Macromolecular Nanotechnology Physical properties of silicone foams filled with carbon nanotubes and functionalized graphene sheets Raquel Verdejo a, * , Cristina Saiz-Arroyo b , Javier Carretero-Gonzalez a , Fabienne Barroso-Bujans a , Miguel Angel Rodriguez-Perez b , Miguel Angel Lopez-Manchado a, * a Institute of Polymer Science and Technology (CSIC), Juan de la Cierva, 3, Madrid 28006, Spain b Cellular Materials Group (CellMat), Condensed Matter Physics Department, University of Valladolid, Valladolid 47011, Spain article info Article history: Received 11 June 2008 Received in revised form 19 June 2008 Accepted 24 June 2008 Available online 1 July 2008 Keywords: Functionalized graphene sheets Carbon nanotubes Foams Silicone abstract Free-rising silicone foams were made with loading fractions of up to 0.25 wt.-% function- alized graphene sheets (FGS) and up to 1.0 wt.-% carbon nanotubes (CNTs) using hydrogen as blowing agent. Scanning electron microscopy of the samples revealed an open cellular structure and a homogeneous dispersion of both types of nanofillers. The incorporation of nanofiller affected the foaming process and thus the final foam density and cellular structure. Transmission electron microscopy revealed the formation of a CNT network throughout the sample, while FGS presented an exfoliated and intercalated dispersion. The thermal stability of the samples was drastically affected by the presence of both nano- fillers. Both nanofillers showed a positive effect on the compressive response of the foams. However, the nanocomposite foams were found to decrease the acoustic absorption with nanofiller content probably due to the variable foam structure and improved stiffness. Ó 2008 Elsevier Ltd. All rights reserved. Introduction The addition of carbon nanotubes (CNTs) to polymer matrices has already been shown to improve their mechanical, electrical and thermal properties [1,2]. How- ever, progress has been partly limited by the availability of high-quality nanomaterials, price and by fundamental composite issues relating to dispersion, alignment, and interfacial adhesion. Hence, a successful approach was to reinforce delicate systems where conventional fibres cannot be physically accommodated, such as films [3–8], fibres [8–10] and foams [11–17]. Lately, the challenge has been to exfoliate the graphite to single graphene sheets [18–20] to use it as an inexpensive and feasible substitute to CNTs. The predicted properties of this type of nanofillers suggest a number of applications on mechanical, electrical and chemical engineering processes [21]. Previous at- tempts to produce graphite nanolayers used expanded graphite, which is made from the rapid thermal expansion of sulphuric acid-intercalated graphite [22–28]. However, none of these materials achieved the complete exfoliation of graphite in its individual graphene sheets as evidenced by the presence of graphite diffraction peaks in the XRD patterns [23,26,27]. Recently, it has been suggested that the starting material to achieve single graphene sheets is graphite oxide (GO). The GO is made by the oxidation of natural graphite and gives way to functionalized graphene sheets (FGS) [19] through an adequately thermal expan- sion, or to single graphene sheets [20] through the chemi- cal reduction of exfoliated GO. Successful examples of graphene-based or FGS-based nanocomposites have re- cently been reported [29–31]. The aim of the present study was to investigate the effects of two types of carbon-based nanofillers, in partic- ular CNTs and FGS, on the cellular structure, morphology, and properties of silicone foams. These carbon nanostruc- tures, with their high mechanical properties and high as- pect ratios, have particular potential to modify both the 0014-3057/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2008.06.033 * Corresponding authors. E-mail addresses: rverdejo@ictp.csic.es (R. Verdejo), lmancha- do@ictp.csic.es (M.A. Lopez-Manchado). European Polymer Journal 44 (2008) 2790–2797 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj MACROMOLECULAR NANOTECHNOLOGY