Micellization of alpha-olefin sulfonate in aqueous solutions studied by turbidity, dynamic light scattering and viscosity measurements

Abstract

Dynamic light scattering, turbidity, viscosity and density measurements were performed to study micellization phenomenon in a novel biodegradable surfactant, alpha-olefin sulfonate (AOS), at 25 °C with the AOS concentration varying from 0 to 100 mM and mono-valent salt concentration ranging from 0 to 100 mM. The free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) of micellization along with micellar radii (Rm), molecular weight (M), hydration (Wη and Wdls) (derived from viscosity Wη and scattering data Wdls) have been determined as function of salt concentration. Effect of counterion binding on M and critical micellar concentration (cmc) are evaluated empirically. Three independent estimations of inter-micellar interactions were performed, namely by evaluating second virial coefficient by fitting turbidity data to Debye equation, by fitting viscosity data to Huggin’s equation and by fitting the concentration dependence of Rm to a virial expansion in reduced concentration (c-cmc), these are compared. With increased salt concentration, the inter-micellar attraction was observed to increase thus facilitating formation of larger micelles with aggregation numbers exceeding 100. Sphere to cylinder transition in micellar structure was not observed in the experimental concentration range.