DIELECTRIC-SPECTROSCOPY OF REVERSIBLY FLOCCULATED DISPERSIONS DURING FLOW

The dielectric properties and the conductivity of carbon black suspens ions in mineral oil have been investigated during shear. The presence of shear modifies the properties considerably. The experimental result s for this reversibly flocculated system show a shear-rate-dependent p ower law behavior of the dielectric susceptibility in a frequency rang e above 100 Hz. A structural explanation for this dielectric behavior is suggested. At lower frequencies resonance phenomena are observed. A t a shear-rate-dependent frequency a maximum polarization is found, wh ile time-dependent measurements in a constant electric field show a sl ight minimum in conductivity. Measurements performed in the time domai n and in the frequency domain are in quantitative agreement. The resul ts illustrate the usefulness of dielectric spectroscopy in analyzing t he structure of flocculated suspensions under shear. (C) 1994 Academic Press, Inc.