Simulations were made of water-filled silica nanopores, such as those that occurred in ordered oxide ceramics, controlled pore glasses (Vycor), mesoporous silica, bioglasses and hydrous silica gel coatings of weathered minerals and glasses. The simulations overlapped the range of pore diameters (1 to 4nm) where confinement caused the disappearance of bulk-liquid-like water. In ≥2nm diameter pores, the silica surface carried three statistical monolayers of density-layered water, the interfacial water structure was independent of confinement or surface curvature, and bulk liquid-like water existed at the center of the pore (contradicting the assumptions used in most previous neutron diffraction studies and in some molecular dynamics simulation studies of silica nanopores). In 1nm-diameter pores, bulk liquid-like water did not exist and the structural properties of interfacial water were influenced by confinement. The predicted water diffusion coefficients in 1 to 4nm diameter pores agreed with quasi-elastic neutron scattering data and were roughly consistent with a very simple core-shell conceptual model in which the first statistical water monolayer was immobile and the rest of the pore water diffused as rapidly as bulk liquid water.

Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores. Bourg, I.C., Steefel, C.I.: Journal of Physical Chemistry C, 2012, 116[21], 11556-64