Isobaric heat capacity per unit volume, Cp, and excess molar enthalpy, hE, were determined in the vicinity of the critical point for a set of binary systems formed by an ionic liquid and a molecular solvent. Moreover, and, since critical composition had to be accurately determined, liquid-liquid equilibrium curves were also obtained using a calorimetric method. The systems were selected with a view on representing, near room temperature, examples from clearly solvophobic to clearly coulombic behavior, which traditionally was related with the electric permittivity of the solvent. The chosen molecular compounds are: ethanol, 1-butanol, 1-hexanol, 1,3-dichloropropane, and diethylcarbonate, whereas ionic liquids are formed by imidazolium-based cations and tetrafluoroborate or bis-(trifluromethylsulfonyl)amide anions. The results reveal that solvophobic critical behavior—systems with molecular solvents of high dielectric permittivity—is very similar to that found for molecular binary systems. However, coulombic systems—those with low permittivity molecular solvents—show strong deviations from the results usually found for these magnitudes near the liquid-liquid phase transition. They present an extremely small critical anomaly in Cp—several orders of magnitude lower than those typically obtained for binary mixtures—and extremely low hE—for one system even negative, fact not observed, up to date, for any liquid-liquid transition in the nearness of an upper critical solution temperature.
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7 December 2011
Research Article|
December 06 2011
Thermal properties of ionic systems near the liquid-liquid critical point
Pablo Méndez-Castro;
Pablo Méndez-Castro
1Departamento de Física Aplicada,
Universidad de Vigo
, Campus As Lagoas, 32004 Ourense, Spain
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Jacobo Troncoso;
Jacobo Troncoso
a)
1Departamento de Física Aplicada,
Universidad de Vigo
, Campus As Lagoas, 32004 Ourense, Spain
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Germán Pérez-Sánchez;
Germán Pérez-Sánchez
2Departamento de Física Aplicada, Facultade de Ciencias do Mar,
Universidad de Vigo
, Campus Lagoas-Marcosende, 36200 Vigo, Spain
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José Peleteiro;
José Peleteiro
1Departamento de Física Aplicada,
Universidad de Vigo
, Campus As Lagoas, 32004 Ourense, Spain
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Luis Romaní
Luis Romaní
1Departamento de Física Aplicada,
Universidad de Vigo
, Campus As Lagoas, 32004 Ourense, Spain
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a)
Author to whom correspondence should be addressed. Electronic mail: jacobotc@uvigo.es.
J. Chem. Phys. 135, 214507 (2011)
Article history
Received:
June 02 2011
Accepted:
November 04 2011
Citation
Pablo Méndez-Castro, Jacobo Troncoso, Germán Pérez-Sánchez, José Peleteiro, Luis Romaní; Thermal properties of ionic systems near the liquid-liquid critical point. J. Chem. Phys. 7 December 2011; 135 (21): 214507. https://doi.org/10.1063/1.3663857
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