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Abstract  

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 (∆H dil) was calculated and graphed versus concentration in order to determine the micellization enthalpy (∆H mic) and CMC. In addition to the CMC and ∆H mic, 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 (∆G mic), entropy of the micellization (∆S mic), and specific heat capacity of the micellization (∆C P,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 ∆G mic was found to be negative, implying, as expected, that micellization occurs spontaneously once the CMC has been reached. The values of ∆G mic were found to become more negative with increasing temperature and the ∆S mic was found to decrease with increasing temperature in both models.

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Abstract  

Thermal behavior of aqueous hydroxypropylmethylcellulose (HPMC)/surfactant mixtures was studied in the dilute concentration regime using micro-differential scanning calorimetry (DSC). The surfactant used was sodium n-dodecyl sulfate (SDS). The heat capacity of HPMC gel with various concentrations of SDS was much higher than that of the pure HPMC gel. The addition of SDS at different concentrations showed dissimilar influences on the gelation of HPMC; SDS at lower concentrations (≤6 mM) did not affect gelation temperature significantly except for enhancing the heat capacity whilst SDS at higher concentrations (≥6 mM) not only resulted in the gelation of HPMC at higher temperatures but also changed the pattern of the gelation thermograph from a single mode to a bimodal. On the basis of the observed thermal behavior of HPMC/SDS systems, the mechanism behind the sol-gel transition was discussed in terms of the properties of the surfactant and their influences on the extent of polymer/surfactant binding and polymer/polymer hydrophobic association. Gelation kinetics was analysed using the results from the DSC measurements. The kinetic parameters were determined.

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2008 93 : 429 – 438 10.1007/s10973-007-8698-z . 4. Taheri-Kafrani , A , Bordbar , AK 2009 Energetics of micellization of sodium n -dodecyl sulfate at physiological conditions using

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, AK 2009 Energitics of micellizaion of sodium n -dodecyl sulfate at physiological conditions using isothermal titration calorimetry . J Therm Anal Calorim 98 2 567 – 575 10.1007/s10973-009-0170-9 . 20

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Binding mechanisms of nano-baskets toward alkali metals

Isothermal titration calorimetric study

Journal of Thermal Analysis and Calorimetry
Authors: Bahram Mokhtari and Kobra Pourabdollah

.1007/s10973-009-0040-5 . 3. Taheri-Kafrani , A , Bordbar , AK . 2009 . Energitics of micellizaion of sodium n -dodecyl sulfate at physiological conditions using isothermal titration

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