A process is described to produce single sheets of functionalized graphene through thermal exfoliation of graphite oxide. The process yields a wrinkled sheet structure resulting from reaction sites involved in oxidation and reduction processes. The topological features of single sheets, as measured by atomic force microscopy, closely match predictions of first-principles atomistic modeling. Although graphite oxide is an insulator, functionalized graphene produced by this method is electrically conducting. The study demonstrates that through an optimal combination of graphite oxide (GO) preparation and thermal treatment, bulk quantities of functionalized single graphene sheets can be produced. The mechanism of exfoliation is mainly the expansion of CO₂ evolved into the interstices between the graphene sheets during rapid heating. While the decomposition of functional groups of GO yielding CO₂ is exothermic, the vaporization of water is endothermic and delays the heating process. For the success of the process, it is essential to completely eliminate the intergraphene spacing associated with the native graphite during the oxidation stage and also to minimize the detrimental role of water vaporization. An NMR study showed that GO contains aromatic regions randomly interspersed with oxidized aliphatic six-membered rings. The oxidized rings contain C–O–C (epoxide) and C–OH groups, while the sheets terminate with C–OH and –COOH groups. Some of these functional groups are retained in the thermally exfoliated nanoplates of graphene stacks. When used as a nanofiller in a polymer (poly(methyl methacrylate)) matrix, these functionalized graphene stacks offer comparable or better thermal, mechanical, and electrical property enhancements than SWCNTs. The exfoliation process is associated with the thermal expansion of the evolved gases trapped between the graphene sheets. The detrimental effect of water is attributed to the fact that while the decomposition of functional groups is exothermic, vaporization of water is endothermic and thus slows down the heating process. The maximum pressures generated by both water and carbon dioxide estimated by using the spacing of the layers from diffraction measurements are determined to be in excess of 60 and 100 MPa for water and CO₂, respectively. The CO₂ evolution, corresponding to a weight loss of 30%, is the predominant mechanism driving exfoliation. The study shows that the exfoliated sheets are well dispersed and exhibit a lateral extent of a few hundred nanometers. The sheets display height variations at two length scales: (i) the flat areas of the sheet have an average height of about 2 nm with respect to the HOPG surface and are covered with ~0.2-0.4 nm "bumps", and (ii) several large, meandering wrinkles with peak heights up to 10 nm. The bumpy texture of the flat regions is attributed to the presence of isolated epoxy and hydroxyl reaction sites. The wrinkles correspond to defects in the carbon latticeA process is described to produce single sheets of functionalized graphene through thermal exfoliation of graphite oxide. The process yields a wrinkled sheet structure resulting from reaction sites involved in oxidation and reduction processes. The topological features of single sheets, as measured by atomic force microscopy, closely match predictions of first-principles atomistic modeling. Although graphite oxide is an insulator, functionalized graphene produced by this method is electrically conducting. The study demonstrates that through an optimal combination of graphite oxide (GO) preparation and thermal treatment, bulk quantities of functionalized single graphene sheets can be produced. The mechanism of exfoliation is mainly the expansion of CO₂ evolved into the interstices between the graphene sheets during rapid heating. While the decomposition of functional groups of GO yielding CO₂ is exothermic, the vaporization of water is endothermic and delays the heating process. For the success of the process, it is essential to completely eliminate the intergraphene spacing associated with the native graphite during the oxidation stage and also to minimize the detrimental role of water vaporization. An NMR study showed that GO contains aromatic regions randomly interspersed with oxidized aliphatic six-membered rings. The oxidized rings contain C–O–C (epoxide) and C–OH groups, while the sheets terminate with C–OH and –COOH groups. Some of these functional groups are retained in the thermally exfoliated nanoplates of graphene stacks. When used as a nanofiller in a polymer (poly(methyl methacrylate)) matrix, these functionalized graphene stacks offer comparable or better thermal, mechanical, and electrical property enhancements than SWCNTs. The exfoliation process is associated with the thermal expansion of the evolved gases trapped between the graphene sheets. The detrimental effect of water is attributed to the fact that while the decomposition of functional groups is exothermic, vaporization of water is endothermic and thus slows down the heating process. The maximum pressures generated by both water and carbon dioxide estimated by using the spacing of the layers from diffraction measurements are determined to be in excess of 60 and 100 MPa for water and CO₂, respectively. The CO₂ evolution, corresponding to a weight loss of 30%, is the predominant mechanism driving exfoliation. The study shows that the exfoliated sheets are well dispersed and exhibit a lateral extent of a few hundred nanometers. The sheets display height variations at two length scales: (i) the flat areas of the sheet have an average height of about 2 nm with respect to the HOPG surface and are covered with ~0.2-0.4 nm "bumps", and (ii) several large, meandering wrinkles with peak heights up to 10 nm. The bumpy texture of the flat regions is attributed to the presence of isolated epoxy and hydroxyl reaction sites. The wrinkles correspond to defects in the carbon lattice