Size Effects on Aggregation Structure for Polymer electrolyte Thin Films

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We have demonstrated the thickness effects on the surface aggregation state and on the water-uptake behaviors of Nafion thin films. Water contact angle measurements and neutron reflectivity measurements showed that the hydrophobic surface structures exist in Nafion thin films. Models obtained from fitting the neutron reflectivity data indicate that the surface segregation of tetrafluoroethylene backbone was significant with decreasing film thickness. Moreover, we found that the water sorption behavior was also depended on the film thickness. The findings of this work shed light the improvement of the fuel cell proton exchange membranes and membrane electrode assemblies.