Nanotechnologies / Materials
Flexible device, Thermoelectric conversion

Visualization of the temperature distribution on carbon
nanotube bundles
Department of Mechanical Engineering, Graduate School of Engineering
Postdoctoral Researcher Hiromu Hamasaki
Associate Professor Kaori Hirahara

https://researchmap.jp/hiraharakaori?lang=en

Abstract

Nanotechnologies / Materials

Despite the superior thermal conductivity of single carbon nanotubes, that of macroscopic assemblies are poor, mainly due to thepresence of numerous intertube boundaries. Here, we report anin-situ nanoscale observation on the anisotropic thermal transportof a single bundle of carbon nanotubes to investigate the difference of thermal conductivity within and between carbon nanotubes. The experimental results indicate that even a small bundle
shows colossal thermal anisotropy due to the intertube boundaries.

▍ Background & Results
Carbon nanotubes are popular nanomaterials known for theirsuperior thermal properties. However, rope or film-based assemblies of carbon nanotubes show relatively low thermal conductions.
One of the most critical causes may be the thermal transport atboundaries between carbon nanotubes. In this regard, several
experimental studies have been conducted on macroscopic specimens which have revealed that the aligned nanotube films show
significant thermal anisotropy pertaining to the alignment directions. However, in the macroscopic specimens, numerous nontrivial
intertube boundaries occur and therefore the inherent difference inthermal conductivities between the intra- and inter- nanotubes remains unclear. In order to address this issue, we have focused on
the thermal transport in nanotube bundles in which the nanotubes
are self-organized into vertically close-packed structure (Fig. 1).
Consequently, extremely high anisotropy of thermal conductivity
along the directions parallel and perpendicular to the alignment ofbundled carbon nanotubes was observed by in situ observation of
the phase transition of metal nanoparticles decorating the bundle(Fig. 2). With the aid of finite element calculation, we demonstrated
that the high anisotropy estimated in this study could cause thedecrease of apparent thermal conductivity of the bundled carbon
nanotubes.

Fig. 1 Schematic illustration of the experimentFig. 2 Carbon nanotube bundle which is anisotropically heated▍ Significance of the research and Future perspective
The reported results provides semi-quantitative benchmarksin the design of carbon-nanotube-based materials for directing
the heat flow. Additionally, the methodology aids in visualizing thenanoscale thermal transport that is not restricted to carbon nanotubes.

P a t e n t
Tr e a t i s e

Hamasaki, Hiromu; Takimoto, Seiya; Hirahara, Kaori. Visualization of thermal transport within and between carbon nanotubes. Nano Letters. 2021, 21 (7),p. 3134–3138, doi: 10.1021/acs.nanolett.1c00336
Hamasaki, Hiromu; Kawase, Takumi; Hirahara, Kaori. Anisotropic temperature distribution in carbon nanotube bundles determined using two types ofphase transitions of nanoparticles. Physical Review Materials. 2022, 6, p. L023001-1–6, doi: 10.1103/PhysRevMaterials.6.L023001

URL
K e y w o r d carbon nanotubes, thermal transport, transmission electron microscopy