Radially Grown Graphene Nanoflakes on Carbon Fibers as Reinforcing Interface for Polymer Composites

The development of nanoscale reinforcements, which can tailor the interfacial strength and impart multiple functionalities on carbon fiber reinforced polymer (CFRP) composites, remains a challenge for their largescale adoption in diverse applications ranging from aerospace to transportation and construction industries. In this work radially aligned graphene nanoflakes (GNFs), grown directly on carbon fibers (CFs) via a simple one-step microwave plasma enhanced chemical vapor deposition method, without any catalyst, were used as a novel nano-reinforcement interface. A remarkable 28% enhancement in the tensile strength of the hybrid fibers was observed via singlefiber tensile strength tests, whereas the interfacial shear strength (IFSS) increased by 101.5%. Our results demonstrate that GNFs not only improve the interfacial strength between the GNFs and the epoxy resin but also enhance the in-plane mechanical strength of the CFsa well-known problem encountered with the direct growth of carbon nanotubes on CFs. In addition, GNFs provided embedded functionality via increased electrical conductivity (60.5% improvement for yarns and 16% for single fiber) and electrochemical capacitance (157% for yarns). This work indicates the potential of GNFs as an interphase for the simplified and costeffective production of stronger multifunctional CFRP composite materials.