Highly Thermally Conductive Nanocomposites Prepared by the Ice-Templating Alignment of Nanodiamonds in the Thickness Direction

In electronic devices, thermal management, such as heat dissipation, is challenging. Therefore, polymer composites including thermally conductive fillers with high thermal conductivities, low weights, and high flexibility and processability have attracted attention. In particular, a high thermal conductivity in the thickness direction via filler alignment is important. In this study, we aligned isotropic, thermally conductive nanodiamond (ND) fillers using an ice-templating method and achieved high thermal conductivity and thermal dimensional stability in the thickness direction. Notably, the thermal conductivity in the thickness direction was 3 times higher than that in the in-plane direction and 16 times higher than that of an epoxy resin without the ND filler. We evaluated the mechanism of thermal percolation using three-dimensional X-ray computed tomography and demonstrated that the formation of thermally conductive paths in the thickness and in-plane directions is crucial for thermal conduction. Despite the use of a spherical ND filler, the thermal conductivity was remarkably enhanced compared to those of other reported composites, including one- and two-dimensional anisotropic fillers.