Y. Feldman et al., DIELECTRIC-SPECTROSCOPY OF MICROEMULSIONS, Colloids and surfaces. A, Physicochemical and engineering aspects, 128(1-3), 1997, pp. 47-61
The dielectric spectroscopy method (DS) has become a useful technique
for the investigation of the structural and dynamic features of the co
mponents of both microemulsions and microdroplets over a wide temperat
ure and frequency range. The dielectric parameters obtained by DS dete
rmine the geometry of the association structures as well as the overal
l picture of the dynamics of the different polar groups, aggregates, a
nd association structures representing dipole modes. In this paper the
results of a comprehensive study of the different types of microemuls
ions (ionic and nonionic) by DS are presented. The static and dynamic
dielectric properties of microemulsions as a function of temperature,
frequency and concentration of water, oil, surfactant and cosurfactant
are considered. The dielectric properties have been investigated in t
he frequency range 10(5)-10(10) Hz using time domain dielectric spectr
oscopy (TDDS) and over a broad temperature interval enabling us to cov
er all the main dynamic processes occurring in such systems. The data
treatment for the dynamic behavior of the microemulsions was carried o
ut in the time domain in terms of dipole correlation functions and in
the frequency domain in terms of complex dielectric permittivity. The
correlation functions of the investigated systems exhibit complex none
xponential relaxation behavior, which must be deconvoluted into normal
modes and represented as a sum of the simple exponential, exp(-t/tau)
, and nonexponential terms, exp [-(t/tau)(v)]. The parameter v charact
erizes the shape of the relaxation function and the cross-correlation
effects, and describes the morphology of the system. The molecular mec
hanisms responsible for dielectric polarization in microemulsions of d
ifferent nature are discussed. Knowledge of the amount of hydrate wate
r and co-surfactant in the interface can be obtained for nonionic micr
oemulsions. In the case of ionic microemulsions, TDDS is a powerful te
chnique for monitoring the organization of clusters and for investigat
ion of relaxation processes involving rearrangement and movement of th
e droplets forming the clusters. (C) 1997 Elsevier Science B.V.