DIELECTRIC-PROPERTIES OF ANIONIC AND NONIONIC SURFACTANT MICROEMULSIONS

The dielectric permittivities of anionic and nonionic oil-continuous microemulsions have been measured with varying water content, temperature, alkane carbon number, and electrolyte concentration. The data confirm the hypothesis that underlying phase behavior and consequent morphology have a profound effect on the dielectric properties of microemulsions. The results make it abundantly evident that it is not possible to understand permittivity by use of a simple drop model for microemulsions. It is proposed that water-in-oil domains coexist with oil-in-water domains even at low water concentrations and low electrical conductivities and that the dielectric constant is sensitive to the fraction of each type of domain present in a system. A mean field approximation is used to evaluate the fraction of water-in-oil domains that coexist with oil-continuous domains in these predominately oil-in-water microemulsions. © 1990, American Chemical Society. All rights reserved.