Using isothermal titration calorimetry heats of dilution of the aqueous ionic liquid solutions [C4MIM][C8SO4], [C12MIM]Cl, [C16MIM][BF4], and [C16MIM]Cl have been measured in the concentration range of (1–80, 1–35, 0.2–2.2, and 0.1–2.6)mmoldm−3 respectively at different temperatures between 283K and 338 K. Formation of micelles has been observed. The CMC, the equilibrium constant of micellization as well as the enthalpy of micellization has been determined from the experimental data using a mass-action model with 3–5 parameters adjusted to the experimental data points of the heat of dilution over the whole concentration range. Three modified versions of the model have been tested providing similar results with exception of [C16MIM][BF4] solutions where one of the versions failed. The consistency of the model has been tested by comparing the model parameters of our own experimental results of Na[C12SO4] solutions with those obtained from experimental data of other authors in the literature. Our evaluation process shows that theCMCdecreases in the order of [C4MIM][C8SO4], [C12MIM]Cl, [C16MIM]Cl and [C16MIM][BF4]. The enthalpy of micellization changes its sign with temperature in all cases studied in aqueous solutions. It is positive at lower temperatures and becomes negative at higher temperatures. Also solutions of [C16MIM][BF4] and [C16MIM]Cl in ethylammonium nitrate (EAN) have been studied in the same way. In contrast to the aqueous solutions the enthalpy of micellization is always negative without significant dependence on temperature.

Micelle formation of alkylimidazolium ionic liquids in water and inethylammonium nitrate ionic liquid: A calorimetric study

BALANTSEVA, ELENA;
2010

Abstract

Using isothermal titration calorimetry heats of dilution of the aqueous ionic liquid solutions [C4MIM][C8SO4], [C12MIM]Cl, [C16MIM][BF4], and [C16MIM]Cl have been measured in the concentration range of (1–80, 1–35, 0.2–2.2, and 0.1–2.6)mmoldm−3 respectively at different temperatures between 283K and 338 K. Formation of micelles has been observed. The CMC, the equilibrium constant of micellization as well as the enthalpy of micellization has been determined from the experimental data using a mass-action model with 3–5 parameters adjusted to the experimental data points of the heat of dilution over the whole concentration range. Three modified versions of the model have been tested providing similar results with exception of [C16MIM][BF4] solutions where one of the versions failed. The consistency of the model has been tested by comparing the model parameters of our own experimental results of Na[C12SO4] solutions with those obtained from experimental data of other authors in the literature. Our evaluation process shows that theCMCdecreases in the order of [C4MIM][C8SO4], [C12MIM]Cl, [C16MIM]Cl and [C16MIM][BF4]. The enthalpy of micellization changes its sign with temperature in all cases studied in aqueous solutions. It is positive at lower temperatures and becomes negative at higher temperatures. Also solutions of [C16MIM][BF4] and [C16MIM]Cl in ethylammonium nitrate (EAN) have been studied in the same way. In contrast to the aqueous solutions the enthalpy of micellization is always negative without significant dependence on temperature.
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Ionic liquid; Water; Ethylammonium nitrate; Titration calorimetry Micelle; Mass-action model
Andreas Heintz; Jochen K. Lehmann; Svetlana A. Kozlova; Elena V. Balantseva; Ala B. Bazyleva; Daniel Ondo
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2318/82456
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