Nanostructure of Clusters in Nafion Studied by DSC

The nanostructure that consists of clusters and channels between the clusters in Nafion with absorbed water is studied by Differential Scanning Calorimeter (DSC) measurements with stepwise temperature programs. A cluster size distribution (CSD) is fitted reasonably by a log normal distribution function. The fitted CSD has a peak of approximately 4nm in diameter. In comparison of the water content from gravimetry with that from the fitted CSD, at least three kinds of water states are found, two of which are freezable and non-freezable water in a cluster and another is the non-freezable water in a channel between the clusters. From the assumption of a simple cubic lattice model, the channel length L ch between the clusters and the cross section S ch of the channel can be estimated. Also, the degree of desulfonation in the terminal of the side chain by thermal degradation depends on the nanostructure consisting of the clusters and channels in Nafion with absorbed water. The channel length L ch decreases monotonically with increasing water content. Essentially the channel cross section S ch increases with increasing water content.