Rheological behavior of electrorheological fluids: effect of the dielectric properties of liquid phase

Electrorheological (ER) fluids composed of non-colloidal silica gel particles of irregular shape and liquids with different dielectric properties are studied in this work. The rheological behavior of the suspensions is analyzed in the diluted and semiconcentrated regimes under different constant dc electric fields. Primarily, the dielectric properties of the suspensions are studied with particular attention to the dependence of the dielectric relaxation process on particle concentration and their relation with the conductive behavior. Rheological tests under applied electric fields elucidate the influence of the electric field strength and dielectric properties of the solid and liquid phases on the yield stress. It was found that the yield stress scales as (φE2)α, where E is the electric field, φ is the particle volume concentration and α is a constant which depends on the spatial arrangement of the particles and dielectric properties of the suspensions. For high particle concentrations in liquids with high permittivity (or conductivity), the relative viscosity of the suspension in the presence of an electric field is lower than that observed in liquids with low permittivity, presumably due to an electrohydrodynamic (EHD) instability.