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Open AccessArticle

Transport Properties of Protic Ionic Liquids Based on Triazolium and Imidazolium: Development of an Air-Free Conductivity Setup

by

Eduardo Maurina Morais

,

Alexander Idström

,

Lars Evenäs

and

Anna Martinelli

Molecules 2023, 28(13), 5147; https://doi.org/10.3390/molecules28135147 - 30 Jun 2023

Viewed by 599

Abstract

The dynamical properties of four protic ionic liquids, based on the ethyltriazolium ([C

_{2}

HTr

_{124}

]) and the ethylimidazolium ([C

_{2}

HIm]) cation, were investigated. The associated anions were the triflate ([TfO]) and the bistriflimide ([TFSI]). Ionic conductivity values and self-diffusion coefficients [...] Read more.

The dynamical properties of four protic ionic liquids, based on the ethyltriazolium ([C

_{2}

HTr

_{124}

]) and the ethylimidazolium ([C

_{2}

HIm]) cation, were investigated. The associated anions were the triflate ([TfO]) and the bistriflimide ([TFSI]). Ionic conductivity values and self-diffusion coefficients were measured and discussed, extending the discussion to the concept of fragility. Furthermore, in order to allow the measurement of the ionic conductivity of very small volumes (<0.5 mL) of ionic liquid under an inert and dry atmosphere, a new setup was developed. It was found that the cation nature strongly affected the transport properties, the [C

_{2}

HTr

_{124}

] cation resulting in slower dynamics than the [C

_{2}

HIm] one. This was concluded from both conductivity and diffusivity measurements while for both properties, the anion had a lesser effect. By fitting the conductivity data with the Vogel–Fulcher–Tammann (VFT) equation, we could also estimate the fragility of these ionic liquids, which all fell in the range of very fragile glass-forming materials. Finally, the slower dynamics observed in the triazolium-based ionic liquids can be rationalized by the stronger interactions that this cation establishes with both anions, as deduced from the frequency analysis of relevant Raman signatures and density functional theory (DFT) calculations. Full article

(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)

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Open AccessArticle

Confined Silver Nanoparticles in Ionic Liquid Films

by

Alexandre C. P. M. Alves

,

Luís M. N. B. F. Santos

,

Margarida Bastos

and

José C. S. Costa

Molecules 2023, 28(7), 3029; https://doi.org/10.3390/molecules28073029 - 28 Mar 2023

Viewed by 955

Abstract

This work reports the formation of silver nanoparticles (AgNPs) by sputter deposition in thin films of three different ionic liquids (ILs) with the same anion (bis(trifluoromethylsulfonyl)imide) and cation (imidazolium), but with different alkyl chain lengths and symmetries in the cationic moiety ([C₄ [...] Read more.

This work reports the formation of silver nanoparticles (AgNPs) by sputter deposition in thin films of three different ionic liquids (ILs) with the same anion (bis(trifluoromethylsulfonyl)imide) and cation (imidazolium), but with different alkyl chain lengths and symmetries in the cationic moiety ([C₄C₁im][NTf₂], [C₂C₂im][NTf₂], and [C₅C₅im][NTf₂]). Ionic liquid (IL) films in the form of microdroplets with different thicknesses (200 to 800 monolayers) were obtained through vacuum thermal evaporation onto glass substrates coated with indium tin oxide (ITO). The sputtering process of the Ag onto the ILs when conducted simultaneously with argon plasma promoted the coalescence of the ILs’ droplets and the formation, incorporation, and stabilization of the metallic nanoparticles in the coalesced IL films. The formation/stabilization of the AgNPs in the IL films was confirmed using high-resolution scanning electron microscopy (SEM) and UV-Vis spectroscopy. It was found that the IL films with larger thicknesses (600 and 800 monolayers) were better media for the formation of AgNPs. Among the ILs used, [C₅C₅im][NTf₂] was found to be particularly promising for the stabilization of AgNPs. The use of larger IL droplets as capture media was found to promote a better stabilization of the AgNPs, thereby reducing their tendency to aggregate. Full article

(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)

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Open AccessArticle

New Protic Ionic Liquids as Potential Additives to Lubricate Si-Based MEMS/NEMS

by

,

,

,

and

Molecules 2023, 28(6), 2678; https://doi.org/10.3390/molecules28062678 - 16 Mar 2023

Cited by 2 | Viewed by 1001

Abstract

The motivation for this work was to develop new protic ionic liquids (PILs) as additives for the lubrication of micro and nanoelectromechanical systems (MEMS and NEMS). Ten PILs based on the combination of methylimidazolium ([MIMH]), 4-picolinium ([4-picH]), pyridinium ([PyrH]), 1,8-diazabicyclo[5.4.0]-undec-7-ene-8-ium ([DBUH]) and tetramethylguanidinium [...] Read more.

