Charge and Electrical Double Layer Formation in a Nonpolar Solvent Using a Nonionic Surfactant

In this work, we study the charge formation and the characteristics of the electrical double layer in a nonpolar medium using electrical impedance spectroscopy. To stabilize the free ionic species, a nonionic surfactant is added to the system. The conductivity and permittivity of the medium are obtained from high- to medium-frequency impedance data. Based on the correlation between (viscosity-adjusted) conductivity and surfactant concentration, we conclude that charge formation occurs due to a disproportionation mechanism. We accordingly estimate the concentration of the charge carriers in the sample and the Debye length of the diffuse double layer. The capacitance of the electrical double layer can be extracted from the low-frequency impedance data. We use this data to calculate the electrode distance of an equivalent parallel-plate capacitor. It is found that this distance is on the order of magnitude of Angstroms, indicating that the measured electrical double-layer capacitance is in fact the Stern layer capacitance.