Electrorheological Fluids & Flows

The electrorheological effect is recognized as the phenomenon of a rapid reversible change in mechanical (rheological) properties of dielectric suspensions of fine particles in a non-conducting oil in the presence of strong electric fields. It was discovered in 1947 by W. Winslow, who observed a change in the effective viscosity (fluidity) of dispersions. An electrorheological fluid consists of a carrier medium (any nonconducting oil) with excellent insulation capability and a filler (particles) with a different dielectric constant dispersed in this medium. Chlorinated paraffin, silicone oil, and mineral oils are the most common carrier fluids. The filler consists of suspended solid particles of 0.1- 100 μmin diameter. The dispersed phase may be either organic material such as microfine powders of soybean casein or starch cellulose or inorganic material such as micro powder mica, silica gel (barium titanate), various polymers such as phenolic resin, or metallic powders. These micro powders are used either untreated or after surface treatment-to improve their dispersability. Although a simple electrorheological fluid such as cornstarch in cooking oil can be easily mixed, it is quite difficult to manufacture an electrorheological fluid which meets commercial expectations.