Introduction

The experimental observation of carbon nanotubes by Sumio Iijima in 1991 [1], sparked a significant effort in theoretical and experimental investigation of carbon nanotubes and related structures. The studies of thermal properties, although very important from fundamental and applications points of view, have received less attention in comparison with other aspects such as the electrical and mechanical properties [2-18]. This might be due to the fact that one associates the nanoscale aspect of nanotubes with quantization of transport properties which applies to electrons at room temperature. On the other hand, thermal transport involves many phonon modes and these can form a continuum at room temperature and phonon quantization manifests itself in nanotubes at very low temperatures (less than 8 K) [5]. Carbon nanotubes can be viewed as rolled-up graphene sheets and therefore one can infer their thermal properties by comparing them with graphite. Graphite has a large in-plane thermal conductivity, second only to type II diamond, and significantly lower out-of-plane thermal conductivity [19,20]. Therefore, in carbon nanotubes or nanotube ropes, one can expect very high thermal conductivity along the tube axis compared to the radial component due to the large separation between the different layers in multiwall nanotubes [22,13].

The ability to grow single-wall nanotube (SWNT) and multiwall nanotubes (MWNT) with different diameters and chiralities opens the possibility of developing materials with tailored thermal properties for different applications including thermal management, switches, and sensors. Carbon nanotubes can be added to other materials to enhance the magnitude and directionality of their thermal properties. This has motivated several groups to investigate the thermal properties of carbon nanotubes using experimental and theoretical approaches. The physical structure of nanotubes and their electrical properties are briefly discussed in Section

7.2. In Section 7.3, the theoretical analytical approaches to thermal conductivity and specific heat calculations are introduced. This is followed by a review of the recent experimental measurement of thermal conductivity of single- and multiwall nanotubes. Sections 7.4 and 7.5 focus on the molecular dynamics (MD) simulation

Figure 7.1. The unrolled hexagonal lattice of a nanotube.

approach and its application to investigation of thermal conductivity of SWNT, Y-junction nanotubes, and heat pulse propagation in SWNT.

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