| 131. |
- Nordström, Jonas, 1980, et al.
(författare)
-
Effect of Lithium Salt on the Stability of Dispersions of Fumed Silica in the Ionic Liquid BMImBF4
- 2012
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 28:9, s. 4080-4085
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the stability and the interactions in dispersions of colloidal fumed silica, Aerosil 200, and the ionic liquid 1-butyl-3-methylimidazolium tetraflouroborate (BMImBF4) as a function of Li-salt concentration (LiBF4). Photon correlation spectroscopy was used to study the aggregation behavior at low silica concentration and Raman spectroscopy was used to investigate the interactions in the ionic liquid and with the silica surface. We find that the addition of LiBF4 increases the stability of the dispersions, with smaller agglomerates of silica particles and higher gelation concentrations in the presence of Li-salt. The increased stability with the addition of Li-salt is explained by the formation of a more stable solvation layer, where Li-ions accumulate on the surface. This leads to an increased interaction between lithium ions and the BF4- anions in the solvation layer as seen by Raman spectroscopy. Upon gelation the Li-ions are expelled from the surface as hydrogen bonding between the silica particles are formed. For both neat BMImBF4 and Li-salt doped BMImBF4/silica dispersions a weak gel phase was found preceding the formation of a strong gel at slightly higher silica concentrations.
|
|
| 132. |
- Nordström, Jonas, 1980, et al.
(författare)
-
Silica/alkali ratio dependence of the microscopic structure of sodium silicate solutions
- 2013
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 397, s. 9-17
-
Tidskriftsartikel (refereegranskat)abstract
- Alkaline sodium silicate solutions with SiO2:Na2O molar ratios in the range 4-10 are known to be colloidaily unstable manifested in phase separation or gelation. The mechanistic understanding of this instability is generally poor. To improve this situation the microscopic structure of a series of solutions with ratios in the range 3.3-8.9 has been characterised using small-angle X-ray scattering, Dynamic light scattering, Fourier transformed infrared spectroscopy, and Si-29 Nuclear magnetic resonance spectroscopy to cover the relevant length scales related to silica clusters, aggregates, and particles present. In the starting solution, with ratio 3.3, there are silica present in three fractions. The main part is present as small silica clusters with a radius of 0.7 nm. There are also a significant portion of monomers/small oligomeric silica species as well as a minute amount of larger colloidal silica particles. At a higher SiO2:Na2O ratio, above approximately 4, smaller spherical colloidal particles are formed due to condensation reactions. However, as a result of a too high ionic strength the suspension is not stable and the particles aggregate to fractal structures with a size that depends on ratio and ageing time. At the highest SiO2:Na2O ratio, fractals are not formed because of the lower ionic strength and the smaller colloidal particles are stable in the solution. By carefully adding small amounts of NaCl to the high ratio solution it is possible to induce gelation of the solution confirming the hypothesis that the instability region is due to too high electrolyte concentration for the silica species present under those conditions.
|
|
| 133. |
- Olsson, Martina, 1996, et al.
(författare)
-
Multiscale X-ray imaging and characterisation of pharmaceutical dosage forms
- 2023
-
Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 642
-
Tidskriftsartikel (refereegranskat)abstract
- A correlative, multiscale imaging methodology for visualising and quantifying the morphology of solid dosage forms by combining ptychographic X-ray computed nanotomography (PXCT) and scanning small- and wide-angle X-ray scattering (S/WAXS) is presented. The methodology presents a workflow for multiscale analysis, where structures are characterised from the nanometre to millimetre regime. Here, the method is demonstrated by characterising a hot-melt extruded, partly crystalline, solid dispersion of carbamazepine in ethyl cellulose. Characterisation of the morphology and solid-state phase of the drug in solid dosage forms is central as this affects the performance of the final formulation. The 3D morphology was visualised at a resolution of 80 nm over an extended volume through PXCT, revealing an oriented structure of crystalline drug domains aligned in the direction of extrusion. Scanning S/WAXS showed that the nanostructure is similar over the cross section of the extruded filament, with minor radial changes in domain sizes and degree of orientation. The polymorphic forms of carbamazepine were qualified with WAXS, showing a heterogeneous distribution of the metastable forms I and II. This demonstrates the methodology for multiscale structural characterization and imaging to enable a better understanding of the relationships between morphology, performance, and processing conditions of solid dosage forms.
|
|
| 134. |
- Oyedotun, Kabir O., et al.
