Using cellulose nanocrystals for graphene/hexagonal boron nitride nanosheet films towards efficient thermal management with tunable electrical conductivity

High-efficiency thermal management materials have attracted increasingly more attention in the heat dissipation of electronic chips, LED light and electro-thermal heating. Herein, we judiciously designed and synthesized thermally conductive nanocomposite films with tunable electrical conductivity, by assembly of graphene oxide (GO) and hexagonal boron nitride (h-BN) nanosheets. Specfically, the GO/BN/cellulose nanocrystal (CNC) hybrid dispersions, which were prepared by mixing and stirring GO and BN/CNC dispersions, were converted into macroscopic films through the evaporation-induced self-assembly. Cellulose nanocrystals (CNC) played a key role in the assembly process, becuase they acted as a dispersant for h-BN nanosheets and formed chiral-structured connection between h-BN and GO. The thermal and electrical performance was tuned by different ratios of reduced GO (RGO) to h-BN with an appropriate reduction procedure. When a thermally conductive yet electrically insulating BN/GO/CNC (mass ratio 76/5/19) film was reduced by hydrazine, it showed thermal conductivity of 107.6 Wm(-1).K-1 and resistivity over 10(9) Omega.cm. On the other hand, an RGO/BN/carbonized CNC nanorods (CNR) (mass ratio 7.5/4.0/1.0) film which was annealed at 1500 degrees C exhibited thermal conductivity of 2037.9 Wm(-1).K-1 and electrical conductivity of 1930.5 S.cm(-1). These improvements were attributed to the conductive network consisting of RGO, h-BN and CNR. This research would provide a new platform for development of the next-generation thermal management materials.