| 1. |
- Filippov, Andrei, PhD, 1957-, et al.
(author)
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Effect of rotating magnetic field on the diffusivity of ethylammonium nitrate ionic liquid confined between micrometer-spaced glass plates
- 2021
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In: Journal of Molecular Liquids. - : Elsevier. - 0167-7322 .- 1873-3166. ; 323
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Journal article (peer-reviewed)abstract
- We studied changes in the diffusion coefficients in layers of EAN confined between glass plates, placed in a strong magnetic field with a magnetic flux density B0, and rotated around the axis directed along and normal to B0. Under the rotational conditions along B0, the diffusion coefficient decreases with time after placement in the magnetic field at the same rate as for a static sample, observed previously (Filippov and Antzutkin, Phys. Chem. Chem. Phys. 2018. 20. 6316). However, when the EAN layers are rotating around the axis perpendicular to B0, the duration of exposure to the magnetic field does not affect the diffusion coefficient until the rotation stops. On the other hand, the diffusivity after extended exposure to a static magnetic field increases as the sample starts to rotate around the axis perpendicular to B0. The observed effects are due to either the periodic change in the orientation of the thin surface layers of EAN or inhomogeneity of B0 in the sample due to the B0 fluctuation.
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| 2. |
- Filippov, Andrei, et al.
(author)
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NMR study of nitrate ionic liquids confined between micrometerspaced plates
- 2024
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In: Applied Chemical Engineering. - : Arts and Science Press Pte. Ltd.. - 2578-2010. ; 7:2
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Journal article (peer-reviewed)abstract
- This review paper presents the results of a study conducted using nuclear magnetic resonance (NMR) methods to investigate the dynamic behaviour of ionic liquid-based compositions in micrometre-spaced confinement. Ethylammonium nitrate (EAN) and other ionic liquid (IL) systems with nitrate anion in glass or quartz spaced confinement demonstrate anomalous cation dynamics that differ from those observed in bulk and in nano-confinement. It was demonstrated that the principal axis of the nitrate anion exhibits preferential orientation to the surface, akin to that in liquid crystals. It was shown that the cation translational mobility reversibly changes during exposure to a static magnetic field. This phenomenon was interpreted as a result of intermolecular structure transformations occurring in the confined ILs. The mechanisms of these transformations were discussed.
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| 3. |
- Filippov, Andrei, PhD, 1957-, et al.
(author)
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Self-diffusion in ionic liquids with nitrate anion : Effects of confinement between glass plates and static magnetic field
- 2020
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In: Journal of Molecular Liquids. - : Elsevier. - 0167-7322 .- 1873-3166. ; 312
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Journal article (peer-reviewed)abstract
- Alkylammonium nitrate protic ionic liquids (ILs), when placed between flat polar borosilicate glass plates, have demonstrated enhanced diffusivity and the gradual decrease of diffusivity after exposure to an external static magnetic field (Filippov et al., 2018). This phenomenon has been explained by phase transformations taking place in the ILs. In this study, we observed similar processes occurring in systems prepared with ethylammonium nitrate confined between quartz plates. A higher content of silicon oxide in the plates does not significantly alter the phenomenon previously found in the system prepared with borosilicate glass plates. For the first time, we have observed similar effects of confinement and magnetic field on the aprotic IL, 1‑ethyl‑3‑methylimidazolium nitrate. Substitution of the ethylammonium cation with a 1‑ethyl‑3‑methylimidazolium cation slows down the kinetics and increases magnitude of the processes occurring in the IL exposed to a magnetic field. We suggested that the main factor determining these effects is the presence and modification of the hydrogen-bonding network in the studied protic and aprotic ILs. The process of inverse phase transformation for the confined ethylammonium nitrate after removing the sample from the magnetic field was observed and analysed.
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| 4. |
- Filippov, Andrei, PhD, 1957-, et al.
