石墨纳米片/聚乙烯复合物分子动力学模拟
Molecular dynamics simulation of graphite-nanoplatelet/polyethylene composites

通过分子动力学模拟对石墨纳米片（GNP）/聚乙烯（PE）复合物的结构、力学和气体输运性质进行计算研究，分析其随模拟温度和GNP填充量的变化规律，探讨纳米界面形成、复合机制及结构与特性的关系。GNP/PE复合物呈现二维结构，GNP趋向于平面取向排列并通过范德华力和纳米石墨片层表面上的碳氢-π键使周围几个原子尺度内的PE分子固化为有序原子层，而PE基体仍然为各向同性的无定形结构。GNP/PE界面上纳米复合作用使体系能量降低，与PE体系相比，GNP/PE的杨氏模量和泊松比分别显著增高和降低。GNP平面取向导致GNP/PE的力学特性表现出二维各向异性的弹性常数张量，在石墨纳米片层平面方向上的杨氏模量明显增高，并且随温度的降低和GNP填充量的提高而增大，填充GNP有效改善了GNP/PE的力学性质。GNP/PE复合物的气体输运性质明显受到填充GNP的气体阻隔和取向的影响并且对3种气体渗透没有明显的选择性。GNP与基体的纳米复合导致N2、O2和CO2的分子输运呈现二维各向异性，随着石墨纳米颗粒填充量的增加，取向GNP层面方向的扩散系数比垂直方向高5~8倍，可用于气体分子屏障与渗流控制。 Molecular dynamics simulations of polyethylene(PE)/graphite-nanoplatelet(GNP) composites has been implemented to investigate the morphological structures, mechanical and gas transport properties by calculation of dynamical energy, atomic radial distribution function, XRD, elastic tensor and gas diffusion coefficient, analyzing their relationship with nanofiller concentration and simulation temperature. The results indicate that GNP/PE composites exhibit in two-dimensional anisotropic structures with the graphite-nanoplatelets orientating in parallel to each other and compositing with PE matrix by evident Van der Waals force and CH-π bonding on nanoplatelet surface causing a few ordered atomic layers of PE at interface, while the PE matrix is in isotropic amorphous morphology. The nanocomposite effect of nanoplatelet with matrix leads to explicitly lower energy and results in higher Young's modulus and lower Poisson's ratio compared with pure polyethylene system. Due to the parallel orientation of GNP, the improved mechanical property represents as two-dimensional anisotropic elastic constant tensor with remarkably larger Young's modulus in orientated plane increasing with reduced temperature and incremental nanofiller concentration. Gas transports in GNP/PE composites are significantly affected by the gas barrier and orientation of GNP without gas selectivity for percolation. The graphite nanocomposites present two-dimensional anisotropic permeation of N2, O2 and CO2 molecules that the diffusion coefficients are 5-8 times higher along orientation plane than in perpendicular direction of GNP when the composite nanofiller concentration increases, reasonably suggesting the material application to gas barrier and percolation control. 中国博士后科学基金（2013M531058）；黑龙江省普通本科高等学校青年创新人才培养计划（UNPYSCT-2015047）