An Electrorheological (ER) process occurs when the viscosity of fluids with dispersed particulates is modified by the application of an electric field. The ER fluids discussed in this study are dispersions of solid polymers in low dielectric base oil, an insulating fluid. When these special composite fluids are subjected to the electric field they exhibit increased shear stresses, static yield stresses and viscosity. A mechanism for ER behavior is based on the polarization of the dispersed polymer particulates. A crucial property of the ER event is the ability of the system to respond to the applied field. For example, in semi-passive shock absorbers, the response time is crucial to commercial development.
Dielectric Thermal Analysis (DETA) can measure a polarization response in an AC electric field at isothermal temperatures or by scanning temperature techniques. A Debye Plot of Tan Delta, a ratio of dielectric loss divided by the relative permittivity, versus frequency can fix the limits of a polarization or relaxation time. The critical peak frequency in the Debye Plot is inversely related to the polarization time. The ER response time in a commercial system is directly related to the polarization time. A series of polymer types have been studied in low dielectric oil and their DETA properties are reviewed.