The yield stress equation for the electrorheological fluids

From the internal energy and entropy change of an electrorheological (ER) fluid under an external electric field, a general yield stress equation for the particle-type ER fluids is derived. Experiments were designed for testing the validity of our yield stress equation, and it is found that the experimental results and the prediction obtained from our yield stress equation agree very well. The currently observed ER phenomena reported in the literature are also able to be well understood by using our equation, especially the experimental facts which could not be explained well using the previous yield stress equations, for example, the ER behaviors of the BaTiO3/silicone oil system. Our present yield stress equation essentially differs from the previous ones, as it includes not only the dielectric constants of both liquid and solid materials but also a very important parameter related to the dielectric loss. The previous ER mechanism model proposed by us on the basis of experimental results,(1) which emphasizes the role of the dielectric loss and particle turning process in the ER response, is thus materialized in this paper. Our results present a powerful tool to precisely estimate the yield stress based on the physical parameters of the suspension materials. They also provide insight into the mechanism of the ER effect and offer the clear implications on how to design high-performance ER fluids.