STRUCTURE-INDUCED NONLINEAR DIELECTRIC-PROPERTIES IN ELECTRORHEOLOGICAL FLUIDS

The structure-induced nonlinear dielectric properties of electrorheolo gical (ER) fluids have been studied in anhydrous KNbO3-silicone oil an d SrTiO3-silicone oil systems. We find that the permittivities of ER f luids increase linearly with the increase of the field strength as the electric field exceeds a threshold value E(1), and tend to saturated constants beyond a high field strength E(2). The alignment of particle s in the direction of the electric field causes variation of the diele ctric properties of the ER fluids. Below E(1), when the particles are randomly dispersed, and beyond E(2), when almost all the particles are form chains and columns, the permittivities do not vary with E and at tain their lowest and highest values, respectively. Correspondingly, t he current densities of ER fluids no longer follow Ohm's law between E (1) and E(2), whereas they still show Ohmic behavior in the regions be low E(1) and beyond E(2).