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Thermodynamics of Micellization from Heat-Capacity Measurements

Authors

  • Dr. Bojan Šarac,

    Corresponding author
    1. Department of Physical Chemistry, Faculty of Chemistry and Chemical Technology, Aškerčeva 5, SI-1000, Ljubljana (Slovenia), Fax: (+386) 1-2419-425
    • Department of Physical Chemistry, Faculty of Chemistry and Chemical Technology, Aškerčeva 5, SI-1000, Ljubljana (Slovenia), Fax: (+386) 1-2419-425===

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  • Prof. Dr. Marija Bešter-Rogač,

    1. Department of Physical Chemistry, Faculty of Chemistry and Chemical Technology, Aškerčeva 5, SI-1000, Ljubljana (Slovenia), Fax: (+386) 1-2419-425
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  • Prof. Dr. Jurij Lah

    Corresponding author
    1. Department of Physical Chemistry, Faculty of Chemistry and Chemical Technology, Aškerčeva 5, SI-1000, Ljubljana (Slovenia), Fax: (+386) 1-2419-425
    • Department of Physical Chemistry, Faculty of Chemistry and Chemical Technology, Aškerčeva 5, SI-1000, Ljubljana (Slovenia), Fax: (+386) 1-2419-425===

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Abstract

Differential scanning calorimetry (DSC), the most important technique for studying the thermodynamics of structural transitions of biological macromolecules, is seldom used in quantitative thermodynamic studies of surfactant micellization/demicellization. The reason for this could be ascribed to an insufficient understanding of the temperature dependence of the heat capacity of surfactant solutions (DSC data) in terms of thermodynamics, which leads to problems with the design of experiments and interpretation of the output signals. We address these issues by careful design of DSC experiments performed with solutions of ionic and nonionic surfactants at various surfactant concentrations, and individual and global mass-action model analysis of the obtained DSC data. Our approach leads to reliable thermodynamic parameters of micellization for all types of surfactants, comparable with those obtained by using isothermal titration calorimetry (ITC). In summary, we demonstrate that DSC can be successfully used as an independent method to obtain temperature-dependent thermodynamic parameters for micellization.

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