Dielectric Properties of Glycerol—Water Mixtures

Abstract

The frequency dependence of the complex dielectric constant of glycerol—water mixtures has been measured in the megacycle frequency range at −7.5°, −15.3°, and −19.5°C. for various concentrations between nearly pure glycerol and an equal molar mixture. Cole—Cole plots of the data indicate a single main relaxation with an asymmetric distribution of relaxation times of the Davidson—Cole form. The limiting dielectric relaxation time of the Davidson—Cole distribution was found to be strongly dependent on the water content and to vary exponentially with the molar concentration of water. The width of the distribution of relaxation times is independent of the concentration over the range studied and only slightly temperature dependent. The average dielectric relaxation times of the mixtures were extrapolated to 100% water. The dielectric relaxation time of water obtained by this extrapolation agrees satisfactorily with the measured value, indicating a smooth transistion between the average relaxation time of pure glycerol and pure water, as well as indicating a change in the distribution of times from that of the Davidson—Cole form to a single time. These experimental findings can be explained in terms of the ``group'' concept of Schallamach in which it is assumed that in mixtures of associated—associated liquids, such as glycerol and water, dielectric orientation occurs through a cooperative effect in groups of molecules, these groups containing molecules of both kinds. The concentration dependence of the dielectric relaxation time is also compared to that of viscosity. The comparison indicates that the variation of dielectric times with water content is similar to, but not exactly the same as, the variation of viscosity.