76 research outputs found
The Hildebrand Solubility Parameters of Ionic LiquidsâPart 2
The Hildebrand solubility parameters have been calculated for eight ionic liquids. Retention data from the inverse gas chromatography measurements of the activity coefficients at infinite dilution were used for the calculation. From the solubility parameters, the enthalpies of vaporization of ionic liquids were estimated. Results are compared with solubility parameters estimated by different methods
Ionic Liquid Ordering at an Oxide Surface
The interaction of the ionic liquid [C4C1Im][BF4] with anatase TiO2, a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The system is of interest as a model for fundamental electrolyteâelectrode and dye-sensitized solar cells. The initial interaction involves degradation of the [BF4]â anion, resulting in incorporation of F into Oâ
vacancies in the anatase surface. At low coverages, [C4C1Im][BF4] is found to order at the anatase(101) surface via electrostatic attraction, with the imidazolium ring oriented 32±4° from the anatase TiO2 surface. As the coverage of ionic liquid increases, the influence of the oxide surface on the topmost layers is reduced and the ordering is lost
The Solubility Parameters of Ionic Liquids
The Hildebrandâs solubility parameters have been calculated for 18 ionic liquids from the inverse gas chromatography measurements of the activity coefficients at infinite dilution. Retention data were used for the calculation. The solubility parameters are helpful for the prediction of the solubility in the binary solvent mixtures. From the solubility parameters, the standard enthalpies of vaporization of ionic liquids were estimated
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X-ray photoelectron spectroscopy of pyridinium-based tonic liquids: comparison to imidazolium- and pyrrolidinium-based analogues
We investigate eight 1âalkylpyridiniumâbased ionic liquids of the form [CnPy][A] by using Xâray photoelectron spectroscopy (XPS). The electronic environment of each element of the ionic liquids is analyzed. In particular, a reliable fitting model is developed for the Câ1s region that applies to each of the ionic liquids. This model allows the accurate charge correction of binding energies and the determination of reliable and reproducible binding energies for each ionic liquid. Shakeâup/off phenomena are determinedfor both Câ1s and Nâ1s spectra. The electronic interaction between cations and anions is investigated for both simple ionic liquids and an example of an ionicâliquid mixture; the effect of the anion on the electronic environment of the cation is also explored. Throughout the study, a detailed comparison is made between [C8Py][A] and analogues including 1âoctylâ1âmethylpyrrolidiniumâ ([C8C1Pyrr][A]), and 1âoctylâ3âmethylimidazoliumâ ([C8C1Im][A]) based samples, where X is common to all ionic liquids
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The ionic liquidâvacuum outer atomic surface: a low-energy ion scattering study
We have identified elements present in the ionic liquidâvacuum outer atomic surface of 23 ionic liquids using high sensitivity low-energy ion scattering (LEIS), a very surface sensitive technique. We show that the probability of cationic heteroatoms being present at the ionic liquidâvacuum outer atomic surface is very low; we detected imidazolium nitrogen for only one of the 18 imidazolium based ionic liquids investigated, no nitrogen for the two ammonium based ionic liquids and a very small amount of phosphorus for two of the three phosphonium-based ionic liquids. We determine that the anion is always present at the ionic liquidâvacuum outer atomic surface, even for very large cations containing dodecyl alkyl chains or longer; these chains dominate the ionic liquidâvacuum outer atomic surface, but are not sufficiently densely packed to completely cover the anions. We demonstrate the presence of strong hydrogen bond acceptor adsorption sites at the ionic liquidâvacuum outer atomic surface. We demonstrate that the amount of ion present at the ionic liquidâvacuum outer atomic surface can be tuned by varying the size of the other ion; larger cations (or anions) occupy more of the ionic liquidâvacuum outer atomic surface, leaving less room for anions (or cations). By identifying elements present at the ionic liquidâvacuum outer atomic surface, conclusions can be drawn on the orientations of anions nearest the vacuum. We show that for five different anions there is a most probable ion orientation, but other anion orientations also exist, demonstrating the presence of multiple anion orientations. The imidazolium cations nearest to the vacuum also show similar multi-orientation behaviour. This variety of atoms present and therefore ion orientations is expected to be central to controlling surface reactivity. In addition, our results can be used to quantitatively validate simulations of the ionic liquidâvacuum surface at a molecular level. Overall, our studies, in combination with literature data from different techniques and simulations, provide a clear picture of ionic liquidâvacuum outer atomic surfaces
Computational approaches to understanding reaction outcomes of organic processes in ionic liquids
This review considers how various computational methods have been applied to explain the changes in reaction outcome on moving from a molecular to an ionic liquid solvent. Initially, different conceptual approaches to modelling ionic liquids are discussed, followed by a consideration of the limitations and constraints of these approaches. A series of case studies demonstrating the utility of computational approaches to explain processes in ionic liquids are considered; some of these address the solubility of species in ionic liquids while others examine classes of reaction where the outcome in ionic liquids can be explained through the application of computational approaches. Overall, the utility of computational methods to explain, and potentially predict, the effect of ionic liquids on reaction outcome is demonstrated
Electrospray ionization deposition of ultrathin ionic liquid films:[C 8C1Im]Cl and [C8C1Im][Tf 2N] on Au(111)
\u3cp\u3eWe introduce a new method for preparing ultrathin ionic liquid (IL) films on surfaces by means of electrospray ionization deposition (ESID) under ultraclean and well-defined ultra-high-vacuum (UHV) conditions. In contrast to physical vapor deposition (PVD) of ILs under UHV, ESID even allows deposition of ILs, which are prone to thermal decomposition. As proof of concept, we first investigated ultrathin [C\u3csub\u3e8\u3c/sub\u3eC\u3csub\u3e1\u3c/sub\u3eIm][Tf\u3csub\u3e2\u3c/sub\u3eN] (=1-methyl-3-octyl imidazolium bis(trifluoromethyl)imide) films on Au(111) by angle-resolved X-ray photoelectron spectroscopy (ARXPS). Films obtained by ESID are found to be virtually identical to films grown by standard PVD. Thereafter, ESID of [C\u3csub\u3e8\u3c/sub\u3eC\u3csub\u3e1\u3c/sub\u3eIm]Cl on Au(111) was studied as a first example of an IL that cannot be prepared as ultrathin film otherwise. [C \u3csub\u3e8\u3c/sub\u3eC\u3csub\u3e1\u3c/sub\u3eIm]Cl forms a wetting layer with a checkerboard arrangement with the cationic imidazolium ring and the chloride anion adsorbed next to each other on the substrate and the alkyl chain pointing toward vacuum. This arrangement within the wetting layer is similar to that observed for [C\u3csub\u3e8\u3c/sub\u3eC\u3csub\u3e1\u3c/sub\u3eIm][Tf\u3csub\u3e2\u3c/sub\u3eN], albeit with a higher degree of order of the alkyl chains. Further deposition of [C\u3csub\u3e8\u3c/sub\u3eC \u3csub\u3e1\u3c/sub\u3eIm]Cl leads to a pronounced island growth on top of the wetting layer, which is independently confirmed by ARXPS and atomic force microscopy. This behavior contrasts the growth behavior found for [C\u3csub\u3e8\u3c/sub\u3eC \u3csub\u3e1\u3c/sub\u3eIm][Tf\u3csub\u3e2\u3c/sub\u3eN], where layer-by-layer growth on top of the wetting layer is observed. The dramatic difference between both ILs is attributed to differences in the cation-anion interactions and in the degree of order in the wetting layer of the two ILs.\u3c/p\u3
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