The property of surface activity is usually due to the fact that the molecules of
the substance are amphipathic or amphiphilic
, meaning that each contains both a hydrophilic
and a hydrophobic (lipophilic
) group. This assumes that one of the two phases is aqueous, and the other non-aqueous.
If both are non-aqueous (e.g. oil/air), molecules containing organophilic and organophobic
groups may be amphipathic and surface active.
PAC, 1972, 31, 577
(Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix
II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry)
on page 612