| 1. |
- Orädd, Greger, et al.
(author)
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Diffusion: a comparision between liquid and solid polymer LiTFSI electrolytes
- 2001
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In: 13th International Conference on Solid State Ionics (8-14 July 2001), Cairns, AUSTRALIA. ; 152-153, s. 131-6
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Conference paper (peer-reviewed)abstract
- From careful analyses of pfg-NMR data, it is demonstrated that the size of the diffusing Li+·xH2O complex in an aqueous solution of LiTFSI is strongly dependent on salt concentration, with the number of solvating water units ranging from six in dilute (H2O)500LiTFSI to two in highly concentrated (H2O)5LiTFSI. Such a relationship is explained by a mass tendency toward a lower solvation number as the number of available H2O molecules per lithium ion decreases. In a liquid (PEO)nLiTFSI system, a contrasting situation prevails, since the size of the diffusing Li+ complex is almost constant over a large salt concentration range (5≤n≤50). Our interpretations of these data imply that one PEO chain, containing on average nine ether oxygen units, is able to dissolve up to two lithium ions, but exclude the possibility of cationic crosslinks between different PEO chains and direct ionic interactions. For solid P(EO)nLiTFSI eletrolytes, a significantly lower value for the diffusion coefficient of the small lithium ions as compared to that of the large TFSI ions (DLi=0.2DTFSI) was found for all salt concentrations investigated (5≤n≤50). This observation fits in with recent structural observations, which suggest that lithium ions move as single entities in this specific system and require a rather complicated solvation–desolvation step for long-range motion. In all electrolytes investigated, both liquid and solid, the large and bulky TFSI ion appears to be moving as a single unit, thus manifesting the excellent ionization properties of the LiTFSI salt.
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| 2. |
- Adebahr, J, et al.
(author)
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Ion and solvent dynamics in gel electrolytes based on ethylene oxide grafted acrylate polymers
- 2002
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In: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106 .- 1089-5647. ; 106:47, s. 12119-12123
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Journal article (peer-reviewed)abstract
- Multinuclear pulsed field gradient NMR measurements and theological viscosity measurements were performed on three series of polymer gel electrolytes. The gels were based on a lithium salt electrolyte swollen into a copolymer matrix comprising an acrylate backbone and ethylene oxide side chains. In each series the side chains differed in length and number, but the acrylate-to-ethylene oxide ratio was kept constant. It was found that the self-diffusion coefficient of the cations was much lower than that of the anions, and that it decreased rapidly when the side chains got longer. In contrast, the self-diffusion coefficient of the anions was found to be independent of chain length. In the gel electrolytes, the diffusion coefficients of the solvent molecules are relatively constant despite an increased viscosity with increasing length of the side chains. However, in saltfree gels made for comparison, the diffusion coefficients of the solvent molecules decreased with, increasing length of the side chains, which is consistent with an increased viscosity.
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| 3. |
- Danino, Dganit, et al.
(author)
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Microstructures in the aqueous solutions of a hybrid anionic fluorocarbon/hydrocarbon surfactant
- 2003
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In: Journal of Colloid and Interface Science. ; 259:2, s. 382-90
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Journal article (peer-reviewed)abstract
- The aqueous solutions of the anionic hybrid fluorocarbon/hydrocarbon surfactant sodium 1-oxo-1[4-(tridecafluorohexyl)phenyl]-2-hexanesulfate (FC6HC4) shows peculiar rheological behavior. At 25 °C the viscosity vs concentration curve goes successively through a maximum and a minimum, while the viscosity vs temperature curve of the 10 wt% aqueous FC6HC4 solution goes through a marked maximum at 36 °C [Tobita et al., Langmuir 13 (1997) 5054]. In an attempt to explain these properties the microstructure of aqueous solutions of FC6HC4 has been investigated by means of digital light microscopy, transmission electron microscopy at cryogenic temperature (cryo-TEM), rheology, and self-diffusion NMR. At 20 °C, the increase of the FC6HC4 concentration was found to result in a progressive change of structure of the surfactant assemblies from mainly spherical micelles at 0.5 wt% to mainly cylindrical micelles at 10 wt%. At intermediate concentrations small disklike micelles and small complete and incomplete vesicles coexisting with cylindrical micelles were visualized. The occurrence of stretched cylindrical micelles is responsible for the effect of the surfactant concentration on the solution viscosity. Cryo-TEM, rheology, and self-diffusion NMR all suggest that an increase of the temperature brings about a growth of the assemblies present in the 10 wt% solution of FC6HC4. The structure of the assemblies present at the temperature where the viscosity is a maximum could not be elucidated by cryo-TEM because of the probable occurrence of an on-the-grid phase transformation, the result of blotting during specimen preparation. Nevertheless, the results show that the observed large assemblies break up at higher temperature to give rise to a more labile bicontinuous structure that consists of multiconnected disordered lamellae, with many folds and creases, and that may well be the L3 phase.
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| 4. |
- Edman, Ludvig, et al.
