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: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:Y. Li, G. Fei, Z. Honglin, L. Zhen, Z. Liqiang, and L. Ganzuo
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 (
) 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.
density increases up to 3 mass% of compatibilizer concentration followed by a decrease at higher loading. This indicates clearly that the compatibilizer leaves the interface after criticalmicelleconcentration (CMC). This is in agreement with the results
the solution ends and a new equilibrium relation between added surfactant and compound resulting from the previous equilibrium relation starts. The criticalmicelleconcentration (cmc) value of a surfactant is also a sc point and there may be some sc