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

L Cui and YH Feng and XX Zhang, JOURNAL OF PHYSICAL CHEMISTRY A, 119, 11226-11232 (2015).

DOI: 10.1021/acs.jpca.5b07995

Focusing on carbon nanopeapods (CNPs), i.e., carbon nanotubes (CNTs) filled with fullerene C-60 molecules, the thermal conductivity and its dependence on the filling ratio of C-60 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 C-60 molecules, the mass transfer contribution, the phonon vibrational density of states, and the relative contributions of tube and C-60 molecules to the total heat flux. The mass transfer in CNPs is mainly attributed to the rotational and translational motion of C-60 molecules in tubes. As the filling ratio is larger than 50%, the axially translational motion of C-60 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 C-60, 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 C-60 molecules. This work may offer valuable routes for probing heat transport in CNT hybrid structures, and possible device applications.

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