  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. However, the relationship between the
alignment and the anisotropic thermal conductivities was not well understood
due to the challenges in both the preparation of high-quality super-aligned CNT
film samples and the thermal characterization of such highly anisotropic and
porous thin films. Here, super-aligned CNT films with different alignment
configurations are designed and their anisotropic thermal conductivities are
measured using time-domain thermoreflectance (TDTR) with an elliptical-beam
approach. The results suggest that the alignment configuration could tune the
cross-plane thermal conductivity k_z 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.
