Effects of finite chain extensibility on segmental orientation and stress in biaxially deformed polymers

Abstract Development of biaxial segmental orientation and stresses in flexible chain polymers subjected to affine deformation of end-to-end vectors or to steady biaxial extensional flow is discussed. A closed-formula theory with non-Gaussian chain statistics and a Padè approximation of the inverse Langevin function is considered. The approach accounts for finite chain extensibility and is free from the problems of weak convergence of series-expansion expressions at higher molecular deformations. Average orientation tensor, global anisotropy tensor, and axial orientation factors characterise segmental orientation. Axial orientation factors and normal stress differences, in the deformation and normal planes, are discussed for biaxial affine deformation and steady biaxial elongational flow in a wide range of molecular deformations using inverse Langevin chain statistics. Orientation characteristics predicted for biaxial flow deformation are higher, and change in a wider range, than those in affine biaxial stretch. Also sensitivity to transversal deformation is different in both types of deformation.