The dielectric properties of monodisperse latex particles with mean diameters in the range 5-10 wm have been studied by single-particle rotation. The surface conductance is readily deduced from the medium conductivity dependence of the rotation peak seen in the 30-1 000-kHz range. This peak satisfies the equations describing the surface-conductance-modified Maxwell-Wagner dispersion for these particles, with respect to both the optimum field frequency and the speed of rotation. The observed surface conductivities of the particles are constant over the medium conductivity range of 2-16 wS/cm. The magnitude of this conductance depended upon particle type and pretreatment, the range of values being 0.2-2.1 nS. The rotation spectra indicate the presence of an additional rotation peak at field frequencies below 1 kHz. Possible causes of this effect, such as the modification of the field seen by the particle by its own ionic atmosphere or a "negative" dielectric dispersion due to the frequency dependence of electrophoretic motion, are suggested.
Electrode polarization is a major nuisance while determining dielectric properties of cell and particle suspensions and tissues, particularly at low frequencies. Understanding of these interfacial phenomena and appropriate modelling are essential in order to correct for its distortion of the dielectric properties of the sample of interest. I survey the following topics, concentrating on contributions from our laboratory: Linear properties of electrode polarization and relevant models. Effects of electrode polarization on sample impedance. Effects of sample on polarization impedance. Techniques of correction. Extension of linear to nonlinear models Harmonics generated in the nonlinear range.
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