Monte Carlo simulation test of pore blocking effects

We present a Monte Carlo (MC) simulation study of capillary condensation and desorption in a spherical cavity connected with the bulk phase by cylindrical necks of smaller diameter. We confirm two mechanisms of spontaneous evaporation from the cavity and, correspondingly, two types of adsorption hysteresis, which depend on the relation between the sizes of the cavity and the connecting pores. When the necks are sufficiently wide, evaporation from the cavity is determined by the conditions of evaporation from the neck. This is a classical ink-bottle or pore blocking effect: desorption from the cavity is controlled by the size of the neck. When the necks are narrow, evaporation from the cavity is determined by the conditions of cavitation in the stretched metastable liquid and thus does not depend on the size of blocking pores. MC simulations were performed for a Lennard-Jones fluid at the normal boiling temperature mimicking sorption of nitrogen at 77.4 K in silica mesopores. The simulation results agree with the density functional theory of capillary condensation hysteresis in spherical cavities and the experimental data reported recently (Ravikovitch, P. L; Neimark, A. V. Langmuir 2002, 18, 1550 and 9830).