计算机模拟聚合物纳米复合材料导电导热的研究进展
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摘要
总结了作者课题组采用分子动力学模拟方法,在聚合物纳米复合材料导电导热方面取得的研究进展。研究结果表明,高的聚合物导电填料相互作用能、中等的分子链功能化改性度、中等的导电填料表面接枝分子链数目、中等的本体交联密度以及中等比率的聚合物共混有利于导电填料网络的形成,进而得到高的材料电导率。另外,外加剪切场和电场会显著地致使导电填料沿着外场方向取向,进而获得导电各向异性材料。当外加剪切场和电场撤去后,导电网络会逐渐地回复到初始值,这个回复过程可以用一个模型来描绘。对于导热性能,聚合物填料界面热导率与填料接枝密度成正比;随着接枝长度的增加,聚合物填料界面热导率先上升后逐渐趋于恒定;然而填料热导率随着接枝密度的上升而显著下降,最终在中等接枝密度下材料的热导率达到最大值。此外,填料间热阻可以用一个热环流模型来描绘。最后,分子链接枝填料末端会显著提高材料的热导率。这些基础问题的探讨将为制备高导电高导热的聚合物纳米复合材料提供重要的科学依据与理论指导。
We summarize recent progress in molecular dynamics simulation studies of the electrical and thermal conductivity of polymer nanocomposites. The simulation results show that a strong polymer-nanofiller interaction,a moderate chain functionalization degree,a moderate number of grafted chains,a moderate cross-linking density and an intermediate ratio of polymer blends all favor the formation of a conductive network,leading to enhanced conductive probability. In addition,an external shear field or electric field can induce orientation of the nanofiller along the external direction,which leads to a high anisotropy of the electrical conductivity. When the external fields are removed,the conductive probability gradually recovers its original value. This process can be described by a model. In the case of the thermal conductivity,the interfacial thermal conductivity is proportional to the grafting density,while it first increases and then saturates with increasing grafting length. Meanwhile,the intrinsic thermal conductivity of the nanofiller drops sharply as the grafting density increases. The maximum overall thermal conductivity of the nanocomposites appears at an intermediate grafting density because of these two competing effects. Meanwhile,the heat transfer process from one nanofiller to another can be approximately described by a thermal circuit model. Finally,a large increase in the thermal conductivity is observed when chains are grafted at the end atoms of nanofillers. Our work provides both a firm scientific basis and theoretical guidelines for preparing polymer nanocomposites with high electrical conductivity and high thermal conductivity.
We summarize recent progress in molecular dynamics simulation studies of the electrical and thermal conductivity of polymer nanocomposites. The simulation results show that a strong polymer-nanofiller interaction,a moderate chain functionalization degree,a moderate number of grafted chains,a moderate cross-linking density and an intermediate ratio of polymer blends all favor the formation of a conductive network,leading to enhanced conductive probability. In addition,an external shear field or electric field can induce orientation of the nanofiller along the external direction,which leads to a high anisotropy of the electrical conductivity. When the external fields are removed,the conductive probability gradually recovers its original value. This process can be described by a model. In the case of the thermal conductivity,the interfacial thermal conductivity is proportional to the grafting density,while it first increases and then saturates with increasing grafting length. Meanwhile,the intrinsic thermal conductivity of the nanofiller drops sharply as the grafting density increases. The maximum overall thermal conductivity of the nanocomposites appears at an intermediate grafting density because of these two competing effects. Meanwhile,the heat transfer process from one nanofiller to another can be approximately described by a thermal circuit model. Finally,a large increase in the thermal conductivity is observed when chains are grafted at the end atoms of nanofillers. Our work provides both a firm scientific basis and theoretical guidelines for preparing polymer nanocomposites with high electrical conductivity and high thermal conductivity.
引文
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[2]YU A,RAMESH P,ITKIS M E,et al.Graphite nanoplatelet-epoxy composite thermal interface materials[J].The Journal of Physical Chemistry C,2007,111(21):7565-7569.
[3]KREMER K,GREST G S.Dynamics of entangled linear polymer melts:a molecular-dynamics simulation[J].The Journal of Chemical Physics,1990,92(8):5057-5086.
[4]GAO Y,MULLERPLATHE F.Molecular dynamics study on the thermal conductivity of the end-grafted carbon nanotubes filled polyamide-6.6 nanocomposites[J].The Journal of Physical Chemistry C,2018,122(2):1412-1421.
[5]GAO Y,CAO D,LIU J,et al.Molecular dynamics simulation of the conductivity mechanism of nanorod filled polymer nanocomposites[J].Physical Chemistry Chemical Physics,2015,17(35):22959-22968.
[6]GAO Y,WU Y,LIU J,et al.Controlling the electrical conductive network formation of polymer nanocomposites via polymer functionalization[J].Soft Matter,2016,12(48):9738-9748.
[7]FENG Y,ZOU H,TIAN M,et al.Relationship between dispersion and conductivity of polymer nanocomposites:a molecular dynamics study[J].The Journal of Physical Chemistry B,2012,116(43):13081-13088.
[8]GAO Y,CAO D,WU Y,et al.Destruction and recovery of a nanorod conductive network in polymer nanocomposites via molecular dynamics simulation[J].Soft Matter,2016,12(12):3074-3083.
[9]DENG H,SKIPA T,ZHANG R,et al.Effect of melting and crystallization on the conductive network in conductive polymer composites[J].Polymer,2009,50(15):3747-3754.
[10]GAO Y,CAO D,WU Y,et al.Controlling the conductive network formation of polymer nanocomposites filled with nanorods through the electric field[J].Polymer,2016,101:395-405.
[11]GAO Y,MULLERPLATHE F.Increasing the thermal conductivity of graphene-polyamide-6,6 nanocomposites by surface-grafted polymer chains:calculation with molecular dynamics and the effective-medium approximation[J].Journal of Physical Chemistry B,2016,120(7):1336-1346.
[12]GAO Y,MULLERPLATHE F.Effect of grafted chains on the heat transfer between carbon nanotubes in a polyamide-6.6 matrix:a molecular dynamics study[J].Polymer,2017,129:228-234.