Uncovering the Thermal Conductivity Anisotropy of Highly Deformed Graphene/Epoxy Composites

Graphene/epoxy composites, as popular thermal interface materials (TIMs), commonly experience severe mechanical deformation due to packing pressure. Their thermal conductivity, which relies closely on the orientations of the graphene fillers, is expected to be significantly different from that of the as-fabricated undeformed ones but is unclear so far. In this work, we have systemically investigated the thermal conductivity of graphene/epoxy composites subjected to a large uniaxial mechanical compression using nonequilibrium molecular dynamics simulations. The results show that the thermal conductivity could increase by up to 80% in the perpendicular direction to the compression, yet it decreases by up to 14% in the parallel direction, largely enhancing the thermal conductivity anisotropy. In addition, thermal anisotropy increases with the increase in the filler’s orientation. The vibrational density of states, accumulated correlation factor, and density of interaction have been analyzed to reveal the underlying thermal transport mechanism. The results show that increasing the compression in the perpendicular direction leads to strong correlations between graphene fillers and epoxy and enhanced thermal coupling, while in the parallel direction, the correlation and the resultant thermal coupling are weak. Atomic heat flux contours also reveal that graphene has more contributions to heat transfer when it is aligned toward the heat flux direction. These findings suggest that controlling the orientation of graphene fillers and applying uniaxial compression can be used to regulate the thermal conductivity of graphene/epoxy composites in thermal management applications.