Spontaneous Emulsification & the Ouzo Effect

The aniseed-based alcoholic beverage Ouzo consists of a three-component mixture of ethanol (≈ 45 vol%), water (55 vol%) and an essential oil called trans-anethol (≈ 0.1%). It is commonly consumed with the addition of three to five volumes of water to one volume of Ouzo. From the phase equilibrium diagram it appears that the inter-mixing of Ouzo and water must follow a non-linear composition trajectory in order to enter the meta-stable zone in which the oil spontaneously nucleates into tiny droplets.. The tiny 1 nm sized droplets scatter light, causing the drink to appear milky white. Vitale and Katz have coined the generic term “Ouzo effect” to describe such a process of creating meta-stable liquid-liquid dispersions. Since no input of mechanical energy is involved, this offers an energy-efficient method of producing nanospheres and nanoparticles.
For background read
Vitale, S. A.; Katz, J. L. Liquid Droplet Dispersions Formed by Homogeneous Liquid-Liquid Nucleation: “The Ouzo Effect”. Langmuir 2003, 19, 4105-4110.
Ganachaud, F.; Katz, J. L. Nanoparticles and Nanocapsules Created Using the Ouzo Effect: Spontaneous Emulsification as an Alternative to Ultrasonic and High-Shear Devices ChemPhysChem 2005, 6, 209-216.
Solans, C.; Morales, D.; Homs, M. Spontaneous Emulsification. Curr. Opin. Colloid Interface Sci. 2016, 22, 88-93.

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