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 foundation for regulating scCO_(2)-assisted polymer processing techniques and advancing the understanding of the dynamic response of polymer systems to external shear.
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)
出处
《高分子学报》
SCIE
CAS
CSCD
北大核心
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.
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
Linear polymer
Supercritical carbon dioxide
Non-equilibrium molecular dynamics
Shear orientation
Shear flow
Plasticizing effect
作者简介
通信联系人:米皓阳,E-mail:mihaoyang@zzu.edu.cn。
