Remarks on the determination of low-frequency measurements of the dielectric response of colloidal suspensions

Abstract

Electrode impedance is a significant artifact in low frequency dielectric measurements involving conducting media. In their recent review article regarding the dielectric dispersion of aqueous colloidal systems, Grosse and Delgado [1] presented an electrode polarization model that provides a physical explanation of the effect of electrolyte concentration and mobility, electrode spacing, and frequency. Although the model properly predicts the undesired phenomenon, the low frequency scaling, often used to identify electrode polarization effects, is incorrect. The apparent dielectric constant actually follows an ω−2 frequency dependence for ω/κ2D≪1, where κ−1 is the Debye length and D is an average ion diffusion coefficient. Strictly speaking, the predicted scaling with exponent −1.5 is applicable only for sufficiently high frequencies, where electrode polarization is insignificant. This letter is intended to help clarify matters: the asymptotic behavior of the polarization model is examined, and the approximate expressions representing the real part of the complex dielectric constant of a parallel plate cell containing electrolyte solutions or colloidal suspensions are discussed.