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Electrorheological Materials

  1. Frank Filisko

Published Online: 15 JUL 2002

DOI: 10.1002/0471216275.esm028

Encyclopedia of Smart Materials

Encyclopedia of Smart Materials

How to Cite

Filisko, F. 2002. Electrorheological Materials. Encyclopedia of Smart Materials. .

Author Information

  1. University of Michigan, Ann Arbor, MI

Publication History

  1. Published Online: 15 JUL 2002

Abstract

Electrorheological (ER) materials are materials whose rheological properties, flow and deformation behavior in response to a stress, are strong functions of the electric field strength imposed upon them. The materials are typically fluids in the absence of an electric field (although they may be pastes, gels, or elastomers) but under constant shear stress at high enough fields, the materials can solidify into viscoelastic solids. In their solid state, various properties of the solid such as shear and tensile strengths and damping capacity, internal friction, and the ability to adsorb energy under impact are also strong functions of the electric field. Further, all physical and mechanical changes induced by the applied field are virtually instantaneously reversible upon removal of the field. In brief, these are materials whose mechanical properties and physical state are determined at any instant by the electric field to which they are exposed.

ER materials are typically dispersions of fine hygroscopic particles in a hydrophobic nonelectrically conducting dispersion medium. Materials that work well as the dispersed phase include such diverse materials as corn starch, various clays, silica gel, talcum powder, and various polymers. The fluid phase also may consist of a very wide range of liquids or greases which have the common properties of high electrical resistivity (so that high fields may be applied over the fluids without significant currents) and hydrophobicity. Liquids such as kerosene, mineral oil, toluene and silicone oil work well as do many other fluids. With few very significant exceptions, the vast majority of systems also require that significant amounts of water (10–30%) or other activators be adsorbed onto the particulate phase. This requirement severely limited the potential use of these materials. Dry particulate systems are discussed.

Although it is not necessary for an appropriate dispersion to demonstrate ER activity, various other types of additives, called activators, have been reported and are commonly incorporated into the mixtures, including various surfactants, to enhance the effect and to increase the stability of the dispersions. How they work is unclear, but as are, they most certainly affect the particulate surface, the dispersing liquid, and the water on the particles.

Keywords:

  • Electrorheological (ER) materials;
  • Mechanical properties;
  • Mechanical models;
  • ER theories;
  • Applications;
  • Damping devices;
  • Torque transmission devices;
  • Hydraulic circuits