Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth
Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth
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DOI：
10.1021/acsnano.6b07251
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发表时间：
2016-12-01
期刊：
影响因子：
17.1
通讯作者：
Hart, A. John
中科院分区：
文献类型：
--
作者：
Balakrishnan, Viswanath;Bedewy, Mostafa;Hart, A. John
碳纳米管（CNT）网络和包含碳纳米结构的类似材料的性质由固有的细丝性质及其分层组织和互连决定。因此，CNT合成和自组织的集体动力学的直接知识是必不可少的工程改进CNT材料的应用，如膜和热界面。在这里，我们使用实时环境透射电子显微镜（E-TEM）观察成核和自组织的碳纳米管垂直排列的森林。在引入碳源后，我们观察到单个CNT的成核开始和随后的生长速率的大的分散。在不同温度和催化剂颗粒密度下进行的实验显示了CNT密度对自组织动力学的关键作用;低密度CNT成核导致CNT被钉扎到衬底上并形成随机网络，而较高密度CNT成核导致CNT自组织成束，所述束垂直于衬底取向。我们还发现，生长中的CNT之间的机械耦合改变了它们的生长轨迹和形状，导致CNT壁中的显著变形、屈曲和缺陷。因此，看来CNT CNT耦合不仅对自组织至关重要，而且直接影响CNT质量和可能产生的森林性质。我们的研究结果表明，CNT成核和束形成的时间分布动力学的控制是至关重要的制造组织良好的CNT组件和E-TEM可以是一个强大的工具来调查的CNT网络的介观动力学。
The properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates. Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. Our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.