Pieter Hoekstra

Dielectric relaxation of surface adsorbed water

Abstract The dielectric behavior of water adsorbed on Na-montmorillonite and γ-alumina oxide is determined at a microwave frequency of 9.8 × 10 9 Hz and over the temperature range from +20°C to −100°C. The dielectric data are correlated with results from previous experiments showing the changes that take place in the sample upon freezing. At temperatures below −10°C all water in excess of two layers between the clay plates has formed ice. Nevertheless, when dielectric data at these temperatures are compared with measurements on similar samples at radiofrequencies, it becomes evident that a dispersion in two layer thick films of adsorbed water, takes place at a frequency of about 10 9 Hz. The variation of the log of the dielectric loss versus the reciprocal of the absolute temperature is linear, and enables one to make the calculation of the Arrhenius activation energy. At radiofrequencies the activation energy in the temperature region from −15°C to −80°C is approximately 12 kcal/mole; at microwave frequencies and in the temperature range from −15°C to −52°C the activation energy is 6 kcal/mole. Various models to explain the results are discussed.