Nonequilibrium statistical thermodynamic theory for viscoelasticity of polymers

Abstract

In this paper, we propose a new molecular relaxation mechanism for polymers by considering the change in the actual microscopic structure under macroscopic stress fields. The effects of both intramolecular and intermolecular forces on the inner rotation and the relative slippage of links are taken into account. A constraint potential function, along with a constraint tensor, is introduced to describe the constraint exerted by the surrounding medium. A unified three-dimensional constitutive framework for the viscoelasticity of polymers including thermal effects is established by making use of nonequilibrium statistical thermodynamics, which can be reduced to James and Guth's (1943) non-Gaussian polymer network theory for rubber elasticity. The model compares well with the experimental data for PMMA and plasticized PVC over a wide range of temperatures.