VESICLES AND ONIONS FROM CHARGED SURFACTANT BILAYERS - A NEUTRON-SCATTERING STUDY

We study the phase behavior of a nonionic ternary surfactant system to which we add small amounts of an ionic surfactant. At sufficiently hi gh cosurfactant to surfactant ratio, we find at moderate concentration in amphiphiles a non-birefringent phase having very elastic rheologic al properties analogous to those previously reported by Hoffmann et al . (Langmuir 1994, 10, 3972) for similar systems. Our neutron scatterin g study agrees with the onion structure found by these authors for thi s remarkable phase. In addition, we also studied the structure of the fluid isotropic phase found at the same cosurfactant to surfactant rat ios but in the dilute range. The present neutron scattering data indic ate that it consists of a quasi-monodisperse dispersion of very small vesicles. We discuss the structures of these two phases, where the bil ayers show finite curvatures, in terms of the bending elasticity of we akly charged membranes.