Study of the thermal conductivity in metal-coated carbon nanotubes using molecular dynamics atomistic simulations

Advisors: Iman Salehinia.Committee members: Nicholas Pohlman; John Shelton.Includes illustrations.Includes bibliographical references.To improve the energy efficiency in many electronics and machinery applications, advanced Thermal Interface Materials (TIMs) with high heat dissipation ability and more pliability must be employed. Among a variety of promising choices to make the advanced TIMs, Vertically Aligned Carbon Nanotube (VACNT) turfs (arrays) outstand with their exceptional mechanical and thermal properties. Individual CNTs are quite flexible due to their quasi-one-dimensional structure and presence of strong sp2 bonds among the carbon atoms gives them great strength. Also, the dominance of ballistic phonon transport in the CNTs endows them superior thermal conductivity when compared to many metallic substrates. However, the defects in CNTs, misaligned axial contacts between CNTs in a CNT turf, and the CNTs/substrate resistance reduce the practical thermal conductivity of the material. It is hypothesized that the application of metal coatings on each CNT in a CNT turf would enhance the overall thermal conductivity of the material and improve the connectivity between the CNT turfs and the metallic substrate. As the diameter of the CNTs in a CNT turf is in the order of several nanometers, Molecular Dynamics (MD) atomistic simulations is selected as a tool which provide a deeper understanding in studying the thermal transport at the fundamental level. Thermal conduction in the metals is electron dominant whereas regular MD procedures are incapable of considering the energy exchange between these electrons and phonons. Therefore, a different mechanism called Two-temperature Model (TTM) coupled with Non-Equilibrium MD is used in this study and proved to be effective. MD code to procure the coefficient of thermal conductivity (kappa) was developed and the effects of the metal thickness, number of walls in the CNT and the role of diameter of CNT on kappa of the metal-coated CNTs was individually investigated. It was shown that the increase in the thickness of metal coating would impede the kappa of individual CNTs following an inverse power trend. Also, it was found that among the number of shells in the CNT and its diameter, the former parameter tends to contribute more towards the thermal transport than the latter. The results of this work are capable of predicting the optimal design structure for metal-coated VACNT composite for advanced thermal management applications.M.S. (Master of Science