Dielectric relaxation and percolation phenomena in ternary microemulsions

Dielectric relaxation of water/AOT/oil (iso-octane, undecane, dodecane, cyclohexane) microemulsions was studied by means of time-domain spectroscopy. [Here AOT is an abbreviation for sodium bis(2-ethylhexyl)sulfosuccinate.] The experiments were carried out for several values of the volume fraction φ (water + AOT) and of the molar ratio n= [water]/[AOT]. They showed the presence of a maximum of static permittivity ${\epsilon }_s$ associated with a minimum of the relaxation frequency ${\nu }_R$ and a maximum of the frequency-spread parameter α. The influence of the salt content was also considered. The results are discussed with reference to the theory of percolation, and were found to be in close agreement with the theoretical predictions. By analogy with previous results on conductivity [M. Moha-Ouchane, J. Peyrelasse, and C. Boned, Phys. Rev. A 35, 3027 (1987)], the influence of temperature is discussed. The important part played by interactions and the phenomenon of ‘‘hopping’’ are demonstrated in connection with an already existing model (an off-lattice simulation). Finally, the results show the importance of the notion of ‘‘percolation threshold lines’’ introduced previously (Moha-Ouchane, Peyrelasse, and Boned).