The role of the dielectric loss of dispersed material in the electrorheological effect

A set of electrorheological (ER) suspensions composed of solid materials with different dielectric losses and dielectric constants were examined by means of dielectric and rheological methods. We found that the dielectric loss of dispersed material, which was only slightly stressed in previous works, plays a considerable role in ER response; a large dielectric loss value is necessary for a clear ER effect. Two processes, the turning of randomly distributed microparticles toward the direction of an applied external electric field, probed recently by an x-ray diffraction method, and a coalescing of ordered microparticles, widely observed in ER fluids under a microscope, are suggested for understanding the ER mechanism. The first process is dominated by the dielectric loss of dispersed material, and the second one by the dielectric constant. Our result can be used to understand why certain materials of high dielectric constant but low dielectric loss would have shown an obvious ER effect according to the polarization and the conduction models, yet only displays weak or even no detectable ER effect experimentally. Our findings help to further understand the ER mechanism and also offer a clear implication on how to design high performance ER fluids. (C) 1997 American Institute of Physics.