The Significance of Flow-Modified Permittivity: A New Model and Computer Simulation of Electrorheology

Abstract

We propose a model that takes into account the effect of flow-modified permittivity on electrorheology (ER). Due to dielectric relaxation, a shear flow causes the induced particle dipole moments in an ER fluid to tilt in a direction away from the direction of the applied DC electric field. Results from our computer simulation indicate that at high shear rates this misalignment (tilt angle) between the particle dipole moments and the applied electric field plays a crucial role in producing ER effects. By choosing particle-fluid dielectric and conductive mismatches to optimize the tilt angle, our simulation produces ER effects at much higher shear rates than those in earlier simulation work, even though there is no chain structure at these high shear rates. The increase in shear stress due to the applied electric field in our simulation is nearly constant over the wide range of shear rates examined, in qualitative agreement with experimental results. In addition, our model generates results that agree with earlier simulation work at low shear rates, where the particle dipole moments are essetially aligned with the field and the chain model is adequate.