Mechanism of Degradation in Hydrous Electrorheological (ER) Systems

The degradation mechanism of the electrorheological (ER) effect in hydrous ER systems was studied by using two kinds of ER fluids. One contained titania and the other microcrystalline cellulose as dispersoids in silicon oil. The ER effect of the fluids with different water content was measured for several samples during a time interval of several months. The interval of several months degraded the ER effect in all the fluids. After the degradation, the water content of the dispersoid was found to decrease. The electric current density decreased and the dielectric properties changed. The relation between the ER effect and the electric current density and the relation between the ER effect and the dielectric properties were investigated before and after the degradation. The amount of water in the silicon oil was measured using TG (thermogravimetry) to detect the amount of water in the silicon oil after removal of particles from an aged fluid. There was no detectable water in as-received silicon oil, but water was detected in the silicon oil after the degradation. It was suggested that the water diffused from the surface of the dispersoid to the silicon oil. Finally, a suspension made up of a used silicon oil and a dispersoid was subject to the evaluation of ER effect. No degradation was found for the fluid.