The motivation for this work was to develop new protic ionic liquids (PILs) as additives for the lubrication of micro and nanoelectromechanical systems (MEMS and NEMS). Ten PILs based on the combination of methylimidazolium ([MIMH]), 4-picolinium ([4-picH]), pyridinium ([PyrH]), 1,8-diazabicyclo[5.4.0]-undec-7-ene-8-ium ([DBUH]) and tetramethylguanidinium ([TMGH]) cations with hydrogen sulfate([HSO₄]) and mesylate ([MeSO₃]) anions were tested as additives in polyethylene glycol (PEG200) to lubricate steel/silicon and silicon/silicon contacts. The best additive was [4-picH][HSO₄], which adsorbed strongly on the Si surface, leading to a protective film that reduced wear by up to 15 times compared to PEG200. Full article

(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)

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Open AccessArticle

The Role of the Anion in Imidazolium-Based Ionic Liquids for Fuel and Terpenes Processing

by

,

,

,

,

and

Molecules 2023, 28(6), 2456; https://doi.org/10.3390/molecules28062456 - 07 Mar 2023

Viewed by 893

Abstract

The potentialities of methylimidazolium-based ionic liquids (ILs) as solvents were evaluated for some relevant separation problems—terpene fractionation and fuel processing—studying selectivities, capacities, and solvent performance indices. The activity coefficients at infinite dilution of the solute (1) in the IL (3),

γ_{13}^{\infty}

[...] Read more.

The potentialities of methylimidazolium-based ionic liquids (ILs) as solvents were evaluated for some relevant separation problems—terpene fractionation and fuel processing—studying selectivities, capacities, and solvent performance indices. The activity coefficients at infinite dilution of the solute (1) in the IL (3),

γ_{13}^{\infty}

, of 52 organic solutes were measured by inverse gas chromatography over a temperature range of 333.2–453.2 K. The selected ILs are 1-butyl-3-methylimidazolium hexafluorophosphate, [C₄mim][PF₆], and the equimolar mixture of [C₄mim][PF₆] and 1-butyl-3-methylimidazolium chloride, [C₄mim]Cl. Generally, low polar solutes follow

γ_{1, [C_{4} mim] Cl}^{\infty}

>

γ_{1, [C_{4} mim] [{PF}_{6}] + [C_{4} mim] Cl}^{\infty}

>

γ_{1, [C_{4} mim] [{PF}_{6}]}^{\infty}

while the opposite behavior is observed for alcohols and water. For citrus essential oil deterpenation, the results suggest that cations with long alkyl chains, such as

{[C_{12} mim]}^{+}

, promote capacity, while selectivity depends on the solute polarity. Promising results were obtained for the separation of several model mixtures relevant to fuel industries using the equimolar mixture of [C₄mim][PF₆] and [C₄mim]Cl. This work demonstrates the importance of tailoring the polarity of the solvents, suggesting the use of ILs with mixed anions as alternative solvents for the removal of aliphatic hydrocarbons and contaminants from fuels. Full article

(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)

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Open AccessArticle

The Nanostructure of Alkyl-Sulfonate Ionic Liquids: Two 1-Alkyl-3-methylimidazolium Alkyl-Sulfonate Homologous Series

by

Hugo Marques

,

José Nuno Canongia Lopes

,

Adilson Alves de Freitas

and

Karina Shimizu

Molecules 2023, 28(5), 2094; https://doi.org/10.3390/molecules28052094 - 23 Feb 2023

Viewed by 1154

Abstract

The functionalization of polymers with sulfonate groups has many important uses, ranging from biomedical applications to detergency properties used in oil-recovery processes. In this work, several ionic liquids (ILs) combining 1-alkyl-3-methylimidazolium cations [C_nC₁im]⁺ (4 ≤ n ≤ 8) [...] Read more.

The functionalization of polymers with sulfonate groups has many important uses, ranging from biomedical applications to detergency properties used in oil-recovery processes. In this work, several ionic liquids (ILs) combining 1-alkyl-3-methylimidazolium cations [C_nC₁im]⁺ (4 ≤ n ≤ 8) with alkyl-sulfonate anions [C_mSO₃]⁻ (4 ≤ m ≤ 8) have been studied using molecular dynamics simulations, totalizing nine ionic liquids belonging to two homologous series. The radial distribution functions, structure factors, aggregation analyses, and spatial distribution functions reveal that the increase in aliphatic chain length induces no significant change in the structure of the polar network of the ILs. However, for imidazolium cations and sulfonate anions with shorter alkyl chains, the nonpolar organization is conditioned by the forces acting on the polar domains, namely, electrostatic interactions and hydrogen bonding. Full article

(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)

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Open AccessArticle

Investigation of H₂O₂ Electrochemical Behavior on Ferricyanide-Confined Electrode Based on Ionic Liquid-Functionalized Silica-Mesostructured Cellular Foam

by

,

,

,

,

and

Molecules 2022, 27(24), 9028; https://doi.org/10.3390/molecules27249028 - 18 Dec 2022

Viewed by 1112

Abstract

In this work, ionic liquid (IL) of 1-propyl-3-methyl imidazolium chloride-functionalized silica-mesostructured cellular foam (MCF) was prepared. The obtained MCF-IL was used to construct the Fe(CN)₆³⁻-confined electrode (MCF-IL-Fe(CN)₆³⁻/PVA) and H₂O₂ electrochemical behavior on the electrode [...] Read more.

