Nanoparticles and Nanocapsules Created Using the Ouzo Effect: Spontaneous Emulsification as an Alternative to Ultrasonic and High-Shear Devices

The preparation of polymeric particles and capsules by means of spontaneous droplet formation and subsequent polymer precipitation or synthesis is well‐known. However, spontaneous emulsification is a phenomenon that has often been erroneously interpreted. This Minireview provides new insights into the preparation of metastable liquid dispersions by homogeneous liquid–liquid nucleation, and is based primarily on a recent study by Vitale and Katz (Langmuir, 2003, 19, 4105–4110). This spontaneous emulsification, which they named the Ouzo effect, occurs upon pouring, into water, a mixture of a totally water‐miscible solvent and a hydrophobic oil—and optionally some water—thus generating long‐lived small droplets, which are formed even though no surfactant is present. Herein, we review and reinterpret the most relevant publications on the synthesis of a variety of dispersions (pseudolatexes, silicone emulsions, biodegradable polymeric nanocapsules, etc.), which we believe have actually been synthesized using the Ouzo effect. The Ouzo effect may also become a substitute for high‐shear techniques, which, to date, have only been of limited utility on industrial scales. New interpretations: The preparation of polymer aqueous dispersions by means of the spontaneous emulsification of polymers or monomers is reviewed. The results are correlated with recent observations on the process governing spontaneous emulsification—otherwise named the Ouzo effect—which entails the formation of silicone microgels, polymer particles, and air‐ or oil‐filled capsules (see figure).