On the structure of Lennard-Jones fluids confined in crystalline slitlike pores

Abstract

The structure of Lennard-Jones fluid in slitlike pores with crystalline walls is studied by canonical ensemble Monte Carlo simulation method. It is assumed that each pore wall is a perfect (100) plane of the face centered cubic crystal. The effects of the wall–wall separation on the ordering and freezing of a confined fluid are investigated for a series of systems with the density corresponding to the two completely filled layers of commensurate c(2×2) phase. It is demonstrated that the structure of a solid phase very strongly depends on the pore diameter. Thus, the formation of partially filled film that spans the space between the both pore walls occurs only when the pore width is smaller than a certain value. For wider pores only two monolayers at each pore wall occur. Then, the formation of commensurate structures of square symmetry in each layer occurs only over certain ranges of the pore width, while for other pore widths, the incommensurate phases of hexagonal symmetry in each layer are formed. The melting of solid phases has been found to be either the first order or continuous transition. In particular, the first order melting transitions have been found to be accompanied by a change (decrease) in the number of adsorbate layers within a pore. We have been able to single out seven regions of the pore width, which exhibit different structure and properties of adsorbed phases.