MECHANISM OF THE COOPERATIVE RELAXATION IN MICROEMULSIONS NEAR THE PERCOLATION-THRESHOLD

Cooperative dynamics of three-component water-oil-surfactant microemul sions based on sodium bis(2-ethylhexyl) sulfosuccinate surfactant were investigated near the percolation threshold. The measurements were ma de by means of the time domain dielectric spectroscopy method in the t emperature interval 12 degrees C-40 degrees C, including the percolati on range. The data treatment was carried out in time domain in terms o f the macroscopic dipole correlation functions (DCFs) related to the s tructural and kinetic properties of the system. It is shown that the D CF can be described by the Kohlrausch-Williams-Watts (KWW) expression exp[-(t/tau)(nu)] (where tau is the relaxation time and nu is the stre tched parameter), reflecting the peculiarities of the dipole interacti ons in a self-similar medium. For a physical interpretation of the phe nomenological parameters tau and nu, a generalization of the known mod el of the cooperative relaxation was made. The model developed was adj usted for a description of the relaxation in microemulsions that have a fractal nature in the percolation region. The results obtained testi fy that parameters tau and nu in the KWW function are related to the s tructure of the system and reflect the cooperative behavior of microem ulsion droplets near the percolation threshold. It was shown also that the macroscopic law of the relaxation of the KWW type is insensitive to the microscopic details of charge transport in the system and that there is a limited temporal range for the applicability of the stretch ed law of relaxation in time domain. In order to extend the initial te mporal interval of the applicability of the relaxation function the co rrelation to the KWW term was found.