Flow Birefringence of Polymer Solutions

By making use of a gaussian chain model for a polymer molecule, a theoretical calculation on the flow birefringence of polymer solution is carried out, in which the optical internal field in the polymer molecule in solvent is taken into account. The obtained expression for the intrinsic birefringence contains a quadratic form of the refractive index of solvent, and this can account for several experimental results. The expression for the intrinsic extinction angle also has a certain optical factor, and thus it predicts that the extinction angle depends on the refractive index of the solvent. Assuming that there is no hydrodynamic interaction between molecular segments, we carried out some numerical calculations to the optical factors. The result can well reproduce the recent experimental values of the polystyrene molecules, and of the polymethylmethacrylate molecules.