ABSTRACT
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Microemulsions or micellar emulsions are dened as single optically isotropic and thermodynamically stable multicomponent £uids composed of oil, water, and surfactant (usually in conjunction with acosurfactant). The droplets in amicroemulsion are in the range of 1-100 nm in diameter. It is well established that dispersed particles having adiameter less than one-fourth of the wavelength of visible light, that is, less than approximately 120 nm, do not refract light and therefore microemulsions appear transparent to the eye. The basic difference between emulsions and microemulsions are that emulsions exhibit excellent kinetic stability but are thermodynamically unstable when comparedwith microemulsions. The concept of microemulsion was introduced as early as 1943 by Hoar and Schulman (Hoar and Schulman, 1943). They generated clear single-phase solution by titrating a milky emulsion with hexanol. Schulman et al. introduced the term “microemulsion” for this system in 1959. In recent years, microemulsions have attracted agreat deal of attention because of their biocompatibility, biodegradability, ease of handling and preparation, and appreciable solubilization capacity for both water-and oil-soluble drugs. The differences between emulsions and microemulsions are enlisted in Table 17.1.
