The influence of ionic charges on the structural and dynamical behavior of O/W microemulsion droplets

An O/W microemulsion system has been investigated where the droplet size can be controlled via the concentration of cosurfactant (1-hexanol), In that system the charge density of the droplets was varied by substitution of the original nonionic surfactant by a cationic surfactant. SANS measurements showed that the droplet radii are unaffected by the charging process, whereas the polydispersity decreases with increasing charge density. SANS and also static light scattering experiments are well described by a simple electrostatic model, which renders this droplet system a good model system. In contrast to that the diffusion coefficient shows a somewhat more complicated behavior. It increases strongly with rising ionic content but goes through a maximum around 3 mol% ionic surfactant and then decreases again. The magnitude of the increase and the position of the maximum are well described by theory, whereas the steepness of the decrease at still higher ionic surfactant content is not accounted for.