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In this study, the effect of interfacial interaction between solvent and sheets on the exfoliation of sulfur-doped reduced graphene oxide (SrGO) sheets was studied, using molecular dynamics simulations. Four organic solvents of toluene, tetrahydrofuran, N-methyl-2-pyrrolidone, and sulfolane, were used in this simulation. An insertion simulation considering the size effect of insertion molecules was used to determine the insertion efficiency of the solvent molecules. The insertion efficiency of toluene was the best among the four solvents due to the influence of the effective thickness of the solvent. An exfoliation simulation considering electrostatic interaction was conducted to evaluate the exfoliation efficiency of the SrGO sheets. Unlike the insertion efficiency case, the sulfolane was found to have the best exfoliation efficiency among the four solvents, due to the strong electrostatic repulsion and weak attractive energy between the SrGO sheets. The exfoliation efficiency of the SrGO sheets was improved by increasing the sulfur content and the ratio of the thiol type to the total number of sulfur-doped groups. These results reveal that decreasing the attractive energy and increasing the electrostatic repulsion between the solvent and SrGO sheets are a useful way to improve the exfoliation efficiency of SrGO sheets.

In this study, the influences of the carboxyl functionalization of intercalators on exfoliation of graphite oxide were analyzed using molecular dynamics (MD) simulations. Molecular models of four-layered graphene oxide (GO) sheets, four different solvents (ethanol, dimethylformamide, tetrahydrofuran, and N-methyl-2-pyrrolidone), and four different intercalators (anthracene, 2-anthracenecarboxylic acid, 2,3-anthracenedicarboxylic acid, and 2,6-anthracenedicarboxylic acid) were used in the MD simulations. A separation simulation of GO sheets was performed to determine the point at which the GO sheets begin to exfoliate. An insertion simulation was used to obtain the minimum kinetic energy required for exfoliation and to calculate GO-solvent and GO-intercalator interaction energies. As the simulation result, GO-solvent and GO-intercalator interactions affected the minimum kinetic energy required for exfoliation. Having more carboxyl functional groups on the anthracene improved both the GO-intercalator interaction and the efficiency of the intercalators during exfoliation. These results reveal that increasing the interaction energy between the GO sheets and the insertion molecules is an efficient way to improve the performance of the solvents and the intercalators for the exfoliation of GO sheets.