Probing Solvation in Ionic Liquids via the Electrochemistry of the DPPH Radical

The electrochemistry of the radical species 2,2-diphenyl-1-picrylhydrazyl, DPPH, has been studied in a range of common ionic liquids and its voltammetric response found to vary with the choice of anion. The trend observed is used to provide a relative Lewis basicity scale of nine ionic liquids commonly used as solvents

Hydrogen Oxidation and Oxygen Reduction at Platinum in Protic Ionic Liquids

H₂ oxidation and O₂ reduction have been studied as a function of temperature at Pt electrodes in the protic ionic liquid diethylmethylammonium trifluoromethanesulfonate. Hydrodynamic voltammetry showed that the H₂ oxidation reaction (HOR) became hindered at positive potentials (>1.0 V). Electrochemical analysis and X-ray photoelectron spectroscopy revealed that this drop in HOR activity was due to the formation of an adsorbed blocking oxide layer, which formed on the Pt surface due to trace H₂O oxidation at positive potentials. Electrochemical analysis also revealed that the O₂ reduction reaction (ORR) occurred at an appreciable rate only when pre-existing surface oxides were reduced. As the temperature increased, the potential at which the surface oxides were reduced shifted to more positive potentials and the reduction peak narrowed. The net result was significantly higher rates of the ORR at positive potentials at higher temperatures. Finally, even when Pt surfaces were not initially covered with an oxide adlayer, the rate of the ORR increased significantly upon increasing the temperature and some possible reasons for this temperature dependence are discussed

Chlorostannate(II) Ionic Liquids: Speciation, Lewis Acidity, and Oxidative Stability

The anionic speciation of chlorostannate­(II) ionic liquids, prepared by mixing 1-alkyl-3-methylimidazolium chloride and tin­(II) chloride in various molar ratios, χ_SnCl2, was investigated in both solid and liquid states. The room temperature ionic liquids were investigated by ¹¹⁹Sn NMR spectroscopy, X-ray photoelectron spectroscopy, and viscometry. Crystalline samples were studied using Raman spectroscopy, single-crystal X-ray crystallography, and differential scanning calorimetry. Both liquid and solid systems (crystallized from the melt) contained [SnCl₃]⁻ in equilibrium with Cl^– when χ_SnCl₂ < 0.50, [SnCl₃]⁻ in equilibrium with [Sn₂Cl₅]⁻ when χ_SnCl₂ > 0.50, and only [SnCl₃]⁻ when χ_SnCl₂ = 0.50. Tin­(II) chloride was found to precipitate when χ_SnCl₂ > 0.63. No evidence was detected for the existence of [SnCl₄]^2– across the entire range of χ_SnCl₂, although such anions have been reported in the literature for chlorostannate­(II) organic salts crystallized from organic solvents. Furthermore, the Lewis acidity of the chlorostannate­(II)-based systems, expressed by their Gutmann acceptor number, has been determined as a function of the composition, χ_SnCl₂, to reveal Lewis acidity for χ_SnCl₂ > 0.50 samples comparable to the analogous systems based on zinc­(II). A change of the Lewis basicity of the anion was estimated using ¹H NMR spectroscopy, by comparison of the measured chemical shifts of the C-2 hydrogen in the imidazolium ring. Finally, compositions containing free chloride anions (χ_SnCl₂ < 0.50) were found to oxidize slowly in air to form a chlorostannate­(IV) ionic liquid containing the [SnCl₆]^2– anion

Tunable Ionic Control of Polymeric Films for Inkjet Based 3D Printing

Inkjet printing is a powerful additive manufacturing (AM) technique to generate advanced and complex geometries. However, requirements of low viscosity and surface tension are limiting the range of functional inks available, thus hindering the development of novel applications and devices. Here, we report a method to synthesize materials derived from highly viscous or even solid monomers in a simple, flexible fashion and with the potential to be integrated in the printing process. Polymerizable ionic liquids (PILs) have been employed as a proof of principle due to the broad range of properties available upon fine-tuning of the anion-cation pair and the high viscosity of the monomers. The method consists of the deposition and polymerization of a PIL precursor, followed sequentially by quaternization and anion metathesis of the films. The fine control over the mechanical and superficial properties of inkjet printable polymeric films of neutral and cationic nature by postpolymerization reactions is demonstrated for the first time. A family of different polycationic materials has been generated by modification of cross-linked copolymers of butyl acrylate and vinyl imidazole with liquid solutions of functional reagents. The variation in the mechanical, thermal, and surface properties of the films demonstrates the success of this approach. The same concept has been applied to a modified formulation, designed for optimal inkjet printing. This work will pave the way for a broad range of applications of inkjet printing, with a plethora of anion–cation combinations characteristic of PILs, thus enormously broadening the range of applications available in additive manufacturing