Comparison of physical models used to explain condensation effects in lecithin-cholesterol mixed films.

The apparent condensation effect observed with mixed monolayers of lecithin and cholesterol has been examined with respect to both molecular interaction and molecular cavity models. For each, model equations are presented which predict the surface areas of the film components as a function of the mole fraction of each component. For mixed monolayers where linearity does not exist in plots of mean surface area vs. mole fraction, and where there are breaks in the curve at mole fraction values other than 0.5, the size of the cavities are not invariant with respect to mole fraction.