Permeation dynamics of small molecules through silica membranes: molecular dynamics study

The permeation of He, CO₂, and N₂ through a thin silica membrane was investigated using molecular dynamics. The permeance of He follows Knudsen flow. The permeation of CO₂ is higher than the estimated value from Knudsen theory. Inside the pore, CO₂ tends to be parallel to the pore wall. This orientation is suitable for diffusion. In contrast, N₂ shows lower permeance compared to the value from Knudsen theory. The molecules present perpendicular orientations inside the pore wall, which reduces their diffusion. In mixed CO₂/N₂ gas simulation, the selective permeation of CO₂ relative to N₂ was observed.