物理化学学报 >> 2019, Vol. 35 >> Issue (10): 1150-1156.doi: 10.3866/PKU.WHXB201901002

所属专题： 二维材料及器件

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参杂缺陷石墨烯的高分子复合材料导热特性分子动力学模拟

熊扬恒1,吴昊1,高建树1,陈文1,张景超2,*(),岳亚楠1,*()   

  1. 1 武汉大学动力与机械学院，水力机械过渡过程教育部重点实验室，武汉 430072
    2 Holland Computing Center,内布拉斯加大学林肯分校，美国林肯 68588
  • 收稿日期:2019-01-02 录用日期:2018-12-04 发布日期:2019-02-21
  • 通讯作者: 张景超,岳亚楠 E-mail:zhang@unl.edu;yyue@whu.edu.cn
  • 基金资助:
    国家自然科学基金(51576145)

Toward Improved Thermal Conductance of Graphene-Polyethylene Composites via Surface Defect Engineering: a Molecular Dynamics Study

Yangheng XIONG1,Hao WU1,Jianshu GAO1,Wen CHEN1,Jingchao ZHANG2,*(),Yanan YUE1,*()   

  1. 1 Key Laboratory of Hydraulic Machinery Transients (MOE), School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, P. R. China
    2 Holland Computing Center, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
  • Received:2019-01-02 Accepted:2018-12-04 Published:2019-02-21
  • Contact: Jingchao ZHANG,Yanan YUE E-mail:zhang@unl.edu;yyue@whu.edu.cn
  • Supported by:
    The project was supported by the National Natural Science Foundation of China(51576145)

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摘要：

传统高分子材料由于内部分子链无规则缠绕的特点，导致其热导率较小。近年来，拥有高导热特性的新型高分子材料在众多领域都显示出了极大的发展潜力。随着研究的不断深入，具有优秀导热能力的石墨烯等低维碳材料引起越来越多人的关注。引入石墨烯制作的高分子复合材料具有较高的导热性能，在热管理方面具有很大的应用前景。本文使用非平衡态分子动力学方法计算了石墨烯点缺陷对石墨烯-高分子复合材料界面热导和整体热导率的影响。石墨烯层的界面热导受点缺陷密度的影响较大。当石墨烯缺陷密度由0%增大到20%时，其界面热导由75.6 MW·m−2·K−1增加为85.9 MW·m−2·K−1。石墨烯点缺陷造成sp2共价键断裂、结构刚性下降，导致其振动态密度的低频分量增加，增强了与高分子基质间的低频能量耦合，进而提高了界面热导。而点缺陷密度的增大对复合材料整体热导率也具有相似的提升效果(从40.8 MW·m−2·K−1增加为45.6 MW·m−2·K−1)。此外，高分子基体在石墨烯界面处会造成局部密度提高，但石墨烯点缺陷对高分子材料局部密度提升并无显著影响。这些计算结果加深了对石墨烯与高分子基体间导热机理的理解，并有助于开发和设计具有优异热学性能的高分子复合材料。

关键词: 石墨烯, 高分子复合材料, 热导, 点缺陷, 分子动力学

Abstract:

Polymers are widely used advanced materials composed of macromolecular chains, which can be found in materials used in our daily life. Polymer materials have been employed in many energy and electronic applications such as energy harvesting devices, energy storage devices, light emitting and sensing devices, and flexible energy and electronic devices. The microscopic morphologies and electrical properties of the polymer materials can be tuned by molecular engineering, which could improve the device performances in terms of both the energy conversion efficiency and stability. Traditional polymers are usually considered to be thermal insulators owing to their amorphous molecular chains. Graphene-based polymeric materials have garnered significant attention due to the excellent thermal conductivity of graphene. Advanced polymeric composites with high thermal conductivity exhibit great potential in many applications. Therefore, research on the thermal transport behaviors in graphene-based nanocomposites becomes critical. Vacancy defects in graphene are commonly observed during its fabrication. In this work, the effects of vacancy defects in graphene on thermal transport properties of the graphene-polyethylene nanocomposite are comprehensively investigated using molecular dynamics (MD) simulation. Based on the non-equilibrium molecular dynamics (NEMD) method, the interfacial thermal conductance and the overall thermal conductance of the nanocomposite are taken into consideration simultaneously. It is found that vacancy defects in graphene facilitate the interfacial thermal conductance between graphene and polyethylene. By removing various proportions of carbon atoms in pristine graphene, the density of vacancy defects varies from 0% to 20% and the interfacial thermal conductance increases from 75.6 MW·m−2·K−1 to 85.9 MW·m−2·K−1. The distinct enhancement in the interfacial thermal transport is attributed to the enhanced thermal coupling between graphene and polyethylene. A higher number of broken sp2 bonds in the defective graphene lead to a decrease in the structure rigidity with more low-frequency (< 15 THz) phonons. The improved overlap of vibrational density states between graphene and polyethylene at a low frequency results in better interfacial thermal conductance. Moreover, the increase in the interfacial thermal conductance induced by vacancy defects have a significant effect on the overall thermal conductance (from 40.8 MW·m−2·K−1 to 45.6 MW·m−2·K−1). In addition, when filled with the graphene layer, the local density of polyethylene increases on both sides of the graphene. The concentrated layers provide more aligned molecular arrangement, which result in better thermal conductance in polyethylene. Further, the higher local density of the polymer near the interface provides more atoms for interaction with the graphene, which leads to stronger effective interactions. The relative concentration is insensitive to the density of vacancy defects. The reported results on the thermal transport behavior of graphene-polyethylene composites provide reasonable guidance for using graphene as fillers to tune the thermal conduction of polymeric composites.

Key words: Graphene, Polymeric composite, Thermal conductance, Vacancy defect, Molecular dynamics