Home Browse the Journal Articles ASAP Current Issue Submission & Review Open Access Subscribe About the Journal J. Phys. Chem. A B C Letters Pre-1997 System Maintenance: Thursday, October 22, 5pm to 9pm EDT Please be aware that pubs.acs.org will undergo maintenance from 5pm on Thursday, October 22 with all applications expected to resume normal operation by 9pm. This upgrade will impact applications that require a login or ACS ID, including the "Registration" and "MyAccount" functions. Log-in will be temporarily disabled for features including C&EN Delivery, ChemWorx and Galleys. Individual users will not be able to log-in to access their subscribed content; purchase single articles; or change their e-Alert subscriptions; some searches are returning no results on the ACS Publications website. We appreciate your patience as we make improvements to the ACS Publications platform. Article Prev. Article Next Article Table of Contents Temperature-Driven Mixing-Demixing Behavior of Binary Mixtures of the Ionic Liquid Choline Bis(trifluoromethylsulfonyl)imide and Water Peter Nockemann*†, Koen Binnemans†, Ben Thijs†, Tatjana N. Parac-Vogt†, Klaus Merz‡, Anja-Verena Mudring‡, Preethy Chirukandath Menon§, Ravindran Nair Rajesh§, George Cordoyiannis§, Jan Thoen§, Jan Leys§ and Christ Glorieux§ Department of Chemistry, Laboratory of Coordination Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, bus 2404, B-3001 Leuven, Belgium, Anorganische Chemie I - Festkörperchemie and Materialien, Ruhr-Universität Bochum, D-44780 Bochum, Germany, and Department of Physics and Astronomy, Laboratory for Acoustics and Thermal Physics, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium. J. Phys. Chem. B, 2009, 113 (5), pp 1429–1437 DOI: 10.1021/jp808993t Publication Date (Web): January 9, 2009 Copyright © 2009 American Chemical Society * To whom correspondence should be addressed. E-mail: Peter.Nockemann@chem.kuleuven.be., † Department of Chemistry, Laboratory of Coordination Chemistry, Katholieke Universiteit Leuven., ‡ Ruhr-Universität Bochum., § Department of Physics and Astronomy, Laboratory for Acoustics and Thermal Physics, Katholieke Universiteit Leuven. 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.