Monolayers of lipids at the water-air interface

Spread monolayers of dipalmitoyl phosphatidylcholine, methyl palmitate and their mixtures were studied. For this purpose, the surface pressure (pi)-average molecular area (A) isotherms were recorded using a Langmuir film balance. From the pi-A results information on the mutual miscibility of the two components in the two-dimensional state was deduced. Then classical surface chemistry thermodynamic analysis was performed on these isotherms, which involved calculating the excess free energy of mixing, DeltaG(mix)(E). The negative values of DeltaG(mix)(E) indicate that the compounds in the two-dimensional state experience mainly attractive interactions.