Thermal transport in isolated carbon nanostructures and associated nanocomposites

Carbon nanostructures, namely carbon nanotubes, nanofibers and graphene, owing to their extremely high thermal conductivities, hold promise for use as fillers in materials required for thermal management of electronics. Efficient thermal characterization holds the key to understanding the heat conduction mechanisms in the particular nanostructures and continued development of materials for novel applications. The present work involves development of dedicated techniques for characterization of the thermal conduction in individual carbon nanostructures and nanocomposites. The thermal flash technique developed for characterizing individual nanostructures provides a simple, accurate and reliable means for measuring thermal conductivity while managing to avoid the issues associated with conventional techniques. The thermal conductivities measured for vapor--grown carbon nanofibers and various graphene nanoplatelets were consistent with theoretical estimates based on the fundamentals of heat conduction in solids. Moreover, the results provide valuable evidence to support existing theories for explaining the differences between the various nanoscale manifestations of graphite. The investigation on isolated nanostructures was followed with the development and characterization of epoxy nanocomposites comprising graphite and graphene as fillers with the overarching goal of preparing composites with a thermal conductivity higher than 40 W/m-K. The thermal conductivities measured for some of the nanocomposites using the dual-mode heat flow meter, a steady-state heat technique developed in this work, were higher than the highest reported value in literature. The presence of large graphite flakes in conjunction with small amounts of graphene to reduce the overall thermal interface resistance were the principal reasons behind the extremely high thermal conductivity of 42.4 +/- 4.8 W/m-K (nearly 250 times enhancement) for an epoxy composite with 30 wt% of graphite and 5 wt% of graphene.