DIELECTRIC-RELAXATION OF COLLOIDAL PARTICLE SUSPENSIONS AT RADIO FREQUENCIES CAUSED BY SURFACE CONDUCTANCE

We measured the dielectric properties of suspensions of colloidal part icles over a broad frequency range from 5 Hz to 13 MHz. The dielectric response is characterized by two distinct dispersions alpha and beta that occur at low kilohertz and meghhertz frequencies, respectively. T he alpha-response is identical with the counterion relaxation previous ly observed. The beta-response is a Maxwell-Wagner effect resulting fr om the interaction of the suspended particles surrounded by a surface admittance element with the medium. The particle and surface admittanc es display relaxation only in the alpha-range. The beta-effect is stro ng for particles suspended in an electrolyte of low salt concentration . It is weak for high concentrations and does not significantly contri bute to the dielectric response of biological cell suspensions and tis sues. The beta-response permits calculation of the surface admittance at high frequencies. The results show that surface conductance and cap acitance are independent of frequency above the alpha-range.