(9e) Electrical Conductivity of Aqueous Solutions of Surfactants with Added Electrolytes

We analyze the electrical conductivity of aqueous solutions of sodium dodecyl sulphate (SDS) and lithium dodecyl sulfate (LDS) with added electrolytes as a function of the surfactant and electrolyte concentrations. A molecular thermodynamic model of surfactant aggregation in aqueous solutions was used to predict the micelle concentration, the average size and shape of aggregates, and the detailed size distribution of aggregates. Based on these characteristics, the electrical conductivity of a solution was then computed within the framework of the classical Onsager theory for a multicomponent electrolyte. Theoretical predictions were compared with experimental data. Measurements were carried out on a broadband dielectric spectrometer BDS-80, Novocontrol. Experiments cover a broad range of the surfactant and electrolyte concentrations, from above the critical micelle concentration (CMC) to infinite dilution. Deviation of theoretical predictions from experimental data provides insight into the formation of micellar aggregates.

This work was supported by NSF Engineering Research Center on Structured Organic Particulate Systems.