Rheological experiments were carried out on aqueous dispersions of cetyltrimethylammoniumhydroxynaphthalenecarboxylate (CTAHNC) as a function of temperature. The results indicate the formation of very long elongated wormlike micelles at temperatures higher than about 50 °C, conferring to the system a very high viscosity. This behavior is explained by the combined effect of a large end cap energy and a low ionization degree resulting from a strong binding of the weakly soluble counterions. At lower temperature the surfactant forms a much more fluid vesicle phase, which is observed by videomicroscopy. Experiments performed on mixtures of CTAHNC and of cetyltrimethylammonium bromide (CTAB) show also a vesicle to micelle transition for a ratio of CTAB/CTAHNC that decreases upon increasing the temperature. The rheological behavior of the micellar phase obtained by mixing CTAB and CTAHNC is similar to that obtained for other charged micellar solutions.

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The basic results of the sticky hard sphere model are derived using a perturbative solution of the factorized form of the Ornstein–Zernike equation and the Percus–Yevick closure relation. The perturbation parameter is Δ/(σ+Δ), where Δ and σ are, respectively, the width of the attractive square well pair potential and the hard core diameter. This derivation leads naturally to an expression for the stickiness parameter, different from the one conventionally used, without invoking the concept of an infinitely deep potential. The theoretical structure factor is compared with two sets of Monte Carlo simulation data and excellent agreement is observed in both cases without the scaling of the square well potential suggested in literature.

We have studied the effect of the lipophilicity of the counterions Xon the rheological properties of aqueous solutions of cetyltrimethylammonium-based surfactants (CTAX): cetyltrimethylammonium n-hexane sulfonate (CTAC6SO3), cetyltrimethylammonium n-heptane sulfonate (CTAC7SO3), and mixtures of cetyltrimethylammonium 3-hydroxy-2-naphthalenecarboxylate (CTAHNC) and cetyltrimethylammonium bromide (CTAB) in the molar ratio 1:1 and 2:1. Both linear and nonlinear viscoelasticity properties have been investigated as a function of surfactant volume fraction and temperature. For the system CTAHNC + CTAB (1:1), the effect of added salt (NaBr) was also studied. In the concentration and temperature ranges used in this study, all the systems exhibit a viscoelastic behavior characteristic of wormlike micellar solutions. By changing the lipophilic character of the counterion, one varies the net electrical charge carried by the micelle, which allows us to present a general description of the effect of the electrostatic interactions on the viscoelasticity of micellar systems.