Title: Construction of highly aligned graphene-based aerogels and their epoxy composites towards high thermal conductivity

Abstract: Three-dimensional (3D) graphene skeletons constructed from two-dimensional (2D) graphene layers can overcome the limitation caused by the physical dimensions of surrounding composite matrices under certain reinforcement limits to effectively transfer heat. However, eliminating the interfacial thermal resistance remains challenging in improving the thermal conductivity of composites. In this study, we reduced the interface thermal resistance of graphene layers in a graphene aerogel (GA) by controlling the stacking structure of the graphene layers. Based on the experimental analyses, theoretical calculation and molecular dynamics simulation, we demonstrated that the oxidation degree of the graphene layers affected the self-assembly behaviour of GA during the directional freezing procedure, which governed the thermal contact resistance among the layers and the final thermal conductivity of the GA-based epoxy composites. In addition, we also found that reducing the thermal resistance among graphene layers was the dominant factor in the thermal conductivity of the composite rather than the thermal resistance between the graphene layers and the epoxy matrix. The in-plane thermal conductivity increased with an increase in the reduction degree, and reached up to 2.69 W m⁻¹ K⁻¹ at an ultra-low GA loading of 1.11 vol%, corresponding to a dramatic enhancement of 1070% compared to that of the pure epoxy. This strategy provides an effective approach for controlling the thermal conductive properties of polymer-based composites, which can potentially satisfy the requirements of the modern electronic industry.