Predictions of birefringence and dichroism of hard sphere suspensions in combined electric and shear fields

We present the optical anisotropy of a hard sphere suspension subjected to combined electric and shear fields. We model the particle structure factor as a shear induced perturbation of the anisotropic structure induced by electric field. We renormalize the nonconvergent birefringence integral to allow calculation of birefrigence from the particle structure factor. The principle axes of the birefringence and dichroism tensors vary with the Mason number, a measure of the relative strength of shear forces to electric dipole interaction forces. The principle axes only coincide in the shear dominated and the electric field dominated limits. The magnitudes of birefringence and dichroism are sensitive to the particle size relative to the wave-length of light employed. We compare theoretical predictions in the limit of pure shear to the experiments of Wagner et al., J. Chem. Phys. 89, 1580 (1988), employing a simple affine deformation theory for the structure factor, which yields fair agreement with experiment for the dichroism but poor agreement for the birefringence. The prediction of optical properties provides both a test for theories of microstructure and insight into the effects of shear and electric fields on microstructure.