surfaceactive

Surface-active compounds, commonly referred to as surfactants, are substances that preferentially adsorb at interfaces between two dissimilar phases, such as air and water or oil and water. By concentrating at the interface, they reduce interfacial or surface tension and modify wetting, spreading, and the stability of dispersions.

Most surfactants are amphiphilic, bearing a hydrophobic tail and a hydrophilic head. This dual affinity drives their self-assembly: at concentrations below the critical micelle concentration (CMC) they populate interfaces; above the CMC they form micelles and other aggregates, enabling solubilization of otherwise poorly soluble compounds and enhanced transport properties.

Surfactants are classified by the charge of their head group: anionic, cationic, nonionic, and zwitterionic (amphoteric). Common examples include anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB), nonionic alkyl polyglucosides, and zwitterionic betaines. Many are biodegradable, but some persist in the environment or exhibit aquatic toxicity, prompting regulation and testing.

Key properties include surface tension reduction, emulsification, foaming, detergency, and wetting. Applications span cleaners and detergents, cosmetics and personal care, pharmaceuticals, food processing, paints and coatings, and enhanced oil recovery.

Measurement and characterization commonly involve tensiometric methods to determine surface or interfacial tension, such as the Du Noüy ring or Wilhelmy plate, and determination of the CMC from the surface tension versus concentration plot. Interfacial tension can be measured using spinning-drop or pendant-drop methods.