A comprehensive review on microemulsions

Microemulsions are thermodynamically stable, transparent and isotropic liquid mixtures which are consisted of oil, water and surfactant. The particle size of the microemulsions may range from 10 to 300 nanometers. In this review, properties, structure, types, theories, characterization and applications of the microemulsions are discussed in detail. They can be prepared simply by mixing the different components without specific equipment and conditions. In w/o type, oil is the continuous phase and water as droplets are dispersed in it, whereas in o/w type microemulsion there is an aqueous continuous phase and oil droplets are dispersed in it. Microemulsions are widely used in pharmaceutical industries, cosmetics and analytical techniques. Microemulsions permit self-emulsification owing to the thermodynamically stable system and are utilized for the palatability of unpleasant drugs. The characterization of the microemulsions can be done by various methods, including microscopy, nuclear magnetic resonance and light scattering methods. Comprehensive knowledge of microemulsions will guide their physicochemical and biopharmaceutical properties that could be beneficial in designing the drug formulations and cosmetics.