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New Trends in Ionic Liquids Application

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Molecular Liquids".

Deadline for manuscript submissions: closed (15 June 2021) | Viewed by 18065

Special Issue Editor


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Guest Editor
1. Centro de Ciências e Tecnologias Nucleares (C2TN), Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela, LRS, Portugal
2. Centro de Química Estrutural (CQE), Instituto Superior Técnico, Estrada Nacional 10, 2695-066 Bobadela, LRS, Portugal
Interests: ionic liquids; thermochemical and thermophysical properties; new materials

Special Issue Information

Dear Colleagues,

Ionic liquids have, in a few years, gone from being a curiosity to being one of the most fruitful fields of science. Their variety is as wide as that of other organic or inorganic compounds, but some of their properties are transversal to almost all of them and make ionic liquids a family of extremely interesting compounds. Among these properties, we can highlight the following: virtually no vapor pressure; excellent thermal stability; high mechanical, and chemical, stabilities; high electrochemical stability; nonflammability; low compressibility; specific solvation properties; good lubrication properties; and highly tunable properties by cation and anion combination.

These unique properties and their variability have led to the use of ionic liquids in an increasing number of areas of various sciences: chemistry, physics, biology, medicine, and mechanics. They have been used as solvents, chelators, lubricants and additives, liquid crystals, thermal fluids, electrolytes, and artificial muscles, and in a variety of separation techniques. They have also been identified as green chemicals, although not all of them are. The search for ionic liquids that have less of a negative impact on the environment is also gaining ground.

In such a vast and interesting field of research, we are especially focused on exploring new frontiers, and on novelty (both in knowledge and in application) in the use of ionic liquids. This is the challenge we present to researchers to contribute to this Special Issue entitled ‘’New Trends in Ionic Liquids Application’’. Reviews articles by experts in the field are also welcomed if they contribute to defining the direction in which research and new applications will evolve.

Prof. Dr. João Paulo Leal
Guest Editor

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Keywords

  • Ionic liquids
  • Solvents
  • Chelators
  • Liquid crystals
  • Thermal fluids
  • Electrolytes
  • Separation techniques

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Published Papers (5 papers)

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Research

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11 pages, 20981 KiB  
Article
Flexo-Ionic Effect of Ionic Liquid Crystal Elastomers
by C. P. Hemantha Rajapaksha, M. D. Tharindupriya Gunathilaka, Suresh Narute, Hamad Albehaijan, Camilo Piedrahita, Pushpa Paudel, Chenrun Feng, Björn Lüssem, Thein Kyu and Antal Jákli
Molecules 2021, 26(14), 4234; https://doi.org/10.3390/molecules26144234 - 12 Jul 2021
Cited by 15 | Viewed by 5283
Abstract
The first study of the flexo-ionic effect, i.e., mechanical deformation-induced electric signal, of the recently discovered ionic liquid crystal elastomers (iLCEs) is reported. The measured flexo-ionic coefficients were found to strongly depend on the director alignment of the iLCE films and can be [...] Read more.
The first study of the flexo-ionic effect, i.e., mechanical deformation-induced electric signal, of the recently discovered ionic liquid crystal elastomers (iLCEs) is reported. The measured flexo-ionic coefficients were found to strongly depend on the director alignment of the iLCE films and can be over 200 µC/m. This value is orders of magnitude higher than the flexo-electric coefficient found in insulating liquid crystals and is comparable to the well-developed ionic polymers (iEAPs). The shortest response times, i.e., the largest bandwidth of the flexo-ionic responses, is achieved in planar alignment, when the director is uniformly parallel to the substrates. These results render high potential for iLCE-based devices for applications in sensors and wearable micropower generators. Full article
(This article belongs to the Special Issue New Trends in Ionic Liquids Application)
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14 pages, 1683 KiB  
Article
Phase Behavior of Aqueous Biphasic Systems with Choline Alkanoate Ionic Liquids and Phosphate Solutions: The Influence of pH
by Paula Berton, Hongzhe Tian and Robin D. Rogers
Molecules 2021, 26(6), 1702; https://doi.org/10.3390/molecules26061702 - 18 Mar 2021
Cited by 12 | Viewed by 2376
Abstract
Aqueous biphasic systems (ABS) composed of the choline alkanoate ionic liquids (ILs) choline acetate [Cho][OAc], choline propanoate [Cho][Pro], choline butyrate [Cho][But], and choline hexanoate [Cho][Hex], mixed with K3PO4 solutions at pH 7.2 and 14.5, were prepared and their phase diagrams [...] Read more.
Aqueous biphasic systems (ABS) composed of the choline alkanoate ionic liquids (ILs) choline acetate [Cho][OAc], choline propanoate [Cho][Pro], choline butyrate [Cho][But], and choline hexanoate [Cho][Hex], mixed with K3PO4 solutions at pH 7.2 and 14.5, were prepared and their phase diagrams were compared. The ability to form ABS with alkaline K3PO4 solutions decreased in the order [Cho][OAc] ≈ [Cho][Pro] > [Cho][But] > [Cho][Hex], while with neutral K3PO4 solutions, [Cho][OAc] could not form an ABS, and the other three ILs performed similarly. All of the biphasic regions of the ABS decreased with the increase in pH. 1H-NMR data indicated anion exchange between phases in ABS at neutral pH. The ABS at neutral pH were evaluated to extract the triazine herbicides simazine, cyanazine, and atrazine, and the ABS formed by [Cho][Pro] and the pH 7.2 K3PO4 solution has shown extraction recoveries higher than 90%. Full article
(This article belongs to the Special Issue New Trends in Ionic Liquids Application)
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28 pages, 9193 KiB  
Article
Ionic Liquids as Performance Ingredients in Space Lubricants
by Erik Nyberg, Christoph Schneidhofer, Lucia Pisarova, Nicole Dörr and Ichiro Minami
Molecules 2021, 26(4), 1013; https://doi.org/10.3390/molecules26041013 - 14 Feb 2021
Cited by 14 | Viewed by 3591
Abstract
Low vapor pressure and several other outstanding properties make room-temperature ionic liquids attractive candidates as lubricants for machine elements in space applications. Ensuring sufficient liquid lubricant supply under space conditions is challenging, and consequently, such tribological systems may operate in boundary lubrication conditions. [...] Read more.
Low vapor pressure and several other outstanding properties make room-temperature ionic liquids attractive candidates as lubricants for machine elements in space applications. Ensuring sufficient liquid lubricant supply under space conditions is challenging, and consequently, such tribological systems may operate in boundary lubrication conditions. Under such circumstances, effective lubrication requires the formation of adsorbed or chemically reacted boundary films to prevent excessive friction and wear. In this work, we evaluated hydrocarbon-mimicking ionic liquids, designated P-SiSO, as performance ingredients in multiply alkylated cyclopentane (MAC). The tribological properties under vacuum or various atmospheres (air, nitrogen, carbon dioxide) were measured and analyzed. Thermal vacuum outgassing and electric conductivity were meas- ured to evaluate ‘MAC & P-SiSO’ compatibility to the space environment, including the secondary effects of radiation. Heritage space lubricants—MAC and perfluoroalkyl polyethers (PFPE)—were employed as references. The results corroborate the beneficial lubricating performance of incorporating P-SiSO in MAC, under vacuum as well as under various atmospheres, and demonstrates the feasibility for use as a multifunctional additive in hydrocarbon base oils, for use in space exploration applications. Full article
(This article belongs to the Special Issue New Trends in Ionic Liquids Application)
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Review