(author)
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Analysis of diffusion in a solid polymer electrolyte in the context of a phase-separated system
- 2002
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In: Physical Review E 65, 042803. ; :4, s. 1-4
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Journal article (peer-reviewed)abstract
- The salt and ionic diffusion coefficients of the salt LiN(CF3SO2)2 (LiTFSI) dissolved in high-molecular-weight poly(ethylene oxide) [PEO] have been measured over a broad concentration range, and the interrelationship of the measured values is demonstrated to be in good agreement with basic electrochemical theory. In the light of recently published structural findings, we propose a biphasic model for the conducting amorphous state, consisting of a stoichiometric P(EO)6LiTFSI phase dispersed into a salt-containing disordered phase, and analyze the ionic diffusion data within the framework of the Bruggeman-Landauer theory. The agreement between experimental and fitted data is shown to be excellent. We conclude by pointing out and discussing potential weaknesses of our analysis.
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| 5. |
- Every, Hayley A, et al.
(author)
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Room temperature fast-ion conduction in imidazolium halide salts
- 2001
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In: Journal of Materials Chemistry Articles. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 11:3031-6
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Journal article (peer-reviewed)abstract
- Fast-ion conduction has been observed in the iodide and bromide salts of 1-methyl-3-ethylimidazolium at ambient temperatures. The melting point of these two compounds is above 350 K and even at 273 K the ionic conductivity in the solid-state is greater than 10–3S cm–1. Cation diffusion coefficients have been measured using fringe field gradient and/or pulse field gradient 1H NMR techniques, which indicated cation diffusion coefficients of the order of 10–10 m2 s–1 in the solid-state. Remarkably, these values are up to an order of magnitude higher than the cation diffusion coefficient in the supercooled liquid at 293 K. The activation energy for diffusion in the solid-state is extremely small, as is typical of solid-state fast-ion conductors and indicates a change in transport mechanism from the melt to the crystal. The inability to detect an 127I signal together with the modelling of the conductivity using the Nernst–Einstein equation suggests that the solid-state conduction is primarily due to cation diffusion. The solid-state fast-ion conduction is most likely related to vacancy diffusion along the cation layers in the crystal. The temperature dependence of the NMR signal intensity indicates that the number of mobile species is increasing with increasing temperature with an activation energy of approximately 20–30 kJ mol–1.
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| 6. |
- Every, HA, et al.
(author)
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Transport properties in a family of dialkylimidazolium ionic liquids
- 2004
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In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS. - 1463-9076. ; 6:8, s. 1758-65
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Journal article (peer-reviewed)abstract
- The transport properties of 1,3-methylalkylimidazolium based ionic liquids are sensitive to their chemical structure. In this work, two key features of the chemical structure were investigated: the role of the anion and the length of the alkyl chain. Four different anions were examined for the 1,3-methylethylimidazolium salt (MeEtlmX): bromide (Br-), iodide (I-), trifluoromethanesulfonate (Tf-) and bis(trifluoromethanesulfonyt)-amide (NTf2-) anions. Increasing the size of the anion resulted in a decrease of the melting point and a slight increase in the cation diffusion coefficient. The differences in cation diffusion behaviour reflect the differences in viscosity, with much higher viscosities expected for the halide salts. In contrast to this diffusion behaviour, the melt conductivities are all very similar. The inconsistency between the calculated conductivity (based on diffusion measurements) and the conductivity measured, however, is attributed to correlated ion motions and/or the diffusion of neutral species that do not contribute to the conductivity. The effect of the length of the alkyl substituent was also studied for 1,3-methylalkylimidazolium iodide (MeRImI). Increasing the length of the alkyl chain, from methyl to a linear heptyl chain, suppresses the melting point and decreases both the conductivity and cation diffusion coefficients. In this case, the viscosity, as well as the size of the cation, influence ion transport in these materials.
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| 7. |
- Filippov, Andrey, et al.
(author)
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Influence of Cholesterol and Water Content on Phospholipid Lateral Diffusion in Bilayers
- 2003
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:6397-400
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Journal article (peer-reviewed)abstract
- The dependence of lipid lateral diffusion on temperature, cholesterol, and water contents has been studied in oriented bilayers in three phosphatidylcholine lipid systems and one sphingomyelin system. The lateral diffusion of lipids is found to be reduced both by the addition of cholesterol and by decreasing the water content. This reduction can be ascribed to the increase in the ordering of the lipid acyl chains upon cholesterol addition and/or reduced water content. The dependence of the lateral diffusion coefficient on the water content is similar in both the liquid ordered and the liquid disordered phase, while the apparent activation energy for the diffusion process is larger in the liquid ordered phase. We also report an anomalous increase in the lipid diffusion upon small additions of cholesterol to bilayer systems at low water content and temperatures. The increased diffusion is tentatively explained by a reduction of lipid chain entanglements.
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| 8. |
- Filippov, Andrey, et al.
