Synthesis of Highly Dispersed and Conductive Graphene Sheets by Exfoliation of Preheated Graphite in a Sealed Bath and its Applications to Polyimide Nanocomposites

Abstract

E-mail: cnt@kist.re.kr Received January 28, 2014, Accepted March 17, 2014A simple method for exfoliating pristine graphite to yield mono-, bi-, and multi-layers of graphene sheets as ahighly concentrated (5.25 mg/mL) and yielded solution in an organic solvent was developed. Pre-thermaltreatment of pristine graphite at 900 °C in a sealed stainless steel bath under high pressures, followed bysonication in 1-methyl-2-pyrrolidinone solvent at elevated temperatures, produced a homogeneous, well-dispersed, and non-oxidized graphene solution with a low defect density. The electrical conductivities of thegraphene sheets were very high, up to 848 S/cm. These graphene sheets were used to fabricate graphene-polyimide nanocomposites, which displayed a higher electrical conductivity (1.37 S/m) with an improvedtensile strength (95 MPa). The synthesized graphene sheets and nanocomposites were characterized bytransmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray photo-electron spectroscopy, and Raman spectroscopy. Key Words : Graphene sheets, Thermal exfoliation, Polyimide nanocomposites, Electrical conductivity, Ten-sile strengthIntroductionGraphene is formed by a single atomic layer of sp