High thermal conductivities of carbon nanotube films and micro-fibres and their dependence on morphology

• Published in: Carbon (New York) 2017-04, Vol.114, p.160-168
• Main Authors: Gspann, Thurid S., Juckes, Stefan M., Niven, John F., Johnson, Michel B., Elliott, James A., White, Mary Anne, Windle, Alan H.
• Format: Article
• Language: English
• Subjects: Alignment; Bundling; Carbon; Carbon nanotubes; Catalysts; Chemical synthesis; Chemical vapor deposition; Condensates; Conductivity; Electrical resistivity; Evaporation; Fibers; Heat conductivity; Heat transfer; Heat treatment; Materials selection; Morphology; Purity; Resistance; Scattering; Stretching; Thermal conductivity; Vapor deposition; Vapors
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2016.12.006

Thermal conductivity of carbon nanotube (CNT) films and micro-fibres synthesised by floating catalyst chemical vapour deposition was measured by the parallel thermal conductance method. CNT films showed in-plane thermal conductivities of 110 W m−1 K−1. Online condensation into a micro-fibre morphology – a two-dimensional reduction in the transverse plane, including some axial stretching during solvent evaporation – resulted in room-temperature thermal conductivity values as high as 770 ± 10 W m−1 K−1, which is the highest thermal conductivity reported for CNT bulk materials to date. In specific terms, this matches the maximum thermal conductivity of heat-treated carbon fibre, but with a higher onset temperature for Umklapp scattering processes (300 K rather than 150 K). We selected four sample types to investigate effects of alignment, purity, and single- or multi-wall character on their thermal conductivity. For both the electrical and thermal conductivity of as-spun material, i.e. without any post-synthesis treatment, we show that the density and quality of CNT bundle alignment are still the predominant factors affecting these properties, outweighing the influence of single- or multi-walled character of the nanotubes. This raises the promise that, with optimal alignment and junction points, even higher values of thermal conductivity are achievable for macroscopic CNT fibres. [Display omitted]