Computer Simulation Study of the Diffusion of Water Molecules Confined in Silica Gel

Abstract

The molecular dynamics simulations are used to study the dynamic properties of SPC/E water molecules confined in silica gel. The model proposed in this study covers three main features that characterize systems of that kind: the excluded volume due to the substrate presence, strong attraction between pore surface and water molecules, randomness of confinement structure. The gel-like structure is modelled as an array of silica composite spheres that are randomly dispersed in volume. Therefore, the spherical SiO 2 composite bearing silanol groups on the surface is designed as an element of the porous medium of silica gel. The diffusion coefficients of water molecules are calculated at different temperatures and water densities. To illustrate the model proposed and the behavior of molecules near the pore surface, several snapshots are presented.

Self-diffusion coefficient of bulk and confined water: a critical review of classical molecular simulation studies

“…Several works use silica as confining material to study water dynamics due to this mineral's importance in catalysis and separation technology. Either as parallel planes or cylindrical pores, self-diffusion of water was analysed to assess water behaviour with changes in pore size (Zhang et al [237], Renou et al [238], Dickey and Stevens [239]), temperature (Ishikawa et al [240], Patsahan and Holovko [241]), surface composition (Siboulet et al [242], Jeddi and Castrillón [243], and Lerbret et al [244]), and water content (Spohr et al [223]). The results show that, due to its hydrophilic nature, silica has a strong interaction with water which significantly decreases the diffusion coefficient near the surface due to partial adsorption of water layer near the walls.…”

“…This effect was also noticed for higher temperatures. The diffusion coefficient increases with temperature, hydration, and with pore size, but decreases with density (Patsahan and Holovko [241]).…”