Density profiles of Ar adsorbed in slits of CO2: Spontaneous symmetry breaking revisited

Int. J. Bifurcation Chaos

Urrutia

2010

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A density functional formalism is applied to investigate the wetting behavior of Ne confined in slits composed of two parallel solid identical alkaline walls with increasing attractive strength leading to a variety of wetting situations. The study is performed over the complete range of temperature spanned from the triple point T t up to the critical one T c of Ne. Attention is paid to the slit's width. It was found that in the case of weaker substrates for temperatures below a certain critical T sb the density profiles corresponding to the lowest free energy are asymmetric, i.e. exhibit a spontaneous breaking of symmetry. For T > T sb the phenomenon of symmetry breaking disappears leading to a first-order phase transition.

Section: Introductionmentioning

confidence: 94%

Spontaneous Symmetry Breaking and First-Order Phase Transitions of Adsorbed Fluids

Int. J. Bifurcation Chaos

Urrutia

2010

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“…12 They analyzed a slit of width L =15 f f and stated that SSB occurs for temperatures below a critical value T sb = 106 K. In a revisited study of this system reported in Ref. 13, we found that the conditions for the occurrence of SSB had been fulfilled in Ref. 11 because the well depth of the s-f attraction was diminished by the presence of an extra hard-wall repulsion.…”

Section: Introductionmentioning

confidence: 99%

“…Since such a behavior was carefully discussed in previous works, 5,8,13 here we shall restrict ourselves to briefly outline the main features. When the liquid is adsorbed symmetrically like in the case of profile 3 in Fig.…”

Section: A Symmetry Of Density Profilesmentioning

confidence: 99%

Confinement of Ar between two identical parallel semi-infinite walls

The Journal of Chemical Physics

2010

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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 .

“…However, in practice, it is usual 7,8,35 to solve the adsorption problem by fixing n together with V and T, that is by applying the CE scheme, which is much easier to manage numerically than the GCE one. Notice that μ and n are conjugate Legendre variables.…”

Section: Canonical Ensemblementioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

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

2011

AIP Advances

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Adsorption on single planar walls and filling of slits with identical planar walls are investigated in the frame of the density functional theory. In this sort of slits the external potential is symmetric with respect to its central plane. Calculations were carried out by applying both the canonical and grand canonical ensembles (CE and GCE, respectively). The behavior is analyzed by varying the strength of the adsorbate-substrate attraction, the temperature T, and the coverage Γℓ. Results obtained for physisorption of Xe on alkaline surfaces are reported in the present work. Prewetting (PW) lines and wetting temperatures, Tw, are determined from the analysis of adsorption on single walls. The filling of slits is analyzed for temperatures T > Tw. It is found that whenever for a given Xe-substrate combination the adsorption on a single wall exhibits a first-order wetting transition then asymmetric profiles that break the left-right symmetry of the external potential appear in the filling of an equivalent slit. These spontaneously symmetry breaking (SSB) solutions occur in a restricted range of Γℓ with a T-dependent width. In the case of closed slits analyzed in the CE scheme, the obtained asymmetric profiles exhibit lower Helmholtz free energies than the symmetric species and, therefore, could be stabilized in this geometry. For open slits, the GCE scheme yields all the symmetric and SSB states in the corresponding convex regimes of the free energy. It is shown that both the CE and the GCE frames yield three coexistent states, two symmetric and one asymmetric twofold degenerate. Both a PW line and the related SSB effect terminate at the same temperature. For rather strongly attractive surfaces reentrant SSB states are found at a fixed value of T.