Thermal Properties of the Binary-Filler Composites with Few-Layer Graphene and Copper Nanoparticles

TL;DR

This study investigates how combining graphene and copper nanoparticles in epoxy composites enhances thermal conductivity through a synergistic effect, revealing thresholds and mechanisms for optimizing thermal performance.

Contribution

It demonstrates the interaction mechanisms between graphene and copper nanoparticles and identifies loading thresholds for maximizing thermal conductivity in epoxy composites.

Findings

Thermal conductivity sharply increases near 40 wt% copper at 15 wt% graphene.

Electrical percolation occurs at less than 7 wt% graphene.

Thermal transport remains phonon-dominated across all filler concentrations.

Abstract

The thermal properties of an 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 ~15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approaches ~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, ~40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. The electrical percolation is observed at low graphene loading, less than 7 wt.%, owing to the large aspect ratio of graphene. At all concentrations of the fillers, below and above the electrical percolation threshold, the thermal transport is dominated by phonons. 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.