Cation Dynamics in the Pyridinium Based Ionic Liquid 1-N-Butylpyridinium Bis((trifluoromethyl)sulfonyl) As Seen by Quasielastic Neutron Scattering

Abstract

Quasielastic neutron scattering (QENS) has been used to study the cation dynamics in the pyridinium based ionic liquid (IL) 1-N-butylpyridinium bis((trifluoromethyl)sulfonyl)imide (BuPy-Tf(2)N). This IL allows for a detailed investigation of the dynamics of the cations only, due to the huge incoherent scattering cross section of the cation (σ(inc)(cation) >> σ(inc)(anion)). The measured spectra can be decomposed into two Lorentzian lines, indicative of two distinct dynamic processes. The slower of these two processes is diffusive in nature, whereas the faster one can be attributed to localized motions. The temperature dependence of the diffusion coefficient of the slow process follows an Arrhenius law, with an activation energy of E(A) = 14.8 ± 0.3 kJ/mol. Furthermore, we present here results from experiments with polarized neutrons. These experiments clearly show that the slower of the two observed processes is coherent, while the faster one is incoherent in nature.

Water Dynamics in Hydrated Carboxylated Cellulose Nanofibril Membranes

“…Such plateau indicated a dynamic process is in a confined space, which is related to the cage or cagelike structure in the system. Similar phenomena has been reported for ionic liquid systems 53,54 .…”

QENS Study of Diffusive and Localized Cation Motions of Pyridinium-Based Ionic Liquids

“…It is necessary to keep in mind that the coherent contribution becomes more significant with increasing degree of deuteration. But from our previous investigation [2] we may draw a conclusion that collective dynamics can influence unrestricted jump-diffusion, the localized dynamics remaining unaffected. A broad QENS-contribution, which is related to the localized dynamics, appears in the spectra of both partially deuterated samples (Fig.4).…”

“…On the basis of this, the further analysis was performed under the assumption that we observe single particle dynamics only of the cations. Both protonated and partially deuterated samples were synthesized as described in our paper [2] previously. The water content was controlled by means of Karl Fischer titration, 1 H NMR spectra were used to check the purity of the samples and the quality of partial deuteration.…”

Linking Structure to Dynamics in Protic Ionic Liquids: A Neutron Scattering Study of Correlated and Single-Particle Motions

“…Due to the large neutron incoherent cross section of hydrogen, the method is predominantly sensitive to single-particle (uncorrelated) motions of protons ubiquitous in organic cations of ILs 13 – 16 . Selective deuterium/hydrogen (D/H) isotope substitution can be applied to intensify coherent scattering 14 , 17 , 18 and to shift the research focus to collective (correlated) processes governed by the charge alteration in ILs 19 , 20 .…”

“…During the last years, several publications on single-particle dynamics in PILs have appeared in the literature 14 – 16 . In general, the PIL spectra are interpreted in an analogous way as those of more extensively studied aprotic ILs 17 , 18 , 24 , 25 , assuming long-range diffusion and various subdiffusive (localized) motions. As acidic protons can hypothetically contribute to anhydrous conductivity of PILs via Grotthus mechanism (proton hopping through the hydrogen bond network), much attention is also explicitly paid to its dynamics.…”