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Molina-Bolivar J.A.,Grupo de Fluidos Estructurados y Sistemas Anfifilicos | Hierrezuelo J.M.,Grupo de Fluidos Estructurados y Sistemas Anfifilicos | Carnero Ruiz C.,Grupo de Fluidos Estructurados y Sistemas Anfifilicos
Journal of Chemical Thermodynamics | Year: 2013

The clouding behavior of two non-ionic mixed surfactant systems (n-dodecyl-β-d-maltoside/n-dodecyl-hexaethylene-glycol and n-decyl-β-d-maltoside/n-dodecyl-hexaethylene-glycol) was investigated over the entire composition range in pure water and in 1 M NaCl. The evolution of micellar size as a function of temperature was monitored by dynamic light scattering and a unimodal distribution pattern of aggregates consistent with a single scattering species was found. Our results confirm that an increase of temperature induces micellar growth and that clustering of micelles occurs as the temperature approaches the cloud point. It was observed that, with increasing temperature, the higher the n-dodecyl-hexaethylene-glycol content the greater the micellar growth. The presence of sugar surfactant monomers in the mixed micelle enhances the cloud point of the system. This phase behavior is sensitive to the presence of NaCl in the micellar solution which induces cloud point depression. For a certain system composition, the cloud point decreases as the alkyl chain length of the sugar-based surfactant increases. Cloud-point thermodynamics were evaluated assuming that clouding indicates the solubility limit when phase separation occurs. The micelle-solvent interactions were characterized from the compensation temperatures, which were determined from the enthalpy-entropy plots. © 2012 Elsevier Ltd. All rights reserved. Source

Naous M.,CNRS Macromolecular Chemistry and Physics Laboratory | Aguiar J.,Grupo de Fluidos Estructurados y Sistemas Anfifilicos | Carnero Ruiz C.,Grupo de Fluidos Estructurados y Sistemas Anfifilicos
Colloid and Polymer Science | Year: 2012

Mixtures of n-octyl-β-D-thioglucoside with three different n-alkyltrimethylammonium bromides (n012 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied by using fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by the pyrene 1:3 ratio method. The experimental results were treated by using thermodynamic mixing approaches based on the pseudophase separation model. It was found that all the mixed systems show a negative deviation from ideal behavior, more pronounced as the larger the alkyl tail of the co-surfactant. It was also observed that the three mixed systems fulfill the conditions of synergism, this behavior being also dependent on the alkyl chain length. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In all the cases, it was observed that the aggregation number is initially reduced with the participation of the cationic surfactant, remaining almost constant and close to the aggregation number of the pure cationic micelles. The local viscosity of pure and mixed micelles was examined by the photophysical response of the hydrophobic probe coumarin 6 solubilized in the micellar medium. It was found that the participation of the ionic component induces the formation of a less ordered structure than that of pure nonionic micelles. This effect being less pronounced as the chain hydrocarbon length of the co-surfactant increases. © Springer-Verlag 2012. Source

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