Influence of the entanglements on steady elongational viscosity for monodisperse polymer melts

While the linear viscoelastic properties of linear polymers are quite well understood and can be predicted at the quantitative level, many questions still need to be answered in order to understand and model their non-linear extensional rheology. The molecular picture presently used to represent the chain dynamics under extension does not allow capturing the different scaling laws observed experimentally. With the help of a tube model in order to distinguish the different processes contributing to the polymer relaxation, we revisit the extension rheological data provided in literature, and propose a different point of view to interpret them. In particular, we define different levels of stretch that a chain can reach in function of the extensional rate, and their implication in the steady viscosity value. We also discuss the important role played by reptation and contour length fluctuations in the dynamics of a stretched chain. We show that this simple approach well matches the experimental observations, providing new directions to explore, towards the understanding of extensional rheology.status: publishe