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  • 1 Laboratoire de Physico-Chimie des Systèmes Polyphasés URA 330 du CNRS Université de Montpellier II Place Eugène Bataillon 34095 Montpellier Cedex 05 France
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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.