HIGH-FREQUENCY DIELECTRIC DISPERSIONS IN DILUTE WATER-IN-OIL MICROEMULSIONS

A set of measurements of the dielectric constant of a three-component microemulsion system sodium bis (2-ethylhexyl) sulfosuccinate-water-decane as a function of frequency (10(6) to 10(9) Hz) and temperature (5 to 35-degrees-C) and for two values of the volume fraction of the dispersed phase (0.025 and 0.050) has been made. The frequency dependence of the dielectric constant clearly shows a low-frequency dispersion and a high-frequency one, both describable in terms of a Cole-Cole type relaxation. The high-frequency dispersion is characterized by a relaxation time of the order of 10(-9) s and a dielectric increment of few units, both largely independent of temperature and composition. We try to identify the origin of the high-frequency dielectric dispersion and to relate it to the dynamics of the surfactant polar heads within the single droplet.