Correlation between asymmetric profiles in slits and standard prewetting lines
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, T_t, to the critical point, T_c. 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 T_w in a range of average densities rho*_ssb1 <= rho*_av <= rho*_ssb2, which diminishes with increasing temperatures until its disappearance at the critical prewetting point T_cpw. 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 T_cpw can be precisely determined by analyzing the asymmetry coefficients.