Recent Advances in Constitutive Modeling of Polymer Melts

Abstract

The pressures exerted by a polymer chain on the walls of an anisotropic confinement are anisotropic. In a tube model with variable tube diameter, this leads to an evolution equation for the chain stretch with an interchain pressure term, which is inverse proportional to the 3rd power of the tube diameter a and is characterized by a tube diameter relaxation time τa [1, 2]. The tube diameter relaxation time in the evolution equation of the Molecular Stress Function (MSF) model [2] is shown to be equal to 3 times the Rouse time in the limit of small chain stretch. From this result an advanced version of the MSF model is proposed allowing modelling of the transient and steady‐state elongational viscosity data of two monodisperse polystyrene melts without using any nonlinear parameter, i.e. solely based on the linear‐viscoelastic characterization of the melts. The same approach is extended to model experimental data of two polybutadiene solutions [3] in shear flow. Thus for monodisperse polymer melts and solutions, for the first time a constitutive equation is available to model quantitatively nonlinear extension and shear rheology on the basis of linear‐viscoelastic data alone.