Title: Temperature-Driven Mixing-Demixing Behavior of Binary Mixtures of the Ionic Liquid Choline Bis(trifluoromethylsulfonyl)imide and Water
Authors: Nockemann, Peter ×
Binnemans, Koen
Thijs, Ben
Parac-Vogt, Tatjana
Merz, Klaus
Mudring, Anja-Verena
Menon, Preethy Chirukandath
Rajesh, Ravindran Nair
George, Cordoyiannis
Thoen, Jan
Leys, Jan
Glorieux, Christ #
Issue Date: Feb-2009
Publisher: American Chemical Society
Series Title: Journal of Physical Chemistry B vol:113 issue:5 pages:1429-1437
Abstract: The ionic liquid (2-hydroxyethylammonium)trimethylammonium) bis(trifluoromethylsulfonyl)imide (choline bistriflimide) was obtained as a supercooled liquid at room temperature (melting point = 30 °C). Crystals of choline bistriflimide suitable for structure determination were grown from the melt in situ on the X-ray diffractometer. The choline cation adopts a folded conformation, whereas the bistriflimide anion exhibits a transoid conformation. The choline cation and the bistriflimide anion are held together by hydrogen bonds between the hydroxyl proton and a sulfonyl oxygen atom. This hydrogen bonding is of importance for the temperature-dependent solubility properties of the ionic liquid. Choline bistriflimide is not miscible with water at room temperature, but forms one phase with water at temperatures above 72 °C (equals upper critical solution temperature). 1H NMR studies show that the hydrogen bonds between the choline cation and the bistriflimide anion are substantially weakened above this temperature. The thermophysical properties of water-choline bistriflimide binary mixtures were furthermore studied by a photopyroelectric technique and by adiabatic scanning calorimetry (ASC). By photothermal analysis, besides highly accurate values for the thermal conductivity and effusivity of choline bistriflimide at 30 °C, the detailed temperature dependence of both the thermal conductivity and effusivity of the upper and lower part of a critical water-choline bistriflimide mixture in the neighborhood of the mixing-demixing phase transition could be determined with high resolution and accuracy. Together with high resolution ASC data for the heat capacity, experimental values were obtained for the critical exponents α and β, and for the critical amplitude ratio G+/G−. These three values were found to be consistent with theoretical expectations for a three dimensional Ising-type of critical behavior of binary liquid mixtures.
Description: Temperature-driven mixing-demixing behavior of binary mixtures of the ionic liquid
ISSN: 1520-6106
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Molecular Design and Synthesis
Soft Matter and Biophysics
× corresponding author
# (joint) last author

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