Experimental investigation of dielectric properties on electrorheological fluids

A home-made electrorheological (ER) fluid, known as ETSERF, has been created with suspension-based powders dispersed in silicon oil. Because of the special structure of their particles, ETSERF suspensions present a complex behavior. In the absence of an electric field, an ETSERF fluid will manifest a near-Newtonian behavior, but when an electric field is applied, it exhibits a pseudoplastic behavior with yield stress. The ER effect under DC electric fields has been experimentally investigated using both hydrous and anhydrous ER fluids. ER properties are strongly dependent on the dielectric properties of ETSERF suspensions and hydrous ER fluids have a high dielectric constant and a high relaxation frequency which show a strong electrorheological effect. The relationship between the electrorheological effect and the permittivity of ER fluids has also been extensively studied. Experimental results show that the interfacial polarization plays an important role in the electrorheological phenomenon. The ageing of ETSERF fluids was also studied and it was found that the dielectric properties (mainly the dielectric loss tangent) and ER properties are strongly related to the duration of ageing. A fresh ETSERF suspension exhibits a high relaxation frequency and a high dielectric constant. These results are mainly explained by the effect of interfacial polarizations.