Self-assembled complexes of graphene oxide and oxidized vapor-grown carbon fibers for simultaneously enhancing the strength and toughness of epoxy and multi-scale carbon fiber/epoxy composites

Reinforcement of polymers with small addition of nanofillers has been intensively investigated. It has been suggested that combination of few-layer graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) is more effective than single nanofillers for polymer reinforcement. Herein, we report that the complexes of single-layer graphene oxide (GO) and oxidized vapor-grown carbon fibers (OVGCFs), with dimensionalities of 2 and 1, respectively, simultaneously improve the strength and toughness of epoxy and multi-scale carbon fiber reinforced composites at an extremely low content (∼0.2 wt%). The GO-OVGCF complexes are formed in water by the π-π stacking-induced self-assembly of OVGCFs and GO, and then rapidly transferred to a tertiary amine type epoxy oligomer for the preparation of epoxy and multi-scale composites. OVGCFs were observed to be wrapped by small GO sheets, which greatly improve the dispersion uniformity of OVGCFs in epoxy matrix and the filler-matrix interfacial interactions. The influences of the complexes with various GO-to-OVGCF ratios on the mechanical properties of epoxy and multi-scale composites were investigated systematically. At the optimized GO-to-OVGCF ratio, the complexes increase the mechanical properties of epoxy and multi-scale composites more significantly than previously reported individual nanofillers and the CNT-GNP hybrids.