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+.
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