The interfacial dynamics of water sandwiched between graphene sheets are governed by the slit width

Abstract

Atomic scale characterization and fluxional properties of water molecules in the vicinity of the graphene interface is carried out using molecular dynamics (MD) simulations. The structural properties of proximal water molecules near the graphene interface are strongly correlated to their vibrational densities of states while being studied as a function of the slit width of the graphene sheets. Our simulations indicate that the local orientation, ordering and solvation dynamics of interfacial water molecules are a strong function of the graphene slit width. Systematic trends in libration, bending, and stretching bands are correlated with local ordering of water molecules and hydrogen-bonding network. Smaller blue shifts in the intermolecular O…O…O bending mode and larger blue shifts in the O…O intermolecular stretching modes of water molecules are observed for strongly confined water molecules in comparison to bulk water, which is attributed to the interfacial proximity effects resulting in the restricted transverse oscillations of confined water. The O―H stretching band is red-shifted for confined water in comparison to bulk water whereas the libration and bending bands for interfacial water are blue shifted with respect to bulk water. The observed frequency shifts are a consequence of the distortion of the tetrahedral order in confined water caused by lateral diffusion being reduced and also by changes in the distribution of hydrogen bonds. These simulations suggest that the extent of the shifts of confined water in comparison to bulk water are due to the proximity from the hydrophobic surface, their local confinement and hydrogen bonding status.