碳纳米管在电学、力学、热学、场发射等方面有着非常优良的特性，自从它被发现以来，就引起了人们极大的关注。人们不仅通过碳纳米管来研究一维体系的性质，而且借助其优越的性能进行多方面的技术开发和实际应用。本论文针对碳纳米管的热传导性质做了较深入的研究，不仅测量更新了碳纳米管本身的热导率值，而且探讨了碳纳米管与其他材料在界面处的传热性质。碳纳米管可以看成是由石墨片层卷曲而成的无缝管。理论计算表明，室温下单根单壁碳纳米管沿着轴向的热导率高达6000Wm-1K-1，虽然几个研究组测量了单根碳纳米管的热导率，但结果之间的出入很大，其主要原因是测量中的接触热阻会对实验结果有相当的影响。于是我们设计了一种非接触式的光谱测量法：在自行设计的微器件上生长单根碳纳米管，使其中间部分悬空并用四电极进行加热，利用碳纳米管拉曼频率随温度成线性变化的特性来测量其悬空部分中心点与端点的温差，即可计算出碳纳米管的热导率。我们测量了单根单壁、多壁碳纳米管的热导率，数值分别为2400Wm-1K-1和1400Wm-1K-1 。这种方法不仅能有效的避免接触热阻的影响，而且适用于其他一维材料的热导率测量。碳纳米管因为热导率很高，有望被应用于界面传热中。但碳管与对偶材料之间的界面热阻被怀疑是阻碍碳管高导热性能发挥的主要因素。我们对此做了实验和理论研究以探究碳管界面热阻的成因、影响因素及应用改进。通过红外加热和非接触测温的方法，我们测量了碳纳米管与6种代表性金属、6种代表性聚合物之间的界面热阻，发现碳纳米管与热导率较低的聚合物之间的界面热阻要明显小于碳管与金属之间的界面热阻。理论分析表明：界面处的声子透过率是影响界面热阻的关键因素，此外界面两侧材料的声子振动模式的匹配度也会影响界面热传导；由此得出：由于聚合物和碳管之间有较多低频声子模式的重叠，加上低频区域有较高的声子透过率，就导致了聚合物－碳纳米管的界面热阻较低；而金属与碳管的低频振动模式重叠较少，加之中高频区域的声子透过率太低，就导致了金属－碳纳米管的界面热阻较高。本研究工作对更深入的认识碳纳米管的界面热阻和对界面热传进一步的改进及应用都有着重要意义。
The carbon nanotube (CNT) has attracted researchers’ great attention due to its superior electrical, mechanical, thermal and field-emission properties since it has been discovered. People not only study the nature of one-dimensional system through the CNT, but also do extensive works in technology developments and practical applications with its various superior performances.This thesis focuses on the thermal conduction of the CNT. We not only measured and updated the thermal conductivity of the CNT itself, but also further studied the heat transfer properties at the interface of CNTs and other materials.A CNT can be regarded as a seamless tube curled by graphite layers. Theoretical calculations show that the axial thermal conductivity of an individual single-walled CNT is as high as 6000Wm-1K-1. Several research groups measured the thermal conductivity of an individual CNT, but there are significant differences among these experimental results. The main reason is that the thermal contact resistance caused considerable impacts to the measurements. So we designed a non-contact spectral measurement as follows: an individual CNT was grown on a self-designed micro-device, and the middle part of the CNT was suspended and heated by electricity through four electrodes. Using the characteristics that the Raman frequencies of the CNT change with temperature linearly, we determined the temperature difference between the center and the endpoint of the suspended CNT. Then the thermal conductivity of the CNT can be calculated. We have measured the thermal conductivity of an individual single-walled CNT and a multi-walled CNT with the above method, and the values are 2400Wm-1K-1 and 1400Wm-1K-1, respectively. This measurement not only can eliminate the impact of thermal contact resistance, but also is applicable to measure the thermal conductivity of other one-dimensional materials.Due to the high thermal conductivity, CNTs are expected to be applied in interface heat transfer. However, the thermal boundary resistance (TBR) between the CNTs and target materials largely restrains the CNTs’ high-heat-transfer capability into full play. Withal, we did the experimental and theoretical researches to explore the origin of the TBR, impact factors and application improvements. Through infrared heating and non-contact temperature detecting method, we measured the TBRs between the CNTs and 6 typical metals as well as 6 typical polymers, and found that the CNT-polymer TBRs are obviously less than the CNT-metal TBRs, although the thermal conductivities of the polymers are much lower. Based on the experimental results, the subsequent theoretical analyses show that the interface transmission coefficient is the key factor which affects the TBR. In addition, the TBR is also influenced by the phonon mode matching of the two materials on both sides of the interface. Hence, the measurement results can be interpreted as follows: more low-frequency phonon mode overlapping between CNTs and polymers as well as the high phonon transmission coefficient in low-frequency region results in the lower CNT-polymer TBRs; in addition, less low-frequency phonon mode overlapping between CNTs and metals as well as the very low intermediate and high-frequency phonon transmission coefficient leads to the larger CNT-metal TBRs. The above experimental and theoretical researches may inspire deeper and clearer understandings of the TBRs between CNTs and various materials, and are of great significance for the further improvements and applications of the CNTs in the interface heat transfer field.
