Application of Power Law in Conductivity of Binary Mixed Rhamnolipid Surfactant Systems

Abstract The limiting molar conductivity (Λ0) reflects the dissociation and the interaction of the electrolyte, and for the surfactant, it also reflects the interface adsorption and aggregation behavior of the molecules. A commonly used calculation method of Λ0 is the extrapolation of conductivity. In this article, a new approach known as Power law were used to improve the accuracy of the determination of Λ0 comparing the Ostwald's dilution law. The Law of independent migration proposed by Kohlrausch was used to explain the ionization and aggregation of surfactants in extremely dilute solutions. The effect of additives (N-Butanol, Diethanolamine (DEA) and PEG400) on Rhamnolipid (RL) aqueous solution were studied by conductivity method. From the obtained conductive results, we can calculate the critical aggregation concentration (CAC), the counter ion dissociation degree (α), the Gibbs standard free energy of micellization (ΔGmic°), molar conductivity (Λ), and aggregation numbers (nagg). Henry's law coefficient (H) and surface tension (γ) were also tested. The result shows that the α calculated by Power law is in good agreement with obtained by the conductivity method, and the CAC, α, Λ0, γ, nagg and H had a good correlation.