It may happen that a component is virtually insoluble in both of two adjoining phases, but is present as a @M04015@ between them. Such a layer can be produced by spreading.
Source: 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 591 [Terms] [Paper]