The effects of chain segment motion on ionic diffusion in solid polymer electrolytes

The “vehicular effects” of chain segment motion on ionic diffusion in solid polymer electrolytes have been investigated via numerical simulation on a two-dimensional square lattice where the dynamical variation of chain configuration is presented by translational or rotational bond movement. It is found that (a) both types of bond motion promote continuous diffusion when the fraction (p) of available bonds is below the static percolation threshold of p=0.5 in two dimensions; (b) translational motion of bonds parallel to the direction of diffusion produces larger diffusion coefficients (D) than that by random renewal of the dynamic bond percolation model (DBPM), while the perpendicular motion or rotational motion gives smaller values of D; (c) Smooth lines instead of “stair-case like” curves generated by DBPM are obtained in the mean-squared displacement versus time plot, when bonds are shifting along the diffusion route. The dependence of diffusion coefficients on the variation of motion patterns of bonds is expected to be related to the temperature change under which these patterns are excited accordingly, such that VTF behavior of certain polymer electrolytes may be deduced.