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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found that the addition of salt to aqueous cationic surfactant weakens electrostatic interactions and enhances micellar growth, in which the spherical surfactant micelles undergo a transition to larger rodlike aggregations with a molar weight of about 10 6 , named as wormlike micelles. They have high surface activity, high viscosity, and the property of shear thinning, which make them have such wide uses in many fields that people pay more and more attention to them. However, for anionic micelles, there are fewer reports.Recently, we have been interested in the micellar growth induced by an increase in the amount of anionic surfactant, sodium dodecyl trioxyethylene sulfate (SDES), and salts, AlCl 3 , CaCl 2 , MgCl 2 , KBr, NaCl, etc. in systems where wormlike micelles or network structures are formed. In this work, rheological methods and freeze-fracture transmission electron microscopy (FF-TEM) were applied to investigate the effect of surfactant concentration on the formation and viscoelasticity of wormlike micelles and network structures in anionic surfactant SDES aqueous solutions in the presence of the multivalent counterion electrolyte AlCl 3 . Some interesting and noticeable conclusions will enrich the theory and application of wormlike micelles.Abstract Wormlike micelles and network structures were obtained for the samples with the anionic surfactant, sodium dodecyl trioxyethylene sulfate (SDES), and multivalent counterion electrolyte AlCl 3 fixed in a proper concentration according to rheological measurements and the technique of freeze-fracture transmission electron microscopy (FF-TEM). The characteristics of a non-Newtonian fluid and the phenomenon of shear-induced structures transition were acquired from the steady-shear experiments. The TEM micrographs show the coexistence of wormlike micelles, entangled network structures, rod-and sphere-like micelles in the solutions.The Cole-Cole plot shows the rheological behavior of the non-linear viscoelasticity, the departure from the Maxwell model, and a relaxation time that is not simple. The plateau modulus G 0 and the relaxation time s were also investigated to express the rheological properties of the wormlike micellar solutions.

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The interaction and synergism of some polyoxyethylenated fatty alcohol ether (POE) nonionic surfactants (C 12 E 2 , C 12 E 3 , C 10 E 5 , C 10 E 7 , where C x indicates number of carbon atoms in the chain and E y indicates number of oxyethylene glycol ethers) with trioxyethylenated dodecyl sulfonate (C 12 E 3 S) in mixed monolayer formation at the surface and in mixed micelle formation in aqueous solutions were studied at 25 and 40°C by calculating interaction parameters (β σ , β M ) from surface tension-concentration data by use of Rosen's equations based on the nonideal solution theory. All the systems investigated adapt reasonably well to the nonideal model, with negative values of β σ and β M (where M means micelle and σ refers to the air-liquid interface) indicating a favorable interaction between the mixed surfactants. Either at a monolayer or in a mixed micelle, the attractive interaction becomes stronger when the alkyl chain in the POE surfactant is longer, i.e., when the POE becomes more hydrophobic. The interaction increases in the order C 10 E 7 < C 10 E 5 < C 12 E 3 , C 12 E 2 . For the two C 10 E n (n = 5,7)/C 12 E 3 S systems, as temperature increases from 25 to 40°C, the interaction increases in a mixed micelle, but it decreases in a mixed monolayer. Synergism in mixed micelle formation exists for C 12 E 3 S/C 10 E n mixtures when X 1 M , the mole fraction of POE in a mixed micelle, is ~0.4-0.8, whereas synergism does not occur in the systems of C 12 E 3 S/C 12 E m due to the large difference between CMC 1 and CMC 2 , i.e., large ln(C 1 M /C 2 M ) value (where CMC = critical micelle concentration). The degree of synergism in mixed micelle formation is temperature independent and is 0.23, 0.18, and close to zero for C 10 E 5 /C 12 E 3 S, C 10 E 7 /C 12 E 3 S, and C 12 E m (m = 2,3)/C 12 E 3 S systems, respectively. Synergism in surface tension reduction effectiveness occurs in C 12 E 3 S/C 12 E 2 and C 12 E 3 S/C 12 E 3 systems. The mole fractions of POE in the solution phase are 0.302 and 0.333 for the two mixtures at the point of maximum synergism.