Dielectric Spectroscopy of Co-Ion Effects on Microemulsion Dynamics and Phase Behaviour

Wolfgang Wachter and Richard Buchner*

Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93040 Regensburg, Germany
* Corresponding author: E-mail: Buchner@chemie.uni-regensburg.de

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

Keywords: Microemulsions, dielectric spectroscopy, phase behaviour, co-ion effect