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1. Start a new blog entry
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Thermal conductivity of carbon nanotubes

Che, Cagin, Goddard. Thermal conductivity of carbon nanotubes. Nanotechnology 11 (2000) 65-69.

Purpose of the study

Use molecular dynamic simulations to calculate thermal conductivity of CNTs and its dependence on vacancies and defects.

 

Methods

Simulations were performed instead of experiments because it is difficult to synthesize high-quality, well ordered nanotubes.  There are two simulation approaches: one involving Boltzmann equation (BE), which uses parameters obtained from experiments and the other uses molecular dynamic (MD)simulations simulations.  For novel materials where no experimental results are available, the BE can’t be used to predict transport properties.

 

Key findings

1. The theoretical predicted thermal conductivity (k) of single-wall carbon nanotubes increases with tube length.  Calculations of k at short tube lengths are underestimated because of the overestimation of phonon scattering.  As the simulation size gets larger, thermal conductivity  converges to a constant value of 2900 W/mK.  For comparison, bulk carbon has k = 25 – 470 W/mK.
2. Thermal conductivity decreases as vacancy concentration increases, but not as quickly as expected – probably due to presence of strong valence double bonds, which provide additional path ways for phonons to bypass vacancy sites.
3. Defects also reduce conductivity, but effect not as sever as that for vacancies.  Effect is milder because defects do not change basic bonding characteristics and causes less overall structural deformation.
4. Thermal conductivity along axis is much greater than thermal conductivity perpendicular to axis.

 

Phonon : vibrating atom