Thermodynamic relation of an insoluble monolayer at the oil/water interface and at the air/water interface in contact with oil

Phospholipid monolayers are studied at three different types of interfaces : air/water, oil/water, and air/water in contact with oil. The thermodynamic data can be explained by a simple model explaining why the lateral pressures of the latter two interfaces basically differ by the spreading coefficient. Fluorescence microscopic observations reveal that the three interfaces can be prepared in pressure equilibrium exhibiting comparable phase sequences.