Mikellien

Mikellien, or micelles, are aggregates of amphiphilic molecules such as surfactants that form in liquids, most commonly in water. They arise when the concentration of surfactant exceeds the critical micelle concentration (CMC). In aqueous solutions, the hydrophobic parts of the molecules tuck inward away from the water, while the hydrophilic heads remain exposed to the solvent, creating a core–shell structure. Micelles can adopt various shapes, most commonly spherical, but also cylindrical or worm-like, depending on the surfactant and conditions. In nonpolar solvents, reverse micelles can form, with polar cores surrounded by outward-facing nonpolar heads.

Formation and properties: Micelle formation reduces the system’s free energy by shielding hydrophobic tails from water. Micelles are dynamic assemblies; individual molecules continuously exchange between micelles and the surrounding solution. Typical sizes range from about 2 to 20 nanometers, and the aggregation number—the number of surfactant molecules per micelle—varies with the surfactant type, concentration, temperature, and salinity.

Types and applications: Spherical micelles are common for many conventional surfactants, while rod-like or worm-like micelles occur with certain lipids or block copolymers. Practical uses include enhancing the solubility of hydrophobic compounds, detergency, and cosmetic formulations. In medicine and chemistry, micelles serve as delivery vehicles for drugs, nanoreactors for reactions, and components in analytical techniques for solubilizing samples.

Characterization: Micelles are studied by light scattering, small-angle X-ray or neutron scattering, cryo-electron microscopy, and other spectroscopic methods. See also surfactant, amphiphile, and detergents.