Electrical Double Layer in Polar and Nonpolar Media in the Presence of Surfactants

Abstract

The objective of this thesis is to improve our understanding of the concept of electrical double layer (EDL). The EDL is the basis of all electrokinetic phenomena. Despite numerous studies in the span of over a century, our perception of this concept is far from complete owing to its complex nature. In this work, we revisit the structure and properties of EDL in polar and nonpolar media. First, we investigate the change of the zeta potential of a representative polymeric particle in the presence of various types of surfactants using electrophoretic light scattering. This study allows us to comprehend the tuning of the zeta potential of a polymeric substrate as well as the adsorption mechanisms of the different types of surfactants. Second, we use dielectric relaxation spectroscopy (DRS) to understand the EDL formation around the micelles in an aqueous medium. This method can be implemented for determining the surface conductivity as well as the zeta potential of the dispersed species in an opaque sample. Third, electrical impedance spectroscopy (EIS) is used to resolve the structure of an EDL in aqueous electrolyte and surfactant solutions. This study allows us to infer the dominance of the compact layer in determining the equivalent capacitance of the EDL as well as the change in the permittivity of the medium within this compact layer. Finally, the EIS measurements are also conducted in a nonpolar medium in the presence of a nonionic surfactant. The electric charge formation and the emergence of the EDL are explored and compared to the charge formation mechanisms proposed in the literature.