(författare)
-
Comparison of ionic liquid electrolyte to aqueous electrolytes on carbon nanofibres supercapacitor electrode derived from oxygen-functionalized graphene
- 2019
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 375
-
Tidskriftsartikel (refereegranskat)abstract
- A facial force-driven reflux technique was used to develop fibre-like carbon material from freeze-dried reduced graphene oxide (RGO) firstly prepared by using a modified Hummers method. The carbon nanofibres displayed a high specific surface area of ∼1317.8 m2 g−1, with good pore size distributions which could be beneficial for energy storage applications. Electrochemical measurements of the carbon nanofibre electrodes in a symmetric configuration with aqueous (1 M Na2SO4, 6 M KOH), and protic ionic liquid (1-ethylimidazolium bis(trifluoromethanesulfonly)imide) electrolytes (ILE) displayed excellent electrochemical performance with the dominant electric double layer capacitor (EDLC) behaviour. The fabricated device shows higher electrochemical performance in the ILE due to its larger cell operating potential (3.0 V) as compared with the aqueous electrolytes (0.8 V). The optimized electrochemical properties especially in terms of higher specific energy and superior stability, suggest the material's potential applications as electrode for supercapacitors.
|
|
| 135. |
- Palluzzi, Matteo, et al.
(författare)
-
Ionic Liquids as Cathode Additives for High Voltage Lithium Batteries
- 2024
-
Ingår i: Batteries and Supercaps. - 2566-6223. ; 7:7
-
Tidskriftsartikel (refereegranskat)abstract
- Two oxalatoborate ionic liquids (ILs), which are commonly utilized as electrolyte additives that form a protective layer on the cathode surface, are investigated for the first time as electrode additives. Cathodes based on LiNi0.5Mn1.5O4 (LNMO) containing 3 wt % ILs, i. e., “IL-enriched cathodes”, exhibit capacity values above 120 mAh/g with high Coulombic efficiencies throughout cycling over 200 times. A cathode without ILs also exhibits a capacity of 119 mAh/g but its Coulombic efficiency becomes low and unstable after 109 cycles. In addition, when 0.3 M ILs are added to conventional carbonate-based electrolytes, the battery cycle life improves but there is a reduction in the capacity probably due to low ionic conductivity of the electrolyte mixtures. Post-mortem analyses of electrodes retrieved from cycled cells highlight less electrolyte decomposition and less cathode corrosion, enabled by using the IL as the additive in LNMO, which are confirmed by a particle shape with smooth surface identical to the fresh cathode. The study demonstrates that oxalatoborate ILs can be used as the electrode additive, and this provides a new concept for cathode formulations for high performance batteries with a small amount of ILs.
|
|
| 136. |
- Phan Xuan, Tuan, 1984, et al.
(författare)
-
Aggregation behavior of aqueous cellulose nanocrystals: the effect of inorganic salts
- 2016
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:6, s. 3653-3663
-
Tidskriftsartikel (refereegranskat)abstract
- Natural anisotropic building-blocks such as cellulose nanocrystals (CNCs) have attracted considerable attention due to their biodegradability and nanometer-size. In this work the colloidal behavior of CNCs, obtained from sulfuric acid hydrolysis of microcrystalline cellulose, has been studied in presence of salts of different valences. The influence on the colloidal stability and nature of aggregates has been investigated for monovalent salts (LiCl, NaCl, KCl, CsCl), divalent salts (CaCl2 and MgCl2), and a trivalent salt (AlCl3), both experimentally by means of turbidity and small angle X-ray scattering (SAXS) measurements, as well as by Monte Carlo simulations using a simple coarse-grained model. For the entire salt series, a critical aggregation concentration (CAC) could be determined by turbidity measurements, as a result of the reduction of effective Coulomb repulsions due to the presence of sulfate groups on the CNC surface. The CACs also followed the Schulze-Hardy law, i.e. the critical aggregation concentration decreased with increasing counterion valence. For the monovalent ions, the CACs followed the trend Li+ > Na+ > K+ > Cs+, which could be rationalized in terms of matching affinities between the cation and the sulfate groups present at the surface of CNCs. From the SAXS measurements it was shown that the density of the aggregates increased with increasing salt concentration and ion valence. In addition, these findings were rationalized by means of simulation, which showed a good correlation with experimental data. The combination of the experimental techniques and the simulations offered insight into interaction-aggregation relationship of CNC suspensions, which is of importance for their structural design applications.
|
|
| 137. |
- Pitawala, Jagath, 1976, et al.
(författare)
-
Coordination and interactions in a Li-salt doped ionic liquid
- 2015
-
Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093. ; 407, s. 318-323
-
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.
|
|
| 138. |
- Pitawala, Jagath, 1976, et al.
(författare)
-
Phase behaviour, transport properties, and interactions in Li-salt doped ionic liquids
- 2012
-
Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 154, s. 71-80
-
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.
|
|
| 139. |
- Pitawala, Jagath, 1976, et al.
(författare)
-
Physical Properties, Ion-Ion Interactions, and Conformational States of Ionic Liquids with Alkyl-Phosphonate Anions
- 2013
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 117:27, s. 8172-8179
-
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.
|
|
| 140. |
- Pitawala, Jagath, 1976, et al.
(författare)
-
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
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 245, s. 830-835
-
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).
|
|
