Breakdown of the Capillarity Approximation in Binary Nucleation:  A Density Functional Study

The binary classical nucleation theory is known to produce unphysical predictions of gas−liquid nucleation in systems in which the surface tension has a strong composition dependence. It has been shown earlier, using thermodynamic methods, that the unphysical predictions are related to the capillarity approximation, i.e., the assumption that the critical nucleus surface tension equals the surface tension of a flat interface. In this paper, we apply the density functional theory of nucleation to a surface active system and show by numerical calculations that the capillarity approximation breaks down severely for critical nuclei of intermediate composition. In these nuclei, the concentration profile of the surface active component shows a strong maximum in the nucleus surface layer.