Dielectric spectroscopy of cosurfactant facilitated percolation in reversemicroemulsions

Percolation in reverse microemulsion systems can be driven by various field variables, including temperature and cosurfactant concentration. We use di electric spectroscopy and a macroscopic dipole correlation function (DCF) d erived therefrom to examine mesoscale structural aspects of charge transpor t in a water, AOT, toluene reverse microemulsion that is driven into percol ation by cosurfactant (acrylamide). A multiexponential fitting of the DCF d ata gives firm support to the importance of a parameter marking the onset o f percolation, as distinguished from the percolation threshold. A stretched exponential fitting of the DCF data reveals microstructural and mesoscale similarities and differences between this case of cosurfactant-induced perc olation and a previously examined case of temperature-induced percolation. This cosurfactant-driven system appears to exhibit a critical slowing down on approach to the percolation threshold, as does the temperature-driven ca se, but a much shorter relaxation time suggests the development of much les s fractal structure in this cosurfactant case. The effective fractal dimens ionality and number of self-similarity stages of the fractal structure are only weak functions of the reduced field variable in the case of cosurfacta nt-driven percolation, and contrast sharply with the temperature case. (C) 1999 American Institute of Physics. [S0021-9606(99)71839-8].