THEORY OF STRAIN BIREFRINGENCE BASED ON A REALISTIC MODEL OF RUBBER-LIKE ELASTICITY

A new theory of strain birefringence of amorphous networks is presented. The theory is based on the constrained chain model of rubberlike elasticity recently developed by Erman and Monnerie. The quantitative treatment is molecular in nature and uses two adjustable parameters in order to fully describe the dependence of birefringence on deformation. The constrained chain theory and the birefringence of phantom networks are briefly reviewed with emphasis on the points relevant to strain birefringence. The contribution of the topological constraints to birefringence is developed, as well as the dependence of birefringence on stress. Illustrative calculations document the results for an unswollen tetrafunctional network prepared in bulk. Final comments include remarks on the connection of the adjustable parameters of the theory to molecular characteristics. © 1990, American Chemical Society. All rights reserved.