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 be low percolation in the frequency range from 1 MHz to 1.8 GHz have been anal yzed on the basis of the electrical modulus formalism. In the frequency ran ge investigated, this approach clearly evidences the presence of a particul ar polarization mechanism, resulting in a well-defined dielectric dispersio n, located between that due to the orientational polarization of the bulk a queous phase and that due to the ionic structure of the interface, usually occurring in heterogeneous systems. This polarization mechanism has been at tributed to the "in-phase" correlation displacement of surfactant polar hea d groups surrounding each water droplet dispersed in the oil phase. This me chanism differs from the usual interfacial Maxwell-Wagner effect. The advan tage of the electrical modulus formalism, in comparison with the analysis o f the directly measured quantities, the permittivity epsilon'(omega), and t he total electrical conductivity sigma(omega), are briefly discussed. (C) 2 001 Academic Press.