Rheological Properties and Microstructures of Anionic Micellar Solutions in the Presence of Different Inorganic Salts

• Published in: The journal of physical chemistry. B Vol. 106; no. 44; pp. 11685 - 11693
• Main Authors: Mu, Jian-Hai, Li, Gan-Zuo, Jia, Xiao-Lei, Wang, Hong-Xia, Zhang, Gao-Yong
• Format: Journal Article
• Language: English
• Published: American Chemical Society 07.11.2002
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp014096a

Wormlike micelles, obtained firstly in anionic surfactant sodium dodecyl trioxyethylene sulfate (SDES) solutions in the presence of AlCl3, were studied using zero-shear viscosities and freeze-fracture TEM micrographs. Then the effects of inorganic salts with different cations, AlCl3, MgCl2, CaCl2, and NaCl, on the rheological properties and microstructures of the SDES micellar solutions were investigated generally. The steady-shear viscosity followed the Cross empirical equation, and the dynamic vlscoelasticity was well modeled by the simple Maxwell model. There exists an optimal molar ratio R m of surfactant to salt at which the micelles reach maximum growth. We find R m ≤ 1/5 for SDES/NaCl system, and R m ≈ 1/3 for the other three systems. Variations in the surfactant packing parameter R p help explain the changes of rheology and microstructure of the solutions, according to the cationic radii and charges and the interaction between the cations and surfactant molecular headgroups. The ability of cations that make the micelles reach a maximum growth followed the order of Al3+ > Mg2+ > Ca2+ > Na+.