Electrical relaxation in poly (propylene oxide) with and without alkali metal salts

Previously published audio frequency complex impedance studies of poly(propylene oxide) (PPO) containing various ions at pressures up to 0.6 GPa over the temperature range 250-350 K have been reanalyzed in terms of electric modulus. Peaks in the electric modulus plots (conductivity relaxation) are found which are characterized in terms of the stretched exponential. It is shown that those fits are not perfect, in part due to the presence of a low temperature relaxation. As a consequence, different values of the stretched exponential parameter, ß_SE, are obtained when different portions of the curve are analyzed. The effect results in an apparent increase in ß_SE with increasing temperature or decreasing pressure. However, when the same portion of the peak is fit, ß_SE is found to be approximately 0.5 and independent of temperature and pressure. Next, data for the α-relaxation in pure PPO were reanalyzed. It is shown that while the value of ß_SE for the α-relaxation data is similar to the values determined for the conductivity relaxation, ß_SE for the electric modulus representation of the α-relaxation data is somewhat smaller. In addition, the temperature dependence of the average relaxation time for the electric modulus representation is better fit by the BENSH equation than by the Vogel equation while the opposite is true for the dielectric constant data.