Measurement of critical micelle concentration of nonionic surfactant solutions using impedance spectroscopy technique

Critical micelle concentrations (CMCs) of nonionic surfactant solutions are determined by a conductance technique. A four-terminal cell and an impedance spectrometer are employed. An equivalent circuit of the sample cell is determined and the solution resistance is obtained from the impedance plane plot. The CMC of the nonionic surfactant solution is then determined from the slope break in a conductivity concentration ($\mathrm{\kappa -C}$ ) diagram. Some nonionic surfactants, including both pure and industrial surfactants, are used to examine this technique. The CMCs obtained are in good agreement with that from the surface tension method, but the time required is much less than that for the surface tension method. The conductivities of nonionic surfactant aqueous solutions are only several times that of pure water, whereas they are two to three orders of magnitude lower than that of ionic surfactant solutions. The technique of impedance spectroscopy is found to be an effective tool for measuring the CMC of nonionic aqueous surfactant solutions.