The Dielectric Properties of Water–Dielectric Interphases

Abstract

When a dielectric dispersed in water is placed in an electrical field a part of the current passes through the system at the interphases and these become polarized, as shown under certain conditions by the occurrence of electrochemical reactions ( 1 , 3 ) . For this reason the dielectric properties of such systems are generally different from what would be expected from the contributions of the single phases, on the basis, for example, of the Clausius-Massotti-Maxwell theorem, for the particular case of a suspension of spherical particles. This influence of the interphases is especially pronounced when measurement is made with direct current or with alternating current of low frequency, in which case the dielectric properties may be radically different from those of either of the components, as measured in the bulk.Recent measurements by Fricke and Curtis (11, 12) of the dielectric constant and electric conductance of suspensions show this influence of the interphases clearly; there is a rapid increase of the dielectric constant and a decrease of the conductance as the frequency decreases, the change in both being approximately as powers of the frequency. The high dielectric constant often found for colloidal solutions is undoubtedly also of this origin (6, 11, 14, 15, 16,20,21). This property was first observed by Errera on colloidal vanadium pentoxide (6), and explained by him as due t o electric moments of the colloidal particles.I n spite of the importance of these interphasial properties for the dielectric characteristics of a number of important systems, such as living cells (5, 9), soil (7, 23, 24), and many of the insulating (hygroscopic) materials used in the electrical industry (paper, fabrics, rubber) (19, 25), experimental data suitable for reaching an understanding of their nature are largely lacking. The present study is based upon alternating current measurements of the dielectric constant and electric conductance of suspensions, particularly those with particles of spherical form.The measurements were made with a Wheatstone bridge by a substitution method which is based upon the comparison of the suspension with a 729

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