超临界二氧化碳流场作用下线型聚乙烯剪切塑化行为的分子动力学模拟研究  

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

作　　者：崔文豪 顾瑞星 米皓阳 Wen-hao Cui;Rui-xing Gu;Hao-yang Mi(National Engineering Research Center for Advanced Polymer Processing Technology,Zhengzhou University,Zhengzhou 450000)

机构地区：[1]郑州大学橡塑模具国家工程研究中心,郑州450000

出　　处：《高分子学报》2024年第10期1414-1429,共16页Acta Polymerica Sinica

基　　金：国家自然科学基金(基金号52173049);河南省科技研发计划联合基金优势学科培育项目(基金号222301420032);中国博士后面上基金(基金号2021M701797)资助项目.

摘　　要：通过非平衡分子动力学模拟探讨了聚乙烯(PE)及其与超临界二氧化碳(scCO_(2))共混体系在剪切流下的热力学和构象性质.发现scCO_(2)的增塑作用可显著改变PE的热力学和构象性质,如降低分子间作用力、减少体系剪切应力、降低体系黏度、减少分子链构象参数、提高PE链gauche plus构象,从而增加分子链的卷曲和自由体积,减少剪切下的分子取向排列.scCO_(2)还显著降低了体系的弛豫时间,加强了PE分子链抵抗剪切的能力,从而增强了动态性质和热稳定性.这些发现为scCO_(2)在PE体系中的作用提供了微观见解,为调控scCO_(2)辅助聚合物加工工艺,开发高性能聚合物材料提供了理论依据.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(τ_(xy) and σ_(v))-strain(γ)curves,mean square end-to-end distance(R_(ete)),radius of gyration(R_(g)),orientation parameters(P_(2θ)),and the autocorrelation function of the relaxation process under three shear flow,the peak shear stressτxy decreased from 0.18 in the PE system to 0.068 in the PE+scCO_(2) system at γ=4.686×10^(-1)τ^(-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 τ_(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 foun

关 键 词：线型聚合物 超临界二氧化碳 非平衡分子动力学 剪切取向 剪切流 增塑作用 

分 类 号：TQ325.12[化学工程—合成树脂塑料工业]