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 30C,
but a higher stress level at 70C. 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 60C. Based on the observation, the
relationship between the microstructure and mechanical
properties is explained.