Occurrence of an intermediate relaxation process in water-in-oil microemulsions below percolation: The electrical modulus formalism

The dielectric and conductometric spectra of water-in-oil microemulsions below percolation in the frequency range from 1 MHz to 1.8 GHz have been analyzed on the basis of the electrical modulus formalism. In the frequency range investigated, this approach clearly evidences the presence of a particular polarization mechanism, resulting in a well-defined dielectric dispersion, located between that due to the orientational polarization of the bulk aqueous phase and that due to the ionic structure of the interface, usually occurring in heterogeneous systems. This polarization mechanism has been attributed to the "in-phase" correlation displacement of surfactant polar head groups surrounding each water droplet dispersed in the oil phase. This mechanism differs from the usual interfacial Maxwell-Wagner effect. The advantage of the electrical modulus formalism, in comparison with the analysis of the directly measured quantities, the permittivity epsilon'(omega), and the total electrical conductivity sigma(omega), are briefly discussed. (C) 2001 Academic Press.