Abstract
The rheological and electric properties of various ER fluids in strong electric fields have been investigated simultaneously. From the measured data the dependences of shear stress and real and imaginary part of the high field permittivity on field strength, temperature and frequency have been derived. One group of ER fluids containing perovskite type particles obeys a polarization mechanism which is attributed to the local displacement of ions in the crystal structure of the particles. The contribution of conduction to ER activity is low and the electric properties of these ER fluids are nearly constant. The increase of shear stress with frequency is in accordance with the polarization model. In contrast, another group of ER fluids containing zeolite or ion conducting polymer particles shows a strong dependence of the complex permittivity on field strength and temperature demonstrating the pronounced nonlinearity of the electric properties. It is assumed that both conduction and polarization contribute to the ER activity in these systems. The relative extent of the contributions changes with external conditions like field strength and temperature.