Carbon nanotubes (CNTs), because of their superior mechanical, electrical, and thermal properties and possible low-cost, large volume production, have been projected as promising nanostructure additives in polymer composites to achieve tunable and enhanced materials properties. Transport properties of CNT-polymer composites have been widely studied over the past decade and it is well-accepted that when the added CNTs exceed the percolation limit, the electrical conductivity of CNT-polymer composites can usually increase by several orders of magnitude. However, thermal conductivity measurements present mixed results and even for positive results, the enhancement is much lower than that expected from traditional theories. For example, Biercuk et al. [1] demonstrated that 1 wt% of single-wall CNTs (SWCNTs) in industrial epoxy could increase the thermal conductivity by 125% at room temperature, three-times higher than that from 1 wt% loading of carbon nanofibers. However, similar studies [2] showed that thermal conductivity only increased marginally for multi-wall CNT (MWCNT)-epoxy composites and more surprisingly, the thermal conductivity for SWCNT-epoxy composites was even lower than that of pure epoxy.
