Molecular dynamics study of the interfacial thermal conductance of multi-walled carbon nanotubes and van der Waals force induced deformation

Abstract

Thermal boundary resistance (TBR) plays an important role in the thermal conduction of carbon nanotube (CNT)-based materials and CNT networks (e.g., thin films, arrays, and aerogels). Although individual CNTs have extremely high thermal conductivity, interfacial resistances can dominate the overall resistance and largely influence their thermal performance. Using molecular dynamics simulations, we systematically study the interfacial thermal conductance (ITC, the inverse of TBR) of multi-walled carbon nanotube (MWNT)-substrate interfaces and MWNT-MWNT junctions, and compare the CNT-CNT junctions with graphene-graphene junctions. The results show that for CNTs with the diameter of a few nanometers, the total ITCs first decrease and then stabilize with the increase of the number of walls, mainly due to the changes of mechanical strength and adhesive energy. Increasing the CNT diameter leads to a larger total ITC and it is mainly due to a larger contact area. The area normalized ITC of CNT-CNT junctions increases and then saturates with the number of walls, and it behaves non-monotonically with the diameter. Furthermore, a trapezoidal model of multi-layer graphene-graphene junctions is used to explain the number of wall dependence of ITC. We also find that with the same adhesive energy, total ITCs of CNT-CNT junctions and graphene-graphene junctions are similar, which allows us to roughly estimate ITCs of CNT-CNT junctions without performing numerical simulations.