Binary Blends of Monodisperse Polymers: Use of a Kinetic Network Model for Nonlinear Shear Stress Predictions in Entangled Polymer Fluids

Abstract

A molecular network theory incorporating the concept of entanglement disruption and regeneration was previously developed to describe not only steady‐state but also transient rheological properties of monodisperse polymer melts and concentrated solutions. The viscoelastic responses of these systems are dominated by a rapid segmental motion at short times and a more sluggish, structure‐dependent network relaxation process at long times. In a binary blend of monodisperse fractions, the entangled network is composed of chains of two different lengths. The chain dynamics, and thus the characteristic response time, of each component in such a system is influenced by the presence of the coexistent component. This interaction is accommodated by a simple mixing assumption, which leads to accurate predictions of composition‐dependent linear viscoelasticproperties, such as zero‐shear viscosity. In addition, the model gives an excellent description of the shear‐rate‐dependent viscosity curves of binary blends of various compositions and concentrations. Time‐dependent viscoelasticproperties, such as shear stress growth and relaxation functions, have also been predicted. Comparison of these results with experimental data indicates good agreement, reinforcing confidence in both the basic model and the mixing rule selected here for blends. The latter provides the critical step to predict ultimately the nonlinear rheological properties of polydisperse polymers from knowledge of their molecular weight distribution, as the established mixing rule can be easily generalized to account for multiple interactions among the constituent chains.