DETERMINATION OF THE STRUCTURE OF A WATER IN OIL MICROEMULSION

Two surfactants (the sodium salts of paradihexyl benzenesulfonate and 2,3-dimethyl-5-dodecylbenzenesulfonate), found to form cosolvent-free microemulsions, have been used as the basis for a series of experimental studies on microemulsion structure. By varying the electrolyte concentration, one can obtain them as Winsor type I, II, or III systems; however, the studies reported here concentrated on microemulsions of water in oil (Winsor type II). These microemulsions were characterized by a variety of techniques: dynamic light scattering, lifetime measurements, fluorescence, fluorescence polarization, and electrical conductivity. Dynamic light scattering has been used to investigate the effect of dilution and electrolyte concentration on the physical and structural properties of the microemulsions. Excimer emission indicated that the composition of many of the systems tested was not changed during the dilution process. However, electrical conductivity experiments showed that for systems close to the middle-phase region (Winsor III), the structure of the microemulsions may have been affected during the dilution. The microviscosity of the micelle-oil interfaces was examined by fluorescence polarization measurements and the interface was found to increase in fluidity when the composition of the system approached that of the middle-phase region. © 1990.