DIELECTRIC-RELAXATION STUDIES OF WATER-CONTAINING SHORT SIDE-CHAIN PERFLUOROSULFONIC ACID MEMBRANES

The storage and loss components of the complex dielectric permittivities of short side chain perfluorosulfonic acid membranes were determined as a function of water content, temperature, and membrane equivalent weight. As in our previous studies of electrolyte-containing long and short side chain perfluorosulfonate ionomers, a low-frequency graphical feature on isothermal loss spectra was identified that is suggested to be reflective of, and that crudely quantifies the tortuousity of, long-range (intercluster) proton-conductive pathways. When the long-range ion transport contribution was subtracted from the loss spectra, a distinct bimodal relaxation was uncovered. It is suggested that these two relaxation peaks are a manifestation of two distinct types of hydrated polar clusters. At least one of the peaks is assumed to arise from a cluster/TFE interfacial polarization that fluctuates with a characteristic frequency as indicated by the maximum loss factor. Finally, preliminary studies suggest that the Cole-Cole distribution of relaxation times parameter for nominally dry membranes may be an index of distribution of cluster size or of cluster structure.