Computational Studies of the Structure, Behavior upon Heating, and Mechanical Properties of Graphite Oxide

A Monte Carlo based scheme for the formation of graphite oxide (GO) was developed and implemented. A Rosenbluth factor was used to select intermediate structures in an attempt to form stable, low-energy, and realistic GO. The scheme resulted in the production of GO that has an interplanar spacing of 5.8 Å, in good agreement with the experimental value (5.97 Å). Epoxide and hydroxyl functional groups dominate the basal planes, a finding that is consistent with experiment. Individual sheets are wrinkled with an average root-mean-square deviation of 0.33 ± 0.04 Å. Hydrogen bonding between hydroxyl groups and between hydroxyl and epoxide groups has significant impact on the stability of many structures. Molecular dynamics simulations, guided by forces from electronic structure calculations, were performed to examine the behavior of GO when heated to room (300 K) and thermal exfoliation (1323 K) temperatures. Hydrogen-transfer reactions that catalyze the migration of epoxide groups were observed at both temperatures. At 1323 K, the evolution of CO was also observed, and the mechanisms for this process have been elucidated. This process provides a plausible explanation of the source of the 30% carbon mass loss that occurs during the experimental thermal exfoliation of GO. The mechanical properties of GO were examined and compared to those of graphene. Although significantly weaker in tensile deformation than graphene (fracture stress = 116 GPa), GO (fracture stress = 63 GPa) potentially has great strength provided it does not contain large holes. An epoxide line defect, recently reported as playing an important role in the failure of oxidized graphene, was also examined. The observed very large fracture stress (97 GPa) suggests that this structure does not play a major role in the fracture process.