micellize

Micellize is the process by which amphiphilic molecules, most commonly surfactants, self-assemble into micelles in an aqueous solution when their concentration reaches the critical micelle concentration (CMC). In water, surfactants arrange so that hydrophobic tails are shielded in the interior and hydrophilic heads face the solvent, forming nanoscale aggregates known as micelles. Below the CMC, surfactants exist mainly as individual molecules; above it, micelles dominate the solution.

Micelles are typically spherical but can adopt cylindrical or other morphologies depending on the surfactant type, concentration, temperature, and ionic strength. Sizes commonly range from about 5 to 20 nanometers in diameter. In nonpolar solvents, inverse micelles can form, with polar interiors and nonpolar exteriors, by analogous self-assembly.

The formation of micelles lowers the system’s free energy by sequestering hydrophobic portions away from water and by reducing interfacial tension. Micellization enables solubilization of hydrophobic compounds within the micellar core, aiding detergency, dispersion, and drug delivery. It underpins many cosmetic and pharmaceutical formulations, as well as some enhanced oil recovery techniques.

Factors such as tail length, headgroup, ionic strength, temperature, and the presence of co-solvents influence the CMC and micelle characteristics. Ionic surfactants exhibit a Krafft temperature, above which micellization proceeds; temperature can also influence micelle shape and size.