Surfactancy

Surfactancy is the quality or state of being surface-active, describing the ability of a substance to reduce surface or interfacial tension and to accumulate at interfaces such as air–water or oil–water. Substances with surfactant activity are typically amphiphilic, possessing both hydrophilic and lipophilic regions. When present in solution, these compounds orient at interfaces with their hydrophobic tails in nonpolar media and their polar heads in polar media, lowering interfacial tension and often leading to the formation of micelles at higher concentrations.

Key measures of surfactancy include reduction of surface tension, dynamic surface tension, and interfacial tension. The concept of critical micelle concentration (CMC) describes the concentration at which micelles form in many systems. The hydrophilic-lipophilic balance (HLB) scale helps predict surfactant behavior in emulsions and detergency. Surfactants also enable solubilization of nonpolar compounds and stabilization of emulsions and foams, affecting wetting and dispersion.

Classification and examples: surfactants are commonly categorized as ionic (anionic, cationic), nonionic, and zwitterionic. Examples include sodium dodecyl sulfate (anionic), cetyltrimethylammonium bromide (cationic), polysorbates (nonionic), and betaines (zwitterionic). Biosurfactants such as rhamnolipids are produced by microorganisms and are noted for biodegradability.

Applications span detergents, emulsifiers, foaming agents, wetting agents, and dispersants in cleaning, cosmetics, food, pharmaceuticals, and petroleum. Measurement techniques include tensiometry (Wilhelmy plate or Du Noüy ring), interfacial tension tests, and CMC determination via surface tension plots. While the term surfactant is common, surfactancy as a descriptor is less widely used in modern literature.