Authors:V. M. Garamus, G. E. Milkereit, Regine Willumeit, and V. Vill
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.
Authors:J. Galán, A. Gonzáles-Pérez, J. Del Cactillo, and J. Rodríguez
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.
Authors:J. Galán, J. Del Castillo, A. González-Pérez, V. Fuentes-Vázquez, and J. Rodríguez
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.
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.
Authors:B. Faucompre, M. Bouzerda, M. Lindheimer, J. Douillard, and S. Partyka
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.
Authors:Henryk Piekarski, Katarzyna Łudzik, and Michał Wasiak
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 criticalmicellesconcentration c.m.c. Such an approach makes it
the criticalmicelleconcentration (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
Authors:Elena Blanco, J. Ruso, J. Sabín, G. Prieto, and F. Sarmiento
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, Tm,
and the heat capacity change, ΔCp,
between the native and denatured states.
Authors:Guangyue Bai, Vasco Castro, Marieta Nichifor, and Margarida Bastos
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.
Authors:P. Repossi, W. A. Massad, and G. A. Argüello
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 (ksq) shows a larger value in micellar than in a SDS monomeric solution. This fact should be interpreted by micelles favoring the localized concentration of UO22+ 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 KD = (134±2) . 10M-1 and KS= (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.
Adsorption of Zn(II) and Cd(II) ions on soil TLC plates was studied using aqueous solutions of surfactants as mobile phases. The effects of decomposition of soil organic matter, cation saturation, soil pH, and sewage sludge on the
values (or adsorption) of Zn(II) and Cd(II) were investigated. Among these conditions, soil pH was the most important factor affecting adsorption of Zn(II) and Cd(II) ions by soil layers. Aqueous solutions of cationic (cetyltrimethylammonium bromide, CTAB), nonionic (
-octylphenoxydecaethoxyethanol, Triton X-100), and anionic (sodium dodecyl sulfate, SDS) surfactants at different concentrations (below, near, and above their critical micelle concentrations, CMC) were tested as mobile phases to examine their effect on the efficiency of adsorption of zinc(II) and cadmium(II) by soil stationary phases. Furthermore, the combined effect of surfactants and fertilizers on the adsorption characteristics of Cd(II) and Zn(II) was also investigated. Fertilizers such as KCl and CaCl
in SDS remain insoluble whereas MgCl
) in SDS was highly viscous and causes difficulty during development of soil TLC plates. Addition of Cl-fertilizers to aqueous surfactant mobile phases led to increases in the
values (or reduced adsorption) of Zn(II) and Cd(II) ions on soil layers. Among the mobile phases examined, 1.0 M MgCl
in aqueous CTAB (at concentrations above the CMC) was found to be the best mobile phase for separation of Cd and Zn ions on soil layers. RSD of
values were calculated for both Zn(II) and Cd(II). Cd(II) was found to migrate through the soil layer more quickly than Zn(II). Thus, Zn(II) is strongly retained by the soil surface and Cd(II) is able to pass through the soil layer. The limit of detection of these metal ions was also determined.