In this work, ionic liquid (IL) of 1-propyl-3-methyl imidazolium chloride-functionalized silica-mesostructured cellular foam (MCF) was prepared. The obtained MCF-IL was used to construct the Fe(CN)₆³⁻-confined electrode (MCF-IL-Fe(CN)₆³⁻/PVA) and H₂O₂ electrochemical behavior on the electrode was investigated. It was found that H₂O₂ was oxidized on the freshly prepared electrode while catalytically electro-reduced on the acid pretreated one. Cyclic voltametric results revealed that the real catalyst for catalytic reduction of H₂O₂ was Prussian blue (PB) rather than Fe(CN)₆³⁻. The electrocatalytic ability of the acid-pretreated MCF-IL-Fe(CN)₆³⁻/PVA electrode offered a wide linear range for H₂O₂ detection. The present study on H₂O₂ electrochemical behavior on an MCF-IL-Fe(CN)₆³⁻/PVA electrode might provide useful information for further developing integrated Fe(CN)₆³⁻-mediated biosensors as H₂O₂ is extensively involved in the classic reaction containing oxidase enzymes. Full article

(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)

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Open AccessEditor’s ChoiceArticle

Direct Correlation of Surface Tension and Surface Composition of Ionic Liquid Mixtures—A Combined Vacuum Pendant Drop and Angle-Resolved X-ray Photoelectron Spectroscopy Study

by

,

,

,

and

Molecules 2022, 27(23), 8561; https://doi.org/10.3390/molecules27238561 - 05 Dec 2022

Cited by 3 | Viewed by 911

Abstract

We investigated the surface tension and surface composition of various mixtures of the two ionic liquids (ILs) 1-methyl-3-octyl-imidazolium hexafluorophosphate [C₈C₁Im][PF₆] and 1,3-bis(polyethylene glycol)imidazolium iodide [(mPEG₂)₂Im]I in the temperature range from 230 [...] Read more.

We investigated the surface tension and surface composition of various mixtures of the two ionic liquids (ILs) 1-methyl-3-octyl-imidazolium hexafluorophosphate [C₈C₁Im][PF₆] and 1,3-bis(polyethylene glycol)imidazolium iodide [(mPEG₂)₂Im]I in the temperature range from 230 to 370 K under ultraclean vacuum conditions. The surface tension was measured using a newly developed apparatus, and the surface composition was determined by angle-resolved X-ray photoelectron spectroscopy (ARXPS). In the pure ILs, the alkyl chains of [C₈C₁Im][PF₆] and the PEG chains of [(mPEG₂)₂Im]I are enriched at the IL/vacuum interface. In the mixtures, a strong selective surface enrichment of the alkyl chains occurs, which is most pronounced at low [C₈C₁Im][PF₆] contents. For the surface tension, strong deviations from an ideal mixing behaviour take place. By applying a simple approach based on the surface composition of the mixtures as deduced from ARXPS, we are able to predict and reproduce the experimentally measured temperature-dependent surface tension values with astonishingly high accuracy. Full article

(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)

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Review

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Open AccessReview

Recent Progress in Vacuum Engineering of Ionic Liquids

by

Yuji Matsumoto

Molecules 2023, 28(4), 1991; https://doi.org/10.3390/molecules28041991 - 20 Feb 2023

Viewed by 1074

Abstract

Since the discovery of ionic liquids (ILs) as a new class of liquid that can survive in a vacuum at room temperature, they have been aimed at being characterized with vacuum analysis techniques and used in vacuum processes for the last two decades. [...] Read more.

Since the discovery of ionic liquids (ILs) as a new class of liquid that can survive in a vacuum at room temperature, they have been aimed at being characterized with vacuum analysis techniques and used in vacuum processes for the last two decades. In this review, our state-of-the-art of the vacuum engineering of ILs will be introduced. Beginning with nanoscale vacuum deposition of IL films and their thickness-dependent ionic conductivity, there are presented some new applications of the ellipsometry to in situ monitoring of the thickness of IL films and their glass transitions, and of the surface thermal fluctuation spectroscopy to investigation of the rheological properties of IL films. Furthermore, IL-VLS (vapor-liquid-solid) growth, a vacuum deposition via IL, has been found successful, enhancing the crystallinity of vacuum-deposited crystals and films, and sometimes controlling their surface morphology and polymorphs. Among recent applications of ILs are the use of metal ions-containing IL and thin film nano IL gel. The former is proposed as a low temperature evaporation source of metals, such as Ta, in vacuum deposition, while the latter is demonstrated to work as a gate electrolyte in an electric double layer organic transistor. Full article

(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)

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