A Lattice Model for Segmental Orientation in Deformed Polymeric Networks. 2. Effect of Chain Stiffness and Thermotropic Interactions

The lattice model of segmental orientation developed in the preceding paper for athermal network chains subject to uniaxial deformation is extended in the present work to the case of (i) Kuhn segments with increased stiffness characterized by a relatively large length-to-width ratio, x, and (ii) thermotropic systems with anisotropic polarizabilities. Those two factors, of entropie and energetic character, respectively, contribute both to a first-order transition from a relatively disordered to a highly oriented structure, upon imposition of an external perturbation. This transition is observed from the abrupt rise in the orientation function accompanying the stretch under well-defined molecular characteristics and environmental conditions.