Thermal properties of single-walled carbon nanotube forests with various volume fractions

Needs of a material for thermal management in reduced-sized electronic devices drive single-walled carbon nanotubes (SWCNTs) to be one of the most promising candidates due to their excellent thermal properties. Many numerical and experimental studies have reported on understanding thermal properties of the SWCNT for thermal device applications. In the present study, thermal diffusivity and conductivity of SWCNT forests in the axial direction with various volume fractions of SWCNTs were measured by laser flash analysis technique and the same properties of an individual SWCNT were derived. The volume fraction was controlled up to 25 vol% by biaxial mechanical densification which maintains SWCNT alignment. While the thermal diffusivity of SWCNT forests was almost constant, it increased when the volume fraction was higher than 17 vol%, suggesting that some SWCNTs, which did not serve as a thermal path in the case of lower volume fraction, were connected with the other SWCNTs. Through the increase of inferred thermal conductivity equivalent to an individual SWCNT after 17 vol%, we also realized that the enhancement of volume fraction of SWCNT forest diminished thermal boundary resistance in good agreement with the tendency inferred from the reported numerical data.