Evaporating liquid droplets are omnipresent in nature and technology, such asin inkjet printing, coating, deposition of materials, medical diagnostics,agriculture, food industry, cosmetics, or spills of liquids. While theevaporation of pure liquids, liquids with dispersed particles, or even liquidmixtures has intensively been studied over the last two decades, theevaporation of ternary mixtures of liquids with different volatilities andmutual solubilities has not yet been explored. Here we show that theevaporation of such ternary mixtures can trigger a phase transition and thenucleation of microdroplets of one of the components of the mixture. As modelsystem we pick a sessile Ouzo droplet (as known from daily life - a transparentmixture of water, ethanol, and anise oil) and reveal and theoretically explainits four life phases: In phase I, the spherical cap-shaped droplet remainstransparent, while the more volatile ethanol is evaporating, preferentially atthe rim of the drop due to the singularity there. This leads to a local ethanolconcentration reduction and correspondingly to oil droplet nucleation there.This is the beginning of phase II, in which oil microdroplets quickly nucleatein the whole drop, leading to its milky color which typifies the so-called'Ouzo-effect'. Once all ethanol has evaporated, the drop, which now has acharacteristic non-spherical-cap shape, has become clear again, with a waterdrop sitting on an oil-ring (phase III), finalizing the phase inversion.Finally, in phase IV, also all water has evaporated, leaving behind a tinyspherical cap-shaped oil drop.
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