Phonon Optimized Engineered Materials (POEM) Center, Materials Science and Engineering Program , University of California , Riverside , California 92521 , United States.
Nano-Device Laboratory (NDL), Department of Electrical and Computer Engineering , University of California , Riverside , California 92521 , United States.
ACS Appl Mater Interfaces. 2018 Oct 31;10(43):37555-37565. doi: 10.1021/acsami.8b16616. Epub 2018 Oct 22.
We investigated thermal properties of the epoxy-based composites with the high loading fraction-up to f ≈ 45 vol %-of the randomly oriented electrically conductive graphene fillers and electrically insulating boron nitride fillers. It was found that both types of the composites revealed a distinctive thermal percolation threshold at the loading fraction f > 20 vol %. The graphene loading required for achieving thermal percolation, f, was substantially higher than the loading, f, for electrical percolation. Graphene fillers outperformed boron nitride fillers in the thermal conductivity enhancement. It was established that thermal transport in composites with high filler loadings, f ≥ f, is dominated by heat conduction via the network of percolating fillers. Unexpectedly, we determined that the thermal transport properties of the high loading composites were influenced strongly by the cross-plane thermal conductivity of the quasi-two-dimensional fillers. The obtained results shed light on the debated mechanism of the thermal percolation, and facilitate the development of the next generation of the efficient thermal interface materials for electronic applications.
我们研究了具有高填充分数（高达 f ≈ 45 体积%）的随机取向导电石墨烯填充剂和电绝缘氮化硼填充剂的环氧基复合材料的热性能。结果发现，这两种类型的复合材料在填充分数 f > 20 体积%时都显示出明显的热渗流阈值。实现热渗流所需的石墨烯填充分数 f 远高于实现电渗流所需的填充分数 f。石墨烯填充剂在导热性能增强方面优于氮化硼填充剂。我们确定，在填充分数 f ≥ f 较高的复合材料中，热传递主要通过渗流填充剂网络的热传导进行。出乎意料的是，我们确定高填充复合材料的热输运性能受到准二维填充剂的面内热导率的强烈影响。所得到的结果阐明了有争议的热渗流机制，并有助于开发下一代用于电子应用的高效热界面材料。
