Hydrodynamic and Electrokinetic Properties of Decane Droplets in Aqueous Sodium Dodecyl Sulfate Solutions

Abstract

Electrophoretic mobilities of sodium dodecyl sulfate (SDS)-stabilized decane droplets are converted to ζ-potentials with the aid of light scattering and SDS surface excess measurements. Static light scattering measurements of droplet size and shape in conjunction with dynamic light scattering measurements of droplet diffusion are used to determine the droplet hydrodynamic mobility coefficient. For the SDS concentrations used here between 0.01 and 1 mM SDS, the droplet's mobility coefficient is consistent with the droplet being a nondeformable, solid, spherical particle with no interfacial momentum transfer. The decane droplets display decreasing monodisperse radii with increasing bulk SDS concentration. The percent ionization of the SDS, or degree of counterion binding, is considered by comparing the charge corresponding to the measured ζ-potentials with the charge due to the SDS surface excess inferred from interfacial tension data. After the droplet hydrodynamic mobility coefficient and percent ionization of the interfacial SDS are considered, ζ-potentials for the SDS concentrations studied are found to be between −100 and −125 mV.