Electrorheological fluids of coated microspheres

We study model electrorheological (ER) fluids which consist of three materi al components in an attempt to explain recent experimental results, in whic h the ER effects can be promoted by adding some water. At low water concent ration, the droplets tend to aggregate on the surfaces of the dispersed par ticles, forming coated microspheres. The ER effects are analyzed via spectr al representation, and the experimental conditions for optimal ER responses are obtained. At low frequencies, it is found that by tuning the thickness and dielectric properties of the coating materials, it is possible to enha nce the effective dielectric constant, thereby increasing the applicability of the ER fluids.