The theory for the dielectric behavior of colloidal systems This paper presents the application of electrochemical impedis not new. Schwarz ( ) and Schwan et al. (2) studied ance spectroscopy as an interfacial electrokinetic characterization colloidal polystyrene spheres in electrolyte solutions in the tool for high-solids, carboxylated, styrene-butadiene latex disperlate 1950s. Subsequent refinements were introduced by Duksions. The frequency-dependent conductivity and the characterishin and co-workers (3) and others. Derjaguin and Dukhin tic relaxation frequency (CRF) were studied for both ''as-pro-(4) treated the polarized diffuse double layer theoretically duced'' latexes and latexes purified through an ion-exchange resin.
and were successful in describing its electrokinetic behavior.
CRF is a measure of the speed with which the interface perturba-These and other theoretical developments (5), particularly tion disappears, with high values of CRF indicating a more rigid with regard to high-solids dispersions (6), formed a potendouble-layer structure. For the as-produced and purified latex samples, the magnitude of both conductivity and CRF increased tially powerful set of tools to probe the electrokinetic behavwith increasing latex particle concentration (percent solids), ior of colloidal systems by examining the response of the added electrolyte level, and decreasing latex particle size. The CRF system over a wide range of frequencies. In particular, reshowed a minimum with increasing pH. Latex particle concentrasearchers gained insight into the mechanism by which contion, electrolyte, and pH appear to affect latex dispersion dielectric centration polarization of the double layer led to strong lowproperties in a predictable manner consistent with the understandfrequency dispersion (3, 4). The experimental difficulties, ing gained from rheological measurements. ᭧ 1997 Academic Press however, were significant (3, 5) until recent developments in