Impact of Edge Groups on the Hydration and Aggregation Properties of Graphene Oxide.

Molecular dynamics simulations were used to describe and quantify the role of edge groups on the hydrating properties of graphene oxide (GO). For this, six different oxygen concentrations were investigated, and in four of them, carboxyl groups were present. Structural analysis indicates a greater probability for the water solvation around the GO edges in detriment of the region of its basal plane, while hydrogen bonding analyses indicates that edge groups are very expressive, participating in about 60% of the total number of bonds. The impact of this bond network formed by edge groups is rationalized in energetic and thermodynamic terms. The resulting hydrophilicity observed, as expected, is of electrostatic origin and has a larger contribution from the edge groups that varies from 22 to 57% depending on the concentration. Hydration free energy and potential of mean force calculations support these findings. It was observed that the edge groups contribute up to 51% of the total hydration-free energy and that the PMF indicates the tendency for spontaneous aggregation at all investigated concentrations, being lower the higher the concentration of oxygen.