Water-Lubricated CO₂ and CH₄ Transport in Crystalline Silica Mesopores: A Molecular Dynamics Study

In this study, we use molecular dynamics simulation to study slippage behaviors of pressure-driven CO2 and CH4 flows with water films in β-cristobalite mesopores. Significant differences in water-induced enhancement in gas slippage are observed in comparison to pure CO2 and CH4 flows: the presence of water films leads to a notable increase in slippage for CO2 flow, whereas its effect on CH4 flow is insignificant. The water films on surface generally deplete gas molecules. The density peak significantly decreases in the CO2 adsorption layer, whereas the CH4 adsorption layer shows a negligible density change. Water molecules tend to accumulate at the center of surface ring structures, forming strong hydrogen bonds with the surface hydroxyl groups parallel to surface. As a result, water molecules fill the interfacial roughness by squeezing out CO2, which is supposed to penetrate into the ring structure. Therefore, CO2-averaged topologically accessible planes are less curved, which enhances the mobility of the interfacial CO2 molecules. However, CH4-averaged topologically accessible planes show an insignificant change with water films. Consequently, CO2 transport behaviors are more sensitive to the presence of water films on β-cristobalite surfaces. This study highlights the influence of water films on gas slippage, offering important insights into gas sequestration.