Xia Xiaodong, Hao Jia, Wang Yang, Zhong Zheng, Weng George J
School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200092, People's Republic of China. Department of Mechanical and Aerospace Engineering, Rutgers University, New Brunswick, NJ 08903, United States of America.
J Phys Condens Matter. 2017 May 24;29(20):205702. doi: 10.1088/1361-648X/aa68ec. Epub 2017 Mar 24.
Highly aligned graphene-based nanocomposites are of great interest due to their excellent electrical properties along the aligned direction. Graphene fillers in these composites are not necessarily perfectly aligned, but their orientations are highly confined to a certain angle, [Formula: see text] with 90° giving rise to the randomly oriented state and 0° to the perfectly aligned one. Recent experiments have shown that electrical conductivity and dielectric permittivity of highly aligned graphene-polymer nanocomposites are strongly dependent on this distribution angle, but at present no theory seems to exist to address this issue. In this work we present a new effective-medium theory that is derived from the underlying physical process including the effects of graphene orientation, filler loading, aspect ratio, percolation threshold, interfacial tunneling, and Maxwell-Wagner-Sillars polarization, to determine these two properties. The theory is formulated in the context of preferred orientational average. We highlight this new theory with an application to rGO/epoxy nanocomposites, and demonstrate that the calculated in-plane and out-of-plane conductivity and permittivity are in agreement with the experimental data as the range of graphene orientations changes from the randomly oriented to the highly aligned state. We also show that the percolation thresholds of highly aligned graphene nanocomposites are in general different along the planar and the normal directions, but they converge into a single one when the statistical distribution of graphene fillers is spherically symmetric.
高度取向的石墨烯基纳米复合材料因其沿取向方向优异的电学性能而备受关注。这些复合材料中的石墨烯填料不一定完美取向，但其取向高度局限于某个角度，[公式：见正文]，90°对应随机取向状态，0°对应完美取向状态。最近的实验表明，高度取向的石墨烯 - 聚合物纳米复合材料的电导率和介电常数强烈依赖于这个分布角度，但目前似乎不存在解决此问题的理论。在这项工作中，我们提出了一种新的有效介质理论，该理论源自包括石墨烯取向、填料负载、长径比、渗流阈值、界面隧穿和麦克斯韦 - 瓦格纳 - 西拉斯极化等基本物理过程，用于确定这两个性质。该理论是在优先取向平均的背景下制定的。我们通过将其应用于还原氧化石墨烯/环氧树脂纳米复合材料来突出这一新理论，并证明随着石墨烯取向范围从随机取向变为高度取向状态，计算得到的面内和面外电导率及介电常数与实验数据一致。我们还表明，高度取向的石墨烯纳米复合材料的渗流阈值通常在平面方向和法线方向上不同，但当石墨烯填料的统计分布呈球对称时，它们会收敛为一个单一的值。
