Geometric and thermodynamic considerations about the lipid vesicles formation in water (I. Unilamellar vesicles)

A parametrization based on the differential geometry and on the thermodynamics of dispersed systems has been developed in order to explain the processes leading to the formation of lipid vesicles in water. Several factors of known importance such as aqueous interlayer, chain-length, lipid chain-packing and membrane asymmetry, as well as the existence of two different surfaces in the vesicular bilayer have been considered. The barrier which amphiphile molecules need to surpass in order to the vesicle be formed has three contributions related to the surface energy, the mechanical energy due to overpressure and the excess of chemical potential. The theoretical results define the conditions at which unilamellar vesicles are formed and are applied to the phospholipids: dilauryl-, dimyristoyl-, dipalmytoyl-, and distearoyl-phosphatidylcholine.