Overview of ER Technology

Electro-rheological materials (ERM) are materials whose rheological properties are strong functions of the electric field strength imposed upon them. ERM are typically fluids in the absence of an electric field but under constant shear stress at high enough fields, the materials can solidify into viscoelastic solids. In the liquid state during flow, these materials exhibit an apparent viscosity which can be increased by thousands of times by the application of an electric field. In their solid state, the materials are viscoelastic and characterized by complex modulii of which both the real and complex parts are strong functions of the electric field. Further, all field induced mechanical changes are virtually instantaneously reversible. The molecular mechanisms responsible for the phenomenon are however poorly understood as are the flow characteristics.