Rheological and dielectric behavior of electrorheological emulsions

The rheological and dielectric behavior of electrorheological (ER) emulsions composed of silicone oil (continuous phase) and two chlorinated paraffins (dispersed phase) are studied in this work. The chlorinated paraffins have different permittivity and conductivity values, and both are more conducting than the silicone oil. The rheological behavior of the emulsions is analyzed under constant dc electric fields, for two chlorinated paraffin concentrations. Results reveal that the magnitude of the ER response in the emulsions increases with the applied voltage but is affected negatively by the concentration of the chlorinated paraffin. The growth of viscosity in the presence of the electric field is less significant in the system with the largest conductivity at high electric fields. At low concentration, a Maxwell-Wagner polarization mechanism (interfacial polarization) is observed. A relationship between the dielectric and ER behavior is established, and also between the microstructural changes in the emulsions and their rheological and dielectric properties. (C) 2003 Elsevier B.V. All rights reserved.