The phase behaviour of a fluid in a slitlike pore with permeable walls

The confinement of a lattice fluid in a set of slitlike pores separated by semipermeable walls with a finite width has been studied. The walls are mod elled by a square-well repulsive potential with a finite height. The thermo dynamic properties and the phase behaviour of the system are evaluated by m eans of Monte Carlo simulations. For some states theoretical calculations h ave been made using a mean-field-type theory. These investigations confirm previous findings for confined Lennard-Jones fluids, obtained from a densit y functional approach. For intermediate and low potential barriers that sep arate the pores, the isotherms exhibit two hysteresis loops and the liquid- vapour coexistence curve divides into two branches describing condensation inside the pore and inside the permeable wall. These two branches are separ ated by a triple point. At temperatures lower than the triple point tempera ture, the condensation takes place instantaneously in both the pore and ins ide the permeable wall. It was found that when the temperature is scaled by the bulk critical temperature, the phase diagram emerging from this simple mean-field treatment is close to the phase diagram obtained from simulatio n.