Electrorheology: Mechanisms and models

Electrorheological (ER) suspensions, typically composed of nonconducting or weakly conducting particles dispersed in an insulating liquid, undergo dramatic, reversible changes when exposed to an external electric field. Apparent suspension viscosities can increase several orders of magnitude for electric field strengths of the order of 1 kV mm(-1), with simultaneous ordering of the microstructure into particulate columns. While this electronic control of momentum transport and structure has many applications, development is severely inhibited by a lack of suitable materials and an incomplete understanding of the underlying mechanisms. This review focuses on the current understanding of the microscopic phenomena believed to control ER and the models used to describe macroscopic behavior. Particular emphasis is placed upon comparing model predictions with experimental observations, relating macroscopic behavior to microscopic mechanisms, and demonstrating the utility of mechanistic models for furthering our understanding of electrorheology.