A DIFFUSED-CONSTRAINT THEORY FOR THE ELASTICITY OF AMORPHOUS POLYMER NETWORKS .2. MOLECULAR DEFORMATION TENSORS AND STRAIN BIREFRINGENCE

A new theory for the elasticity of amorphous polymer networks with continuous placements of constraints along the network chains is used for the derivation of the molecular deformation tenser and strain birefringence in deformed networks. The reduced birefringence obtained from the new theory is compared with predictions from the Flory constrained-junction theory and the subsequent Erman-Monnerie constrained-chain theory. The new assumption of a diffused distribution of constraints along the chains in a network leads to greatly-increased values of the strain birefringence, relative to the values predicted in the constrained-junction and constrained-chain theories.