Structure and dynamics in protic ionic liquids: A combined optical Kerr-effect and dielectric relaxation spectroscopy study

Turton, David A.; Sonnleitner, Thomas; Ortner, A.; Walther, Markus; Hefter, Glenn; Seddon, Kenneth R.; Stana, Simona; Plechkova, Natalia V.; Buchner, Richard; Wynne, Klaas

doi:10.1039/c1fd00054c

Cited by 59 publications

(76 citation statements)

References 48 publications

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“…However, in the light of new results it seems more appropriate to use a so-called "constant-loss" term for this region (Figure 4) consistent with studies of other strongly interacting liquids [28]. This mainly translational mode is associated with the rattling of molecules in their cage of surrounding neighbors superimposed on the formation and decay of these cages.…”

Section: Short-time Dynamicsmentioning

confidence: 72%

“…To capture the wide time-span of intermolecular dynamics, two OKE set-ups were employed. The faster dynamics were measured using a 7 nJ, 20 fs pulse (Coherent Mira-SEED) [27] with weaker relaxations at longer times recorded using a regeneratively-amplified setup (Coherent Mantis Legend USX) with a 1 µJ pulse stretched to a duration of ∼ 1 ps [28].…”

Section: Optical Kerr-effect Spectroscopymentioning

confidence: 99%

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Dynamics of RTILs: A comparative dielectric and OKE study

Sonnleitner

Turton

Waselikowski

et al. 2014

Journal of Molecular Liquids

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The dynamics of room-temperature ionic liquids (RTILs) were studied by investigating their dielectric relaxation (DR) and timeresolved optical Kerr-effect (OKE) spectra in the frequency range of ∼10 MHz to ∼20 THz. For the studied RTILs the OKE and DR spectra are dominated by a relaxation in the GHz region and extend to a relatively sharp band at around 10 THz. Whilst the first feature is mainly associated with the structural relaxation of the fluid through ion rotation (α relaxation), the second indicates the short-time limit of intermolecular dynamics. The rather featureless intermediate region is mainly associated with intermolecular vibrations that are strongly coupled to hindered rotations. In contrast to other RTILs, imidazolium salts show an additional sub-α relaxation which dominates the OKE signal and is indicative of the breathing motion of rather long-lived cages.Mixed with polar solvents RTILs were found to retain their ionic liquid-like character up to relatively high levels of dilution, but with the overall dynamics considerably speeded up. Below RTIL mole fractions of ∼0.2-0.4 these systems behave like conventional electrolyte solutions with more or less pronounced ion pairing.

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Section: Short-time Dynamicsmentioning

confidence: 72%

Section: Optical Kerr-effect Spectroscopymentioning

confidence: 99%

Dynamics of RTILs: A comparative dielectric and OKE study

Sonnleitner

Turton

Waselikowski

et al. 2014

Journal of Molecular Liquids

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“…Additionally, a small high-frequency D equation peaking outside the present frequency range is required to summarize the small contributions from intermolecular vibrations and librations at THz frequencies that extend below 89 GHz. 26 Data analysis revealed that for all mixture spectra a sum of two modes (n = 2 in eqn (3)) yielded the best fit ( Fig. 1 and 2).…”

Section: Choice Of Fit Modelmentioning

confidence: 88%

“…13 The similar friction coefficients also suggest that at least down to x EAN E 0.7 the [EtNH 3 ] + cation relaxes via large-angle jumps as the pure IL. 26,38 3.3.2 Amplitude. Using eqn (5) the conclusions made in Section 3.2.1 can be confirmed and extended quantitatively.…”

Section: Amplitudesmentioning

confidence: 99%

Do H-bonds explain strong ion aggregation in ethylammonium nitrate + acetonitrile mixtures?

Sonnleitner

Nikitina

Nazet

et al. 2013

Phys. Chem. Chem. Phys.

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Binary mixtures of the protic ionic liquid ethylammonium nitrate (EAN) and acetonitrile (AN) were studied at 25 1C over the entire composition range by means of broadband dielectric spectroscopy covering 0.2 r n/GHz r 89. The dielectric spectra could be decomposed into two relaxation processes, both of which proved to be composite modes. For dilute solutions the higher-frequency Debye relaxation centered at B60 GHz is associated with the rotational diffusion of AN molecules, whereas at higher salt concentrations ultra-fast intermolecular vibrations and librations of EAN dominate the process. For EAN-rich solutions the lower-frequency relaxation is mainly due to jump reorientation of the ethylammonium cation, whereas contact ion pairs (CIPs) dominate this mode for dilute solutions. From the relaxation amplitudes effective solvation numbers and ion-pair concentrations were determined. For vanishing EAN mole fraction, x EAN -0, an effective cation solvation number of B7 was found which steeply drops until x EAN E 0.2 but shows only moderate decrease later on. The obtained association constant for EAN, K 0 A = 970 L mol À1 , exceeds that of other 1 : 1 electrolytes in AN by a factor of B30-50. This observation, as well as the fact that CIPs are formed despite strong cation solvation, indicates that ion pairing is mainly driven by the formation of strong hydrogen bonds between anions and cations.

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“…The static structure of ionic liquids has been investigated by X-ray/neutron scattering and molecular simulation techniques to obtain the static structure factor S(Q) and the radial distribution function g(r). [1][2][3][4] Studies of dynamics have also been carried out by nuclear magnetic resonance (NMR), [5][6][7] optical Kerr effect, low-frequency Raman THz and far-IR spectroscopies, [8][9][10][11][12] dielectric relaxation, [11][12][13] and molecular dynamics simulations. 14 Hayamizu et al reported the diffusion coefficients of cation and anion in various ionic liquids by pulsed-gradient spin-echo (PGSE) NMR, and the results were related to macroscopic properties such as viscosity and ionic conductivity.…”

mentioning

confidence: 99%