Adsorption, structure, and stress in binary interfaces

摘要

The physics of fluidndash;fluid interfaces is investigated with the gradient theory of inhomogeneous fluid. The theory is used to predict component density and principal pressure (negative of stress) profiles inflatandcurvedinterfaces formed in carbon dioxide and decane mixtures. In some cases the component density (and total density) profiles are not monotonic, with CO2being prominently surface active. In composition regions near where a perfecthyphen;wetting third phase splits out the composition and pressure profiles are especially structured, a thinhyphen;film appearing which is akin to the perfecthyphen;wetting phase and which almost separates two distinct interfaces. This precursor to the third phase gives rise to Antonovrsquo;s rule for the interfacial tension between the two phases that are nearly in equilibrium with the third, perfecthyphen;wetting phase. Below a perfecthyphen;wetting transition temperatureTcw, such thinhyphen;films do not arise near compositions of the three phase region. Curvature of sufficiently small drops or bubbles significantly affects adsorption at interfaces. The theory predicts that the Youngndash;Laplace equation as traditionally applied overestimates the pressure drop across the interface in some cases (as found earlier in the case of onehyphen;component drops), butunderestimatesthe pressure drop across interfaces related to perfecthyphen;wetting structures. The minimum work of forming critical nuclei is predicted.