Surfactants, sometimes called surface-active agents or detergents, are among the most versatile chemicals avail-
able. They have applications in many areas, including chemistry (chemical kinetics or equilibria), biology (as membrane mimetics), and pharmacy (1). Surfactants are amphiphilic materials containing both apolar long-chain hydrocarbon “tail” and polar, usually ionic, “head” groups. In polar solvents, for example water, this dual character of the amphiphile leads to self-association or micellization: the surfactant molecules arrange themselves into organized molecular assemblies known as micelles (Fig. 1). The hydrophobic part of the aggregate forms the core of the micelle, while the polar head groups are located at the micelle–water interface in contact with and hydrated by a number of water molecules. Depending on the chemical structure of the surfactant, its micelle can be cationic, anionic, ampholitic (zwitterionic), or nonionic. This unique property of surfactants makes aqueous surfactant solutions microheterogeneous media; that is, they are heterogeneous on a microscopic scale, even though they are often homogeneous macroscopically. The concentration (actually an arbitrary concentration within a narrow range) above which micelles form is called the critical micelle concentration (CMC). Above the CMC, monomers and micelles exist in dynamic equilibrium.