Observing grain boundary-induced phonons mean free path in highly aligned SWCNT bundles by low-momentum phonon scattering

Due to their nanoscale scattering cross section, single-walled carbon nanotubes (SWCNTs) have never been reported for crystallite size or similar characteristics. Here, we characterize the average structure thermal domain size of SWCNTs. This characteristic size reflects the average mean free path of low-momentum phonon scattering. The characterization itself involves measuring the thermal reffusivity of SWCNT bundles in the axial direction down to 77 K and determining the residual value at the 0 K limit. This residual value reflects the sole structure-phonon scattering due to vanishing Umklapp scattering. We obtain the average structure thermal domain sizes of two SWCNT bundles, which are 46.0 and 61.9 nm. Since there is no other characteristic size information available to compare for SWCNTs, we compare the structure thermal domain size of other micro-/nanoscale materials with their crystallite size by X-ray diffraction to interpret our results.