Effect of Cosurfactant in the Electrochemical Response of Reverse Microemulsions Formed by the AOT+Pentanol/Isooctane/Solution of [Fe(CN)6]3− System: A Cyclic Voltammetry and Electrochemical Impedance Spectroscopy Study

Abstract

Cyclic voltammetry (CV) is an electrochemical technique that has been used to characterize reverse microemulsions (RMs). By following the oxidation-reduction of an electroactive probe (EP) previously dissolved in the RM water droplets, the diffusion coefficient of such droplets can be obtained by relating the measured current and the concentration of the EP. This approach assumes that the current is due solely to the oxidation-reduction of the EP. Nevertheless, adsorption and other non-faradaic processes that are commonly observed in complex systems like RMs, especially in those that contain cosurfactants, can also contribute to the current. In this work, electrochemical impedance spectroscopy (EIS) is used to study these processes in RMs formed by AOT/isooctane/water, with pentanol as cosurfactant and [Fe(CN)6]3− as EP. The results indicate that pentanol is distributed in the bulk of the RM, which increases the conductivity of the whole system; and also adsorbed at the electrode, which decreases the charge transfer resistance. The combination of both effects explains the increase in the current observed when the amount of cosurfactant increases. As conclusion, using CV in combination with EIS measurement is recommended to characterize RMs and reaching a more complete understanding on the electrochemical behavior of the system.