DIELECTRIC STUDIES ON MICROEMULSIONS (OIL, WATER)
The dielectric properties of several ionic and nonionic oil-in-water (O/W) microemulsions were measured, at frequencies from 1 MHz to 15.4 GHz. At frequencies below 100 MHz, a conventional admittance bridge was used for the dielectric measurements. Above 100 MHz, a computer-controlled automatic network analyzer system was employed, with measurement techniques that were specially developed for the present study.^ At frequencies above ca. 1 GHz, the dielectric properties of the systems exhibit large dispersion phenomena due to the dipolar reorientation of the suspending water. In all casas, the mean relaxation frequency was lower than that of pure water by factors of 2 to 5. In the ionic systems, additional dispersion phenomena were observed at frequencies below 100 MHz, which were attributed to counterion polarization mechanisms.^ The dielectric data are analyzed using the Maxwell-Wagner and Hanai mixture theories, which are valid for suspensions of low permittivity droplets in a high permittivity fluid. The apparent phase volumes of the suspensions, obtained from the microwave dielectric data, were in all casas larger than expected from the known (compositional) phase volumes. A simple model, in which the interfacial water in the system is assumed to have a lower dielectric relaxation frequency and ionic conductivity than the bulk suspending liquid, but the same low frequency permittivity, can adequately explain all of the data. The apparent hydration values for the surfactants and cosurfactants, obtained from the model, agree well with values expected from the chemical composition of the systems. ^
BENJAMIN ROSS EPSTEIN,
"DIELECTRIC STUDIES ON MICROEMULSIONS (OIL, WATER)"
(January 1, 1982).
Dissertations available from ProQuest.