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

• Published in: Journal of physics. Condensed matter Vol. 21; no. 15; pp. 155102 - 155102 (16)
• Main Authors: Kierlik, E, Puibasset, J, Tarjus, G
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 15.04.2009; Institute of Physics
• Subjects: Chemistry; Colloidal state and disperse state; Condensed Matter; Exact sciences and technology; General and physical chemistry; Other; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Physics; Mean field approximation; Adsorption isotherm; Coarse graining model; Porous material; Mesoporosity; Gas solid adsorption; Grand canonical ensemble; Local field; Metastable state; Atomistic model; Size effect; Density functional method; Chemical potential
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/21/15/155102

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 within experimental range may change the shape of the hysteretic isotherms, leading to a 're-entrant' 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.