Tunable anisotropic thermal transport in super-aligned carbon nanotube films

Super-aligned carbon nanotube (CNT) films have intriguing anisotropic thermal transport properties due to the anisotropic nature of individual nanotubes and the important role of nanotube alignment. The exact relation between the alignment and the anisotropic thermal conductivities, however, was not well understood due to the challenges in both the preparation of high-quality super-aligned CNT samples and the thermal characterization of highly anisotropic and porous thin films. Here, super-aligned CNT films with different alignment configurations are fabricated and their anisotropic thermal conductivities are measured using an elliptical-beam approach of time-domain thermoreflectance (TDTR). The results suggest that the alignment configuration can tune the cross-plane thermal conductivity kz from 6.4 to 1.5 W/(mK), and the in-plane anisotropic ratio from 1.2 to 13.5. This work confirms the important role of CNT alignment in tuning the thermal transport properties of super-aligned CNT films and provides an efficient way to design thermally anisotropic films for thermal management.