ABSTRACT
Microemulsions are currently of great interest to the pharmaceutical industry because of their signicant potential of microencapsulating drug and to act as drug delivery vehicles, which can be incorporated with a wide range of drug molecules. They offer numerous advantages: some of them are spontaneous formation, ease of manufacturing and scale-up, thermodynamic stability, improved drug solubilization, and enhanced bioavailability.8 The IUPAC denes microemulsion as “dispersion made of water, oil, and surfactant(s) that is anisotropic and thermodynamically stable system with dispersed domain diameter varying approximately from 1 to 100 nm, usually 10-50 nm.”9 Microemulsions are transparent: the droplet size is less than 25% of the wavelength of visible light. These systems are formed readily and spontaneously, generally without the input of high energy. Microemulsion is a ternary system where water and oil (two immiscible phases) are present with a surfactant, in which the surfactant molecules form a monolayer at the interface of oil and water. The hydrophobic tails of the surfactant molecules orient toward the oil phase and the hydrophilic head groups toward the aqueous phase. The aqueous phase may contain salt(s) and/or other ingredients, and the “oil” may be a mixture of different hydrocarbons and olens. Unlike ordinary emulsions, microemulsions form by simple mixing of the components and do not require the high shear conditions, which are generally used in the formation of ordinary emulsions. Sometimes, a cosurfactant or cosolvent needs to be used in addition to the basic three components (surfactant, the oil phase, and the water phase).10
