Please use this identifier to cite or link to this item: doi:10.22028/D291-34782
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Title: Curled cation structures accelerate the dynamics of ionic liquids
Author(s): Rauber, Daniel
Philippi, Frederik
Kuttich, Björn
Becker, Julian
Kraus, Tobias
Hunt, Patricia
Welton, Tom
Hempelmann, Rolf-Wilhelm
Kay, Christopher
Language: English
Title: Physical chemistry, chemical physics : PCCP
Volume: 23
Issue: 37
Startpage: 21042
Endpage: 21064
Publisher/Platform: RSC
Year of Publication: 2021
Publikation type: Journal Article
Abstract: Ionic liquids are modern liquid materials with potential and actual implementation in many advanced technologies. They combine many favourable and modifiable properties but have a major inherent drawback compared to molecular liquids – slower dynamics. In previous studies we found that the dynamics of ionic liquids are significantly accelerated by the introduction of multiple ether side chains into the cations. However, the origin of the improved transport properties, whether as a result of the altered cation conformation or due to the absence of nanostructuring within the liquid as a result of the higher polarity of the ether chains, remained to be clarified. Therefore, we prepared two novel sets of methylammonium based ionic liquids; one set with three ether substituents and another set with three butyl side chains, in order to compare their dynamic properties and liquid structures. Using a range of anions, we show that the dynamics of the ether-substituted cations are systematically and distinctly accelerated. Liquefaction temperatures are lowered and fragilities increased, while at the same time cation–anion distances are slightly larger for the alkylated samples. Furthermore, pronounced liquid nanostructures were not observed. Molecular dynamics simulations demonstrate that the origin of the altered properties of the ether substituted ionic liquids is primarily due to a curled ether chain conformation, in contrast to the alkylated cations where the alkyl chains retain a linear conformation. Thus, the observed structure–property relations can be explained by changes in the geometric shape of the cations, rather than by the absence of a liquid nanostructure. Application of quantum chemical calculations to a simplified model system revealed that intramolecular hydrogen-bonding is responsible for approximately half of the stabilisation of the curled ether-cations, whereas the other half stems from non-specific long-range interactions. These findings give more detailed insights into the structure–property relations of ionic liquids and will guide the development of ionic liquids that do not suffer from slow dynamics.
DOI of the first publication: 10.1039/D1CP02889H
URL of the first publication: https://pubs.rsc.org/en/content/articlelanding/2021/CP/D1CP02889H
Link to this record: hdl:20.500.11880/31816
http://dx.doi.org/10.22028/D291-34782
ISSN: 1463-9084
1463-9076
Date of registration: 4-Oct-2021
Faculty: NT - Naturwissenschaftlich- Technische Fakultät
Department: NT - Chemie
Professorship: NT - Prof. Dr. Tobias Kraus
Collections:Die Universitätsbibliographie

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