Stress-transfer mechanisms in electrorheological suspensions

Abstract

The stress transferred by many non-aqueous suspensions can be altered reversibly by the application of large (ca. 1 kV mm^–1) electric fields. In the presence of an electric field, the suspension at rest is observed to rearrange to a state where the particles form fibres or columns that span the electrode gap. Application of a shear stress to the suspension degrades these structures and the added work required to overcome the electrically induced particle interactions is observed as an increase in the apparent viscosity. In this paper, the origin of the electrorheological response is reviewed and results indicate that, at intermediate shear rates and field strengths, the electrically induced structural alterations give rise to a direct contribution to the apparent viscosity and an indirect contribution, resulting from viscous interactions between particles in the altered structure. At low shear rates, the indirect contribution to the shear stress decreases with decreasing shear rate, while at high shear rates, the shear field is capable of destroying the electrically induced structures and the indirect contribution is again negligible.