Streaming Birefringence of Polymer Solutions : Anisotropy of Internal Fields

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Abstract
In the case of nonvanishing difference between indexes of refraction of the polymer and the solvent, the anisotropy of the internal electric field contributes a new term, called the form anisotropy, to the difference of polarizabilities of the long chain molecule. The form anisotropy is proportional to the square of the difference between indexes of refraction of the solvent and the polymer; hence it is responsible for the parabolic dependence of the streaming birefringence on the index of refraction of the solvent. Moreover, the form anisotropy is dependent upon the molecular weight of the polymer and on the nature of the solvent in contrast to the intrinsic anisotropy, which is a function of the internal constitution of the long chain molecule only. Different effects, caused by the presence of the form anisotropy, are discussed using the dumbbell model for the soft and the rigid macromolecules for illustration. Some experimental data obtained on polystyrene in different solvents are compared with the theory.