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- Yaghini, Negin, 1976, et al.
(författare)
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Effect of Water on the Local Structure and Phase Behavior of Imidazolium-Based Protic Ionic Liquids
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 119:4, s. 1611-1622
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Tidskriftsartikel (refereegranskat)abstract
- We report on the effect of water on local structure and phase behavior of two protic ionic liquids, C(2)HImTFSI and C(2)HImTfO. Raman and infrared spectroscopy are employed to investigate the local coordination state. We find that water interacts weakly with TFSI- while more specifically with TfO- through the - SO3 group. Additionally, we observe that upon addition of water the - NH stretching frequency does not change in C(2)HImTFSI, while it red-shifts in C(2)HImTfO, indicative of different hydrogen bonding configurations. Supported by the appearance of some additional features in the 800-1000 cm(-1) frequency range where ring out-of-plane bending (?) modes are found, we hypothesize that in C(2)HImTFSI water interacts only with the cation coordinating to the ring C2H and the N3H sites, while it interacts with both cation and anion in C(2)HImTfO forming hydrogen bonds that involve the cationic N-H site as well as the anionic - SO3 group. These different local structures also reflect in the phase behavior investigated by DSC, which reveals a more homogeneous solution when water is added to C(2)HImTfO, as compared to H2O/C(2)HImTFSI mixtures. Finally we report that the addition of water also significantly affects both T-m and T-g.
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| 2. |
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| 3. |
- Pitawala, Jagath, 1976, et al.
(författare)
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Coordination and interactions in a Li-salt doped ionic liquid
- 2015
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093. ; 407, s. 318-323
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Tidskriftsartikel (refereegranskat)abstract
- We report on the coordination and interactions in the LiTFSI doped ionic liquid PyR14TFSI over a large concentration range, 0.01 2. The number decreases with increasing salt concentration and the interaction between the Li-ion and the TFSI anions is rather weak in this concentration range. At intermediate concentrations, 0.1 0.2, N-TFSI/Li decreases further indicating the transition to more complex structures with Li-ions bridging TFSI anions. We also show that the evolution of the microscopic structure as a function of Li-salt concentration is mirrored in the behaviour of macroscopic properties such as the ionic conductivity and the glass transition temperature, which also show a crossover in the same concentration range.
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| 4. |
- Pitawala, Jagath, 1976, et al.
(författare)
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Phase behaviour, transport properties, and interactions in Li-salt doped ionic liquids
- 2012
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 154, s. 71-80
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Tidskriftsartikel (refereegranskat)abstract
- We report on the influence of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) doping on the glass transition temperature (T(g)), the ionic conductivity, and Li-ion coordination of two dicationic ionic liquids (DILs) based on the TFSI anion. The results are compared to the behaviour of traditional mono-cationic ionic liquids. The cations of the DILs contain two imidazolium rings, connected by a decane hydrocarbon chain. Homogeneous mixtures of these ILs and LiTFSI can be obtained in a large concentration range. With increasing Li-salt concentration the ionic conductivity decreases whereas the glass transition temperature increases in both systems. However, the influence of the salt doping on the ionic conductivity and the glass transition temperature is low compared to typical mono-cationic ionic liquids, based on for example the pyrrolidinium cation and the TFSI anion. This behaviour is mirrored in the average coordination number of TFSI anions around Li-ions, determined by Raman spectroscopy. The coordination number is systematically lower in the DILs, suggesting a connection between the difference in the Li-ion environment and the behaviour of the glass transition and the ionic conductivity. A T(g)-scaled Arrhenius plot of the ionic conductivity shows that the ionic conductivity for all LiTFSI concentrations has the same temperature dependence, i.e. the fragility of the liquid is the same. This implies that the conduction process is dominated by the viscous properties of the liquids over the entire concentration range. This provides further support for linking the local environment of the Li-ions to the glass transition and conduction process in the ionic liquid/salt mixtures.
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| 6. |
- Pitawala, Jagath, 1976, et al.
(författare)
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Physical Properties, Ion-Ion Interactions, and Conformational States of Ionic Liquids with Alkyl-Phosphonate Anions
- 2013
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 117:27, s. 8172-8179
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the ionic conductivities, phase behaviors, conformational states, and interactions of three ionic liquids based on imidazolium cations and phosphonate anions with varying alkyl chain lengths. All three ionic liquids show high conductivities, with 1,3-dimethylimidazolium methyl-phosphonate [DiMIm(MeO)(H)- PO2] being the most conductive (7.3 x 10(-3) S cm(-1) at 298 K). The high ionic conductivities are a result of the low glass-transition temperatures, T-g, which do not change significantly upon changing the cation and/or anion size. However, there is a slight dependence of the temperature behavior of the conductivity on the size of the ions, as seen from the fragility parameter (D) obtained from fits, to the Vogel-Fulcher-Tammann equation. The molecular-level structure and interactions of the phosphonate anions were examined by Raman spectroscopy and first-principles calculations: The calculations identify two stable conformations for the methyl- and ethyl-phosphonate anions by rotation of the methyl and ethyl groups, respectively. The broad Raman signatures of the anions suggest the coexistence of anion conformers in the ionic liquids and non-negligible cation-anion interactions, with a dependence the position and shape of the bands of the cation species and the alkyl group of the anion.
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| 7. |
- Pitawala, Jagath, 1976, et al.
(författare)
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Structure and properties of Li-ion conducting polymer gel electrolytes based on ionic liquids of the pyrrolidinium cation and the bis(trifluoromethanesulfonyl)imide anion
- 2014
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 245, s. 830-835
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the structure and physical properties of Li-ion conducting polymer gel electrolytes functionalized with ionic liquid/lithium salt mixtures. The membranes are based on poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, PVdF-HFP, and two ionic liquids: pyrrolidinium cations, N-butyl-N-methylpyrrolidinium (PyR14+), N-butyl-N-ethylpyrrolidinium (PyR24+), and bis(trifluoromethanesulfonyl) imide anion (TFSI). The ionic liquids where doped with 0.2 mol kg(-1) LiTFSI. The resulting membranes are freestanding, flexible, and nonvolatile. The structure of the polymer and the interactions between the polymer and the ionic liquid electrolyte have been studied using Raman spectroscopy. The ionic conductivity of the membranes has been studied using dielectric spectroscopy whereas the thermal properties were investigated using differential scanning caloriometry (DSC).
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| 10. |
- Scheers, Johan, 1979, et al.
(författare)
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Ionic liquids and oligomer electrolytes based on the B(CN)(4)(-) anion; ion association, physical and electrochemical propertiesw
- 2011
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 13:33, s. 14953-14959
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Tidskriftsartikel (refereegranskat)abstract
- The role of B(CN)(4)(-) (Bison) as a component of battery electrolytes is addressed by investigating the ionic conductivity and phase behaviour of ionic liquids (ILs), ion association mechanisms, and the electrochemical stability and cycling properties of LiBison based electrochemical cells. For C(4)mpyrBison and C(2)mimBison ILs, and mixtures thereof, high ionic conductivities (3.4
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