Strong critical adsorption at the liquid-vapor surface of a nonpolar mixture

Abstract

For a critical binary liquid mixture where the surface tension difference between the two components is very large, the component with the lowest surface tension completely saturates the liquid-vapor surface. The variation in the local volume fraction v(z), with depth z into the liquid mixture, is described by a universal surface scaling function P±≡P±(z/ξ±), which takes differing forms in the one- (+) and two-phase (−) regions, where ξ represents the bulk correlation length. Carpenter et al. [Phys. Rev. E 59, 5655 (1999); 61, 532 (2000)] determined P± using the ellipsometric critical adsorption data of four different critical binary liquid mixtures. A deficiency of this prior study was that each of the liquid mixtures possessed at least one polar component, which could have generated distortions in the function P±(z/ξ±). In this publication, we demonstrate that P±, determined in the previous study, provides an excellent description of the nonpolar critical binary liquid mixture 1,1,2,2-tetrabromoethane+n-dodecane.