Nano-graphene/polyimide composites with extremely high rubbery plateau modulus J. Longun, J.O. Iroh * Materials Engineering Program, School of Aerospace Systems, College of Engineering and Applied Science, 2600 Clifton Avenue, University of Cincinnati, OH 45221, USA ARTICLE INFO Article history: Received 28 July 2011 Accepted 15 December 2011 Available online 3 January 2012 ABSTRACT Nano-graphene sheets (NGS) were dispersed in a high performance polyimide (PI) matrix by in situ condensation polymerization. The viscoelastic behavior of PI and NGS/PI compos- ite was investigated by using dynamic mechanical spectrometry (DMS) and extraordinary modulus enhancement was observed in the rubbery plateau region (>400 °C) compared to the glassy region (<400 °C). A modulus enhancement of 11,000%, 52,000% and 400,000% was obtained in the rubbery plateau region for NGS/PI composite at 1.18, 6.12 and 28.08 vol.%, respectively, compared to a modulus enhancement of 100%, 108% and 500%, respectively, in the glassy region. The disparity in the modulus enhancement between the glassy region and the rubbery plateau region is due to the pronounced stiffening effect of hard fillers in a soft and flexible matrix such as rubber. Wide-angle X-ray diffraction (WAXD) was used to study dispersion of nano-graphene in the PI matrix, and graphene aggregates containing up to 46 single graphene sheets were obtained at about 0.29 vol.%. WAXD pattern show the presence of graphitic peak at a diffraction angle of 26.5 o . Raman spectroscopy show the presence of amorphous carbon (D band) and graphitic carbon (G band), at 1360 and 1537 cm 1 , respectively. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Graphene, which contains single-layered sp 2 hybridized car- bon atoms arranged in a two-dimensional lattice structure, has been at the center of immense attention due to its excep- tional thermal, mechanical and electrical properties [1–7]. As a result of the recent advances [8–10] in the production of large quantities of exfoliated graphene sheets from graphite, the fabrication of graphene/polymer composite has been made possible. Graphene filled polymer composites have enhanced mechanical properties [11,12] due to the synergistic combina- tion of high specific surface area, strong nano-filler-matrix adhesion as well as the exceptional mechanical properties. Much work has been dedicated to the study of polyimide- based composites owing to the outstanding properties of polyimide such as: high thermal-oxidative stability, solvent resistance, superior tensile modulus and excellent environ- mental stability. Numerous studies [13–17] have been focused on carbon nanotubes filled polyimide with the goal of com- bining the excellent mechanical and electrical properties of nanotubes with the superior bulk properties of polyimide. Other researchers [18,19] have also dispersed iron-oxide into polyimide matrix for the fabrication of ferromagnetic com- posite materials. In recent years, there been a tremendous drive to develop multifunctional and smart materials for useful applications for aerospace, automobile, sensing, display devices and energy storage applications. In aerospace structures in particular, the current state of the art lightweight materials are developed from graphite fiber composites. Carbon nanotubes based com- 0008-6223/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2011.12.032 * Corresponding author. E-mail address: irohj@ucmail.uc.edu (J.O. Iroh). CARBON 50 (2012) 1823 – 1832 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon