Comparison of Flow Birefringence Data of Polymers by means of Reduced Variables

Abstract

FLOW birefringence is usually characterized by the variation of the extinction angle χ and the birefringence Δn as a function of the velocity gradient q. This holds in particular for flowing polymer systems, including the limiting cases of very dilute solutions and of bulk polymers in the molten state. In principle, q can always be eliminated from the two relationships. Although information is lost in this way, the over-riding advantage is that, for small q, the flow birefringence of polymer systems behaves very much like stress birefringence of rubber-like materials. Such a consideration eliminates the picture of flow, because birefringence is considered as a function only of the stresses.