Interparticle force in polydisperse electrorheological fluids

We have developed a multiple image method and an integral equation approach to compute the interparticle force for a polydisperse electrorheological (ER) fluid in which the suspending particles can have various sizes. As an illustration, we apply the formalism to a pair of dielectric spheres of different radii and calculate the force as a function of the separation. The results show that the point-dipole approximation errs considerably because many-body and multipolar interactions are ignored. The approximation becomes even worse when the particle sizes differ too much in polydisperse ER fluids. From the results, a dipole-induced-dipole (DID) model is proposed for computer simulation. The DID model accounts for many-body and multipolar interactions partially, but is simpler than the coupled-dipole model because a self-consistent solution is not needed. (C) 2000 Elsevier Science B.V. All rights reserved.