New experimental evidence supporting the mesoscopic segregation model in room temperature ionic liquids

Russina, Olga; Triolo, Alessandro

doi:10.1039/c1fd00073j

Cited by 200 publications

(248 citation statements)

References 55 publications

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“…X-ray scattering results.-Transport properties of ionic liquids are intimately linked to their nanoscale structure, and previous structural and molecular dynamics studies of imidazolium, ammonium and phosphonium ILs with pendant ether groups 1,2,28,[39][40][41] have shown that their organization on the molecular scale is different than their normal alkyl chain congeners. While alkyl chains tend to exist in extended conformations, ether chains have a large fraction of gauche conformations, particularly across C-C bonds connected to ether oxygens.…”

Section: Resultsmentioning

confidence: 99%

Connecting Structural and Transport Properties of Ionic Liquids with Cationic Oligoether Chains

Lall-Ramnarine

Zhao

Rodriguez

et al. 2017

J. Electrochem. Soc.

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X-ray diffraction and molecular dynamics simulations were used to probe the structures of two families of ionic liquids containing oligoether tails on the cations. Imidazolium and pyrrolidinium bis(trifluoromethylsulfonyl)amide ILs with side chains ranging from 4 to 10 atoms in length, including both linear alkyl and oligo-ethylene oxide tails, were prepared. Their physical properties, such as viscosity, conductivity and thermal profile, were measured and compared for systematic trends. Consistent with earlier literature, a single ether substituent substantially decreases the viscosity of pyrrolidinium and imidazolium ILs compared to their alkyl congeners. Remarkably, as the number of ether units in the pyrrolidinium ILs increases there is hardly any increase in the viscosity, in contrast to alkylpyrrolidinium ILs where the viscosity increases steadily with chain length. Viscosities of imidazolium ether ILs increase with chain length but always remain well below their alkyl congeners. To complement the experimentally determined properties, molecular dynamics simulations were run on the two ILs with the longest ether chains. The results point to specific aspects that could be useful for researchers designing ILs for specific applications. The focus of the ionic liquid (IL) community is shifting beyond the mere measurement of physical properties and identification of trends arising from particular structural moieties. Researchers are delving deeper into the nanostructural interactions between the ions to determine the topographical landscape of the ions within the liquids that influence IL properties.1-3 Such information is valuable when tuning the properties of ILs for particular applications. The ability to tune the properties of ionic liquids for specific applications is a major factor in their allure as remarkable solvents that make it possible to do extreme chemistry without extreme conditions. It has been acknowledged that although ionic liquids have a combination of physical properties that make them attractive alternatives to traditional solvents, they have relatively high viscosities that hamper their practical application in large-scale processes. For example, in the area of electrochemical energy storage devices there is still an urgent need for improved electrolytes exhibiting properties of combustion resistance, high conductivity, and wide electrochemical windows. ILs with improved transport properties (viscosity, conductivity and diffusivity) would be perfect candidates to address this need. Structural modification of the IL cation and anion is a proven tool to dramatically alter IL properties. In particular, substituting ether functionalities for alkyl functionalities on IL cations has been shown to reduce the viscosity of ionic liquids significantly.2,4-6 In this work we examine the effect of incorporating oligoether side chains of varying lengths (1-3 repeating ethoxy units, Figure 1) on the physical properties and structural characteristics of imidazolium and pyrrolidinium NTf 2 ionic liquids in ...

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Section: Resultsmentioning

confidence: 99%

Connecting Structural and Transport Properties of Ionic Liquids with Cationic Oligoether Chains

Lall-Ramnarine

Zhao

Rodriguez

et al. 2017

J. Electrochem. Soc.

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“…Two typical kinds of contacts have been reported in imidazolium-based ILs: tail-tail and ring-ring (e.g., π + -π + stacking). 1,11,39,74 The former one is known to be at the origin of microheterogeneity observed both experimentally 1,[77][78] and by molecular simulations.…”

Section: Cation-cation Arrangementmentioning

confidence: 95%

Local Structure in Terms of Nearest-Neighbor Approach in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: MD Simulations

et al. 2016

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“…Later on, experimental evidence for nanostructuring in ILs began to appear. Methods such as X-ray diffraction/scattering, [16][17][18]22 neutron diffraction, 26 quasi-elastic neutron scattering 27 were intensively used. Recently, magnetic resonance methods 20,28,29 and electron microscopy 21 were also involved in the study of heterogeneities and nanostructuring in ILs.…”

Section: Introductionmentioning

confidence: 99%

Microscopic rigidity and heterogeneity of ionic liquids probed by stochastic molecular librations of the dissolved nitroxides

Ivanov

Krumkacheva

Dzuba

et al. 2017

Phys. Chem. Chem. Phys.

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abMicroscopic molecular organization and heterogeneities in ionic liquids (ILs) are of significant fundamental and applied interest. Although many theoretical studies have been dedicated to this topic, the development of experimental methods for studying such heterogeneities is still in demand. In this work we propose a new approach for the characterization of microscopic rigidity and heterogeneities in ILs using stochastic librations (small angle motions) of the nitroxide radicals as a probe. Stable nitroxides are dissolved in ILs, which are then shock-frozen and investigated using pulse Electron Paramagnetic The structure, size, solubility and other properties of nitroxides are adjustable for particular tasks, therefore the proposed approach can potentially be implemented to probe the rigidity and heterogeneities of any ILs, thus providing vital insights into their molecular-scale self-organization.

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New experimental evidence supporting the mesoscopic segregation model in room temperature ionic liquids

Cited by 200 publications

References 55 publications

Connecting Structural and Transport Properties of Ionic Liquids with Cationic Oligoether Chains

Connecting Structural and Transport Properties of Ionic Liquids with Cationic Oligoether Chains

Local Structure in Terms of Nearest-Neighbor Approach in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: MD Simulations

Microscopic rigidity and heterogeneity of ionic liquids probed by stochastic molecular librations of the dissolved nitroxides

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