Elucidating the amphiphilic character of graphene oxide.

The amphiphilic character of graphene oxide was analysed in terms of its interfacial activities, using atomistic molecular dynamics. Graphene oxides at four different degrees of oxygenation were investigated considering both the effects of oxidation and carboxyl edge-functionalization. Solvation free energies are strongly negative and of increasing magnitude with the concentration for all systems, even in the toluene phase, indicating that GO presents a favourable solvation in both pure liquids as well as interfaces. The PMF results indicate that only the R20 system is slightly active at the water/vacuum interface, with a PMF minimum of about -2.6 kJ mol-1. Both analyses, free energy and PMF, indicate that all systems with higher oxygen concentrations have lower free energy in water than in toluene, while the R20 system opposes this tendency. Comparison between the reduced GOs (20%) shows that edge-functionalised systems were more active than basal-functionalized systems, indicating that oxygen concentration plays a more relevant role than the distribution of functional groups.