Coexisting multiphase and interfacial behaviour of ouzo

TL;DR

This paper explores the complex bulk and interfacial phase behaviour of ouzo, a multi-component mixture, especially focusing on the coexistence of liquid and vapour phases and the resulting visualisation of phase diagrams.

Contribution

It extends previous work by modeling the coexistence of multiple phases in ouzo, revealing intricate phase diagrams and connecting microscopic and macroscopic interfacial predictions.

Findings

Identification of triple points involving liquid and vapour phases.

Visualization techniques for ternary phase diagrams.

Linking microscopic density functional theory with macroscopic droplet shapes.

Abstract

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 behaviour. 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-coloured liquid is formed. In previous work [Archer et al., Soft Matter 20, 5889 (2024)], the equilibrium phase-diagram for the stable liquid phases of ouzo was captured via experiment and modelling. Here we consider the case when the two liquid phases also coexist with the vapour phase (i.e. along a line of triple points) and within our model uncover the complex bulk phase behaviour for this simple beverage. As a consequence, this leads to some interesting observations, that also apply more widely, about visualising phase diagrams in ternary systems of this type. We also examine the interfacial behaviour, connecting microscopic density functional theory results with macroscopic (Neumann) predictions for the shape of droplets at interfaces.