An electroacoustic and high-frequency dielectric response study of stagnant layer conduction in emulsion systems

Stagnant layer conduction (or anomalous surface conduction) in perfluoromethyldecalin (PFMD) and n-hexadecane emulsions has been measured by electroacoustics and verified by high-frequency dielectric response experiments. The electroacoustic technique can detect the presence of stagnant layer conduction from the salt dependence of the dynamic mobility. As the indifferent electrolyte concentration is increased from low values (<5 mM), the zeta-potential and droplet size, estimated from the dynamic mobility by the normal procedures, gradually increase in magnitude until the size plateaus and the zeta-potential begins to decrease with added salt in the usual fashion. When stagnant layer conduction is taken into account, the dynamic mobility can be fitted to a constant size distribution and more realistic zeta-potential values with varying electrolyte concentration. High-frequency dielectric response has been used to measure the total conduction in a PFMD emulsion system. Very good agreement between these two independent techniques verifies the existence of conduction behind the shear plane and demonstrates that electroacoustics alone can detect and quantify its extent. This is possible because of the unique character of the AcoustoSizer procedure, which estimates both particle size and zeta-potential from the same signal.