Rapid analysis of phase behavior with density functional theory. II. Capillary condensation in disordered porous media

For some time, there has been interest in understanding adsorption and capillary condensation in disordered porous media from a molecular perspective. It has been documented that the free energy landscape in these systems is complex with many metastable states. In this paper we explore the complexity of adsorption and capillary condensation in several simple models of disordered porous media constructed with parallel cylindrical fibers. We present nonlocal density functional theory calculations on a Lennard-Jones model fluid adsorbing in these porous materials coupled with the arclength continuation and phase transition tracking algorithms we presented in Paper I of this series. The arclength continuation algorithm allows us to trace out all the possible states between vapor-filled and liquid-filled pores. We find that capillary condensation is likely to occur in stages at high temperatures and strong wall-fluid interactions while the condensation occurs as a single transition at low temperatures and weak wall-fluid interactions. This paper also compares the extent of hysteresis on adsorption and desorption, discusses the validity of the Gibbs adsorption equation, and considers application of simple pore models in predicting the complexity of phase diagrams in disordered porous media. (C) 2003 American Institute of Physics.