Graphene-coated ZnO tetrapod whiskers for thermally and electrically conductive epoxy composites

Graphene-coated tetrapod ZnO whisker (T-ZnO) hybrids are fabricated by chemical modification of T-ZnO with an aminosilane, covalent coating with graphene oxide (GO) sheets, and reduction of the GO component by UV irradiation or thermal annealing. Compared to the moderately reduced hybrid by UV irradiation, the thermally annealed hybrid at 1000 °C (TGO1000@T-ZnO) is highly efficient in improving both thermal and electrical conductivities of epoxy. A high thermal conductivity of 5.06 W/(m K) is achieved for the epoxy composite with 65 vol.% TGO1000@T-ZnO hybrid. The epoxy composite with 65 vol.% TGO1000@T-ZnO also exhibits a high electrical conductivity of 27.2 S/m due to the efficiently formed electrically conducting network with only ∼4 wt.% well-distributed TGO sheets that are coated on T-ZnO substrates. The excellent thermal and electrical conductivities are attributed to the efficient conductance pathways formed by the skeleton of ZnO whiskers and the enhanced phonon and electron transfers by TGO sheets.