Thermal Transport through Individual Surface Modified Carbon Nanotubes and Their Contacts

碳纳米管（CNTs）由于其优越的机械、电学和热性能，作为纳米结构添加剂被广泛测试，以调整碳纳米管-聚合物复合材料的性能。虽然碳纳米管聚合物复合材料的电导率可以比纯聚合物高7个数量级，但导热系数的增加是温和的，与基于经典粒子混合理论的预测相去甚远。这种明显的差异引起了极大的关注和研究。然而，到目前为止，还没有一个透彻的认识。拟议的研究计划的目标是通过在单个纳米结构水平上的系统测量，了解通过单个碳纳米管的热传递、单个碳纳米管之间的接触以及碳纳米管与聚合物分子之间的界面。测量将通过非共价键或共价键与聚合物分子连接，包括未修饰的CNTs和表面修饰的CNTs。该研究不同于传统的混合和测量方法，即先将CNTs和聚合物混合固化成固体复合材料，然后测量所得材料的导热系数。混合和测量方法导致结果不一致，更重要的是，通过纳米结构及其接触的热传递必须从大量样品的测量结果中推断，并且需要对复合材料的结构和形貌进行许多假设。因此，很难得出可靠的结论。相反，拟议的实验研究将直接测量通过单个纳米结构及其接触的热传输，并仔细表征被测量样品的结构和形态。我们相信，提出的系统研究将产生可靠的实验数据，这些数据将回答以下基本问题：(1)能量载体如何通过碳纳米管-碳纳米管接触传输，接触电导如何随接触面积的变化而变化(2)热能如何通过碳纳米管（硬）和聚合物（软）材料之间的界面传输(3)聚合物分子如何影响碳纳米管-碳纳米管接触的能量传输基于获得的基本认识，我们可以创建新的设计规则，利用碳纳米管调节碳纳米管-聚合物复合材料的传输性能。该项目的智力优势在于以前无法获得的通过表面改性碳纳米管、碳纳米管-碳纳米管接触和碳纳米管-聚合物界面进行热传输的实验数据。更重要的是，这些数据将导致对纳米尺度热输运的新的或更深入的物理理解，可以回答关于通过涉及碳纳米管、它们的接触和碳纳米管-聚合物杂化的各种纳米结构进行能量输运的许多基本科学问题。所提出的系统研究将特别有助于发现通过碳纳米管及其接触的热传输作为碳纳米管直径的函数的依赖关系，这将揭示有趣的纳米限制对能量传输的影响。更广泛的影响包括基于纳米级传输现象的新设计规则，这些规则可用于调整碳纳米管聚合物复合材料的传输特性。这将导致高性能碳纳米管-聚合物混合材料的技术进步，对柔性微电子和热电/光伏能量转换等广泛应用至关重要。此外，拟议的综合研究和教育计划将在跨学科的环境中教育研究生，研究成果将通过科学出版物和课堂教学广泛传播。通过利用范德比尔特大学的各种教育和推广项目，研究的影响还将扩展到本科生、代表性不足的学生和K-12学生。

CBET#1067213PI: Deyu LiThermal Transport through Individual Surface Modified Carbon Nanotubes and Their Contacts Carbon nanotubes (CNTs), because of their superior mechanical, electrical and thermal properties, have been extensively tested as nanostructure additives to tune the properties of CNT-polymer composites. While the measured electrical conductivity of CNT-polymer composites can be seven orders of magnitude higher than that of pure polymers, the increase in thermal conductivity is mild and far from the prediction based on the classical particle mixing theory. This apparent dissimilarity attracted significant attention and studies. However, to date, a thorough understanding is still missing.The objective of the proposed research program is to understand, through systematic measurements at individual nanostructure level, thermal transport through individual CNTs, contacts between individual CNTs, and interfaces between CNTs and polymer molecules. The measurements will be performed with both non-modified CNTs and surface modified CNTs attached with polymer molecules via either non-covalent or covalent bonds.The proposed study is different from the traditional mix and measure approach, in which CNTs and polymers are first mixed and cured into solid composites and then the thermal conductivity of resulted materials is measured. The mix and measure approach leads to inconsistent results and more importantly, thermal transport through nanostructures and their contacts has to be inferred from the measured results of bulk samples with many assumptions of the composite structure and morphology. Therefore, it is difficult to draw solid conclusions. The proposed experimental studies, on the contrary, will directly measure thermal transport through individual nanostructures and their contacts, together with careful characterization of the measured samples structure and morphology. We believe that the proposed systematic study will lead to solid experimental data, which will answer the following fundamental questions: (1) How do energy carriers transport through CNT-CNT contacts and how does the contact conductance scale with the contact area (2) How does thermal energy transport through the interfaces between CNTs (hard) and polymer (soft) materials (3) How do polymer molecules affect energy transport through CNT-CNT contacts Based on the obtained fundamental understanding, we can create new design rules for using CNTs to tune the transport properties of CNT-polymer composites.The intellectual merit of the project resides in the previously unavailable experimental data of thermal transport through surface modified CNTs, CNT-CNT contacts and CNT-polymer interfaces. More importantly, these data will lead to new or deeper physical understanding of nanoscale thermal transport that can answer many fundamental scientific questions about energy transport through various nanostructures involving CNTs, their contacts and CNT-polymer hybrids. The proposed systematic studies will be especially helpful to discover the dependence of thermal transport through CNTs and their contacts as a function of the CNT diameter, which will disclose intriguing nanoconfinement effects on energy transport.The broader impacts include new design rules based on the obtained insights of nanoscale transport phenomena, which could be used to tune the transport properties of CNT-polymer composites. This will lead to technology advancement of high-performance CNT-polymer hybrid materials important for extensive applications such as flexible microelectronics and thermoelectric/photovoltaic energy conversion. In addition, the proposed integrated research and education plan will educate graduate students in an interdisciplinary environment and the research results will be widely disseminated through scientific publications and classroom instructions. The research impacts will also be extended to undergraduate, underrepresented, and K-12 students through leveraging Vanderbilt's various education and outreach programs.