Enhanced mechanical strength of graphene/copper composites by using non-oxidized graphene flakes with non-covalent functionalization

Abstract

Graphene/metal composites have been attracting much attention according to the recent trend of high strength and light weight of metal. In order to effectively strengthen metal by incorporating graphene, it is important to evenly disperse graphene flake within the metal matrix without aggregation of graphene flake. In order to do so, the mixing process plays a crucial role. The most commonly utilized method molecular level mixing method. For this method, the presence of functional groups on graphene surface is crucial since they act as nucleation site of metal particle. However, pristine graphene have no functional groups on its surface, it has been difficult to apply molecular level mixing method. In this study, the surface of non-oxidized graphene flakes (NOGFs) was decorated with non-covalently bonded functional groups which can act as nucleation sites without damaging graphene property. The NOGFs exfoliated from the graphite intercalation compound (GIC) shows very low defect density with an average size of $1~2 \mu m$. Pyrene butyric acid (PBA) was non-covalently functionalized on NOGFs surface to act as nucleation sites. The final graphene/copper composite was fabricated by spark plasma sintering, which does not damage graphene due to low processing temperature. The resulting composite showed 22% increase in Young's modulus at 1 vol% compared to that of pure copper and 4% increase in tensile strength. At 2 vol%, the Young's modulus and tensile strength were enhanced by 6% and 8%, respectively.