Influence of system size on the properties of a fluid adsorbed in a nanopore: Physical manifestations and methodological consequences.

Hysteresis and discontinuities in the isotherms of a fluid adsorbed in a nanopore in general hamper the determination of equilibrium thermodynamic properties, even in computer simulations. A way around this has been to consider both a reservoir of small size and a pore of small extent in order to restrict the fluctuations of density and approach a classical van der Waals loop. We assess this suggestion by thoroughly studying through Monte Carlo simulations and density functional theory the influence of system size on the equilibrium configurations of the adsorbed fluid and on the resulting isotherms. We stress the importance of pore-symmetry-breaking states that even for modest pore sizes lead to discontinuous isotherms and we discuss the physical relevance of these states and the methodological consequences for computing thermodynamic quantities.

Influence of reservoir size on the adsorption path in an ideal pore.

We consider the influence of the relative size of the gas reservoir on the states visited by a simple fluid adsorbed in a nanopore of ideal geometry (a slit). We focus on the intermediate states that appear in between the main hysteresis branches comprising gaslike and liquidlike states and we study the adsorption and desorption paths actually followed by the system as one changes the reservoir size. We find that these paths may display discontinuous sections associated with transitions between different nonuniform states. We also discuss the stability of the states in such situations.