Effect of the reservoir size on gas adsorption in inhomogeneous porous media

Edouard Kierlik (1) , Joël Puibasset (2) , Gilles Tarjus (1, 3)

1 LPTMC - Laboratoire de Physique Théorique de la Matière Condensée
2 CRMD - Centre de Recherche sur la Matière Divisée
3 LPTL - Laboratoire de Physique Théorique des Liquides

We study the influence of the relative size of the reservoir on the adsorption isotherms of a fluid in disordered or inhomogeneous mesoporous solids. We consider both an atomistic model of a fluid in a simple, yet structured pore, whose adsorption isotherms are computed by molecular simulation, and a coarse-grained model for adsorption in a disordered mesoporous material, studied by a density functional approach in a local mean-field approximation. In both cases, the fluid inside the porous solid exchanges matter with a reservoir of gas that is at the same temperature and chemical potential and whose relative size can be varied, and the control parameter is the total number of molecules present in the porous sample and in the reservoir. Varying the relative sizes of the reservoir and the sample may change the shape of the hysteretic isotherms, leading to a ``reentrant'' behavior compared to the grand-canonical isotherm when the latter displays a jump in density. We relate these phenomena to the organization of the metastable states that are accessible for the adsorbed fluid at a given chemical potential or density.

Mots clés: Hysteresis; Molecular simulations; Disordered mesoporous material; Adsorption; Metastable states

Domaines: Mécanique statistique [cond-mat.stat-mech]; Systèmes désordonnés et réseaux de neurones [cond-mat.dis-nn]; Physique Générale [physics.gen-ph]

Edouard Kierlik, Joël Puibasset, Gilles Tarjus. Effect of the reservoir size on gas adsorption in inhomogeneous porous media. 2008. ⟨hal-00321228⟩