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24 pages, 4545 KiB  
Review
Luminescent Ln-Ionic Liquids beyond Europium
by Cláudia C. L. Pereira, José M. Carretas, Bernardo Monteiro and João P. Leal
Molecules 2021, 26(16), 4834; https://doi.org/10.3390/molecules26164834 - 10 Aug 2021
Cited by 6 | Viewed by 2825
Abstract
Searching in the Web of Knowledge for “ionic liquids” AND “luminescence” AND “lanthanide”, around 260 entries can be found, of which a considerable number refer solely or primarily to europium (90%, ~234). Europium has been deemed the best lanthanide for luminescent applications, mainly [...] Read more.
Searching in the Web of Knowledge for “ionic liquids” AND “luminescence” AND “lanthanide”, around 260 entries can be found, of which a considerable number refer solely or primarily to europium (90%, ~234). Europium has been deemed the best lanthanide for luminescent applications, mainly due to its efficiency in sensitization, longest decay times, and the ability to use its luminescence spectra to probe the coordination geometry around the metal. The remaining lanthanides can also be of crucial importance due to their different colors, sensitivity, and capability as probes. In this manuscript, we intend to shed some light on the existing published work on the remaining lanthanides. In some cases, they appear in papers with europium, but frequently in a subordinate position, and in fewer cases then the main protagonist of the study. All of them will be assessed and presented in a concise manner; they will be divided into two main categories: lanthanide compounds dissolved in ionic liquids, and lanthanide-based ionic liquids. Finally, some analysis of future trends is carried out highlighting some future promising fields, such as ionogels. Full article
(This article belongs to the Special Issue New Trends in Ionic Liquids Application)
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Other

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10 pages, 4381 KiB  
Perspective
Ionic Liquids Based on the Concept of Melting Point Lowering Due to Ethoxylation
by Manuel Rothe, Eva Müller, Patrick Denk and Werner Kunz
Molecules 2021, 26(13), 4034; https://doi.org/10.3390/molecules26134034 - 1 Jul 2021
Cited by 5 | Viewed by 2869
Abstract
Most of the commonly used Ionic Liquids (ILs) contain bulky organic cations with suitable anions. With our COMPLET (Concept of Melting Point Lowering due to Ethoxylation), we follow a different approach. We use simple, low-toxic, cheap, and commercially available anions of the type [...] Read more.
Most of the commonly used Ionic Liquids (ILs) contain bulky organic cations with suitable anions. With our COMPLET (Concept of Melting Point Lowering due to Ethoxylation), we follow a different approach. We use simple, low-toxic, cheap, and commercially available anions of the type Cx(EO)yCH2COO to liquefy presumably any simple metal ion, independently of its charge. In the simplest case, the cation can be sodium or lithium, but synthesis of Ionic Liquids is also possible with cations of higher valences such as transition or rare earth metals. Anions with longer alkyl chains are surface active and form surface active ionic liquids (SAILs), which combine properties of ionic and nonionic surfactants at room temperature. They show significant structuring even in their pure state, i.e., in the absence of water or any other added solvent. This approach offers new application domains that go far beyond the common real or hypothetical use of classical Ionic Liquids. Possible applications include the separation of rare earth metals, the use as interesting media for metal catalysis, or the synthesis of completely new materials (for example, in analogy to metal organic frameworks). Full article
(This article belongs to the Special Issue New Trends in Ionic Liquids Application)
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