Uses and selection criteria
Surfactants

The preparation and stabilization of emulsions, dispersions of a liquid (water or oil) in an immiscible liquid (oil or water), requires the presence of one or more surface-active compounds whose role is to reduce the water/oil interfacial tension in order to enable dispersion (increase in interface area).

Consequently, the surfactant's ability to reduce the interfacial tension between the two phases to be emulsified is a key criterion for surfactant selection.

Other, more readily available selection criteria can also be used. As a general rule, the surfactant must have a good affinity for the continuous phase: an oil-in-water (O/W) emulsion requires a surfactant of a more hydrophilic nature, while a water-in-oil (W/O) emulsion requires a surfactant of a lipophilic nature.