Dielectric study of water, ethanol and acetone adsorbed on kaolinite

Abstract

Measurements of dielectric constant and dielectric loss on systems of kaolinite with adsorbed water, ethanol and acetone have been made over a temperature range of 35–115° and a frequency range of from 33 Hz to 20 MHz. Adsorption isotherms and surface areas for nitrogen have also been measured and in some cases electrical conductivities of the samples have been roughly evaluated. Values of ΔH_ads., ΔS_ads., and of ΔH^*, ΔS^* for the relaxation process are reported.

The behaviour of kaolinite proved to be similar in general to that of porous materials. There was a low frequency loss which rose steadily as f decreased, and a high frequency loss which gave a maximum in ε″. The height of ε″_m/β was roughly independent of the amount of adsorbate.

It is suggested that the low frequency loss is due mainly to surface conduction on the solid granules. The kinetics of the high frequency loss are better explained on a dipole relaxation model, and the Maxwell-Wagner model, involving conduction within the granules, is shown to be not wholly successful in explaining the insensitivity of the magnitude of this loss to amount of adsorbate; so it is concluded that on balance the former model is the better one. The magnitude of the loss can be better explained thereon if it is supposed that the dipole relaxation is co-operative and that adsorption occurs in clusters, which subsidiary hypotheses are supported by the kinetics and the adsorption evidence. If this model is correct, the adsorbed polar materials are not in the ordinary liquid state but one which shows markedly the effect of adsorbent-adsorbate interaction.