Refined kelvin theory for capillary condensation under extreme confinement

Capillary condensation is pervasive in nature and plays a pivotal role in technological applications. A comprehensive understanding and analytical description of capillary condensation under extreme confinement remains elusive. Here, we propose a generalized form of the Kelvin equation, in which the size effect of the solid–liquid interface energy is theoretically interpreted by the disjoining pressure. Our model reliably predicts the onset of capillary condensation of methane in molecular dynamics simulations. These findings not only provide a theoretical insight into capillary condensation, but also remedy the validity of the Kelvin equation down to several angstroms.