surface pressure

The change of interfacial tension caused by addition of a given species to a base solution. When an area of liquid covered with a spread substance is separated from a clean area of surface by a mechanical barrier, the force acting on unit length of the barrier is called the surface pressure, $π$ or $π s$ , and is equal to $γ 0 − γ$ where $γ 0$ is the surface tension of the clean surface and $γ$ that of the covered surface.

Source:

PAC, 1972, 31, 49 (Extended chain crystals of linear high polymers) on page 59

PAC, 1983, 55, 1251 (Interphases in systems of conducting phases (Provisional)) on page 1264

Green Book, 2nd ed., p. 63