Martin-Gallego et al. Nanoscale Research Letters 2011, 6:610 http://www.nanoscalereslett.com/content/6/1/610 N A N O E X P R E S S Open Access Thermal conductivity of carbon nanotubes and graphene in epoxy nanofluids and nanocomposites Mario Martin-Gallego1, Raquel Verdejo1, Mohamed Khayet2, Jose Maria Ortiz de Zarate2, Mohamed Essalhi2 and Miguel Angel Lopez-Manchado1* Abstract We employed an easy and direct method to measure the thermal conductivity of epoxy in the liquid (nanofluid) and solid (nanocomposite) states using both rodlike and platelet-like carbon-based nanostructures. Comparing the experimental results with the theoretical model, an anomalous enhancement was obtained with multiwall carbon nanotubes, probably due to their layered structure and lowest surface resistance. Puzzling results for functionalized graphene sheet nanocomposites suggest that phonon coupling of the vibrational modes of the graphene and of the polymeric matrix plays a dominant role on the thermal conductivities of the liquid and solid states. PACS: 74.25.fc; 81.05.Qk; 81.07.Pr. Keywords: carbon nanotubes, graphene, nanocomposites, nanofluids, thermal conductivity Introduction Due to the increasing importance of energy dissipation in the electronic industry, thermal conductivity of cured epoxy resins has been widely investigated over the years. One strategy to improve the thermal transport of epoxy resins has been the addition of highly conductive fillers, such as carbon-based or metallic fillers [1]. However, the effect of such additions on either the uncured sys- tem or the cure reaction of resins has not yet been fully established. The thermal conductivity of the uncured liquid resin plays an important role to define the vari- ables involved in the transformation process, such as time, applied heat, or cooling time, which will then have a profound effect on the cross-link density and hence, on the final properties of the system. Thus, we aimed at studying the effect of two types of carbon-based nanofil- lers, in particular, nanotubes and graphene sheets, on the thermal conductivity of an uncured liquid epoxy resin. There have been considerable interest and effort in the transport properties of carbon nanotube [CNT] * Correspondence: lmanchado@ictp.csic.es 1Instituto de Ciencia y Tecnologia de Polimeros, ICTP-CSIC, Juan de la Cierva 3, Madrid, 28006, Spain Full list of author information is available at the end of the article filled polymer nanocomposites [2,3]. Electrical conduc- tivity of epoxy nanocomposites increases by several orders of magnitude with CNT concentration [4]; this effect can be explained by the established percolation theory [5] with the shift from an insulator into a con- ductive material when a critical concentration of the conductive filler is reached, commonly known as perco- lation threshold. However, the thermal conductivity has shown at best linear enhancements with nanotube con- tent with a lack of thermal percolation. The main reason for this fact is the relatively small thermal conductivity ratio (Kcnt/Kmatrix) by comparison with the correspond- ing ratio of electrical conductivities [6]. Graphene is a two-dimensional carbon nanofiller with a one-atom-thick sheet of sp2 bonded carbon atoms that are densely packed in a honeycomb crystal lattice [7,8]. Single layer graphene is predicted to have a remarkable performance, such as high thermal conductivity of 5,000 W/mK, which corresponds to the upper bound of the highest values reported for single-walled carbon nano- tube bundles [9], high electrical conductivity of up to 6,000 S/cm [10], and superior mechanical properties with Young’s modulus of 1 TPa and ultimate strength of 130 GPa [11]. In addition to these outstanding properties, the recent developments on graphene synthesis routes and © 2011 Martin-Gallego et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.