FORMATION OF POLYMER-LIKE MIXED MICELLES AND VESICLES IN LECITHIN BILE-SALT SOLUTIONS - A SMALL-ANGLE NEUTRON-SCATTERING STUDY

We report a small-angle neutron-scattering (SANS) study of the structu ral properties of mixed bile salt-lecithin micelles and vesicles. The SANS data from a mixed micellar sample are in agreement with the prese nce of flexible cylindrical micelles. We present an expression for the scattering cross section of polydisperse wormlike micelles which is c apable of quantitatively describing the scattering intensity I(q) over an extended range of scattering vectors and which allows us to incorp orate overall size, polydispersity, flexibility, and local structure o f the micelles in a self-consistent way. At concentrations below the m icellar phase limit, where a spontaneous micelle-to-vesicle transition can be observed, we find that the scattering intensity at higher valu es of q is not consistent with a population of vesicles only and that a coexistence of vesicles and wormlike micelles occurs.