Recent demands in the consumer market for light-weight, compact, and cost-effective electronic devices has promoted research into designing new materials to meet the growing heat dissipation requirement. Carbon nanotubes, nanofibers, and graphene are particularly interesting candidates because of their unusually high thermal conductivities. If they are made into thin film/sheet form at a reasonable cost, the resulting bulk material could have wide applications as heat spreaders and thermal interface materials in electronics. In this work, we developed a process to fabricate carbon/graphite nanofiber thin mats by combining electrospinning and thermal treatment. Nanofiber non-woven mats were produced by electrospinning a solution mixture of mesophase pitch and polyimide. Soluble and insoluble pitch provides large graphite like molecules that should act as templates in increasing the graphitic conversion upon subsequent multi-step thermal treatment steps.
A systematic investigation was carried out to develop an understanding of the evolution of structural hierarchy in nanofiber mats as influenced by blend composition at a series of stages from 350 to 3000 °C. In addition, the electrical conductivity was measured for the mats and the thermal conductivity was measured for individual nanofibers and corresponding mats in both in-plane and through-thickness directions. Correlations were made between the structural analysis data and the transport properties. From the trends established, it is shown that the thermal treatment temperature plays a decisive role in determining the onset of progressive transformation from amorphous carbon to graphitic structure. Also, the increase of mesophase pitch fraction in the precursor is found to enhance the order in the graphitic structure that, in turn, is reflected in the higher electrical and thermal conductivities of final nanofiber mats.
Finally, the graphitic nanofiber mats prepared show very good structure integrity, the ability to bend, and an in-plane thermal conductivity as high as 60 W/m•K owing to the well-connected nanofiber networks. Combined with the ability to achieve high-volume production, these mats are promising candidates as thermal interface materials for flexible electronics.