Inter-carbon nanotube contact in thermal transport of controlled-morphology polymer nanocomposites

Directional thermal conductivities of aligned carbon nanotube (CNT) polymer nanocomposites were calculated using a random walk simulation with and without inter-CNT contact effects. The CNT contact effect has not been explored for its role in thermal transport, and it is shown here to significantly affect the effective transport properties including anisotropy ratios. The primary focus of the paper is on the non-isotropic heat conduction in aligned-CNT polymeric composites, because this geometry is an ideal thermal layer as well as constituting a representative volume element of CNT-reinforced polymer matrices in hybrid advanced composites under development. The effects of CNT orientation, type (single-versus multi-wall), inter-CNT contact, volume fraction and thermal boundary resistance on the effective conductivities of CNT composites are quantified. It is found that when the CNT-CNT thermal contact is taken into account, the maximum effective thermal conductivity of the nanocomposites having their CNTs parallel to the heat flux decreases by approximately 4 times and approximately 2 times for the single-walled and the multi-walled CNTs, respectively, at 20% CNT volume fraction.