Correlation between multiple chemical modification strategies on graphene or graphite and physical/electrical properties

Chemical modifications of carbon based materials are often used to improve their dispersion in polymer matrix and increase the nanocomposite electrical properties. This work concerned the control of graphene and graphite physical and chemical structure thanks to different chemical modification (oxidation, copolymer functionalization and reduction). This article exposes a complete study of different chemical modifications impact on graphene and graphite microstructure, chemical structure, and its relative electrical property. A first oxidation step by Hummers or nitric acid method was necessary to further graft a copolymer of methyl methacrylate and hydroxyethyl methacrylate via a versatile "grafting onto" covalent functionalization. Hummers' and nitric acid methods were considered as strong and soft oxidation treatments, respectively. Reduction steps were also performed using hydrazine or thermal treatments to recover high electrical conductivity. Chemical modifications of graphene and graphite were characterized by X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy and pyrolysis–gas chromatography–mass spectrometry. Moreover, a new method for the electrical measurement of the modified particles is presented in this work. This measurement requires adhesive tape and an electrical circuit with a diode using the four probes protocol, it allows the evaluation of the electrical conductivity of the graphene and graphite samples in powder state. Finally, the electrical resistances of the different graphene and graphite submitted to all the chemical treatments are reported.