Effect of aging on flow birefringence of poly(vinyl alcohol) and methyl cellulose solutions

Flow birefringence experiments on aqueous solutions of poly(vinyl alcohol) and of methyl cellulose show that the optical anisotropy changes markedly during aging of the solution. The same effect can be obtained by adding alcohol to fresh aqueous methyl cellulose solutions. The flow birefringence was measured as a function of the velocity gradient on solutions with and without alcohol during the course of aging. The phenomena are attributed to intermolecular and intramolecular interactions between exposed hydroxyl groups of the polymer chains, as these are affected by a change in the degree of hydration during aging or by the addition of a strong hydrophilic agent such as an alcohol. Association or crystallization of the ordered polymer chains may occur and lead to a supermolecular structure in the solutions. By following Sadron's theory and making use of a polar diagram, it was concluded that, after aging or mixing with the additive, the solutions become optically heterogeneous and contain two different components with optical polarizabilities of the same [in poly (vinyl alcohol) solutions] or opposite (in methyl cellulose solutions) sign.