Classical and dynamic light scattering, electric birefringence, kinetic, surface tension, conductivity and rheological measurements were carried out on so called viscoelastic detergent solutions of Cetylpyridiniumsalicylate (CPySal). The results indicate that spherical micelles are formed in these solutions above the critical micelle concentration (cmc) = 1.5 · 10−4 M. From the cmc on the concentration of the micelles increases linearly with the total detergent concentration up to a second critical concentration (cmc11 = 4.5 · 10−4 M). Upon further increase of the total concentration, the concentration of the micelles remains constant and the globular micelles grow to rodlike micelles. The length of the rods increases linearly with the total concentration. The residence time of a detergent molecule in the rod is longer than in the globular micelle. The surface charge density of the rods is smaller than for the spherical micelles. In unstirred solutions the rods are randomly oriented but their center of masses are ordered. As a consequence the rods can rotate freely as long as their main axis is shorter than the mean distance between the aggregates but their translational diffusion is hindered by the existence of lattice like ordering. Shearing of the solution leads to large areas of a new metastable nematic type phase in which the rods are oriented with respect to each other. These oriented domains are the source for the apparent elasticity of the solutions. When the shearing of the solution is stopped, the elasticity decays with rather long time constants that can amount to several minutes. — The complete equilibration of the solution after the system was perturbed by dilution or a change in temperature takes up to several hours.

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Conductivity, kinetic, static and dynamic light scattering, electric birefringence and rheological measurements were carried out on aqueous solutions of Tetradecylpyridinium-n-Heptanesulfonate (C14PyCTSO3) up to high concentrations. In dilute solutions between the critical micelle concentration (cmc) and another characteristic concentration (ct) spherical micelles were detected whose radii were independent of detergent concentration and equal to the length of a detergent molecule ; the aggregation number n of these micelles of about 100 monomers per micelle was also in agreement with the existence of normal spherical micelles of a C~4-detergent. Above the concentration c~ the spherical micelles were found to grow to rodlike aggregates whose short axis was still independent of concentration and equal to the length of a monomer, while the lengths L of the rods increased with increasing detergent concentration. When the lengths L of the rods became comparable with the mean distance a between them, the starting interaction between the rods slowed down their growth. In this concentration range of overlapping rods, the data could be evaluated with a recently developed theory by Doi and Edwards for stiff rods. The rods reached finally a maximum length of about 500 • and decreased again in size upon further increase of concentration when the overlap ratio L/a reached a value of about 1,5.

We have studied aqueous mixtures of tetradecyldimethylaminoxid (C14DMAO) and calciumdodecyl sulfate Ca(DS)2. Surface tension measurements show a stronger synergism for these mixtures than for the combination of C14DMAO and sodiumdodecyl sulfate SDS. With an increasing mole fraction of dodecyl sulfate XDS, for 100 mM solutions one observes a viscoelastic L1-phase, a birefringent Lα-phase, and a viscous L1-phase on the dodecyl side. The maximum of the viscosity in the first L1-phase occurs around X DS = 0.28. At this composition, the viscosity is more than 4 orders of magnitude higher than the viscosity of the single-component solutions. Rheological measurements show that the birefringent Lα-phase is composed of densely packed multilamellar vesicles. For concentrations above 100 mM, the Lα-phase has a yield stress value that is large enough to suspend small dispersed air bubbles. SANS measurements show that the interlamellar spacing between the bilayers at 100 mM is ∼800 Å and is independent of X DS within the existence region of the liquid crystalline phase. To our knowledge, this is the first time that a vesicle phase from combination of a single-chain zwitterionic surfactant and a Ca salt of a single-chain anionic surfactant has been reported. The large synergism between the two surfactants is likely to be the result of strong binding of Ca ions to two dodecyl sulfate ions. The Ca ions act as links for two ionic surfactants, and by doing so, the Ca(DS)2 behaves like a double-chain surfactant. In addition, it is conceivable that the Ca ions coordinate to the polar oxygen of the aminoxide.

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