Dielectric and conduction effects in non-Ohmic electrorheological fluids

Dielectric and conduction effects in electrorheological (ER) suspensions with non-Ohmic conductivity of the host liquid and with ac applied electric field are investigated. It is found that the conductivity ratio Gamma(sigma), the non-Ohmic conductivity parameters A and E-c of the host oil, the dielectric constant ratio Gamma(epsilon), and the applied field frequency are important parameters that determine ER response. The effects of these parameters are more complex than in the case of host liquids with simple Ohmic conductivity. If the ac field frequency is high, the conductivity effect disappears; if the frequency is low the dielectric effect disappears. The current density is independent of the frequency below a critical value, but it increases with frequency beyond the critical value. The critical frequency is larger for ER suspensions having non-Ohmic conductivity of the host liquid than with Ohmic conductivity. Good agreement occurs between experimental measurements of the current density and attractive force between particles (including shear yield stress) and predictions by our model.