Dependence of Thermal Conductivity of Carbon Nanopeapods on Filling Ratios of Fullerene Molecules.

Focusing on carbon nanopeapods (CNPs), i.e., carbon nanotubes (CNTs) filled with fullerene C60 molecules, the thermal conductivity and its dependence on the filling ratio of C60 molecules have been investigated by equilibrium molecular dynamics simulations. It turns out that the CNP thermal conductivity increases first, reaches its maximum value at filling ratio of 50%, and then decreases with increasing filling ratio. The heat transfer mechanisms were analyzed by the motion of C60 molecules, the mass transfer contribution, the phonon vibrational density of states, and the relative contributions of tube and C60 molecules to the total heat flux. The mass transfer in CNPs is mainly attributed to the rotational and translational motion of C60 molecules in tubes. As the filling ratio is larger than 50%, the axially translational motion of C60 molecules gets more and more restricted with increasing filling ratio. For either the mass transfer contribution to heat transfer or the phonon coupling between the tube wall and C60, the peaking behavior occurs at a filling ratio of 50%, which confirms the corresponding maximum thermal conductivity of CNP. With the filling ratio increasing, the dominating contribution to heat transfer changes from tube-wall atoms to fullerene atoms. Their relative contributions almost keep stable when the filling ratio is larger than 50% until it reaches 100%, where the contribution from fullerene atoms suddenly drops because of strong confinement of translational motion of C60 molecules. This work may offer valuable routes for probing heat transport in CNT hybrid structures, and possible device applications.