Structural investigations of charged O/W microemulsion droplets

Structure and properties of charged oil-in-water (O/W) microemulsions have been investigated and a short review of the work done on such systems is given. A particular system made up from a zwitterionic surfactant and hydrocarbon which becomes charged upon the addition of either cationic or anionic surfactant has been studied. A particular feature of this microemulsion system is that the charge density on the droplets can be fixed at a desired value in an easily controllable fashion. These systems have been characterized ed by means of light scattering, small - angle neutron scattering, interfacial tension measurements, electric conductivity, and viscosity measurements. The experiments showed that the aggregates remain of constant size over a large concentration region, i. e. from 0 to ≈ 30 wt %. Moreover there size is not much changed by the addition of the ionic surfactant. The interactions in this microemulsion system could be described by a hard sphere interaction with an additional DLVO - potential term that accounts for the electrostatic repulsion.