Surface-Active Agent (SAA)

Definition - What does Surface-Active Agent (SAA) mean?

A surface-active agent (SAA) is a substance that reduces the surface tension of a liquid in which it is dissolved, thereby increasing its spreading and wetting properties.

SAAs are used in corrosion inhibition, ore flotation, to promote oil flow in porous rocks and to produce aerosols. They are used to disperse aqueous suspensions of insoluble dyes and perfumes.

Surface-active agents are one of the most commonly applied compounds in industrial, agricultural, and household activities, and after use a huge number of surface active agents (and/or their degradation products) are discarded to wastewater-treatment plants.

Surface-active agents are also known as surfactants.

Corrosionpedia explains Surface-Active Agent (SAA)

A surface-active agent is a substance which lowers the surface tension of the medium in which it is dissolved, lowers the interfacial tension with other phases, and is positively adsorbed at the liquid-vapor interface and other interfaces.

In the dyeing of textiles, surface-active agents help the dye penetrate the fabric evenly. Surface-active agents are widely used to impart special characteristics to surface coating formulations.

The surface-active molecule must be partly hydrophilic (water-soluble) and partly lipophilic (soluble in lipids, or oils). It concentrates at the interfaces between bodies or droplets of water and those of oil, or lipids, to act as an emulsifying agent, or foaming agent. Other SAAs that are more lipophilic and less hydrophilic may be used as de-foaming agents, or as demulsifiers.

Classification of surface active agents is based on the charge of hydrophilic parts of their molecules:

  1. Anionic - Based on permanent anions or pH-dependent anions
  2. Cationic - Based on pH-dependent primary, secondary or tertiary amines
  3. Non-ionic - Does not include any charge head
  4. Amphoteric or zwitterionic - Can carry a positive charge on a cationic site and a negative charge on an anionic site

Uses of surface active agents include:

  • Detergents
  • Fabric softeners
  • Emulsifying agents in emulsions
  • Paints
  • Adhesives
  • Inks
  • Anti-fogs
  • Suspending agents in suspensions
  • Laxatives
  • Firefighting
  • Pipelines
  • Alkali surfactant polymers (used to mobilize oil in oil wells)
  • Ferrofluids
  • Leak detectors

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