Viscoelastic solutions of polyoxyethylene lauryl ethers and anionic surfactant mixtures: Headgroup and salt effects

Polyoxyethylene alkyl ethers (C 12 EO x ) are nonionic surfactants extensively employed across various industrial sectors due to their low toxicity and favorable physicochemical properties. Their self-assembly behavior can be tuned by modifying the alkyl chain length and the number of ethoxylated (EO) units. This tunability becomes particularly important when these surfactants are combined with anionic surfactants to form viscoelastic systems. In this study, the rheological properties of binary (C 12 EO x with either sodium dodecylbenzenesulfonate, SDBS, or sodium cholate, NaC) and ternary (C 12 EO 4 /C 12 EO 23 (1,1) with either SDBS or NaC) surfactant mixtures were investigated. Selected systems were further characterized using Cryo-EM and SAXS. Binary mixtures formed wormlike micelles (WLMs), while ternary systems exhibited coexisting WLMs and vesicles, reflecting more complex self-assembly. These differences were linked to the number of EO units and the type of anionic surfactant used. As a complementary aspect of this study, we examined the effect of magnesium—a representative divalent cation—added in both salt and chelated forms, relevant to applications such as gel fertilizers. While divalent ions are known to affect micellar systems, the role of specific counterions in viscoelastic surfactant systems remains underexplored. In our study, magnesium additives produced only minor changes in rheology, suggesting a limited impact regardless of their chemical form • Binary mixtures of C 12 EO x with NaC or SDBS form viscoelastic wormlike micelles. • Ternary systems show coexisting wormlike micelles and vesicles. • EO chain length and anionic headgroup type govern micellar structure and rheology. • Magnesium complexes have minimal effect on the viscosity of surfactant solutions.