Effect of Pressure on the Viscosity and Dielectric Relaxation Time in Glycerol

Abstract

Dielectric relaxation and viscosity data are presented for glycerol as a function of pressure and temperature.Viscosity data are given over a temperature range +10°C to —10°C and over a pressure range of atmospheric to 4000 kg/cm2. Dielectric data are given at —6.7°C over the same pressure range. The form of the pressure dependence of the dielectric relaxation time appears to be Arrhenius and that of the viscosity is approximately Arrhenius. However, the pressure dependences of the dielectric time and the viscosity are significantly different, the ratio of η s to τ D varying by approximately two over the pressure range studied. The pressure dependence of η s and τ D were examined according to both the free volume theory of Williams, Landel, and Ferry (WLF) and the hole theory of Eyring. Both theories fail to give the proper pressure dependence of the data. When the WLF theory is applied to the data, the resulting form of the pressure dependence of η s is incorrect. Although the hole theory of Eyring predicts the correct form of the pressure dependence, a strongly temperature‐dependent hole volume, with a negative temperature coefficient of expansion, is needed to fit the experimental data.