Electric Double Layer at the Rutile (110) Surface. 3. Inhomogeneous Viscosity and Diffusivity Measurement by Computer Simulations

Molecular dynamics simulations were conducted to characterize the dynamic properties of the interface between aqueous electrolyte and the (110) surface of rutile (α-TiO₂). For the first time, the inhomogeneous viscosity of water (at liquid density) in a slab formed by two rutile surfaces was determined computationally. The viscosity and diffusivity profiles show three different regions as a function of distance from the surface: (i) a region of two adsorbed layers of water molecules with apparently infinite viscosity and zero diffusivity, (ii) an interfacial inhomogeneous region consisting of additional 2-3 layers, and (iii) bulk-liquid behavior recovered as close as 15 Å from the surface. The second layer of adsorbed water molecules becomes more loosely bound to the surface with increasing temperature up to 523 K. Our results supplement our previous structural findings and confirm that not only the structural but also the dynamic properties of the interface indicate that bulk properties are recovered within about 15-20 Å from the surface.