Hydration Peculiarities of Graphene Oxides with Multiple Oxidation Degrees

Hydration properties of graphene oxide (GO) are essential for most of its potential applications. In this work, we employ atomistic molecular dynamics simulations to investigate seven GO compositions with different levels of oxygenation. Two atomic charge models for GO are compared: (1) sp2 carbons are purely Lennard-Jones sites; (2) sp2 carbon charges are consistent with the CHELPG scheme. Structural properties were found to depend insignificantly on the charge model, whereas thermodynamics appeared very sensitive. In particular, the simplified model provides systematically stronger GO/water coupling, as compared to the more accurate model. For all GO compositions, hydration free energies are in the range -5 to -45 kJ mol-1 indicating that hydration is thermodynamically favorable even for modest oxidation degrees, thus differing drastically from the case of pristine graphene and graphite. The results and discussion presented hereby provide a physical background for modern applications of GO, e.g. in electrodes of supercapacitors and inhibitors in processes involving biological molecules.