Enhanced thermal conductivity in oriented cellulose nanofibril/graphene composites via interfacial engineering

Efficient thermal management has become an important design consideration for the development of modern electronic devices, seeking to combine excellent thermal conductivity and good mechanical properties. Graphene-based composites are considered as new generation materials for addressing this issue. However, challenges associated with well-oriented structures and well-controlled interactions have so far restrained the achievement of excellent thermal conductivity, limiting the applications of these composites in the fields of thermal management. Here, we describe a composite system which achieves high thermal conductivity and mechanical properties by designing the interfacial interactions between cellulose nanofibrils (CNFs) and oriented graphene. We use polyethylene glycol (PEG) to covalently modify graphene nanosheets (GP), and improve the adhesion with CNF via hydrogen bonds. The CNF/GP composites show clear layered structure with anisotropic thermal conductivities. Increasing the GP content improves the thermal conductivities along in-plane direction, while through-plane thermal conductivities remain low. Surface grafting of PEG chains on the graphene allows further enhancement of thermal conductivities. Moreover, the CNF/GP composites show good mechanical properties. Finally, the combination of thermal conductivities and mechanical performance facilitate thermal management applications for such composites.