Optical activity of electrorheological fluids under external electric field

The optical activity of electrorheological (ER) fluids under an external dc electric field was investigated. According to the nonhomogeneous structure model of ER fluids, we propose an expression of rotation angle from Maxwell's equations and Fresnel reflection. The optical activity of several kinds of ER fluids was measured by varying an applied electric field, the angle theta, and weight concentrations. The experiments show that the rotation angle increases with the concentration and electric field, and it first increases, passes through a maximum at an optimum theta, then monotonically decreases with theta. The experimental results are in qualitative agreement with our theoretical simulations. It is thought that the structure symmetry breaking of ER fluids under an external electric field may be the origin of the optical activity. (C) 2003 American Institute of Physics.