Molecular weight dependence of dielectric behavior of polymer electrolytes under shear flow

We have developed a new apparatus for measuring dielectric relaxation under shear flow, and applied it to a typical polymer electrolyte system, polypropylene oxide (PPO)-lithium perchloride, while changing the molecular weight of PPO. We observed a drastic increase in dielectric increment Δε and a drastic decrease in conductivity σ with increasing shear rate. The molecular weight dependence of σ and the relaxation time τ suggests that the conductivity is due to ion transport assisted by the conformational change of the entire polymer chain and the permittivity is ascribed to the ion fluctuation within a single chain assisted by the segmental motion of a polymer. On applying shear flow, the conformational change of a polymer chain is strongly suppressed, which would cause the decrease in conductivity.