Rheology of the Cetyltrimethylammonium Tosilate−Water System. 2. Linear Viscoelastic Regime

Abstract

In this work, the linear viscoelastic properties of the cetyltrimethylammonium tosilate (CTAT)−water system are examined in detail. This system forms elongated micelles at low and intermediate concentrations, and it yields a hexagonal phase above 27 wt % CTAT at 25 °C. Rheological behavior at low frequencies in a small-amplitude oscillatory shear experiments or at long times in stress relaxation measurements is governed by a single dominant relaxation time, although deviations from the limiting slope of the elastic modulus in the terminal region are observed at high CTAT concentrations. For higher frequencies, however, there is an additional mechanism whose dependence on frequency is analyzed with several rheological models. Analysis of data in terms of the theory of Cates demonstrates that the system consists of flexible micelles in the slow-breaking limit and it exhibits a constant entanglement density along the whole micellar region, even though the average micellar length decreases monotonically with concentration. Under these conditions, reptation speed up by the kinetics process of breaking and re-forming is the controlling relaxation mechanism.

Viscoelastic properties of new mixed wormlike micelles formed by a fatty acid salt and alkylpyridinium surfactant

“…7. They are similar to the values reported in literature for different surfactant systems [30,31]. From Fig.…”

Viscoelastic Behavior of Aqueous Solutions of Charged Hybrid Threadlike Micelles

“…temperature. In the case of the elasticity found in the OTM 14) and previously studied HTM systems, 11) long threadlike micelles entangle each other. In the systems, the magnitude of G N is kept in a nearly constant value in such the narrow temperature range as in the case of present study (20 to 40 °C), and t decreases with increasing temperature.…”

“…13) OTMs are easily formed with equimolar amounts of surfactants, e.g., cetyltrimethylammonium bromide (CTAB), and hydrophobic additive salts, e.g., sodium p-toluenesulfonate (NapTS). 14,15) The unique mechanical relaxation mode observed in fully entangled OTM and HTM systems is explained by a model assuming the fusion and crossing of the threadlike micelles at entanglement points, which is called phantom-crossing model. 16) It has been well known that two factors are important to construct HTMs.…”

Nonlinear Viscoelastic Behavior of Aqueous Hybrid Threadlike Micellar Solutions

“…4,5) Because threadlike micelles are formed by only intermolecular interactions between constituent molecules, they of course belong to the category of supramolecular polymers. Even at low surfactant concentrations less than 1 mM, enormously long threadlike micelles are formed between surfactants with long alkyl chains such as cetyltrimethylammonium bromide (CTAB) and hydrophobic aromatic additive salts like sodium salicylate (NaSal) 6) or sodium p-toluenesulfonate (NapTS) 7,8) , where c D means the concentration of surfactants, 9) is usually observed as well as in the polymer systems. In contrast, it has been well known that relaxation mechanisms of threadlike micellar systems are completely different from that of concentrated polymer systems in good solvent well described by, so called, a reptation mechanism.…”