Effect of high pressure on the electrical conductivity of ion conducting polymers

Abstract

Complex impedance and differential scanning calorimetry (DSC) studies have been carried out on poly(propylene glycol) (PPG) with an average molecular weight of 1025 and poly(ethylene glycol mono-methyl-ether) (PEG) with an average molecular weight of 350, both containing NaCF 3SO 3 in an approximately 20:1 ratio of polymer to salt. The impedance studies were carried out over a range of frequencies, temperatures and pressures. As expected, PEG:NaCF 3SO 3 exhibits the tendency to crystallize while PPG:NaCF 3SO 3 is a glass-forming liquid. The fit to the zero pressure data for PPG:NaCF 3SO 3 using a recently developed generalized Vogel equation (based on a defect diffusion model) is better than that for the standard VTF equation while for PEG:NaCF 3SO 3 the two expressions give about the same level of fit to the data. In the theory, the effect of pressure is due to a pressure dependent critical temperature, T c, and a defect–defect separation that follows the dimensions of the material. It is found empirically that the pressure dependence of T c is similar to the pressure dependence of the glass transition temperature, T g, for structurally related polymers containing no salt. However, the details of the relationship between T c and T g remain to be determined.