Graphene Nanoribbon Composites Mohammad A. Rafiee, † Wei Lu, ‡ Abhay V. Thomas, † Ardavan Zandiatashbar, † Javad Rafiee, † James M. Tour, ‡, * and Nikhil A. Koratkar †, * † Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, 12180, United States, and ‡ Departments of Chemistry and Mechanical Engineering and Materials Science and the Smalley Institute for Nanoscale Science and Technology, Rice University, MS 222, Houston, Texas 77005, United States G raphene nanoribbons (GNRs), thin elongated strips of sp 2 bonded car- bon atoms, can be fabricated by unzipping carbon nanotubes (CNTs). 1-3 The outstanding electronic and spin transport properties of GNRs make them attractive materials in a wide range of device applications. 3-5 GNRs have been produced by several techniques including lithographic, 6,7 chemical, 8 sonochemical, 3 and chemical vapor deposition (CVD). 9 Re- cently, Dai and co-workers have synthesized microscopic quantities of narrow nano- ribbons by unzipping CNTs using the plasma etching route in the gas-phase. 2 In the present study, we applied the solution- based oxidative method, 1,10 synthesizing bulk quantities of thermally treated GNRs, for epoxy nanocomposite applications. While two-dimensional graphene sheets derived from graphite oxide and other graphite intercalation compounds have been extensively used for structural rein- forcement in composites, to the best of our knowledge this is the first report on the me- chanical properties of GNR-polymer com- posites. Herein we investigated the tensile strength, Young’s modulus, ductility, and toughness of an epoxy polymer reinforced with thermally treated GNRs. The results were compared to those of multiwalled car- bon nanotube (MWNT) epoxy composites to establish the effect of the unzipping role of the MWNTs on the mechanical properties of the composite. We also compared the theoretically predicted elastic properties (using the Halpin-Tsai model) of GNR com- posites with our experimental data. The comparison reveals that the dispersion quality of GNR appears to have degraded above 0.3% GNR weight fraction. The model predictions indicate that further im- provements in the mechanical properties are possible if the dispersion of GNRs in the epoxy matrix can be improved at the higher nanofiller loading fractions. MWNTs were unzipped based on a solution-based oxidative mechanism by en- gaging permanganate in an acid. A chemi- cal reduction step was then used to relieve oxygen containing bonds resulting in graphene oxide nanoribbon (GONR) strips. 1 The synthesized GONRs were thermally re- duced (heated to 1050 °C in 35 s) to ex- pel oxygen groups and create GNRs. The protocols employed to thermally treat the GONRs are provided in the Materials and Methods section. The as-produced GNRs were dispersed in a bisphenol A based ther- mosetting epoxy by ultrasonication and high-speed mixing (Materials and Meth- ods). Additional details regarding our dis- persion method are available in refs 11-14. To investigate the mechanical properties of the nanocomposite, uniaxial (static) tensile *Address correspondence to tour@rice.edu, koratn@rpi.edu. Received for review September 24, 2010 and accepted November 09, 2010. Published online November 16, 2010. 10.1021/nn102529n © 2010 American Chemical Society ABSTRACT It is well established that pristine multiwalled carbon nanotubes offer poor structural reinforcement in epoxy-based composites. There are several reasons for this which include reduced interfacial contact area since the outermost nanotube shields the internal tubes from the matrix, poor wetting and interfacial adhesion with the heavily cross-linked epoxy chains, and intertube slip within the concentric nanotube cylinders leading to a sword-in-sheath type failure. Here we demonstrate that unzipping such multiwalled carbon nanotubes into graphene nanoribbons results in a significant improvement in load transfer effectiveness. For example, at 0.3% weight fraction of nanofillers, the Young’s modulus of the epoxy composite with graphene nanoribbons shows 30% increase compared to its multiwalled carbon nanotube counterpart. Similarly the ultimate tensile strength for graphene nanoribbons at 0.3% weight fraction showed 22% improvement compared to multiwalled carbon nanotubes at the same weight fraction of nanofillers in the composite. These results demonstrate that unzipping multiwalled carbon nanotubes into graphene nanoribbons can enable their utilization as high-performance additives for mechanical properties enhancement in composites that rival the properties of singlewalled carbon nanotube composites yet at an order of magnitude lower cost. KEYWORDS: graphene nanoribbons · multiwalled carbon nanotubes · nanocomposites · mechanical properties · structural reinforcement ARTICLE www.acsnano.org VOL. 4 ▪ NO. 12 ▪ 7415–7420 ▪ 2010 7415