Pressure and temperature variation of the electrical conductivity of poly(propylene glycol) containing LiCF3SO3

Complex impedance and differential scanning calorimetry (DSC) studies have been carried out on poly(propylene glycol) with average molecular weight 10 25 (PPG) and PPG containing LiCF3SO3. The impedance studies were made at fr equencies from about 1 mHz to 100 MHz at pressures up to 0.3 GPa (3 kbar) o ver the temperature range 215-365 K. Both the impedance and DSC studies wer e carried out in vacuum or at atmospheric pressure over a temperature range of about 100-375 K. As a consequence, the impedance studies overlap the DS C glass transition temperature. The inadequacy of the widely used Vogel-Tam mann-Fulcher or Williams-Landel-Ferry equations to describe the temperature variation of the vacuum electrical conductivity data is discussed. It is s hown that the Bendler-Shlesinger formalism is a better representation of th e data, particularly in the region close to the glass transition. The first pressure derivative of the electrical conductivity, and hence apparent act ivation volume, decreases strongly as temperature increases. In addition, t he activation volumes are larger for the low molecular weight liquids than the values reported previously for related, high molecular weight rubbery e lectrolytes. Next, there appears to be an exponential relationship between the activation volume and the electrical conductivity. Finally, the pressur e variation of the electrical conductance exhibits negative curvature which shows that the activation volume increases as pressure increases. A qualit ative explanation of each of these results concerning the relationship betw een conductivity, temperature, and pressure is given in terms of free volum e. However, whether free volume can provide a quantitative explanation rema ins to be determined. (C) 1999 American Institute of Physics. [S0021-9606(9 9)50339-5].