The Great Myths of Rheology Part III: Elasticity of the Network of Entanglements

Abstract

The dynamic data of polymer melts are analyzed in a novel way, presenting new correlations between the viscosity, G′ and G′′ (the elastic and loss moduli), and strain rate and the implications of the new formulas on our understanding of melt entanglement network elasticity are discussed. In the two previous articles of this series, Part I and Part II, we showed that the existing models valid in the linear viscoelastic deformation range were not adequate to extrapolate to the nonlinear regime, suggesting that the stability of the network of entanglements was at the center of the discrepancies. In this article, we introduce new tools for the analysis of the dynamic data and suggest new ideas for the understanding of melt deformation based on this different focus. In particular, we express classical concepts, such as shear-thinning, melt diffusion or melt elasticity and viscosity, in a different context, that of the existence of a dual-phase interaction, essential to our treatment of the statistics of interaction of the bonds responsible for the system coherence and cohesion. It is within this framework that viscoelasticity parameters emerge and the new view of the deformation of a polymer melt results in a different definition of the entanglement network.