Basic considerations in flowing electrorheological fluids

The physical and chemical properties of electrorheological (ER) fluids are reviewed, and an outline theory of their mode of action is proposed. Rheologically, the Bingham plastic model gives an acceptable representation of ER fluids flowing in a field and it has recently been shown that the plastic viscosity may be field-dependent in some circumstances, as well as the yield stress. The variation of the former with field is strongly influenced by the specific chemical nature of the ER fluid, while the field dependence of the latter has a similar form in all the ER fluids investigated. However, interpretation of observations is complicated by concentration of solid in the working gap and interplay between local electrical conductivity and shear rate.