Charge transport and charge clustering in polymer electrolytes: results from simulations

Polymer electrolyte materials exhibit charge transfer properties that can be best understood in terms of a concentrated Coulomb fluid moving in an immobile solvent. We report results of molecular dynamics simulations on models for polymer electrolytes. The initial models use reasonable potentials, with proper thermal dynamics and appropriate treatment of boundary conditions. THe solvent pieces themselves range in complexity from simple Lennard-Jones spheres with embedded dipoles to constrained geometry models for small etheric solvents. We report structural, transport and thermal dependencies of these model electrolytes. We observe some important changes in the extent of clustering with temperature and with dielectric constant, as well as with concentration. Mechanistic interpretation, in terms of effective ion flows and charge transport characteristics, are reported. Some remarks will be made on timescale limitations, polymer relaxation, and possible generalization of the technique to longer timescales using effective friction kernels. The importance of host physical properties on the ion transfer process will be discussed, and possible enhancements schemes considered.