Shape transformations in biological mixed surfactant systems: from spheres to cylinders to vesicles

Abstract

Aqueous mixtures of lecithin and bile salt form aggregates of various structures depending on their mixing ratio and concentration. Upon a reduction of the bile salt-to-lecithin ratio they exhibit a characteristic sequence spherical micelle-flexible cylindrical micelle-vesicle-lamellar sheet in the aggregate morphology. Static (SLS) and dynamic (DLS) light scattering as well as small-angel neutron scattering (SANS) experiments were performed to investigate the structural properties of the different types of aggregates as well as the transitions between them. Special attention was paid to the dependence of the size and flexibility of the wormlike mixed micelles on the micellar composition, the coexistence of mixed micelles and vesicles, and the occurrence of large sheetlike structures. The experimental results were interpreted within the framework of current theoretical models for the shape transformations in surfactant systems.