Thermodynamics and dynamics of flowing polymer solutions and blends

Abstract

We review the basic ideas and main results of our analysis of shear-induced effects in polymer solutions and blends. The analysis combines thermodynamic and hydrodynamic descriptions. The flow contribution to the free energy of the solution is described in the framework of extended irreversible thermodynamics, which relates the viscoelastic constitutive equations to a non-equilibrium entropy that depends on the viscous pressure tensor. This yields, by differentiation, the corresponding non-equilibrium equation of state for the chemical potential, which couples diffusion flux to viscous pressure in the presence of a flow. In some conditions, the one-phase system becomes unstable and splits into two phases, leading to a shift in the spinodal line. The theoretical analysis is based on the stability of the mass and momentum balance equations, the constitutive equations for viscous pressure tensor and diffusion flux, and the equation of state for the chemical potential. The resulting predictions corroborate qualitatively the known experimental observations. Results for dilute and entangled polymer solutions and for polymer blends are given.