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Published online by Cambridge University Press: 27 July 2011
The configurations of proton channel network on the surface of Nafion® membranes were studied using current sensing atomic force microscopy after the membranes were annealed at elevated temperatures, aimed at understanding the effect of aging process in the membranes. The results reveal that proton conductance of the membranes becomes more uniform and the proton channels become chain-like aligning in parallel to the membrane surface. Accompanied to the configuration changes, the proton conductivity of the membrane shows an increase. As the annealing continues, the chain-like configuration for the proton channels persists but the conductance of the membranes decreases. The time constant of the conductivity decay decreases with increase of the annealing temperature. The observed changes can be attributed to reorientation of proton channels near the membrane surface from perpendicular to parallel to the surface as the annealing temperature approaches the glass transition of the membranes.