Abstract : We have studied the effect of electrostatic charging of a neutral surfactant system (Triton X-100/octanol/water) by samll amounts of CPCl (Cetyl pyridinium chloride). The main method of analysis was Small Angle Neutron Scattering, together with light scattering and conductivity measurements. When adding small quantities of ionic surfactant, new aggregate morphologies are observed: (i) very small unilamellar vesicle at high dilution and (ii) big multilamellar vesicles at moderate concentrations. We have measured the evolution of the radius of the unilamellar vesicles as a function of experimental parameters by quantitative modelling of the neutron spectra. Moreover, we have also characterized all other aggregates.
We propose a quantitative thermodynamic model describing the vesicle phase. It is based on a numerical resolution of the Poisson-Boltzmann equation in a Wigner-Seitz cell. The predictions agree well with the experimental results.