X-ray Diffraction Characterization of Polymer Intercalated Graphite Oxide

Graphite oxide (GO) is generated by treating graphite with strong oxidizers. GO retains the structure of graphite, but with a larger and irregular basal plane spacing. The oxidation of graphite results in the formation of epoxide groups as well as C-OH and COOH groups. It is the presence of some of these moieties that allows GO to be dispersed in water, allowing for its use in waterborne formulations. Although GO does not possess the electrical properties of singlesheet graphene, it can be swelled in water, which allows for intercalation of hydrophilic polymer between GO sheets, resulting in a composite that can be coated to produce a continuous film. After coating, it may be possible to chemically convert GO to a reduced graphite oxide (r-GO) with improved electrical conductivity. X-ray diffraction (XRD) is ideally suited to evaluate GO – polymer composite samples for evidence of intercalation or exfoliation of GO. Examples of GO – polymer analysis by XRD are presented, along with results that demonstrate the effect of relative humidity (RH) on neat GO. Knowing the ambient RH during XRD data collection was found to be important in order to assess the extent of polymer intercalation within the GO lattice. INTRODUCTION Graphite-based nanoplatelets have garnered considerable attention because of their unique mechanical, thermal and electrical properties (Novoselov et al., 2004). Exfoliated graphite-based platelets, when reduced to a single layer of graphene, have the potential of revolutionizing the flexible electronics market (Geim and Novoselov, 2007). However, the exfoliation process is often cumbersome and has not been reduced to a robust manufacturable practice. Some of the commercially marketed graphene powders or inks are micronized graphite, which often does not have the transparency and conductivity required for display applications. In an interesting approach, several groups have focused on creating graphite oxide (GO), sometimes erroneously referred to as graphene oxide, which is relatively easy to exfoliate in aqueous media and can then be subsequently reduced by chemical means or heat treatment. This approach is attractive, since the process chemistry for creating graphite oxide in large quantities is well established and GO is easily dispersed in water (Dreyer et al., 2010). Various methods of oxidation of graphite can be found in the literature and the chemical structures created by these methods may vary (Dreyer et al., 2010). A commonly used oxidation method is based on the Hummers method (Hummers and Offeman, 1958) or modifications thereof. A proposed molecular structure for GO is based on the Lerf-Klinowski model (Lerf et al., 1998). Per this model, the GO structure includes regions with unoxidized benzene rings and regions with aliphatic six-membered rings; the oxygen-containing species include epoxides (1,2-ether) and C-OH groups with a sprinkling of COOH groups at the edges. Reduction of GO creates a partially reduced version of graphite oxide (r-GO), which is significantly more conductive than GO (Gilje et al., 2007; Yang et al., 2009). Nanocomposites of 186 Copyright ©JCPDS-International Centre for Diffraction Data 2012 ISSN 1097-0002