Correlation between asymmetric profiles in slits and standard prewetting lines

Abstract

The adsorption of Ar on substrates of Li is investigated within the framework of a density functional theory which includes an effective pair potential recently proposed. This approach yields good results for the surface tension of the liquid-vapor interface over the entire range of temperatures, T , from the triple point, Tt, to the critical point, Tc. The behavior of the adsorbate in the cases of a single planar wall and a slit geometry is analyzed as a function of temperature. Asymmetric density profiles are found for fluid confined in a slit built up of two identical planar walls leading to the spontaneous symmetry breaking (SSB) effect. We found that the asymmetric solutions occur even above the wetting temperature Tw in a range of average densities ρ * ssb1 ≤ ρ * av ≤ ρ * ssb2 , which diminishes with increasing temperatures until its disappearance at the critical prewetting point Tcpw. In this way a correlation between the disappearance of the SSB effect and the end of prewetting lines observed in the adsorption on a one-wall planar substrate is established. In addition, it is shown that a value for Tcpw can be precisely determined by analyzing the asymmetry coefficients.

Confinement of Ar between two identical parallel semi-infinite walls

“…In spite of the fact that there is a general idea that a connection exists between the SSB effect and nonwetting, we found, by contrast, that the SSB behavior extends above the wetting temperature. The adsorption of Ar on a single planar substrate of Li exhibits a prewetting line which extends over about 10 K from T w = 110 to T cpw Շ 119 K; 15,20 this feature allows for a detailed study of asymmetric solutions above T w .…”

“…In order to get a deeper insight of the SSB effect, we analyzed the correlation between the values of T sb obtained in the present work and the T cpw determined in a recent study of the adsorption of Ar on single walls performed by utilizing exactly the same MFA. 15,20 The paper is organized in the following way. The theoretical background is summarized in Sec.…”

“…Preliminary results for Ne and Ar confined in such a type of slits have recently been reported elsewhere. 14,15 In the present work we shall report on a rather comprehensive investigation about the behavior of Ar confined in slits of two identical planar walls. The calculations have been carried out within the density functional ͑DF͒ theory.…”

“…This effective potential gives a satisfactory description of the surface tension of the liquid-vapor interface, ␥ lv , of Ar at coexistence for temperatures in the whole range T t ↔ T c . 15,20 The behavior of the systems was studied as a function of the width of the slits. It was found that in the cases of alkali metals ͑Cs, Rb, K, Na, and Li͒ the SSB effect occurs at temperatures lower than certain critical values T sb .…”

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

“…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.…”