The effect of surface characteristics of silica particles on electrorheology

The effect of the surface characteristics of silica particles on electrorheology (ER) was investigated with a suspension that contained monodispersed silica particles in a silicon oil. Two types of adsorbed water exist at the silica surface; one is dehydrated below 200 degrees C (free water) and the other above 200 degrees C (bound water). It was found that the free water was essential for the ER effect and there was an appropriate amount of free water for an optimum ER effect. The silica surface was treated with cetanol. Cetanol-treated silica has less bound water than untreated silica. The amount of free water on the cetanol-treated silica was controlled by vacuum drying and exposure to saturated water vapor. The cetanol treatment of silica lowered the ER effect. With less bound water on the cetanol-treated silica, the control of free water did not change the ER effect. A direct relationship was not found between the ER effect and current density.