Electrorheological effects in suspensions of hydrophobically modified saponite

The electrorheological (ER) properties of suspensions composed of hydrophobically modified particles of a synthetic clay mineral (saponite) in an oil (n-hexadecane) containing a stabilizing additive were investigated. A comparison was made between the ER response of suspensions with the same volume fraction but with different cationic surfactants adsorbed on the saponite surface and with different additives at various concentrations. The results of these investigations indicate that a direct relationship exists between the stability of the suspensions against sedimentation and the magnitude of the ER effect. In a second series of measurements, the type of surfactant on the saponite surface was kept constant and the volume fraction of the particles was changed. Rheological parameters (yield stress, shear viscosity and dynamic moduli) were measured in dependence of field strength, held frequency and particle concentration. (C) 1999 Elsevier Science B.V. All rights reserved.