Confinement of Ar between two identical parallel semi-infinite walls

Abstract

The confinement of Ar in planar slits of two identical parallel semi-infinite walls of alkali metals, alkaline-earth metal Mg, and CO 2 is investigated within the framework of the density functional theory. It is assumed that ͑1͒ the fluid atoms interact via a recently proposed effective attractive pair potential with strength, f f , which reproduces the experimental data of the surface tension of the liquid-vapor interface at the bulk coexistence curve, and ͑2͒ the adsorption on the walls is described by ab initio potentials characterized by a well depth, W sf . In this way the systems were studied in the framework of a realistic approach. We found that for small coverages, the slit is always filled by forming two symmetric vapor films, one at each wall. For increasing coverage the behavior depends on the ratio W sf / f f and the temperature T. In the case of alkali metals, we found at the triple point, T t , of the adsorbate a regime of average density av ‫ء‬ in which the ground state exhibits asymmetric density profiles, leading to the so-called spontaneous symmetry breaking ͑SSB͒ effect. The SSB appears at an average density sb1 ‫ء‬ and disappears at a higher average density sb2‫ء‬ . When T is increased, the range of densities sb1 ‫ء‬ Յ av ‫ء‬ Յ sb2 ‫ء‬ diminishes and eventually the SSB disappears at a critical temperature, T sb , which coincides with the critical prewetting temperature T cpw observed in the adsorption on a single wall. For T Ͼ T cpw the slit is filled symmetrically up to the phase transition to capillary condensation. All these features are examined as a function of the strength of the substrate and the width of the slit. Furthermore, no SSB effect was found for Mg and CO 2 .

Statistical mechanics of fluids confined by polytopes: The hidden geometry of the cluster integrals

“…for only one side (the n-th). Hence, the shape of U(r, ς) ∩ A is determined by the one dimensional position variable r (1) = d(r, ∂A 1,n ) = z, and then, g(r) = g 1 (r) = g 1 r (1) = g 1 (z). vertex (the n-th).…”

“…Besides, from Corollary 3 and using Eqs. (1) to (7) we obtain the explicit form of Ω and P W in terms of X. The expressions for S, U and the EOS in this GCE are easily found by replacing F with Ω in Eqs.…”

“…They constitute a prototypical inhomogeneous system which occupies a small region of the space and may involve a small number of particles. It is well known that the spatial distribution of a fluid confined in a small pore may follow or not the symmetry of the cavity [1,2], and that its properties may be strongly influenced by the geometry of the container. To study the thermodynamic properties of these systems it is customary to introduce several strong assumptions or approximations that simplify the analysis.…”

Full correspondence between asymmetric filling of slits and first-order phase transition lines

“…In a recent simultaneous study of wetting and filling we found some evidence for a correspondence between T cpw of a single PW line obtained in the case of one wall adsorption and T sb determined for the disappearance of SSB in slits. 10,12 Moreover, Rżysko et al 15 have also suggested that the SSB is a result of the first-order nature of the transition. If the transition were of the second order, SSB would not occur.…”

“…In most of the studies, a Canonical Ensemble (CE) statistics was applied to examine filling of closed slits with classical gases. [6][7][8][9][10][11][12] Recently, Berim and Ruckenstein 13 have also investigated the occurrence of SSB for quantum 4 He confined in planar slits. Furthermore, this kind of asymmetric solutions were also found by Merkel and Löwen in open systems.…”