Mechanical properties and microstructure changes of proton exchange membrane under immersed conditions

In this study, mechanical tensile stress-strain response and microstructure changes of proton exchange membranes (PEM) in immersed conditions are studied. The effects of water pretreatment and immersion time on stress-strain responses of NafionVR2212 membranes are discussed. It is found that in the water immersion it took 24 h for the membrane to reach saturation equilibrium. Compared with dry membrane, immersed Nafion membrane shows a lower stress level at 30°C, but a higher stress level at 70°C. In situ small angle neutron scattering (SANS) experiments show that with the increase of temperature and water uptake, domains of the membrane become ordered and stay stable at around 60°C. Based on the observation, the relationship between the microstructure and mechanical properties is explained.