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

Abstract

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.

Structure and solvation forces in confined films of alkanes

“…Theoretical work and computer simulations of Lennard-Jones fluids and hard spheres show that the oscillatory solvation force originates from the stratification or ordering of the molecules in layers when the fluid is confined by the surfaces [5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Confined thin films of linear and branched alkanes

“…Theoretical work and computer simulations of Lennard-Jones fluids and hard spheres show that the oscillatory solvation force originates from the ordering of the molecules in layers when the fluid is confined by the surfaces. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] For finite ranged wall-fluid and fluid-fluid potentials, the solvation force shows an oscillatory behavior at high liquid densities and a pure exponential decay at low liquid densities, provided the liquid is sufficiently far from the critical point and no phase transition will occur.…”

On the question of whether lubricants fluidize in stick–slip friction

“…Such solid sliding is a major cause of frictional dissipation, and can persist even in the presence of lubricants (1). At a nanotribological level, surface force balance (SFB) measurements, supported by theory and computer simulations, have shown that when simple organic liquids are confined between atomically smooth, solid (mica) surfaces to films thinner than some six to eight molecular layers, they may become solid-like, and are often layered (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). Subsequent sliding of the surfaces across such films when they are subjected to shear may then take place via stick-slip motion (15,16).…”