Influence of Hydrated Silica Surfaces on Interfacial Water in the Presence of Clathrate Hydrate Forming Gases

We study the hydrated silica–water interface in the presence of methane or carbon dioxide gas with molecular dynamics simulations. The simulations are performed with a limited amount of water, which forms a meniscus between two hydroxylated silica surfaces separated by 40 to 60 Å. Simulations were performed with the remaining space of the simulation cell left empty or filled with different numbers of methane or carbon dioxide gas molecules. The meniscus is used to determine the contact angle between water and silica in the absence and presence of the gases. The distribution profiles of the water and gas phases are determined over the duration of the simulation. The water number density in the layers adjacent to the silica is higher, and these layers are more structured and less mobile compared with water layers far from the surface. Additionally, the concentrations of the gases are significantly higher at the liquid and silica interfaces than in other locations in the gas phase. We speculate that the enhanced concentration of gases at the interface along with the extended contact area (curved meniscus compared with flat interface in the absence of silica surfaces) between water and guest molecules at the meniscus as well as lesser mobility of water molecules near the silica surface may provide a mechanism for the heterogeneous nucleation of the clathrate hydrate in water-wetting porous medium.