Some binary lipid mixtures form coexisting liquid phases when spread at the air/water interface. This work describes the pressure-composition phase diagrams of binary mixtures of four unsaturated phosphatidylcholines with dihydrocholesteroI. These four binary mixtures have critical compositions of approximately fifty mole percent, and average critical exponents of 0.25 ± 0.07. The data can also be approximated by a regular solution thermodynamic model, yielding parameters for the non-ideality of these mixtures.
Hagen, J. P., & McConnell, H. M. (1997). Liquid-liquid immiscibility in lipid monolayers. Biochimica et Biophysica Acta - Biomembranes, 1329(1), 7–11. https://doi.org/10.1016/S0005-2736(97)00135-1