Delivered by Ingenta to: McMaster University IP: 188.68.3.126 On: Sat, 25 Jun 2016 04:55:06 Copyright: American Scientific Publishers COMMUNICATION Copyright © 2012 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 12, 3165–3169, 2012 Synergy Derived by Combining Graphene and Carbon Nanotubes as Nanofillers in Composites Fazel Yavari 1 , Limeng Chen 2 , Ardavan Zandiatashbar 1 , Zhongzhen Yu 3 , and Nikhil Koratkar 1 2 ∗ 1 Department of Mechanical, Aerospace, and Nuclear Engineering, 2 Department of Materials Science and Engineering Rensselaer Polytechnic Institute, Troy, NY 12180, USA 3 State Key Laboratory of Organic-Inorganic Composites, Department of Polymer Engineering, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China 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 com- binations 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. Keywords: Graphene, Carbon Nanotubes, Synergy, Nanocomposites, Mechanical Properties. Among the unique properties of carbon-based nano- structures such as nanotubes and graphene are their large surface area to volume ratios and outstanding mechani- cal properties. These attributes offer opportunities for the application of these nanofillers in polymer composites to enhance the mechanical properties of the polymer. Many studies have been performed on mechanical properties characterization of composites reinforced with carbon nanotubes 1–5 and graphene 6–13 fillers. Owing to the intrin- sic difference in their geometry, graphene and carbon nanotubes show significant differences when used as nanofillers in composites. For example, graphene is far more challenging to disperse at high loading fractions since two-dimensional sheets are more likely to entangle and aggregate as compared to one-dimensional nanofibers. However if the nanofiller loading content is kept low enough to ensure adequate graphene dispersion, graphene fillers tend to perform better than carbon nanotubes in terms of mechanical properties enhancement. There are several reasons for this which include: enhanced specific ∗ Author to whom correspondence should be addressed. surface area of graphene as compared to carbon nano- tubes, improved mechanical interlocking/adhesion at the nanofiller/matrix interface for graphene due to its wrinkled and rough surface texture, and the two-dimensional geom- etry of graphene which enables the filler to efficiently carry load along both the longitudinal and the lateral directions. However it is surprising that there have been very few studies 14 15 on the combined use of graphene and carbon nanotubes as fillers in composites. In this work, the effect of using a mixture of graphene and carbon nanotube as the filler in epoxy nanocomposites has been investigated. We studied a range of mechani- cal properties of the composites including Young’s mod- ulus, tensile strength and tensile fatigue life. We find that the mixture of graphene and carbon nanotubes gave the best performance in terms of mechanical proper- ties enhancement. Some studies 15 have hypothesized that one dimensional carbon nanotubes help to separate the graphene platelets and thereby prevent the agglomeration and stacking of the two dimensional graphene sheets. Such well separated graphene sheets with the carbon nanotubes between them acting as spacers provide a larger interfacial J. Nanosci. Nanotechnol. 2012, Vol. 12, No. 4 1533-4880/2012/12/3165/005 doi:10.1166/jnn.2012.5847 3165