Qiao Rulan, Qiu Xiaoyu, Boies Adam
Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, United Kingdom.
Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States.
Langmuir. 2024 Oct 15;40(41):21460-21475. doi: 10.1021/acs.langmuir.4c02260. Epub 2024 Sep 30.
In floating catalyst chemical vapor deposition (FCCVD), high-aspect-ratio carbon nanotubes (CNTs) are produced in the gas phase at high number concentrations and undergo collision and agglomeration, eventually giving rise to a macroscale aerogel, enabling functional material forms such as fibers or mats to be obtained directly from the synthesis process. The self-assembly behavior between high-aspect-ratio CNTs dictates the resulting morphology at the nanoscale and subsequently the bulk properties of the CNT product. Reorientation between CNTs after collision is a critical step that results in bundle formation and precedes aerogel formation. However, it has been challenging to study the phenomenon with existing methods as it spans multiple time and length scales. In this study, a physics-based semi-analytical model was developed to study the gas-phase reorientation dynamics of high-aspect-ratio CNTs and their bundles, with ±10% accuracy compared with mesoscale molecular dynamics simulations, but at <0.1% the computational cost. It was revealed that the reorientation time scale is dictated by the interplay among the van der Waals potential, drag, and the geometric configuration of CNTs upon collision. This then allows the time scale of reorientation (i.e., bundle formation) to be compared with other gas-phase dynamics in a typical FCCVD reactor and offers new insights into the self-assembly behavior of 1D nanoparticles in the gas phase.
在浮动催化剂化学气相沉积（FCCVD）过程中，高长径比的碳纳米管（CNT）在气相中以高数量浓度生成，并经历碰撞和团聚，最终形成宏观尺度的气凝胶，从而能够直接从合成过程中获得纤维或垫子等功能材料形式。高长径比碳纳米管之间的自组装行为决定了纳米尺度下的最终形态，进而决定了碳纳米管产物的整体性质。碰撞后碳纳米管之间的重新取向是导致束形成并在气凝胶形成之前的关键步骤。然而，用现有方法研究这一现象具有挑战性因为它跨越了多个时间和长度尺度。在本研究中，开发了一个基于物理的半解析模型来研究高长径比碳纳米管及其束状物气相中的重新取向动力学，与中尺度分子动力学模拟相比，其精度为±10%，但计算成本不到后者的0.1%。研究发现，重新取向时间尺度由范德华势、阻力以及碰撞时碳纳米管的几何构型之间的相互作用决定。这进而使得重新取向（即束形成）的时间尺度能够与典型FCCVD反应器中的其他气相动力学进行比较，并为气相中一维纳米颗粒的自组装行为提供了新的见解。
