Stagnant Layer Conduction in Surfactant-Stabilized Hexadecane Emulsion Systems Measured by Electroacoustics

Abstract

Previously reported zeta-potentials calculated from the electroacoustic behaviour of sodium dodecyl sulfate (SDS) stabilized hexadecane emulsion droplets show certain anomalies. These can be resolved when electrical conduction in the stagnant layer behind the shear plane is included in the analysis. If stagnant layer conduction is ignored the addition of salt causes the apparent droplet size to increase and the magnitude of the zeta-potential to show a maximum. When stagnant layer conduction is included the dynamic mobility spectra can be fitted to a constant size distribution independent of the salt concentration with zeta-potentials that decrease as expected with increasing electrolyte concentration. Increasing SDS concentration, before the homogenization process, causes a decrease in droplet size and an increase in the total surface conductance to a constant value corresponding to the saturation of the surface with SDS. It is shown that the surface conductance and particle size distribution of hexadecane at any given volume fraction are functions of the concentration of SDS and the oil volume fraction. The zeta-potential changes log-linearly with added electrolyte and is independent of the SDS concentration or oil volume fraction used during the emulsification process.