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In this work, we investigated the lyotropic aggregation behaviour in dilute solutions of two synthetic glycolipids with same alkyl chain. The chemical structure of the carbohydrate headgroups is similar, nevertheless as reported the thermotropic phase behaviour is different. We found that the slightly tilted compound showing a complex thermotropic phase behaviour forms large aggregates with substructure already in dilute solutions and the significantly tilted compound with its simple thermotropic phase behaviour forms small spherical micelles near the CMC.

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Abstract  

Electrical conductivity of aqueous solutions of dodecylpyridinium chloride and bromide have been determined. From these data the critical micelle concentration (cmc) was determined. The thermal properties as standard Gibbs free energy, enthalpy and entropy of micellization was estimated from a uncharged-phase separation model and enables to obtain another properties like heat capacity of micellization and the relevant parameters in the minimum of temperature dependence of cmc. The enthalpy-entropy compensation was shown for the studied compounds.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Galán, J. Del Castillo, A. González-Pérez, V. Fuentes-Vázquez, and J. Rodríguez

Abstract  

The specific conductivities of dodecylpyridinium chloride have been determinated in water-butanol/pentanol/hexanol solutions in the temperature range of 10 to 35C, and butanol, pentanol and hexanol concentrations up to 0.05 mol kg–1. From these data the temperature dependence of the critical micelle concentration, (cmc), was determined. The molar fraction of alcohol in the micelle was estimated using the theory suggested by Motomura et al. for surfactant binary mixtures. The standard Gibbs free energy of solubilization of alcohols in the micelles was worked out using the phase separation model.

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Abstract  

The critical micelle concentrations and the enthalpies of micellization of alkyltrimethylammonium bromides having dodecyl, tetradecyl and hexadecyl hydrocarbon chains have been studied using surface tension and calorimetry measurements as a function of temperature. As expected, the change of critical micelle concentrations is very small with an increase of temperature of 10 deg whereas we observe a drastic change of the enthalpies of micellization. As it has been found by applying the Van't Hoff law to thecmc values at different temperatures, the calorimetric measurements show that the enthalpy of micellization, exothermic above a minimal temperature, becomes endothermic below this temperature.

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place in the c.m.c. region where the micelles formation process starts [ 16 , 17 ]. Therefore, it is generally accepted that the position of the inflection point corresponds to the critical micelles concentration c.m.c. Such an approach makes it

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the critical micelle concentration (c.m.c.) within the temperature range investigated. In order to describe the plots of the enthalpy of dilution versus surfactant concentration we adopted the sigmoidal Boltzmann equation (SBE) but with some

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Abstract  

The interactions of lysozyme and myoglobin with anionic surfactants (hydrogenated and fluorinated), at surfactant concentrations below the critical micelle concentration, in aqueous solution were studied using spectroscopic techniques. The temperature conformational transition of globular proteins by anionic surfactants was analysed as a function of denaturant concentration through absorbance measurements at 280 nm. Changes in absorbance of protein-surfactant system with temperature were used to determine the unfolding thermodynamics parameters, melting temperature, T m, enthalpy, ΔH m, entropy, ΔS m and the heat capacity change, ΔC p, between the native and denatured states.

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Summary  

The interaction between the U(VI) and a sodium dodecyl sulfonate (SDS) micelle was studied for intensity and emission lifetime. The measurements of the uranyl ion were done in a 1M H3PO4 medium. The self quenching rate constant (k sq) shows a larger value in micellar than in a SDS monomeric solution. This fact should be interpreted by micelles favoring the localized concentration of UO2 2+ species. Dynamic and static quenching was observed in the interaction between uranyl ion and the surfactant monomer before the induced critical micelle concentration (icmc) (1 mM) yielding a value of K D = (134±2) . 10M-1 and K S= (16±2) . 102M-1 for the dynamic and static quenching constant, respectively. A quantitative description of the binding was obtained by monitoring the emission lifetime of the uranyl excited state as a function of the surfactant concentration (titration curve), assuming that the observed lifetime is related to a weighted fraction of rate constants for the bound and unbound species.

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Abstract  

Dextran modified with deoxycholic acid (Dex-DCA) was synthesized by grafting DCA along the polymer backbone, with degrees of substitution (DS)—2% and 3%. The thermodynamics of the association processes of the mixed systems is followed by isothermal titration calorimetry for sodium deoxycholate/sodium dodecyl sulfate (NaDCA/NaDS), Dex-DCA with different surfactants—Dex-DCA/NaDS, Dex-DCA/NaDCA, and Dex-DCA/DTAB (dodecyltrimethylammonium bromide). Calorimetric measurements for the micellization processes of the pure surfactants in aqueous solution were also performed for comparison with the results obtained for the mixed systems. We have obtained and herein present the enthalpies of micelle formation and critical micelle concentrations for the referred pure surfactants, as well as the interaction and aggregation enthalpies for the mixed systems-surfactant/polymer. The dependence of the observed aggregation behavior on the surfactant and temperature is discussed in detail. Finally, we should stress that calorimetry allowed us to ascertain a very important fact in polymer/surfactant interaction. From the comparison between NaDCA/NaDS and Dex-DCA/NaDS calorimetric titration curves, we could clearly see that the interaction between Dex-DCA and NaDS is driven by the interaction between the bile acid moiety and the surfactant.

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Abstract  

The power–time curves of micellar formation of two anionic surfactants, sodium laurate (SLA) and sodium dodecyl sulfate (SDS), in N,N-dimethyl acetamide (DMA) in the presence of various long-chain alcohols (1-heptanol, 1-octanol, 1-nonanol and 1-decanol) were measured by titration microcalorimetry at 298 K. The critical micelle concentrations (CMCs) of SLA and SDS under various conditions at 298 K were obtained based on the power–time curves. Thermodynamic parameters (
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,
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\Updelta S^\circ_{\text{mic}}$$ \end{document}
and
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\Updelta G^\circ_{\text{mic}}$$ \end{document}
) for micellar systems at 298 K were evaluated according to the power–time curves and the mass action model. The influences of the number of carbon-atom and the concentration of alcohol were investigated. Moreover, combined the thermodynamic parameters at 303, 308 and 313 K in our previous work and those of 298 K in the present work for SLA and SDS in DMA in the presence of long-chain alcohols, an enthalpy–entropy compensation effect was observed. The values of the enthalpy of micellization calculated by direct and indirect methods were made a comparison.
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