Role of Long-Range Electrostatic Interactions and Local Topology of the Hydrogen Bond Network in the Wettability of Fully and Partially Wetted Single and Multilayer Graphene

We report the wetting behavior of graphitic surface-water interfaces through the calculation of the local stress tensor based on the Irving-Kirkwood-Noll theory using detailed atomistic molecular dynamics simulations. We compare the interfacial properties of fully wetted and partially wetted graphene (i.e., in contact with water on one side and vacuum on the other) and observe that the wettability is the result of a fine balance between van der Waals (vdW) and electrostatic interactions. Such a balance is partially perturbed in the case in which graphene is in contact with water on one side and with vacuum on the other. In this scenario, the presence of vacuum and the intrinsic hydrophobic nature of graphene cause water molecules in the proximity of the surface to rearrange the network of hydrogen bonds dominated by pentagonal rings that allow for enhanced packing and diffusion. Our analyses indicate that the surface tension of the fully wetted graphene layers is ca. 8 mNm-1 lower than that of the graphene layers wetted on only one side and this difference only mildly decreases upon adding graphene layers. We rationalize these observations by investigating how the number of graphene layers affects the topology of the hydrogen bond network in the proximity of the graphene surface in both systems. We find that water molecules on one side of the graphene layers in the fully wetted system interact with the water molecules on the other side creating a more stable hydrogen bond network. The investigation of the wettability of graphene and graphite is an important aspect for predicting the behavior of aqueous solutions under nanoconfinement, the permeability of porous materials, the interactions among graphitic surfaces, and their dispersion in aqueous environments. Therefore, our results can be applied to interface-related phenomena to better understand the interface where the local energy varies at the nanoscale.