(author)
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Unusual ion transport behaviour of ethylammonium nitrate mixed with lithium nitrate
- 2021
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In: Journal of Molecular Liquids. - : Elsevier. - 0167-7322 .- 1873-3166. ; 340
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Journal article (peer-reviewed)abstract
- The diffusivity of ions and ionic conductivity of ethylammonium nitrate (EAN) mixed with lithium nitrate (LiNO3) has been carried out as a function of Li-salt concentration and temperature. An unusual behavior of ion diffusivities and ionic conductivities of the mixtures are observed over a range of Li-salt concentration and temperature. The diffusivities of EA+ and Li+, as measured by pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) diffusometry, are found to be comparable in the lower temperature range. An overall decrease in the ion diffusivity is observed with an increase in the concentration of LiNO3. A lower degree of dissociation of ionic complexes in the presence lower concentration of the Li-salt (less than 6 mol. %) resulted in lower ionic conductivity. In the higher concentration range of Li-salt the Li+ diffusivity is monotonously decreased with an increase in the concentration. In the lower concentration range, the Li+ diffusivity exceeded the diffusivity of EA+ cation demonstrating the release of Li+ from the associates. Being enclosed between glass plates, the diffusivities of EA+ and Li+ showed peculiarities similar to the earlier observed results for neat nitrate ILs: accelerated diffusivity of cations and reversible alteration of diffusivities under the influence of strong static magnetic field.
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| 5. |
- Gnezdilov, Oleg I., et al.
(author)
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Temperature dependence of 1H NMR chemical shifts and diffusivity of confined ethylammonium nitrate ionic liquid
- 2020
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In: Magnetic Resonance Imaging. - : Elsevier. - 0730-725X .- 1873-5894. ; 74, s. 84-89
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Journal article (peer-reviewed)abstract
- Some ionic liquids (ILs) change their dynamic properties when placed in a confinement between polar surfaces (Filippov et al., Phys. Chem. Chem. Phys. 2018, 20, 6316). The diffusivities of ions and NMR relaxation times in these ILs also reversibly change under a strong static magnetic field. The mechanisms of these phenomena are not clear, but it has been suggested that they involve modified hydrogen-bonding networks formed in these ILs in the presence of polar surfaces. To obtain a better understanding of these effects, we performed temperature-dependent measurements of chemical shifts and diffusion coefficients for ethylammonium nitrate (EAN) IL in the bulk phase (IB) and confined in layers with a thickness of ~4 μm between quartz plates unexposed (I phase) and exposed (IMF phase) to a static magnetic field of 9.4 T. It was shown that the NMR chemical shift of NH3 protons of EAN in the I phase is strongly shifted upfield, ~0.0145 ppm/K, which is due to weakening of the hydrogen-bonding network of the confined EAN. Exposure to the magnetic field leads to restitution of the hydrogen-bonding (H-bonding network). The temperature dependences of diffusion coefficients follow the order D(I) > D(IB) > D(IMF) and can be described by a Vogel-Fulcher-Tammann approach with variation of the pre-exponential factor, which is determined by the strength of the H-bonding network. Confinement of EAN between plates (IB → I) is an endothermic process, while processes occurring in a magnetic field, I → IMF and IMF → I, are exothermic and endothermic, respectively.
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| 6. |
- Shaikhullina, Milyausha, et al.
(author)
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NMR relaxation and self-diffusion in aqueous micellar gels of pluronic F-127
- 2020
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In: Journal of Molecular Liquids. - : Elsevier. - 0167-7322 .- 1873-3166. ; 306
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Journal article (peer-reviewed)abstract
- We studied the transverse NMR relaxation of protons of different chemical groups and diffusion of molecules in an aqueous pluronic F-127 system. The system was studied at concentrations of 15, 21 and 28 wt% and in the temperature range of 293–333 K. The dynamic peculiarities in different phases were analyzed based on the NMR relaxation and diffusion data. Our study demonstrated a correlation between phase states, T2 relaxation times of “solid-like” and “liquid” protons of selected chemical groups of polypropylene oxide (PPO) and polyethylene oxide (PEO) blocks, and diffusion coefficients. Transverse NMR relaxation established that the presence of a “solid-like” component of CH3 protons of PEO blocks is observed only at temperatures and concentrations corresponding to the rigid-gel phase, due to entanglements between micellar coronas. At all temperatures and concentrations, some CH3 protons of PPO blocks and some CH2 protons of PEO blocks show “liquid-like” transverse NMR relaxation. Under the conditions corresponding to formation of the rigid-gel phase of the pluronic, relaxation of the “liquid-like” protons additionally accelerates due to entanglements of micellar coronas. Transition of the system to the rigid-gel phase is accompanied by decrease of diffusion coefficients by a factor of 10–104 relative to the diffusivity of free-moving pluronic micelles in the sol phase. Diffusion measurements show that there are pre-transition phenomena, which are characteristic for temperatures and concentrations near sol-gel phase boundaries.
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