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.
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
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:J. Zajac, M. Chorro, C. Chorro, and S. Partyka
The importance of calorimetric methods in studies of colloidal phenomena is illustrated by the analysis of the experimental
enthalpies of dilution and adsorption for aqueous solutions of three zwitterionic surfactants: 1–12 betaine, 3–12 betaine,
and 3–12 sulfobetaine. The batch microcalorimeter ‘Montcal 3’, used to obtain these data, is described. The molar enthalpies
of micellization and the differential molar enthalpies of adsorption onto silica gel are shown to be functions of the headgroup
hydrophilicity, fixed by the type of negatively charged center and the number of methylene groups separating the charged sites.
Authors:M. Hutta, S. Rippa, J. Kandráč, and M. Chalanyová
Post-column derivatization detection system based on dithizone solubilized in cetyltrimethyl-ammonium hydrogenesulfate micellar media at pH 2.0 was devised and evaluated for selective detection of mercury(II), methylmercury and phenylmercury in reversed-phase HPLC system with photometric detection at 500 nm. This reagent solution is fully compatible with acidic organo-aqueous mobile phases generally used in RPHPLC. With the aid of the detection systematic study of the retention behaviour of three mercury species on octadecylsilica sorbent was carried out. Influence of pH, acetonitrile volume fraction, complex forming additives was investigated in detail. In mobile phase consisting of 5–30% of acetonitrile in water at pH 2.0 and 2·10–4 mol·I–1 DCTA linear calibration curves were measured in range 20–1000 ppb with correlation coefficient better than 0.99. Detection limits were 1–5 ng for this three mercury species. Interferences of copper(II) and silver(I) are negligible.
of association is the isothermal titration microcalorimetry (ITC). It has been successfully applied in a growing number of studies of surfactant systems [ 7 – 19 ]. The major advantage of ITC for micellization studies is the ability to perform direct
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:Marta Fernandez-Tarrio, Carmen Alvarez-Lorenzo, and A. Concheiro
comprises X-shaped copolymers formed by four poly(propylene oxide) (PPO) and
poly(ethylene oxide) (PEO) block chains bonded to an ethylene diamine central
group. Micellization behaviour of three representative Tetronics (T304, T904
and T1307) was characterized to gain an insight into the interactions between
the copolymer unimers and the state of water in their solutions. The enthalpy
of demicellization, recorded at 37°C in an isoperibol microcalorimeter,
indicated that the process was in all cases exothermic and the enthalpy ranked
in the order T1307≥T904>>T304. Micellization is entropy-driven owing to
hydrophobic interactions between the PPO chains.
showed that the crystallization and melting peaks of the free water remaining
in T304 and T904 solutions were progressively shifted toward lower temperatures
as the surfactant proportion increased, owing to a colligative effect. Bound
water corresponded to 3 water molecules per EO repeating unit. In the case
of T1307, which has longer PEO chains, a splitting of the melting peak was
observed, one peak appearing around 0°C due to free water and another
at –15°C due to interfacial water. As T1307 proportion raised, the
enthalpy of the former decreased, whilst the enthalpy of the latter increased.
In 40% T1307 solutions, interfacial water overcame the proportion of free
water; there being 1 interfacial and 3 bound water molecules per EO repeating
unit. Gaussian deconvolution of FTIR spectra also enabled to characterize
the evolution of free water as a function of Tetronic proportion. The dependence
of micellization and water interaction behaviour on Tetronics structure should
be taken into account to use these copolymers as drug solubilizers and micellar
Authors:S. Lagerge, A. Kamyshny, S. Magdassi, and S. Partyka
A new batch titration microcalorimeter has been used for estimation of thermodynamic properties in various investigated colloidal systems. As examples, we present enthalpic and kinetic data obtained from this calorimetric device for four different processes widely encountered in colloid science:
The dilution/micellization process of cationic gemini surfactants in aqueous solution.
The hydration process of non ionic surfactants in organic solution, i.e. the mechanism of micellar solubilization of water in the aggregates.
The complexation of calcium ions by polyacrylates sodium salts (PaNa).
The adsorption phenomenon of PaNa molecules on the calcium carbonate surface.