Low frequency complex dielectric response of dilute clay suspensions

In this work, we measured the low-frequency complex dielectric dispersion of dilute clay suspensions using a four-point impedance measurement, which can be reliably calibrated in the frequency range between 0.1 Hz and 10 kHz. Complex dielectric spectra of smectite and illite suspensions in brine with different weight fractions were obtained. The brine salinities ranged from 100 to 3000 ppm. We fit our results to an effective medium model incorporating the dielectric response of a charged oblate spheroid immersed in an electrolyte. We found reasonable agreement between our measurements and the model; they both exhibited the same trends when the brine salinities and weight fractions of the clays were varied. When the clay grains have a narrow size distribution, we expect that the dispersion of the complex conductivity phase exhibits a near-resonance peak associated with the size of the particles. In our case, because the clay grains have a broad size distribution, the phase peak is broadened. The parameters obtained from the fit agree reasonably well with independently measured quantities, including the size distribution and cation exchange capacity of the clays.