Evolution of Polymer Melt Conformation and Entanglement under High-Rate Elongational Flow

JP Zhang and LC Ma and YJ Ruan and YY Lu and LJ An, CHINESE JOURNAL OF POLYMER SCIENCE, 42, 2021-2029 (2024).

DOI: 10.1007/s10118-024-3170-0

Using molecular dynamics (MD) simulations, this study explores the fluid properties of three polymer melts with the same number of entanglements, Z, achieved by adjusting the entanglement length N-e, while investigating the evolution of polymer melt conformation and entanglement under high-rate elongational flow. The identification of a master curve indicates consistent normalized linear viscoelastic behavior. Surprising findings regarding the steady-state viscosity at various elongational rates (Wi(R)>4.7) for polymer melts with the same Z have been uncovered, challenging existing tube models. Nevertheless, the study demonstrates the potential for normalizing the steady-state elongational viscosity at high rates (Wi(R)>4.7) by scaling with the square of the chain contour length. Additionally, the observed independence of viscosity on the elongational rate at high rates suggests that higher rates lead to a more significant alignment of polymer chains, a decrease in entanglement, and a stretching in contour length of polymer chains. Molecular-level tracking of tagged chains further supports the assumption of no entanglement under rapid elongation, emphasizing the need for further research on disentanglement in polymer melts subjected to high-rate elongational flow. These results carry significant implications for understanding and predicting the behavior of polymer melts under high-rate elongational flow conditions.

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