Radiofrequency Properties of Polyelectrolyte Systems

Abstract

Abstract. Electrical measurements of heterogeneous media composed of solid polyelectrolytes and dilute aqueous solutions (or pure water) are interpreted in terms of a simple electrical network. It is demonstrated that this model network represents an extension of Maxwell’s equation for the conduc­tance of dilute suspensions of spheres to condensed systems. Discussing past work on cation exchange resinsolution systems, it is shown that the three empirical geometrical parameters of the model explain quantitatively the change of the low-frequency (⩽ 1000 Hz) conductivity of the heterogeneous mixture with the conductivity of the interstitial solution, and that the same parameters also explain (a) the potential differences between two NaCl solutions of different concentration separated by the mixture, and (b) the frequency-dispersion of the dielectric constant and of the conductivity of these mixtures in the radiofrequency range (20–90 MHz).

Application of the model to clay-solution aggregates showed that the radiofrequency dispersions of these systems at 10–50 MHz are fairly well described by the model. These dispersions were found to depend on the clay type (kaolinite, illite, montmorillonite), degree of consolidation, and soil fabric; these properties are reflected in the values of the geometrical parameters and of the dielectric constant of the solid which fit the dispersion curves best.

The influence of the counterion type on the dispersion curves is not well understood.

Frequency-dispersion curves of a commercial anion-exchange membrane in the range 5–50 MHz are shown and discussed.

It is concluded that the simple network used here represents a simple, first approach for the characterization of mixtures of solid polyelectrolytes and electrolyte solutions, and for other similar heterogeneous media.