Light scattering, flow birefringence and generalized hydrodynamics

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Abstract
The stress-optical coefficient ∇, which is measured in flow birefringence experiments, is calculated using the generalized hydrodynamic equations which have been recently used to explain the k-dependent fine structure observed in depolarized (VH) light scattering. The resulting expressions allow a comparison of the strength of the birefiringence effect with that of the light scattering fine structure effect in a given liquid. It is seen that the combination of flow birefringence and VH scattering measurements yields the orientational structure factor g (2) of Ben-Reuven and Gershon. The theory is in reasonable agreement with experiment. The combination of our results with those of Raman and Krishnan yields a simple expression for the parameter δ which measures the strength of the stress-orientational effect. The dependence of the stress-optimal coefficient upon orientational order is briefly discussed.