Nonlinear melt rheology explored by molecular dynamics simulations*

We apply bead-spring based molecular dynamics simulation to study both shear and extensional responses of entangled melts. Shear creep is carried out to show the emergence of entanglement-disentanglement transition (EDT) previously observed in experiment ^[1], confirming that EDT can take place in absence of edge instability. At high Rouse-Weissenberg numbers (larger than ca. 5), entangled melt is observed to undergo melt rupture independent of whether Filament stretching rheometry or Sentmanat extensional rheometry is employed. The lack of yielding suggests intriguing lockup of chain entanglement in melt stretching ^[2]. Such extreme tensile strain localization is observed for the first time in MD simulation, corresponding to the threshold of full chain disentanglement in absence of the chain scission mechanism that in reality triggers the unzipping of chain entanglement.

[1] S. R. Ge, X. Y. Zhu and S. Q. Wang, Polymer 125, 254 (2017); S. Ravindranath and S. Q. Wang, J. Rheol. 52, 957 (2008); P. Tapadia and S. Q. Wang, Macromolecules 37, 9083 (2004).
[2] S. Q. Wang, Nonlinear Polymer Rheology: Macroscopic Phenomenology and Molecular Foundation (2018, Wiley).