Fluid adsorption in linear pores: a molecular simulation study of the influence of heterogeneities on the hysteresis loop and the distribution of metastable states

Porous materials are known to adsorb fluid and can be characterised by measurement of fluid adsorption isotherms. Many nanoporous materials exhibit linear pores such as MCM-41 and porous silicon or alumina. In such systems, data adsorption analysis is considered to be straightforward within the approximation of independent domains. This article, which reviews previous molecular simulation works, aims at showing that the presence of heterogeneities within the pores actually invalidates this hypothesis, with consequences for porosity characterisation. To enlighten the effects, starting from perfect cylinders, the number of heterogeneities is progressively increased, up to large numbers, for which specific simulation tools are used to take into account the interdependence between the domains. The adsorption/desorption isotherms are calculated and correlated to the appearance of an exponentially large number of metastable states.