Effects of heat treatment on the thermal properties of highly nanoporous graphene aerogels using the infrared microscopy technique Zeng Fan a,b , Amy Marconnet c , Son T. Nguyen a , Christina Y.H. Lim a , Hai M. Duong a,⇑ a Department of Mechanical Engineering, National University of Singapore, Singapore b Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, USA c School of Mechanical Engineering, Purdue University, USA article info Article history: Received 21 November 2013 Received in revised form 10 April 2014 Accepted 12 April 2014 Keywords: Thermal conduction Graphene aerogels Thermal interface materials abstract Graphene aerogels (GAs), fabricated from graphene oxide (GO) suspensions using a mild chemical reduc- tion method, are promising for many applications. Here we report the thermal conductivities of GAs hav- ing various graphene volume fractions from 0.67% to 2.5%, with and without annealing treatment, measured using a comparative infrared microscopy technique. The thermal conductivities of the GAs are measured to be 0.12–0.36 W/(m K). This is the first systematical study of the thermal properties of GAs and the results elucidate the factors limiting their thermal conductivities. The developed thermal measurement technique can be applied to other porous material systems. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Thermal management is crucial issue in the electronic indus- tries, owing to the continued miniaturization and rapid increase in the power of microelectronics, optoelectronics and photonic devices [1,2]. Recently, graphene, with its light weight and remark- able thermal conductivities (5300 W/(m K) [3]), has been regarded to be an ideal candidate as nanofillers for next generation thermal interface materials (TIMs). Much effort has been made to develop graphene-based composites by adding randomly oriented graphene nanosheets into a polymer matrix [4–7]. However, the enhancement in thermal conductivity for graphene-based compos- ites is still very limited due to several factors including local agglomeration, defects within the graphene nanosheets, and inter- action between the graphene nanosheets and polymer matrix [8– 10]. In addition, although the properties of pristine graphene are unique and desired for many applications, the time-consuming exfoliation process and low yield manufacturing make utilization of graphene-based materials challenging in practice [11,12]. Thus, chemically-derived graphene from graphite is promising alterna- tive approach to produce graphene in large quantities [13–15]. Assembling chemically-derived graphene nanosheets into three- dimensional (3D) architectures [16–23] creates an interconnected network of graphene sheets with a scalable low-cost production method [23], which is a promising for thermal management applications at the industrial scale. In contrast to the non-uni- formly dispersed graphene observed in composites, graphene aero- gels (GAs) with continuous scaffolds and mesoporous structures (porosity > 90%) may reduce the internal thermal resistance and enhance the thermal efficiency of TIMs. However, studies of the thermal transport in GAs remain very limited. Zhong et al. [23] reported the thermal conductivity of a GA sample with a relatively low surface area (43 m 2 /g) to be 2.18 W/(m K) using the laser flash technique. Several measurement techniques have been developed to char- acterize the thermal conductivities of nanostructured TIMs [24] including the laser flash technique [5,23,25,26], steady-state mea- surement techniques [27,28], transient techniques [29,30], and infrared microscopy techniques [31–33]. Infrared microscopy has several advantages over other methods as it leverages the non-con- tact, two-dimensional temperature mapping eliminating the need for intrusive temperature sensors and is a direct measurement of thermal conductivity (e.g. it does not require knowledge of the sample specific heat and density). Infrared microscopy techniques have been utilized to measure the effective thermal conductivities of a bulk material [31] and thermal resistances of commercial TIMs [33] with a reported approximated uncertainty of 10%. Particularly for thermal conductivity measurements, the heat flux can be extracted even more accurately with the employment of reference materials based on a comparative method similar to the ASTM E1225 standard. In this work, a comparative infrared (IR) microscopy is devel- oped for thermal measurement of highly porous materials. We http://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.04.023 0017-9310/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +65 65161567. E-mail address: mpedhm@nus.edu.sg (H.M. Duong). International Journal of Heat and Mass Transfer 76 (2014) 122–127 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt