Determining the composition of the vacuum–liquid interface in ionic-liquid mixtures

Smoll, Eric J.; Tesa-Serrate, Maria Antonia; Purcell, Simon; D'Andrea, Lucia; Bruce, Duncan W.; Slattery, John M.; Costen, Matthew L.; Minton, Timothy K.; McKendrick, Kenneth G.

doi:10.1039/c7fd00175d

Cited by 26 publications

(89 citation statements)

References 74 publications

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“…This behavior is in contrast to the situation for neat [C 4 C 1 Im][PF 6 ] in Figure a and for neat ILs with longer alkyl chains, and indicates that the alkyl chains in the mixtures studied here are depleted from the liquid/vacuum interface. The driving force is a competing effect between the fluorinated chain of the [PFBMIm] + cation and the non‐fluorinated side chain of the [C 4 C 1 Im] + cation: The selective enrichment of the [PFBMIm] + cations is attributed to a (typically) larger surface tension of ILs with an alkyl chain compared to a fluorinated chain …”

Section: Resultsmentioning

confidence: 99%

“…Therefore, investigations of the topmost layers of IL mixtures are getting more into the focus of research. A variety of studies has been performed, using reactive‐atom scattering with laser‐induced fluorescence detection (RAS‐LIF), neutron scattering, small‐angle X‐ray scattering and X‐ray reflectivity, time of flight secondary ion mass spectrometry (TOF‐SIMS), Rutherford backscattering spectroscopy (RBS), low‐energy ion scattering (LEIS), X‐ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulations …”

Section: Introductionmentioning

confidence: 99%

“…In the case of [C 8 C 1 Im] 1− x [C 8 C 1 ImF 13 ] x [Tf 2 N] mixtures, RAS‐LIF measurements performed by Smoll et al . showed that the fluorinated chain is again preferentially enriched at the surface.…”

Section: Introductionmentioning

confidence: 99%

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Temperature‐Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non‐Fluorinated Ionic Liquids

Heller

Lexow

Greco

et al. 2020

Chemistry A European J

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Using angle-resolved X-ray photoelectron spectroscopy (ARXPS), we investigate the topmost nanometers of various binary ionic liquid (IL) mixtures at differentt emperatures in the liquid state. The mixtures consist of ILs with the same [PF 6 ] À anion but two different cations, namely 3methyl-1- (3,3,4,4,4-pentafluorobutyl)imidazoliumh exafluorophosphate, [PFBMIm][PF 6 ], and 1-butyl-3-methylimidazolium hexafluorophosphate, [C 4 C 1 Im][PF 6 ], with 10, 25, 50 and 75 mol %c ontento f[ PFBMIm][PF 6 ]. We observe ap referential enrichmento ft he fluorinated chain in the topmostl ayer, relative to the bulk composition, which is mostp ronounced for the lowest content of [PFBMIm][PF 6 ]. Upon cooling the mixtures stepwise from 95 8Cu ntil surfacec harging effects in XPS indicate solidification,w eo bserve ap ronouncedi ncreasei ns urfacee nrichmento ft he fluorinated chain with decreasing temperature in the liquid state. In contrast to the mixtures with lower[ PFBMIm] [PF 6 ]c ontents, cooling the 75 mol %m ixture additionallys hows an abrupt decrease of the fluorinated chain signal before complete solidification occurs, whichisa ssigned to partial precipitation effects.[a] B.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Temperature‐Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non‐Fluorinated Ionic Liquids

Heller

Lexow

Greco

et al. 2020

Chemistry A European J

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“…The surface composition of binary IL mixtures with non‐functionalized imidazolium‐based ILs was investigated using various surface science techniques such as time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS),21,22 low‐energy ion scattering (LEIS),23,24 Rutherford backscattering (RBS),22,25, 26, 27 angle‐resolved X‐ray photoelectron spectroscopy (ARXPS),28, 29, 30 reactive atom scattering‐laser‐induced fluorescence (RAS‐LIF),20,31 and by simulations 20,26,32,33…”

Section: Introductionmentioning

confidence: 99%

“…The same [C 2 C 1 Im] 1‐x [C 12 C 1 Im] x [Tf 2 N] mixture as well as a mixture with a fluorinated side chain were recently investigated by RAS‐LIF combined with MD simulations 31. It was shown that the component with the lower surface tension is preferentially located at the surface of the mixture.…”

Section: Introductionmentioning

confidence: 99%

Surface Enrichment in Equimolar Mixtures of Non‐Functionalized and Functionalized Imidazolium‐Based Ionic Liquids

et al. 2018

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For equimolar mixtures of ionic liquids with imidazolium‐based cations of very different electronic structure, we observe very pronounced surface enrichment effects by angle‐resolved X‐ray photoelectron spectroscopy (XPS). For a mixture with the same anion, that is, 1‐methyl‐3‐octylimidazolium hexafluorophosphate+1,3‐di(methoxy)imidazolium hexafluorophosphate ([C8C1Im][PF6]+[(MeO)2Im][PF6]), we find a strong enrichment of the octyl chain‐containing [C8C1Im]+ cation and a corresponding depletion of the [(MeO)2Im]+ cation in the topmost layer. For a mixture with different cations and anions, that is, [C8C1Im][Tf2N]+[(MeO)2Im][PF6], we find both surface enrichment of the [C8C1Im]+ cation and the [Tf2N]− (bis[(trifluoromethyl)sulfonyl]imide) anion, while [(MeO)2Im]+ and [PF6]− are depleted from the surface. We propose that the observed behavior in these mixtures is due to a lowering of the surface tension by the enriched components. Interestingly, we observe pronounced differences in the chemical shifts of the imidazolium ring signals of the [(MeO)2Im]+ cations as compared to the non‐functionalized cations. Calculations of the electronic structure and the intramolecular partial charge distribution of the cations contribute to interpreting these shifts for the two different cations.

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Tailoring the Surface Enrichment of a Pt Catalyst in Ionic Liquid Solutions by Choice of the Solvent

Hemmeter,

Gezmis,

Kremitzl

et al. 2024

Adv Materials Inter

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The so‐called buoy‐effect, that is, the targeted surface enrichment of a Pt catalyst dissolved in ionic liquids (ILs), is achieved by attaching perfluorinated alkyl chains to the ligand system, which drags the metal complex toward the interface. Using angle‐resolved X‐ray photoelectron spectroscopy, it is demonstrated how this surface enrichment can be tailored by variation of the solvent IL. In [CnC1Im][PF6] ILs (n = 2, 4, 8), the surface is fully saturated with the complex at 10%mol bulk content, while in [C4C1Im][Tf2N] only at 20%mol saturation is observed. At low catalyst concentrations of 1%mol, where saturation is not yet reached, the enrichment increases with decreasing length of the IL alkyl chain. As a general rule, the degree of surface enrichment decreases with the decrease in surface tension of the solvent IL, that is, in the order [C2C1Im][PF6] > [C4C1Im][PF6] > [C8C1Im][PF6] > [C4C1Im][Tf2N]. In ILs with very low surface tension, enrichment is even suppressed. These results reveal the surface tension of the solvent IL as rational parameter for tailoring the interfacial structure of IL‐based catalyst systems, such as supported ionic liquid phase (SILP) catalysis, where the nature of the IL/gas interface is expected to strongly influence the performance of the process.

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Determining the composition of the vacuum–liquid interface in ionic-liquid mixtures

Abstract: The vacuum–liquid interfaces of a number of ionic-liquid mixtures have been investigated using a combination of RAS-LIF, selected surface tension measurements, and molecular dynamics simulations.

Cited by 26 publications

References 74 publications

Temperature‐Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non‐Fluorinated Ionic Liquids

Temperature‐Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non‐Fluorinated Ionic Liquids

Surface Enrichment in Equimolar Mixtures of Non‐Functionalized and Functionalized Imidazolium‐Based Ionic Liquids

Tailoring the Surface Enrichment of a Pt Catalyst in Ionic Liquid Solutions by Choice of the Solvent

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