Carbon nanotubes (CNTs) have been expected to enhance thermal conductivity in various materials including composites, for applications such as thermal interface materials. However, the thermal properties of bulk CNTs and CNT composites tend not to achieve the high values of individual nanotubes. Factors that cause such  scaling effects include CNT morphology (length,

alignment, entanglement, etc.), and inter-CNT/CNTmedium boundary properties. It is critical to evaluate and minimize these effects. However, structure-property relationships are not yet well understood, and thus effective use of CNTs has not been achieved for the majority of currently existing CNT polymer composites. 

 

In this work, consistent CNT samples with well-controlled morphology were fabricated by embedding aligned CNTs in polymer to create aligned CNT polymer nanocomposites (A-CNTPNCs), as shown in Figure 1. A-CNT-PNCs were thoroughly evaluated for their anisotropic thermal properties, and a non-linear increasing trend of thermal conductivity has been observed with increasing CNT volume fraction (vCNT). This newly identified trend was understood through comparison with both analytical and numerical models of the transport behavior. Such understanding can help utilize CNTs in the most effective ways for tailoring thermal conductivities for bulk composite and other applications.