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| 2. |
- Angelescu, Daniel, et al.
(författare)
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Viscoelastic properties of sodium dodecyl sulfate with aluminum salt in aqueous solution
- 2003
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:22, s. 9155-9161
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Tidskriftsartikel (refereegranskat)abstract
- The rheological properties of wormlike micellar solutions formed by the pseudo-ternary system sodium dodecyl sulfate (SDS)-Al(NO3)(3)-H2O have been studied at a fixed molar ratio Al(NO3)(3):SDS = 5.92:1 as a function of surfactant concentration. The linear data show that solutions behave as a Maxwell fluid and there are two well-defined domains characterized by scaling laws for surfactant concentration, with a maximum in the viscosity-surfactant concentration curve. Prior to the maximum, the system consists of linear micelles, and eta(0) (zero-shear rate viscosity) and tau(R) (relaxation time) are found to scale with surfactant concentration with exponents higher than those predicted by the theory of Cates. The results in the second domain are not reflected by the dynamic behavior of entangled wormlike micelles, and they are interpreted in terms of formation of connected micelles. The nonlinear rheology is governed by the shear banding effect occurring for viscous entangled wormlike micellar solutions and branched micelles, and the properties identified by reduced stress sigma(p)/G(0) and the Weissenberg number, y(c)tauR, are compared to the values predicted on the basis of the theoretical model.
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| 3. |
- Caragheorgheopol, A, et al.
(författare)
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Structural characterization of micellar aggregates in sodium dodecyl sulfate/aluminum nitrate/urea/water system in the synthesis of mesoporous alumina
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:23, s. 7735-7743
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of templated synthesis of ordered mesoporous alumina according to the recipe proposed by Yada et al. (Yada, M.; Machida, M.; Kijima, T. Chem. Commun. 1996, 769) using sodium dodecyl sulfate (SDS) as template, has been investigated by NMR self-diffusion and spin and fluorescence probe techniques. In the precursor solutions urea was found to produce a substantial shortening of the long entangled cylindrical aggregates characteristic of the SDS micellar solutions with aluminum salt in large excess. The formation of mesostructured hexagonal alumina was followed using spin probes incorporated in the SDS aggregates. No structural changes were observed during urea hydrolysis, before the onset of the precipitation. In the precipitate, the presence of the surfactant template is demonstrated as well as its interaction with the aluminum species. Time evolution of this interaction is also observed. Finally, the influence of the composition of the precursor system on the structure and thermal stability of as-synthesized alumina has been studied. It appears that hexagonally structured alumina is formed over a large range of compositions of the starting solution, with the dimension of the unit cell being almost constant. A model of precipitation is proposed that is based on the analogy with the formation of the hexagonal crystalline Al-DS precipitate in the ternary SDS/Al(NO3)(3)/water system.
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| 4. |
- Vasilescu, M, et al.
(författare)
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Fluorescence study on the size and shape of sodium dodecyl sulphate-aluminium salt micelles
- 2004
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 235:1-3, s. 57-64
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Tidskriftsartikel (refereegranskat)abstract
- The application of time-resolved fluorescence methods to study the aggregation behavior in aqueous solution of anionic surfactant sodium dodecyl sulphate (SDS) in presence of trivalent counterions (Al3+) was investigated. Addition of small amounts of aluminum salt to dilute micellar solutions (< 10 wt.% SDS) resulted in isotropic fluid solutions, but for a molar ratio [SDS]/[Al(NO3)(3)] lower than 6.7:1, precipitation occurred. The precipitate was resolubilized by further addition of aluminum salt (>5 wt.% Al(NO3)(3)). Using the time-resolved fluorescence quenching method and employing pyrene-decylpyridinium chloride as probe-quencher pair, the aggregation numbers and fluorescence quenching rates for spherical micelles were determined. Fluorescence measurements give evidence for different kind of micelles in the two isotropic areas investigated. At low aluminum salt concentration, the micelles are relatively small, but larger than in the absence of salt. At high enough salt concentrations, the precipitate is resolubilized into long rod-like micelles. The strong viscoelastic properties in the linear regime supported the presence of worm-like micelles in the redissolution area. (C) 2004 Elsevier B.V. All rights reserved.
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