DIELECTRIC-SPECTROSCOPY OF COLLOIDAL DISPERSIONS - COMPARISONS BETWEEN EXPERIMENT AND THEORY

Recent development in theory and instrumentation have contributed to renewed interest in the dielectric properties of colloidal dispersions. One motivation is that dielectric measurement appear to be more sensitive to characteristics of the particle surface than conventional electrophoretic mobility measurements. However, the amount of data on well-characterized systems is small and it is premature to generalize. To broaden the database, two different types of particles were studied: an amphorteric polystyrene latex and colloidal silica. In both cases, the dielectric response was found to differ from that predicted by electrokinetic theory using zeta potential measured electrophoretically. The l dielectric constants of the latexes exceeded the theoretical predictions by an order of magnitude or more. At the same time, the characterisitc relaxation frequencies were consistently lower than the theoretical. Experiments with silica yielded smaller dielectric constants than those found with the latex and the differences between theory and experiment were much less. The results indicate that dielectric spectroscopy is sensitive to characteristics of the dispersion other than the particle size and the ionic composition of the suspending electrolyte.