EFFECT OF ADSORBED WATER ON THE ELECTRORHEOLOGY OF SILICA SUSPENSIONS

Monodisperse silica particles were formed by hydrolyzing tetraethylorthosilicate in an ethanol solution and the silica suspensions dispersed in a silicone oil were prepared by a different procedure. The effects of adsorbed water on the electrorheological (ER) behavior were studied under oscillatory shear. The amounts of adsorbed water and surface silanol groups were determined by thermogravimetric analysis. The magnitude of the complex viscosity, |η*|, increases with the application of electric fields. The physically adsorbed water is primarily responsible for the ER effect. However, the fluids containing large amounts of adsorbed water do not always show excellent ER performance. The surface silanol groups have an important role in promoting the ER effect. Not only the amount but also the situation of silanol groups determines the ER activity of adsorbed water. © 1992.