Graphene wrapped hollow glass beads for polymer composites: From thermal insulators to conductors

Currently, graphene is considered to be one of the top filler candidates to improve the thermal conducting ability of polymeric materials. However, agglomeration and in-plane orientation of graphene nanosheets in polymer matrices disfavor the substantial increase in the cross-plane thermal conductivities of the material. In this work, hollow glass beads are wrapped with graphene nanosheets through electrostatic forces. And then the graphene wrapped beads are introduced into epoxy as thermal fillers. At just 1 wt% filler loading (only 0.09 wt% of graphene), the cross-plane thermal conductivity of the epoxy composite can reach 5.1 W m−1 K−1. The original hollow glass beads are thermally insulative. The significant enhancement in the cross-plane thermal conductivity of the composites is merely due to the very small amount of graphene added. It is believed that the hollow beads contribute to the thermal conducting improvements by preventing graphene nanosheets from agglomeration and in-plane orientation.