Grand canonical Monte Carlo (GCMC) and canonical ensemble molecular dynamics (NVT-MD) simulations were performed to investigate water adsorption properties in mesoporous silica thin films. The effect of pore radius on the adsorption properties was assessed using two models of mesoporous silica thin films having different pore radius and film thickness (1.38 and 5.66 nm in Model 1, respectively, and 1.81 and 7.30 nm in Model 2, respectively). In the simulations, a water adsorption layer or water menisci were formed in a mesopore accompanying the growth or shrinkage of stable adsorption layers on the upper and lower surfaces. The stable two water adsorption layers were formed on the pore surface in both models. The curvature radius of a water meniscus decreased monotonically and approached a constant value. In addition, NVT-MD simulations were performed to investigate the kinetics of water uptake into a model of mesoporous silica thin film having a radius and thickness of 1.38 and 7.93 nm (Model 3). The calculation results showed that the kinetics of water uptake depended on the number of water molecules and there were two different transport mechanisms in the pore. One was diffusion of water along the pore surface, and the other was capillary rise of liquid water.
A Hierarchical Study on Load/Release Kinetics of Guest Molecules into/from Mesoporous Silica Thin Films
