Reentrant filling transitions in Lennard-Jones fluids confined in nanoscopic slit-like pores.

The reentrant first-order pore filling transition in a Lennard-Jones (LJ) fluid confined between the parallel (100) planes of the face centered cubic (fcc) crystal is studied by means of Monte Carlo simulations in the canonical as well as grand canonical ensembles. Slit-like pores of the width allowing for the formation of only three adsorbate layers are used. It is demonstrated that the reentrant first-order pore filling transition, associated with the condensation of the middle layer, appears only when the height of the potential barrier between adjacent sites, V(D), fulfills a condition V(D) in [V(D,min),V(D,max)]. The lower limit of V(D) (V(D,min)) is primarily determined by the stability of commensurate monolayers formed at both pore walls during the first step of adsorbate condensation, while the upper limit of V(D) (V(D,max)) depends on the stability of the commensurate three-layer structure. It is also shown that both the misfit between the size of adsorbed atom and the surface lattice as well as the pore width have a great influence on the phase behavior of confined fluids. Moreover, the effects of the phase shift between the confining lattices on the reentrant first-order filling transition are discussed.