Phonon transport in helically coiled carbon nanotubes

We perform theoretical studies on the phonon thermal transport in helically coiled carbon nanotubes (HCCNTs). The Grüneisen parameter, as a function of the phonon wave vector and phonon branch, is numerically evaluated for each vibrational mode, so that the three-phonon Umklapp scattering rates can be calculated exactly by taking into account all allowed phonon relaxation channels. We considered wide temperature range and heat conductor lengths from nano- to macro-scale. We examine the crossover from ballistic to diffusive transport regime and impact of HCCNT geometrical parameters on their heat conduction. Thermal conductivity in HCCNTs is found to be slightly lower than that in single walled carbon nanotubes (SWCNTs). This is interpreted by the competition among three factors. Firstly, threefold reduction of the Grüneisen parameter for the acoustic branches. Secondly, lower phonon group velocities. Finally, availability of purely acoustic scattering channels. Nevertheless, HCCNTs are predicted to be more suitable (than SWCNTs) for thermal management applications due to their spring-like shape. HCCNTs are extremely elastic, natural NanoVelcro material.