Interface-mediated extremely low thermal conductivity of graphene aerogel

Due to the ultra-high thermal conductivity (k) of graphene, graphene-based materials are expected to be good thermal conductors. Here, however, we uncovered extremely low k of ultralight graphene aerogels (GAs). Although our GA (~4 mg cm 3) is about two times heavier than air (~1.2 mg cm 3), the k (4.7 10 3 5.9 10 3 W m 1 K 1) at room temperature (RT) is about 80% lower than that of air (0.0257 W m 1 K 1 at 20 C). At low temperatures, the GA's k reaches a lower level of 2 10 4 4 10 4 W m 1 K 1. This is the lowest k ever measured to our best knowledge. The mechanism of this extremely low k is explored by studying the temperature variation of GA's k, thermal diffusivity (a) and specific heat (cp) from RT to as low as 10.4 K. The uncovered small, yet positive va/vT reveals the dominant interface thermal contact resistance in thermal transport. For normal materials with thermal transport sustained by phononephonon scattering, va/vT always remains negative. The study of cp suggests highly disordered and amorphous structure of GAs, which also contributes to the ultralow k. This makes the GA a very promising thermal insulation material, especially under vacuum conditions (e.g. astronautics areas). © 2015 Elsevier Ltd. All rights reserved.