Impact of Spontaneously Adsorbed Hydroxide Ions on Emulsification via Solvent Shifting

In this study, the influence of interfacial OH ions on spontaneous emulsification of a hexadecane–acetone–water system via the Ouzo effect (solvent shifting) was investigated. It was found that although there is no surfactant utilized in the solvent shifting method, the resulting emulsion droplets are negatively charged in a wide pH range (pH > ∼2.4) due to the spontaneous adsorption of OH ions. The OH ions remarkably affect the size, size distribution, and stability of the emulsions. The emulsion droplets obtained in the absence of OH ions are large and have a wide size distribution. Coalescence of the emulsion droplets and phase separation are prone to take place. At high OH – concentration, the resulting emulsion droplets have a small size, a narrow size distribution, and excellent colloid stability. The results suggest that the spontaneous OH – adsorption affects the nucleation process during the emulsification and the stability of the obtained emulsions during storage.