Dynamically disordered hopping, glass transition, and polymer electrolytes

The central parameter of the dynamically disordered hopping (DDH) model, the renewal time, is correlated with the characteristic time constant of the glass transition relaxation in polymer-salt complexes. With this identification, the frequency-dependent permittivity of these materials can be quite adequately described. In particular, experimental evidence for a high-frequency relaxation predicted by the DDH model is presented. This relaxation corresponds to the polarization of ions in their local percolation clusters as they wait for a renewal event to occur. In light of information on the renewal time, the direct current properties of polymer-salt complexes are used to calculate the size of these local clusters. These calculations suggest that the motion of an ion in the absence of renewal (polymer segmental motion) corresponds to displacements within its local coordination "cage" rather than hopping between several available coordination sites.