Conformation and Ion-Transport Models for the Structure and Ionic Conductivity in Complexes of Polyethers with Alkali Metal Salts

Two ion-transport mechanisms are described for ion transport in polyether-alkali metal salt complexes: an intrahelical jumping process along crystalline (helical) regions of the polymer, and a transport process in the amorphous regions which is dependent on formation of fourfold coordination sites via mutual motion of ether oxygens from two or more polymer chains. The intrahelical jumping process may exhibit Arrhenius behavior, while transport in the amorphous regions should behave like a configurational entropy dominated process, showing a temperature dependence like T−½ e−A/T−T0, where T0 is the equilibrium glass transition temperature. For the highly crystalline poly(ethylene oxide) NaX complexes, an Arrhenius behavior is observed to dominate, whereas for the amorphous polyether salt complexes the configurational entropy behavior is observed. Even for the highly crystalline complexes, however, amorphous regions separate the crystalline regions of the polymer, and segmental motion of the polymer chains is postulated to be crucial here as well. The models are consistent with the observed frequency-dependent ionic conductivity, as well as spectroscopic, x-ray, thermal, and physical characterization measurements. They provide a reasonable microscopic picture for ion motion and yield testable predictions concerning the dependence of the ionic conductivity on pressure, temperature, and crystallinity.