An Ouzo emulsion of toluene in water characterized by NMR diffusometry and static multiple light scattering

• Bimodal droplet size distribution in toluene/ethanol/water Ouzo emulsions.
• Complementary methods by NMR diffusometry and light scattering.
• Spectrometrically time-resolved phase separation study of the Ouzo emulsion.

An Ouzo emulsion is an emulsion that is formed spontaneously by adding water to a system comprising a hydrophobic substance (like anethole in the Ouzo beverage), a water-miscible solvent and (optionally) water. Formation of such an emulsion does not require the use of surfactants, dispersing agents, or mechanical agitation. In this work, Ouzo emulsions were prepared from the ternary mixture toluene–ethanol–water and the emulsion stability was studied by a combination of two techniques: static multiple light scattering and NMR diffusometry. A bimodal distribution of the droplets was found. The light scattering technique revealed the presence of large drops, several micrometer in size. NMR measurements confirmed the large drops but also showed the additional presence of droplets of the order of 100 nm in diameter. The distribution of toluene between the three environments (i) large drops, (ii) small droplets, and (iii) the continuous ethanol–water phase could also be assessed. It was found that addition of an anionic surfactant to the system yielded an improved dispersed system, i.e., more toluene was present as small droplets and less toluene was dissolved in the ethanol–water phase; however the presence of the amphiphile reduced the emulsion stability.

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