Synergy derived by combining graphene and carbon nanotubes as nanofillers in composites

Both one-dimensional carbon nanotubes as well as two-dimensional graphene sheets have been extensively investigated as nanofillers in composites. However there are very few reports on their combined use in composite materials. Here we report the mechanical properties including Young's modulus, tensile strength and fatigue properties of an epoxy polymer reinforced with various combinations of graphene and carbon nanotube fillers- i.e., nanotubes alone, graphene alone and a mixture of graphene and nanotubes. We find that at low nanofillers loadings (< 0.1% weight), the graphene fillers performed better than both singlewalled as well as multiwalled carbon nanotubes. However, interestingly it was the combination of carbon nanotubes with graphene that yielded the greatest improvement in mechanical properties. Optical microscopy of thin micro-tomed slices of the composites indicated that in the presence of the nanotubes the graphene sheets appear to have aggregated into chains forming a network structure. Such long range ordering of the nanofillers is very unusual in a nanocomposite system and is likely responsible for the enhanced mechanical properties.