Electrorheological Fluids

Suspensions of polarizable particles in nonpolarizable solvents form fibrillated structures in strong electric fields. The resulting increase in viscosity of these "electrorheological" fluids can couple electrical to hydraulic components in a servomechanism. The physical properties of these fluids are unusual owing to the long-range, anisotropic nature of the interparticle forces. Immediately after the electric field is applied, elongated chains or columns of particles form parallel to the field. This structure then coarsens as a result of thermal forces between the columns. In shear flows, fluids show yielding behavior at low stresses followed by shear-thinning behavior at higher stresses.