OPTIMUM PARTICLE-SIZE DISTRIBUTION OF AN ELECTRORHEOLOGICAL FLUID

The optimum particle size distribution of an electrorheological fluid (ERF) is studied theoretically by the cubic particle chain model developed by the authors. For simplification purposes, the study is limited to a mixture that consists of two different particle sizes, i.e., small particles and large particles, but of the same permittivity. We adopt periodic boundary conditions with two chains in the unit cell. Static yield stress is calculated for three particle configurations. In the first configuration, each chain contains only one particle size, either small or large. The other configurations use chains which are constructed from small and large particles, arranged alternately. However, whereas the second requires particles of neighboring chains to be complementary, the third requires an alternating arrangement. The relative magnitude of the calculated yield stress in these the situations is tau(2)<tau(3)<tau(1). In the first configuration calculated yield stress is independent of the particle size ratio. However in the second configuration, the yield stress increases as the size ratio approaches unity. From the results of these typical cases, we conclude that the ERF consisting of only the same particles gives the largest static yield stress. Also interactions among the chains as a description of the many-body effect is discussed.