(author)
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Lipid Lateral Diffusion in Ordered and Disordered Phases in Raft Mixtures
- 2004
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In: Biophysical Journal. ; 86, s. 891-6
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Journal article (peer-reviewed)abstract
- Lipid lateral diffusion coefficients in the quarternary system of dioleoylphosphatidylcholine (DOPC), sphingomyelin, cholesterol, and water were determined by the pulsed field gradient NMR technique on macroscopically aligned bilayers. The molar ratio between dioleoylphosphatidylcholine and sphingomyelin was set to 1:1, the cholesterol content was varied between 0 and 45 mol %, the water content was 40 wt %, and the temperature was varied between 293 and 333 K. The diffusion coefficients were separated into fast and slow spectral components by using the CORE method for global analysis of correlated spectral data. A large two-phase region, tentatively assigned to the liquid disordered (ld) and the liquid ordered (lo) phases, was present in the phase diagram. The ld phase was enriched in dioleoylphosphatidylcholine and exhibited diffusion coefficients that were about three to five times larger than for the lo phase. Both the diffusion coefficients and the apparent activation energies for the quarternary systems were compatible with earlier reports on ternary phospholipid/cholesterol/water systems. However, in contrast to the latter ternary systems, the exchange of lipids between the lo and the ld phases was slow on the timescale for the diffusion experiment for the quarternary ones. This means that on the millisecond timescale fluid, ordered domains are floating around in a sea of faster diffusing lipids, assigned to consist of mainly dioleoylphosphatidylcholine.
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| 9. |
- Filippov, Andrey, et al.
(author)
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The Effect of Cholesterol on the Lateral Diffusion of Phospholipids in Oriented Bilayers
- 2003
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In: Biophysical Journal. ; 84, s. 3079-86
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Journal article (peer-reviewed)abstract
- Pulsed field gradient NMR was utilized to directly determine the lipid lateral diffusion coefficient for the following macroscopically aligned bilayers: dimyristoylphosphatidylcholine (DMPC), sphingomyelin (SM), palmitoyloleoylphosphatidylcholine (POPC), and dioleoylphosphatidylcholine (DOPC) with addition of cholesterol (CHOL) up to 40 mol %. The observed effect of cholesterol on the lipid lateral diffusion is interpreted in terms of the different diffusion coefficients obtained in the liquid ordered (lo) and the liquid disordered (ld) phases occurring in the phase diagrams. Generally, the lipid lateral diffusion coefficient decreases linearly with increasing CHOL concentration in the ld phase for the PC-systems, while it is almost independent of CHOL for the SM-system. In this region the temperature dependence of the diffusion was always of the Arrhenius type with apparent activation energies (EA) in the range of 28–40 kJ/mol. The lo phase was characterized by smaller diffusion coefficients and weak or no dependence on the CHOL content. The EA for this phase was significantly larger (55–65 kJ/mol) than for the ld phase. The diffusion coefficients in the two-phase regions were compatible with a fast exchange between the ld and lo regions in the bilayer on the timescale of the NMR experiment (100 ms). Thus, strong evidence has been obtained that fluid domains (with size of µm or less) with high molecular ordering are formed within a single lipid bilayer. These domains may play an important role for proteins involved in membrane functioning frequently discussed in the recent literature. The phase diagrams obtained from the analysis of the diffusion data are in qualitative agreement with earlier published ones for the SM/CHOL and DMPC/CHOL systems. For the DOPC/CHOL and the POPC/CHOL systems no two-phase behavior were observed, and the obtained EA:s indicate that these systems are in the ld phase at all CHOL contents for temperatures above 25°C.
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| 10. |
- Jeong, Sang Won, et al.
(author)
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Encapsulation and Diffusion of Water-Soluble Dendrimers in a Bicontinuous Cubic Phase
- 2002
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:4, s. 1073-6
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Journal article (peer-reviewed)abstract
- Bicontinuous cubic (QII) phases composed of hydrated lipids are a unique mesoporous organic material. The diameter of the water channels in the range of 5-10 nm could be used as a reservoir for macromolecular therapeutic agents. Here, we describe the synthesis of water-soluble poly(amidoamine) (PAMAM) dendrimer derivatives labeled with fluorine and their diffusion in the water channels of a QII phase. A QII phase with Ia3d symmetry was prepared by hydration of a 9:1 molar mixture of polymerizable monoacylglycerol and the corresponding 1,2-diacylglycerol. The dendrimers having fluorine were synthesized by Michael reaction of PAMAM dendrimers with a mixture of ethyl 4,4,4-trifluorocrotonate and methyl acrylate. The hydrated diameter of the fluorinated dendrimer of generation 2.5 (G2.5AFH) is 32.6 Å as measured by 19F NMR. The diffusion coefficient of G2.5AFH at 25 C in the water channels of the QII phase, determined by pulsed field gradient 19F NMR spectroscopy, is 1 × 10-12 m2/s, which is compared to the free diffusion coefficient of the dendrimer in water (1.42 × 10-10 m2/s). These data indicate that small globular proteins or similar molecules can diffuse rapidly enough in stabilized QII phases to be technically useful.
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