Thermodynamic properties of aqueous organic mixtures near the critical demixing: Cases of 2,6-dimethylpyridine and of 2-isobutoxyethanol |
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Authors: | Gérald Perron François Quirion Daniel Lambert Jean Ledoux Lahouari Ghaicha R Bennes Mireille Privat Jacques E Desnoyers |
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Institution: | (1) INRS-Energie et Matériaux, C/O IMI-NRC, 75 de Mortagne, J4B 6Y4 Boucherville, Qué, Canada;(2) Laboratoire de Physico-chimie des Systèms Polyphasés, UA 330, CNRS-Route de Menden, 34033 Montpellier Cedex, France;(3) Department of Chemistry, Université de Bretagne Occidentale, 6 ave le Gorgeu, 29287 Brest Cedex, France |
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Abstract: | Phase diagrams, volumes and heat capacities of aqueous mixtures of 2,6-dimethylpyridine (2,6-L) and 2-isobutoxyethanol (iBE) and activities of 2,6-L in aqueous mixtures were measured in the monophasic region near the lower critical solution temperature (LCST). With 2,6-L some measurement were also made just above the LCST. From the temperature dependence of these data, partial molar relative enthalpies (2,6-L), expansibilities and the temperature derivative of heat capacities were calculated and show that iBE undergoes a microphase transition at low concentration which is not related to the phase separation. On the other hand, the properties of 2,6-L in the water-rich region at temperatures well below the LCST indicates that this solute has only a slight tendency to associate. The heat capacities of 2,6-L show an important increase near the LCST. Such changes are not observed for iBE and other alkoxyethanols and amines since these systems already exist in the form of microphases; the partial molar properties of iBE near the LCST are nearly equal to the molar values of the pure liquid, and the changes in thermodynamic properties corresponding to the macroscopic phase transition, are therefore too small to be measured by the present techniques. |
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Keywords: | Activities relative enthalpies volumes heat capacities expansibilities phase diagrams 2 6-dimethylpyridine-water mixtures 2-isobutoxyethanol-water mixtures critical demixing |
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