Coexisting multiphase and interfacial behavior of ouzo

Multi-component liquid mixtures can be both complex and fascinating, with some systems being amenable to simple experimentation at home, giving valuable insight into fundamental aspects of bulk and interfacial phase behavior. One particularly interesting mixture is the popular drink ouzo, which has charmed both the general public and scientists by virtue of its ability to display spontaneous emulsification when water is added. When these two clear (and potable) liquids are poured into each other, a single milky-colored liquid is formed. In previous work [Archer et al., “Experimental and theoretical bulk phase diagram and interfacial tension of ouzo,” Soft Matter 20, 5889 (2024)], the equilibrium phase-diagram for the stable liquid phases of ouzo was captured via experiment and modeling. Here, we consider the case when the two liquid phases also coexist with the vapor phase (i.e., along a line of triple points) and within our model uncover the complex bulk phase behavior for this simple beverage. As a consequence, this leads to some interesting observations that also apply more widely, about visualizing phase diagrams in ternary systems of this type. We also examine the interfacial behavior, connecting microscopic density functional theory results with macroscopic (Neumann) predictions for the shape of droplets at interfaces.