Adsorption and capillary condensation transitions on nanostructures: Mechanisms of atomic evolution and meniscus growth

Abstract

To investigate the kinetic process from adsorption to capillary condensation within nanostructures, a serious of atomic-scale simulation is devoted to this work. The atomic behavior reveals that with the occurrence of capillary condensation, a liquid meniscus is formed at the base of the nanopillars, accompanied by a rapid increase in the formation of multi-molecular clusters. The critical adsorption amount required for the initiation of capillary condensation is related to the saturation adsorption capacity on a bare surface. In adsorption stage, the adsorption capacity shows a linear increase over time. Meanwhile during condensation stage, the condensation rate within irregular nanostructure space is associated with the curvature radius of meniscus. Higher condensation rates are observed between adjacent pillars compared to other positions. To elucidate the relationship between the capillary condensation rate and vapor pressure, nanopillar spacing, and surface wettability, the Hertz-Kundsen equation is employed. The increase in capillary condensation capacity with pressure is positively correlated with spacing between nanopillars, regardless of surface wettability. No blocking effects are observed and a hysteresis loop is presented within mesoporous irregular space in this study. The width of the hysteresis loop is influenced by the nucleation barrier, which increases with larger spacing or lower surface wettability.