Liquid Phase Behavior in Systems of 1-Butyl-3-alkylimidazolium bis{(trifluoromethyl)sulfonyl}imide Ionic Liquids with Water: Influence of the Structure of the C5 Alkyl Substituent

Phase Transitions and Electrochemical Properties of Ionic Liquids and Ionic Liquid-Solvent Mixtures

Recent advances in studies of ionic liquids (IL) and ionic liquid-solvent mixtures are reviewed. Selected experimental, simulation, and theoretical results for electrochemical, thermodynamical, and structural properties of IL and IL-solvent mixtures are described. Special attention is paid to phenomena that are not predicted by the classical theories of the electrical double layer or disagree strongly with these theories. We focus on structural properties, especially on distribution of ions near electrodes, on electrical double layer capacitance, on effects of confinement, including decay length of a dissjoining pressure between confinig plates, and on demixing phase transition. In particular, effects of the demixing phase transition on electrochemical properties of ionic liquid-solvent mixtures for different degrees of confinement are presented.

Capillary Ionization and Jumps of Capacitive Energy Stored in Mesopores

We study ionic liquid-solvent mixtures in slit-shaped nanopores wider than a few ion diameters. Using a continuum theory and generic thermodynamic reasoning, we reveal that such systems can undergo a capillary ionization transition. At this transition, the pores spontaneously ionize or deionize upon infinitesimal changes of temperature, slit width, or voltage. Our calculations show that a voltage applied to a pore may induce a capillary ionization, which-counterintuitively-is followed by a re-entrant deionization as the voltage increases. We find that such ionization transitions produce sharp jumps in the accumulated charge and stored energy, which may find useful applications in energy storage and heat-to-energy conversion.

Binary Mixtures of Ionic Liquids in Aqueous Solution: Towards an Understanding of their Salting-In/Salting-Out Phenomena

The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of macromolecules in aqueous solutions is known as the Hofmeister series. Taking into account that ionic liquids (ILs) are constituted by ions, they can exert similar effects on the solubility of other ILs in aqueous media. In order to expand the knowledge on the salting-in/-out ability of ILs, experimental studies on the solubility of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) in water in presence of other IL/salts were conducted at 298.15 K at atmospheric pressure. Both the impact of the anion and cation of the IL were evaluated with the following ILs/salts: 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hydrogensulfate, cholinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, in a wide composition range. As happens with common salts, both salting-in and salting-out effects exerted by ILs were observed, with a higher impact exerted by the IL anion on the salting-out phenomenon. These data allow to better understand the ILs impact when designing liquid-liquid separation processes.

Vapor Liquid Equilibria of Binary Mixtures of 1-Butyl-3-methylimidazolium Triflate (C4mimTfO) and Molecular Solvents: n-Alkyl Alcohols and Water

Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate (C₄mimTfO) with either water or short chained n-alkyl alcohols (methanol, ethanol, propan-1-ol, and butan-1-ol) are described in this study. Two different microebulliometers and a classical VLE apparatus were compared and the VLEs were determined in the composition range 0.4 ≤ x(solvent) ≤ 1 at three different pressure levels ( p = 500 mbar, 700 mbar, and 1000 mbar). The experimental data were modeled using the soft-SAFT equation of state, which was able to accurately describe the nonideal behavior of these mixtures. The combined experimental-modeling results obtained contribute to establish the structure-property relationship between the C₄mimTfO and n-alkyl alcohol molecules and to infer about its influence on the phase behavior of these solvents.