Surfactant

A substance that lowers surface or interfacial tension, helping liquids spread, mix, or remove oily material. Surfactant molecules typically have water-attracting and oil-attracting regions.

Surface tension: The energy required to increase a liquid’s surface area, arising from molecular interactions at its boundary. Surfactants reduce this interfacial energy by accumulating at the liquid’s surface.
Detergent: A cleaning substance that uses surfactants and other ingredients to remove soil from surfaces or fabrics. Detergents use surfactants to detach greasy soil and keep it dispersed in wash water.
Intermolecular force: An attraction or repulsion between neighboring molecules, distinct from the bonds within a molecule. Intermolecular forces create the surface-energy differences that surfactants modify.
Anionic surfactant: A surfactant whose hydrophilic group carries a negative charge in solution. Anionic surfactants are common in cleaners and often produce strong foam.
Amphiphile: A molecule or material with distinct regions that interact favorably with different substances, such as water and oil. This split affinity is the molecular design that lets many surfactants work at interfaces.
Emulsion: A mixture in which droplets of one liquid are dispersed in another liquid that does not normally mix with it. Surfactants stabilize droplets and slow their coalescence in many emulsions.
Hydrophobic effect: The tendency of nonpolar substances to aggregate in water, reducing disruption of water’s hydrogen-bond network. It drives surfactant tails away from water and toward oils or one another.
Cationic surfactant: A surfactant whose hydrophilic group carries a positive charge in solution. Cationic surfactants can bind negatively charged surfaces and are used in fabric softeners and disinfectants.
Adsorption: The accumulation of atoms, ions, or molecules at the surface of a material. Surfactant molecules adsorb at interfaces, where they lower the energetic cost of contact.
Wetting agent: A substance that helps a liquid spread across or penetrate a solid surface. Surfactants serve as wetting agents by reducing the liquid’s contact angle on surfaces.

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