Diffusive and segmental dynamics in polymer gel electrolytes

Dynamic light scattering data on a polymer gel electrolyte with a complex relaxation behavior is presented. The electrolyte consists of lithium perchlorate dissolved in an ethylene carbonate and propylene carbonate solution that is immobilized with poly(methyl methacrylate). We attribute the observed relaxation processes to two diffusive and one segmental relaxation processes based on the form of the time decay of the intermediate scattering function and the corresponding temperature and wave vector dependencies. The dynamic light scattering results are compared with the ionic conductivity, which reveals a close connection between the fast diffusive motion of the low molecular weight solvent within the gel and the ionic conductivity. This motion is strongly decoupled from and considerably faster than the segmental motion of the polymer matrix. The results indicate that the ionic transport occurs mainly within the low molecular weight solvent.