Surfactants are compound additives which decrease the surface tension between two liquids or a liquid and a solid. The result is a liquid which spreads farther and wets better. "Surfactant" is a portmanteau of "surface active agent." This surface active molecule contains a lipophilic "tail" and hydrophilic "heads." They are amphiphilic substances that diffuse in water and adsorb at the interfaces between water and oils, fats, or air.
Surfactants often act as detergents, wetting agents, coagulants, emulsifiers/demulsifiers, foaming agents, and dispersants.
Emulsifiers disperse oil in water or water-based liquids, or vice-versa.
Demulsifiers allow oils and greases to be removed from a metal working fluid by rendering the oil droplets insoluble.
Dispersants suspend or disperse fine particles in a liquid or solution.
Deflocculants break up agglomerated particles so they can be more easily suspended or dispersed. These work by creating a charged layer on the surface of the particles, causing them to repel.
Settling agents, coagulants, and flocculants remove fine particles that are dispersed or suspended in a solution. They cause fine particles to coagulate together into larger agglomerates. The agglomerated particulates sink out of suspension from their increase in density.
Water softeners remove metal ions, usually through a precipitation mechanism.
Solubilizers maintain the solubility between disimiliar fluids, such as an active ingredient and the base fluid, or an additive in a product formulation. Hydrotropes are a specific type of solubilizing agent designed to keep a surfactant soluble.
Wetting agents lower the surface tension of a liquid, thereby providing better spreading and coverage.