Molecular Dynamics Simulation Study on the Shear Plasticizing Behavior of Linear Polyethylene under the Influence of Supercritical Carbon Dioxide Flow Field

WH Cui and RX Gu and HY Mi, ACTA POLYMERICA SINICA, 55, 1414-1429 (2024).

DOI: 10.11777/j.issn1000-3304.2024.24076

This research comprehensively examines the thermodynamic behavior and conformational changes in polyethylene (PE) and its blends with supercritical carbon dioxide (scCO(2)) under shear flow conditions using non-equilibrium molecular dynamics (NEMD) simulations, which uncovers the influence of scCO(2), acting as a plasticizer, on the thermodynamic and conformational properties of PE. The study reveals that scCO(2) diminishes intermolecular forces and shear stress within the system, leading to a reduction in viscosity and alterations in the conformational parameters of PE molecular chains. These changes result in an increased free volume and curling of the molecular chains, with a notable decrease in molecular orientation alignment under shear, thereby, enhancing the system's dynamic properties and thermal stability. By analyzing parameters such as stress (tau(xy) and sigma(v))-strain(gamma) curves, mean square end-to-end distance (R-ete), radius of gyration (R-g), orientation parameters (P-2 theta), and the autocorrelation function of the relaxation process under three shear flow, the peak shear stress tau xy decreased from 0.18 in the PE system to 0.068 in the PE+scCO(2) system at gamma=4.686x10(-1) tau(-1), and both R-ete and R-g decreased. The persistence length l(p) of the PE chains is three times that of the PE+scCO(2) system. Additionally, the distribution of the molecular chain dihedral angle's gauche plus conformation is reduced, and the trans conformation distribution has increased. The research elucidates that the presence of scCO(2) reduces the system's Rouse time tau(R) by approximately 3.9 times, highlighting the plasticizing effect of scCO(2), which could effectively promote the conformational freedom and mechanical adaptability of PE under shear flow. This work not only provides deep insights into the complex interactions between PE and scCO(2), but also showcases the potential of utilizing scCO(2) as a sustainable processing aid in the development of high-performance polymer materials. The findings offer a theoretical foundation for regulating scCO(2)-assisted polymer processing techniques and advancing the understanding of the dynamic response of polymer systems to external shear.

Return to Publications page