Fluids in micropores. I: Structure of a simple classical fluid in a slit-pore

• Published in: The Journal of chemical physics 1987-11, Vol.87 (9), p.5464-5476
• Main Authors: SCHOEN, M, DIESTLER, D. J, CUSHMAN, J. H
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.453665

Equilbrium properties of a rare-gas fluid contained between two parallel fcc(100) planes of rigidly fixed rare-gas atoms were computed by means of the grand-canonical ensemble Monte Carlo method. The singlet distribution function ρ(1), and the pair-correlation function g(2) in planes parallel to the solid layers, indicate that the structure of the pore fluid depends strongly on the distance h between the solid layers. As the separation increases from less than two atomic diameters, successive layers of fluid appear. The transitions between one and two layers and three and four layers are especially abrupt and are accompanied by changes in the character of g(2) from dense fluid-like to solid-like. Long-range, in-plane order in the fluid layers diminishes with increasing h, but is still evident in the contact layer (i.e., that nearest the solid layer) at h=16.5 atomic diameters, the largest separation considered. The structure of the contact layer reflects the solid-layer structure and differs significantly from the adjacent inner fluid layers, whose g(2) resembles that of the corresponding bulk fluid. Decreasing the density of atoms in the solid layers blunts the peaks in ρ(1) and g(2), although even for the least dense layer considered the contact layers of fluid evince long-range, in-plane order. Replacing the discrete pairwise fluid–solid interactions with the mean field resulting from smearing the solid atoms over the plane of the solid layer destroys the ‘‘phase transitions’’ and the associated long-range, in-plane order.