The Great Myths of Polymer Melt Rheology, Part I: Comparison of Experiment and Current Theory

Abstract

This article examines the following issues in polymer rheology: Is the separation of temperature and molecular weight in the expression of viscosity an approximation (perhaps even a poor one) that theoretical models should not attempt to explain? Is the universality of the time-temperature superposition restricted to a narrow temperature range, so narrow, in fact, that most of the extrapolated data published as mastercurves in the literature were actually poised to be wrong? Is the concept of local friction coefficient (as related to relaxation time) misconceived to describe the change under stress of the state of interactions between the bonds, a phenomenon called flow? Is the reptation model reaching its limits in the non-linear range because it successfully describes formulas which are only approximations, even in the linear range, or because the network of entanglement must be understood by new concepts? Is there a liquid-liquid transition relaxation in the melt when the data are re-examined properly with the right regression tools? Is it time to consider new interpretations for its existence? Is there a need, in order to reconcile linear and non-linear experimental results, to reconsider the classical concepts of linear viscoelasticity: the terminal time, τd, the plateau modulus, GoN, and the concept of Me, the molecular weight between entanglements? Are these concepts too simplistic and of limited value?