DIELECTRIC-SPECTROSCOPY ON W O EMULSIONS UNDER INFLUENCE OF SHEAR FORCES/

The dielectric properties of concentrated w/o-emulsions have been inve stigated, both at rest and during shear. The volume fraction water ran ged from 0.50 to 0.95. The time domain dielectric spectroscopy techniq ues (TDS) was used to record the dielectric spectra, which covered the frequency region from 25 MHz to 2 GHz. In order to simultaneously rec ord rheological and dielectric data a modified viscometer of the coaxi al cylinder type was applied. A close connection between the viscosity and the dielectric properties of w/o emulsions is demonstrated. The v ery large effects of shear both on the static permittivity and the die lectric relaxation time for the emulsion can partially be ascribed to the degree of flocculation in the system. At high shear rates, at whic h the emulsions are expected to have a low degree of flocculation, the observed dielectric properties differ from those expected from a theo retical model for spherical emulsion droplets.