title: Critical energy barrier for capillary condensation in mesopores: Hysteresis and reversibility.
abstract: Capillary condensation in the regime of developing hysteresis occurs at a vapor pressure, Pcond, that is less than that of the vapor-like spinodal. This is because the energy barrier for the vapor-liquid transition from a metastable state at Pcond becomes equal to the energy fluctuation of the system; however, a detailed mechanism of the spontaneous transition has not been acquired even through extensive experimental and simulation studies. We therefore construct accurate atomistic silica mesopore models for MCM-41 and perform molecular simulations (gauge cell Monte Carlo and grand canonical Monte Carlo) for argon adsorption on the models at subcritical temperatures. A careful comparison between the simulation and experiment reveals that the energy barrier for the capillary condensation has a critical dimensionless value, Wc (*) = 0.175, which corresponds to the thermal fluctuation of the system and depends neither on the mesopore size nor on the temperature. We show that the critical energy barrier Wc (*) controls the capillary condensation pressure Pcond and also determines a boundary between the reversible condensation/evaporation regime and the developing hysteresis regime.
authors.affiliation: Department of Chemical Engineering, Kyoto University, Kyoto 615-8025, Japan.
authors.forename: Tatsumasa
authors.initials: T
authors.lastname: Hiratsuka
authors.affiliation: Department of Chemical Engineering, Kyoto University, Kyoto 615-8025, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Tanaka
authors.affiliation: Department of Chemical Engineering, Kyoto University, Kyoto 615-8025, Japan.
authors.forename: Minoru T
authors.initials: MT
authors.lastname: Miyahara