Application of electrochemical impedance spectroscopy as a technique to characterize phase diagrams of surfactant solutions

Characterizing the phase behavior of surfactants in solution is essential to their application on different industrial and research fields. Nowadays, the methodology to determine surfactant structural changes in solutions relies on measurements of bulk-solution properties, which frequently fail when working at highly low surfactant solution. Therefore, alternative strategies are required to accomplish such evaluations. Here, we demonstrate that electrochemical impedance spectroscopy (EIS) can be easily applied to characterize surfactant-phase behavior by monitoring structural modifications at the surfactant solution-electrode interface. A graphical analysis of EIS measurements in form of Bode-type diagrams allows obtaining two representative electrochemical parameters: the surfactant solution resistance and the characteristic time constant associated with the electrochemical double-layer formation, as a function of both temperature and surfactant concentration. These parameters are found to be correlated with the change on the surfactant phase and therefore, its detection is accurately performed even at low surfactant concentrations. Graphical abstract