Dielectric spectroscopy of co-ion effects on microemulsion dynamics and phase behavior

Abstract

The effect of added cationic co-ions (Li+, Na+, Cs+, (CH3)4N+) on the dielec. spectra of didodecyldimethylammonium bromide / water / n-dodecane microemulsions is reported. At high water/surfactant mole ratios (W ≈ 100-120) small amts. of co-ions drastically change the shape of the dielec. spectra in the 5-500 MHz region whereas for W ≈ 20 almost no effect is obsd. It is shown that the sensitivity of the dielec. spectra towards co-ion addn. correlates with the percolation transition of the microemulsion structure from reverse micelles at high W to a bicontinuous phase at low W.