Magnetic resonance microscopy of heterogeneity in polymer electrolyte membranes

Magnetic resonance microscopy of Nafion 117 is used to measure the spatial variation of solvent dynamics in protonated (acid form) membranes immersed in solvent. Spatial resolution allows determination of membrane material property heterogeneity via T₂ and diffusion variations to be easily studied in the presence of strong free solvent signal. Variation of T₂ and diffusion as a function of solvent methanol-water mole fraction is measured. Spatially averaged T₂ and diffusion data are in general agreement with previous bulk nuclear magnetic resonance studies; however, significant disparities from sample to sample at fixed solvent concentration are present in the spatially averaged data. The variation is determined to be due to changes in solvent mobility within the membrane over scales of the order of 10 mm, indicating macroscale heterogeneity of the solvent saturated membrane morphology.