surfactantssurfaceactive

Surfactants, also known as surface-active agents, are compounds that preferentially adsorb at interfaces between immiscible phases or between a solid and a liquid. Their amphiphilic structure, containing a hydrophobic tail and a hydrophilic head, drives their ability to reduce interfacial tension, promote wetting, emulsification, foaming, and dispersion.

Surfactants can be ionic (anionic, cationic, zwitterionic), nonionic, or amphoteric, and may be synthetic or naturally derived (biosurfactants such as rhamnolipids, sophorolipids, and lipopeptides).

At low concentrations they decrease surface or interfacial tension; above the critical micelle concentration they aggregate into micelles, enabling solubilization of hydrophobic substances and the formation of emulsions or foams. The hydrophilic–lipophilic balance (HLB) guides their expected behavior in mixtures.

Common examples include sodium dodecyl sulfate (SDS, anionic), cetyltrimethylammonium bromide (CTAB, cationic), and polysorbate 20 (Tween 20, nonionic). Biosurfactants offer biodegradability and lower ecotoxicity in some cases.

Applications span cleaning products, cosmetics, foods, pharmaceuticals, paints, and enhanced oil recovery, among others. Key considerations include environmental fate, biodegradability, and toxicity, as well as formulation compatibility and regulatory requirements.

Historical development, extensive study of micellization, and ongoing research into greener, more selective surfactants continue to shape this field.