Experimental and Theoretical Bulk Phase Diagram and Interfacial Tension of Ouzo

TL;DR

This paper combines experimental and theoretical approaches to map the phase diagram and interfacial properties of Ouzo, a ternary mixture, providing insights into its phase behavior and interfacial tension relevant for future applications.

Contribution

It presents the first detailed experimental and theoretical analysis of Ouzo's phase diagram, including tie-lines, critical points, and interfacial tension, with a simple thermodynamic model capturing key features.

Findings

Accurate phase diagram and tie-lines for Ouzo

Theoretical model reproduces experimental phase behavior

Measured interfacial tension and density variations

Abstract

Ouzo is a well-known drink in Mediterranean countries, with ingredients water, alcohol and trans-anethole oil. The oil is insoluble in water, but completely soluble in alcohol, so when water is added to the spirit, the available alcohol is depleted and the mixture exhibits spontaneous emulsification. This process is commonly known as the louche or Ouzo effect. Although the phase boundaries of this archetypal ternary mixture are well known, the properties of coexisting phases have not previously been studied. Here, we present a detailed experimental investigation into the phase behaviour, including tie-lines connecting coexisting phases, determination of the critical point (also called the plait point in ternary systems) and measurements of the surface tension and density for varying alcohol concentrations. Additionally, we present a theory for the thermodynamics and phase diagram of the system. With suitable selection of the interaction parameters, the theory captures nearly all features of the experimental work. This simple model can be used to determine both bulk and non-uniform (e.g. interfacial) properties, paving the way for a wide range of future applications of the model to ternary mixtures in general. We show how our accurate equilibrium phase diagram can be used to provide improved understanding of non-equilibrium phenomena.