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The ouzo effect (also louche effect and spontaneous emulsification) is a milky (''louche'') oil-in-water microemulsion that is formed when water is added to ouzo and other , such as pastis, raki, arak, sambuca, absinthe and Pernod. Because such microemulsions occur with only minimal mixing and are highly stable,〔 the ouzo effect may have commercial applications. ==Observation and explanation== The ouzo effect occurs when a strongly hydrophobic essential oil such as ''trans''-anethole is dissolved in a water-miscible solvent, such as ethanol, and the concentration of ethanol is lowered by addition of small amounts of water. Oil-in-water emulsions are not stable. Oil droplets coalesce until complete phase separation is achieved at macroscopic levels. Addition of a small amount of surfactant or the application of high shear rates (strong stirring) can stabilize the oil droplets. In a water-rich ouzo mixture the droplet coalescence is dramatically slowed without mechanical agitation, dispersing agents, or surfactants. It forms a stable homogeneous fluid dispersion by liquid-liquid nucleation. The size of the droplets has been measured by small-angle neutron scattering to be on the order of a micron. Using dynamic light scattering, Sitnikova et al. showed that the droplets of oil in the emulsion grow by Ostwald ripening, and that droplets do not coalesce. The Ostwald ripening rate is observed to diminish with increasing ethanol concentrations until the droplets stabilize in size with an average diameter of . Based on thermodynamic considerations of the multi-component mixture, the emulsion derives its stability from trapping between the binodal and spinodal curves in the phase diagram.〔 However, the microscopic mechanisms responsible for the observed slowing of Ostwald ripening rates at increasing ethanol concentrations appears not fully understood. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ouzo effect」の詳細全文を読む スポンサード リンク
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