Enhancement of heat conduction in carbon nanotubes filled with fullerene molecules

Heat conduction in carbon nanopeapods (CNPs), i.e. carbon nanotubes (CNTs) filled with fullerene C60 molecules, is investigated using molecular dynamics simulations. The enhancement mechanisms of CNP thermal conductivity, compared with bare CNTs, are discussed via the local heat flux onto a single atom, the relative contributions of different phonon oscillation frequencies to thermal conductivity and the phonon vibrational density of states. The result shows that filled C60 can increase the CNT thermal conductivity by up to 9.6 times in the temperature range of 100-500 K. The constructive phonon mode couplings between the tube and C60 in a frequency range of 0-20 THz, especially in x-, y-direction transverse acoustic modes and the radial breath mode, are primarily responsible for the increment of thermal conductivity. In addition, filled C60 molecules in CNPs enhance the mass transfer contribution to the total heat flux. This contribution accounts for 22-58% in CNPs, much higher than 12% in CNTs. With the temperature going up, the phonon scattering increases and the contribution from mass transfer to total heat flux decreases. Therefore, the CNP thermal conductivity decreases with rising temperature. This study sheds lights on nanoscale thermal/phonon engineering by utilization of CNTs and C60.