exhibit more pronounced serration features and develop a tendency to curl and elongate, while following chemical corrosion, teardrop-shaped pore morphologies emerge in the crack nucleation region, and circumferential slender ligaments develop in the advanced stages of crack propagation. Based on these results, a fatigue joint damage mechanism of PFSA ionomer under the combined effects of hygrothermal conditions and chemical corrosion is proposed.