Enhanced Thermal Conductivity of EpoxyGraphene Composites by Using Non-Oxidized Graphene Flakes with Non-Covalent Functionalization
Enhanced Thermal Conductivity of EpoxyGraphene Composites by Using Non-Oxidized Graphene Flakes with Non-Covalent Functionalization
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DOI：
10.1002/adma.201202736
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发表时间：
2013-02-06
影响因子：
29.4
通讯作者：
Jeon, Seokwoo
中科院分区：
文献类型：
--
作者：
Song, Sung Ho;Park, Kwang Hyun;Jeon, Seokwoo
随着LED、[1]cmos、[2]、汽车[3]和航空航天[4]产品等众多系统对更高效散热的需求，材料的热性能正变得越来越重要。轻质的聚合物纳米复合材料是解决散热问题的有前途的候选材料。例如，碳纳米管良好的导热性能(∼，000W/MK)改善了它们在复合材料中的热传递。[5]然而，石墨纳米材料具有极高的导热系数和低比重，并没有表现出预期的导热性能改善，主要是由于分散不良和不连续的聚合物/纳米材料界面。[6，7]因此，加强了对先进聚合物纳米复合材料的探索，并促进了对纳米材料导热的基础研究。新型二维(2D)石墨烯薄片(GFS)由于其通过声子传输的极端导热系数(∼5,300W/mK)而引起研究人员的兴趣。[8-10]它们在聚合物复合材料中的潜在应用已被证明用于热管理和热导增强。[11-15]Haddon和他的同事报道了含有25vol%石墨纳米小片(∼)的聚合物复合材料的导热系数为6.44W/mK。GNP是通过酸处理制备的几层石墨烯，用于插层，然后通过热冲击剥离，当嵌入到环氧树脂中时提供出色的热增强。[16]Ganguli和他的同事通过硅烷将功能化的氧化石墨烯(GO)分散到环氧树脂中，并在含有20wt%GO的树脂中显示出热导率达到5.8W/mK。[17]在类似的负载水平下，未氧化的GFS将提供比GO更有效的填料来生产高导热系数的聚合物纳米复合材料。然而，非氧化GFS的高粘聚性van der Waals能量(5.9kJ/摩尔)使其不可能形成分散良好的石墨烯聚合物复合材料。[18]尽管从石墨中剥离的氧化石墨烯可以解决分散问题，[19，20]由于氧化过程中的缺陷和π-轨道结构的破坏，即使在还原之后，它们的导热系数也会显著下降。为了解决这些问题，人们提出了几种方法，如溶剂[21]或表面活性剂辅助剥离[22，23]和使用石墨层间化合物(GIC)来制备非氧化性GFS。然而，生成的GFS在聚合物基质中的分散性较差，以获得更好的综合性能。我们的团队最近引入了一种新的GIC方法，通过使用碱盐三元共熔体系来生成GFS，并制备出氧含量极低的高质量GFS(从含氧量为2.1%的原始石墨)。尽管通过非氧化型GFS制备了高透明导电膜(∼930Ω/-at∼75%透过率)，但非氧化型GFS仅在吡啶盐溶液中分散。[27]去除溶液中的碱金属盐，同时保持非氧化型GFS的高度分散性和优异的材料性能是纳米复合材料广泛应用和成膜的关键挑战。一种可能的途径是非共价官能化。最近，人们提出了利用π-π相互作用将碳纳米管[28，29]和还原氧化石墨烯[30]进行非共价官能化的方法，结果表明，氧化石墨烯分散在不同的溶剂中，而不会降低其物理和化学性质。在这里，我们是…
The thermal properties of materials are becoming increasingly important in tandem with the need for more efficient heat removal in numerous systems such as LEDs,[1] CMOS,[2] and automotive [3] and aerospace [4] products. Light-weight, polymeric nanocomposites are promising candidates to address heat dissipation problems. For example, excellent thermal conductivity (∼ 3,000 W/mK) of carbon nanotubes improves heat transports when they are mixed in composites.[5] However, graphitic nanomaterial fillers, which have extremely high thermal conductivity with low specific weight, do not show expected improvement of thermal conductivities, mostly due to poor dispersion and discontinuous polymer/nanomaterial interfaces.[6, 7] Consequently, the search for advanced polymeric nanocomposites has been intensified and fundamental studies of thermal conduction in nanoscale materials have been prompted. Novel two dimensional (2D) graphene flakes (GFs) have drawn interest from researchers due to their extreme thermal conductivity (∼ 5,300 W/mK) through phononic transport.[8–10] Their potential use in polymer composites for thermal management and thermal conductivity enhancement have been demonstrated.[11–15] Haddon and coworkers reported a thermal conductivity of 6.44 W/mK from a polymer composite with∼ 25 vol% of graphite nanoplatelets (GNPs). GNPs, few graphene layers prepared from acid treatment for intercalation and then exfoliated via thermal shock, provide excellent thermal enhancements when embedded in an epoxy matrix.[16] Ganguli and coworkers dispersed a functionalized graphene oxide (GO) by silane into epoxy resin, and showed thermal conductivity reaching 5.8 W/mK in resin containing 20 wt% GO.[17] At comparable loading levels, the non-oxidized GFs will provide more effective fillers than GO for producing polymeric nanocomposites with high thermal conductivity. However, the highly cohesive van der Waals energy (5.9 kJ/mol) of non-oxidized GFs makes it impossible to form well dispersed graphene polymer composites.[18] Although graphene oxide flakes exfoliated from graphite can address the dispersion issues,[19, 20] they undergo significant losses in thermal conductivity even after reduction due to defects and disruption of the π-orbital structure during oxidation. To resolve these problems, several methods such as solvent-[21] or surfactant-assisted exfoliation [22, 23] and use of a graphite intercalation compound (GIC) have been suggested for the fabrication of non-oxidized GFs.[24–27] Still, the poor dispersion of the resultant GFs in polymer matrix should be improved to achieve better composite properties.Our group recently introduced a novel GIC approach to generate GFs by using a ternary eutectic system of alkali salts and fabricated high quality GFs with extremely low oxygen content of 2.9%(from a raw graphite with oxygen content of 2.1%). Even though the highly transparent conducting (∼ 930 Ω/□ at∼ 75% transmission) films were produced through non-oxidized GFs, non-oxidized GFs remained dispersed only in a pyridine-salts solution.[27] Eliminating the alkali metal salts from the solution while preserving the highly dispersive and excellent material properties of the non-oxidized GFs is a key challenge for broad applications of nanocomposites and film formation. One possible route is non-covalent functionalization. Very recently, noncovalent functionalization of CNTs [28, 29] and reduced graphene oxide (RGO)[30] with π–π interaction have been suggested, and it was shown that the GFs dispersed in diverse solvents without degrading the physical and chemical properties. Here, we …