In suspensions of polarizable particles the addition of polar molecules can dramatically increase the yield stress under an applied electric field, leading to a giant electrorheological (GER) effect. We report experiments on dense suspensions of strontium titanyl oxalate in silicon oil, where we find a yield stress of up to 200kPa at 5kV/mm. The magnitude of this yield stress directly correlates with the water content in the particles. In the dynamic response we observe behavior not previously reported for GER fluids and similar to sheared granular materials, including a direct proportionality between shear and normal stresses and the creation of a shear band a few particles in width. An important consequence is that the dynamic response can be varied dramatically by changing the confinement of the suspension or by imposing a normal stress.

1. •Carlos S. Orellana, Jinbo He, and Heinrich M. Jaeger, “Electrorheological response of dense strontium titanyl oxalate suspensions”, Soft Matter, June 29 (2011). pdf