Size of microvesicles from charged surfactant bilayers: Neutron scattering data compared to an electrostatic model

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Abstract
Electrostatic interactions can have a decisive influence on the shape and size of supramolecular aggregates. Recently, we reported on a study of the curvature instability of charged surfactant membranes. At high dilution (volume fraction less than 2 or 3%), microvesicles with a radius of less than 100 Å were found at thermal equilibrium. In the experimental section of this paper, we present a detailed investigation of the size of these vesicles as a function of charge, concentration, and salinity again using small angle neutron scattering. In the theoretical section, we propose a quantitative electrostatic cell model, which predicts vesicle sizes in good agreement with experiment. It is based on a numerical solution of the Poisson-Boltzmann equation, which allows the area densities of amphiphilic ions to equilibrate between the inner and outer monolayers of the vesicles, and the counterions to exchange from the inside to the outside of the vesicle.