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:Asghar Taheri-Kafrani and Abdol-Khalegh Bordbar
The micellization characteristics of sodium n-dodecyl sulfate (SDS) have been investigated by microcalorimetric technique at conditions close to the physiological ones.
The thermodynamics of micellization were studied at 20, 25, 30, 35 and 40 °C in 50 mM HEPES buffer, pH 7.4 and 160 mM NaCl
using isothermal titration calorimetric (ITC) technique. The calorimeter can operate in a stepwise addition mode, providing
an excellent method of determination of critical micelle concentration (CMC) and enthalpy of demicellization (and hence micellization).
It can as well distinguish between aggregating and non-aggregating amphiphiles (solutes) in solution. The dilution enthalpy
(∆Hdil) was calculated and graphed versus concentration in order to determine the micellization enthalpy (∆Hmic) and CMC. In addition to the CMC and ∆Hmic, the effective micellar charge fraction (α) of the ionic surfactant micellization process can also be determined from ITC
curves. The Gibbs free energy of the micellization (∆Gmic), entropy of the micellization (∆Smic), and specific heat capacity of the micellization (∆CP,mic) process have been evaluated by the direct calorimetric method (mass-action model) as well as by the indirect method of van’t
Hoff by processing the CMC and α results of microcalorimetry at different temperatures. The differences of the results obtained
by these two procedures have been discussed. The presence of NaCl (160 mM) in the solutions decreased the CMC of SDS. The
enthalpy changes associated with micelle dissociation were temperature-dependent, indicating the importance of hydrophobic
interactions. The ∆Gmic was found to be negative, implying, as expected, that micellization occurs spontaneously once the CMC has been reached. The
values of ∆Gmic were found to become more negative with increasing temperature and the ∆Smic was found to decrease with increasing temperature in both models.
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 molality dependence of specific conductivity of pentadecyl bromide, cetylpyridinium bromide and cetylpiridinium chloride
in aqueous solutions has been studied in the temperature range of 30–45 °C. The critical micelle concentration (cmc) and ionization
degree of the micelles, β, were determined directly from the experimental data. Thermal parameters, such as standard Gibbs free energy
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: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: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: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: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.