The authors demonstrate a strong enhancement in thermal conductivity of composites with graphene and copper nanoparticle fillers. The dissimilar size and aspect ratios of the fillers result in a “synergistic effect,” which reveals itself as an abrupt change in thermal properties at the thermal percolation threshold. The study shows a possibility of achieving thermal percolation without inducing electrical conductivity. Abstract The thermal properties of epoxy‐based binary composites comprised of graphene and copper nanoparticles are reported. It is found that the “synergistic” filler effect, revealed as a strong enhancement of the thermal conductivity of composites with the size‐dissimilar fillers, has a well‐defined filler loading threshold. The thermal conductivity of composites with a moderate graphene concentration of fg = 15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approaches f Cu ≈ 40 wt%, followed by saturation. The effect is attributed to intercalation of spherical copper nanoparticles between the large graphene flakes, resulting in formation of the highly thermally conductive percolation network. In contrast, in composites with a high graphene concentration, fg = 40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. A thermal conductivity of 13.5 ± 1.6 Wm−1K−1 is achieved in composites with binary fillers of fg = 40 wt% and f Cu = 35 wt%. It has also been demonstrated that the thermal percolation can occur prior to electrical percolation even in composites with electrically conductive fillers. The obtained results shed light on the interaction between graphene fillers and copper nanoparticles in the composites and demonstrate potential of such hybrid epoxy composites for practical applications in thermal interface materials and adhesives.

Published in: "Advanced Functional Materials".