Viscoelastic Properties of Polymer Melts and Solutions under Uniaxial Extension

Predicting the linear viscoelastic (LVE) properties of monodisperse polymers has reached a quantitative level, based on the Doi-Edwards tube-model theory combined with established relaxation mechanisms such as reptation, contour length fluctuations and constraint release (CR). This approach has been confirmed by demonstrating the universality of linear viscoelastic response of polymers with different chemical structures and concentrations as long as they have the same number of entanglements. However, it was shown recently that the universality between polymer melts and solutions seems to breakdown under nonlinear elongational flows. While polymer melts exhibit a monotonic extension-thinning behavior for all applied strain rates, polymer solutions with the same number of entanglements exhibit an initial thinning behavior followed by a strong extension-hardening, which occurs at rates comparable to the reciprocal Rouse time of the chains. As a result, up to now, molecular theories for linear flows could not be extended to nonlinear flows without further considerations. This apparent non-universality is now well established experimentally, however its molecular origin and in particular the absence of an extension thickening for polymer melts is not yet fully understood. Several models were proposed to address this issue, however none of them allow reaching a quantitative description of the observed behavior. Based on recent experimental results and molecular simulations, this work aims at developing a new approach based on the McLeich-Larson model and the tube model parameters to describe and explain both melts and solutions behavior.