Shape of Phospholipid/Surfactant Mixed Micelles: Cylinders or Disks? Theoretical Analysis

We develop a theoretical model for the solubilization of phospholipid bilayers by micelle-forming surfactants. Cylindrical micelles, disklike micelles, and spherical micelles are considered as alternative resultant structures. The main question addressed is, what kind of micelles can be expected under various thermodynamical conditions? Our analysis is based on a theoretical model that accounts for Helfrich energy of curvature of amphiphile monolayers and for the entropy of mixing of lipids and surfactants in mixed aggregates. We conclude that for usual values of the elastic parameters of amphiphile monolayers cylindrical micelles are the most probable aggregates resulting from micellization of phospholipid by surfactants. This conclusion is consistent with available experimental data. Conditions of formation of disklike and spherical micelles are also determined.