Adsorption∕desorption hysteresis of simple fluids confined in realistic heterogeneous silica mesopores of micrometric length: A new analysis exploiting a multiscale Monte Carlo approach

Abstract

Adsorption/desorption isotherms in porous materials are commonly used for characterization. In order to analyze the data, accurate calculations of fluid adsorption in various complex pore models are required. The reversible, low adsorption portion of the isotherm is generally well described by molecular simulation, since the relevant fluid/substrate interactions are described at molecular level. This molecular approach is, however, ineffective in the hysteresis region because the large scale spatial distribution of heterogeneities in the pore network is beyond the computer capabilities. On the other hand, coarse grained approaches are more suited to take into account this porous network complexity at large scale and discuss the hysteresis nature, but the molecular description is lost. In this paper, a multiscale approach is introduced which allows both a molecular description of fluid/substrate interactions, and taking into account the connectivity between the various domains in a porous material. The case of argon confined in heterogeneous tubular silica mesopores (MCM-41 or oxidized porous silicon) is considered. Comparison with the simple independent domain theory shows the strong influence of quenched disorder. It is also shown that the independent pore model significantly overestimates the hysteresis width. The effect of pore ends open at only one or at both ends is addressed.