title: Condensation of Methane in the Metal-Organic Framework IRMOF-1: Evidence for Two Critical Points.
abstract: Extensive grand canonical Monte Carlo simulations in combination with successive umbrella sampling are used to investigate the condensation of methane in the nanoporous crystalline material IRMOF-1. Two different types of novel condensation transitions are found, each of them ending in a critical point: (i) a fluid-fluid transition at higher densities (the analog of the liquid-gas transition in the bulk) and (ii) a phase transition at low densities on the surface of the IRMOF-1 structure. The nature of these transitions is different from the usual capillary condensation in thin films and cylindrical pores where the coexisting phases are confined in one or two of the three spatial dimensions. In contrast to that, in IRMOF-1 the different phases can be described as bulk phases that are inhomogeneous due to the presence of the metal-organic framework. As a consequence, the condensation transitions in IRMOF-1 belong to the three-dimensional (3D) Ising universality class.
authors.affiliation: Institute for Theoretical Physics II, University of Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Höft
authors.affiliation: Institute for Theoretical Physics II, University of Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Horbach