CONDUCTIVITY STUDY OF MICROEMULSIONS - DEPENDENCE OF STRUCTURAL BEHAVIOR OF WATER OIL SYSTEMS ON SURFACTANT, COSURFACTANT, OIL, AND TEMPERATURE

Structural features of w/o microemulsions have been conductometrically evaluated. The radius of the water pool, the effective radius of the droplets, their number per unit volume, the effective surface area of the water pool, and the aggregation number of the surfactant and cosurfactant molecules per droplet in the oil/water interphase have been estimated. Three oils (n-heptane, n-decane, and xylene), three surfactants (CTAB, SDS, and AOT) and two cosurfactants (l-butanol and n-hexylamine) have been used; their effects on the structural properties of microemulsions have been studied at two different temperatures, 293 and 303 K, at two weight ratios of surfactant/cosurfactant, 0.33 and 0.50. The droplet radius has been found to be oil dependent and follows the order n-heptane < n-decane < xylene. The values at 293 K are greater than those at 303 K. The dependence of the radius on the surfactant is in the order SDS > AOT > CTAB. 1-Butanol yields greater radius than n-hexylamine with SDS and AOT, and the order is reversed with CTAB. The aggregation number of the surfactant and cosurfactant per droplet increases and decreases, respectively, with elevation of temperature. The Re/Rw (ratio of the effective radius of the droplet and the radius of its water core) remains fairly constant under all situations, the average value being 1.15 ± 0.10. © 1990 American Chemical Society.