Structural study of concentrated micellar solutions

We have studied the structure of concentrated micellar solutions. We used the iterative method proposed by Hayter and Penfold in order to separate the interference term S(q) from the form factor P(q). We have transposed this method to small angle X-ray scattering and shown that the micellar mass increases with the total surfactant concentration. By high resolution - i.e. wide angle - measurements, we have shown that the hydration molecules, even firmly bound to the ionic headgroups, do not penetrate in the hydrophobic core of the micelle. The core of the micelle is a fluctuating droplet of disordered hydrocarbon chains which we have modelled in the 'confined droplet' model. Using the same investigation methods, we have studied the structure of ternary systems. We have shown that pentanol molecules used as cosurfactant are not bound at the ionic headgroups, but randomly distributed through the hydrocarbon core. By pH variation, we have shown that the surface charge density is invariant, at any surfactant concentration or structural charge. Lastly, a study of the perturbation induced by small amounts of solutes added in reverse micelles allowed us to localize each type of solute at the interface or in the water core of the AOT micelles. (author)