The effects of shape in streaming birefringence of polymer solutions

Abstract

AbstractIn this paper are presented new results obtained during further experimental and theoretical investigations of the form effect in the dynamic double refraction of polymers in solution. The use of the dumbbell theory of W. Kuhn for flexible chains in solution and of the optical modle of an equivalent ellipsoid for the macromolecule, permits the formulation of a theory of flow birefringence which takes account of the form effect for a wide range of shear rates. The conclusions of this theory are compared with new experimental data obtained in a study of polystyrene and p‐tert‐butylphenylmethacrylate in different solvents. In the range of low shear rates and concentrations, the theory is found to be in a good accord with experimental results. On the contrary, the study of the double refraction of several polystyrene fractions in dioxane in a wide range of shear rates and concentrations shows that macromolecules are less deformable in the flow than it follows from the dumbbell theory for ideally flexible chains. A new phenomenon was discovered experimentally—an anomalous dependence of the orientation angle on the shear rate of flow in the range of shear stresses at which the birefringence changes its sign because of compensation of the positive shape effect by the negative intrinsic anisotropy effect. Investigation of the concentration dependence of flow birefringence shows that this dependence is due to two causes—the hydrodynamic and optical interaction of the molecules. The optical interaction is characteristic only for those solutions in which the form effect takes place. A simple theory of concentration dependence of the form effect is proposed which is in good accordance with experimental data.