Emulsions

Abstract

An emulsion is a dispersion of one liquid in another, immiscible liquids usually in the presence of stabilizer molecules are called emulsifiers. Emulsions may be either oil droplets dispersed in water or water droplets dispersed in oil wherein the droplet diameters are in the 0.05–100 µm range. Emulsifiers may be anionic, cationic, nonionic, or combinations of ionic and nonionic. The droplets are usually formed by high shear mechanical processes and stabilized by electrostatic and/or steric barriers around the droplets provided by the emulsifiers. Emulsions often require complex mixtures of emulsifiers and are not thermodynamically stable, therefore preparing them is still somewhat of an art. When an emulsion is destabilized, it is said to break into the separate liquid layers. A less severe form of instability is called creaming and involves the droplets rising to the top of the sample where they can be redispersed with proper mixing. Emulsions can be explained using theories of colloid science. Emulsions are found in a wide variety of applications and include food, cosmetics, household products, pharmaceuticals, agricultural applications, road surfacing, latexes, and oil recovery.