Under the supervision of Researcher Li Liangbin, our team’s master's student Liu Ziwei and collaborators conducted an in-depth investigation into the nonlinear stress response of polymer melts during uniaxial elongation using molecular dynamics simulations. The study elucidates the relationship between microscopic conformational changes and macroscopic mechanical properties, offering new theoretical insights for the field. The related work has been published in the Journal of Chemical Physics.
In the process of polymer processing, complex multiscale coupling phenomena such as necking and edge effects are commonly observed. The essence of these phenomena lies in the nonlinear dynamic response of polymer molecular chains under external fields. In this article, the research team conducted molecular dynamics simulations combined with the generalized Kraynik-Reinelt (KR) boundary condition to perform uniaxial stretching of polymer melts at equilibrium. They first systematically analyzed the evolution of stretch ratio, orientational order parameters, and entanglement state.
In addition, it was found that under nonlinear uniaxial elongational flow, the number of entanglement points exhibits a heterogeneous distribution across different chains as the stretching proceeds. Finally, the study showed that traditional stress prediction models based on average entanglement states deviate significantly at large strains, while the newly developed theoretical model—by introducing entanglement loss and the heterogeneous distribution of entanglement points—significantly improves the prediction accuracy of nonlinear rheological behavior. It is hoped that this work will attract further interest and reflection from researchers in the field.
This work was supported by the Fundamental Research Funds for the Central Universities (Grant No. WK2310000119), the China Postdoctoral Science Foundation (Grant No. 2023M743377), the Institutional Platform Program of the Chinese Academy of Sciences (Grant No. JZHKYPT-2021-04), the Hefei “揭榜挂帅” Major Science and Technology Special Project (Grant No. 2022-SZD-005), and the Hefei Municipal Commissioned Major Project: Research and Development of Polyvinyl Butyral (PVB) Films for Automotive Safety Glass Applications.
Liu Z, Xu T, Peng F, et al. Improved predictions of nonlinear uniaxial tensile stress in polymer melts by accounting for microscopic conformation and entanglement changes[J]. The Journal of Chemical Physics, 2025, 162(20).
Paper link: https://doi.org/10.1063/5.0262152
