VAN DER WAALS INTERACTION IN COLLOIDAL GIANT ELECTRORHEOLOGICAL SYSTEMS

An alternative explanation of the giant eletrorheological (GER) effect is proposed using the van der Waals interaction which can lead to a yield stress of at least 50 kPa when the gap between two colloid spheres 60 nm in diameter is about 0.1 nm. This effect is in addition to the saturation dipole polarization in. When the electric field is removed, an elastic force would allow the colloid particle system to balance in a new position, which makes a larger gap than the one under the field, and the van der Waals force decreases dramatically. When the Laplace equation and the van der Waals interaction are considered, it is proposed that the gap between the colloidal ER particles would change with the external electric field to match the experimental result of the giant ER effect. An attempt is also shown to understand the size effect, base oil effect and tailing phenomenon of GER effect.