Phase behaviour of a Lennard-Jones fluid in a pore with permeable walls ofa finite thickness: a density functional approach

A confinement of a Lennard-Jones fluid in a system of slitlike pores separa ted by semipermeable walls of a finite width is studied. The walls are mode lled by square-well repulsive potential wells. The structure of the confine d fluid is investigated by means of a density functional method. For high p otential barriers separating the pores, the phase behaviour of the system i s similar to that for a single slitlike pore with impenetrable walls. For i ntermediate and low potential barriers the system shows different phase beh aviour. Within some temperature range the isotherms exhibit two hysteresis loops, which characterize the condensation of the fluid in different parts of the system, namely in the pore and inside the semipermeable walls. The s ystems characterized by low and intermediate potential barriers exhibit the triple point, such that at temperatures below that triple point the conden sation instantaneously takes place in both the pore and inside the permeabl e wall.