Related to micelle formation is the technologically important ability of detergent actives to congregate at oil water interfaces in such a manner that the polar (or ionized) end of the molecule is directed towards the aqueous phase and the hydrocarbon chain towards the oily phase. In the cleaning process, sorbed greasy soils become coated in this manner with an oriented film of surfactant. Then during washing, the greasy soil rolls back at the edges so that emulsified droplets can disengage themselves from the sorbed oil mass, with the aid of mechanical action, and enter the aqueous phase. Obviously, a substance which is permanently or temporarily sorbed on the surface in place of the soil will tend to accelerate this process and effectively push off the greasy soil.

Substances other than detergent actives also tend to be strongly sorbed from aqueous media onto surfaces of other contiguous condensed phases. This is particularly true of highly charged ions, especially those ions which fall into the class of polyelectrolytes. Whereas the usual organic surface-active agent is strongly sorbed at oil-water interfaces, the highly charged ions are most strongly sorbed at interfaces between water and insoluble materials exhibiting an ionic structure (see Table 26 -- 2 on p. 1678). Thus, for aqueous media, we can think of the idealized organic active as an oleophilic or hydrophobic surface-active agent, and of an idealized builder as a oleophobic or hydrophilic surface-active agent.