Dynamics of water trapped in transition metal oxide-graphene nano-confinement

Motivated by practical implementation of transition-metal oxide-graphene heterostructures, we use all atom molecular dynamics simulations to study dynamics of water in a nano slit bounded by a transition metal oxide surface, namely, TiO₂termination of SrTiO₃, and graphene. The resultant asymmetric, strong confinement produces square ice-like crystallites of water pinned at TiO₂surface and drives enhanced hydrophobicity of graphene via the proximity effect to the hydrophilic TiO₂surface. This importantly brings in dynamic heterogeneity, both in translational and rotational degrees of freedom, due to coupling between the slow relaxing, strongly adsorbed water layer at the hydrophilic oxide surface, and faster relaxation of subsequent water layers. The heterogeneity is signalled in the ruggedness of the effective free energy landscapes. We discuss possible implications of our findings in drug delivery.