Miclles are formed from molecules called surfactants. These molecules have a dual personality: one end is soluble in water and the other in oil. At low concentrations, surfactants dissolve in water like normal salts. Figure 1 (a) shows such a solution. Upon raising the detergent concentration, structures known as micelles may spontaneously form as illustrated in Fig. 1 (b). Micelles form spontaneously driven by a "force" known as the hydrophobic effect, which, in simple terms, stems from the reluctance of oil and water to mix. By forming spheres, the oil-like parts of the surfactants avoid being in contact with water.
Fig. 1. Surfactant molecules are designed with an oil-like part, represented by the wiggly lines and a water-soluble part represented by the spheres. (a). At low concentrations, surfactant molecules dissolve as any other salt would, but (b) at higher concentrations they spontaneously congregate into nearly spherical aggregates called micelles.
Click here to view a more realistic view of the micelle from molecular dynamics calculations, provided by Dr. A. D. Mackerell (J. Phys. Chem., 99, 1846, 1995).
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Last updated: August 4, 2003