| 1. |
- Sattig, M., et al.
(author)
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Dynamics of DiPGME-Water Mixtures in Mesoporous Silica
- 2017
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:12, s. 6796-6806
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Journal article (peer-reviewed)abstract
- In this study, we have combined dielectric spectroscopy and H-2 NMR to elucidate the molecular dynamics of aqueous solutions of dipropylene glycol monomethyl ether (DiPGME) confined into 2.8 nm pores of MCM-41. The results show that the concentration dependence of the dynamics is completely different compared to the corresponding bulk solutions, where a pronounced nonmonotonic concentration dependence was observed for the glass transition and its related a-relaxation. In the confinement, both the cooperative alpha-relaxation and the more local beta-relaxation are almost unaffected by the water concentration. The main reasons for this seem to be that there is a preferential hydration of the inner pore surfaces, leading to a strong concentration gradient in the pores, as well as ice formation at higher water concentrations (45 wt % and above during heating), also leading to less water and a weaker concentration dependence in DiPGME-rich regions. The beta-process is observed in the DS measurements even for confined DiPGME, without any water. This implies that the beta-relaxation is strongly enhanced, compared to the alpha-relaxation, in the confinement, since it could not be clearly observed in the bulk liquid. A beta-relaxation due to water was observed in the bulk solutions, but this process was rapidly speeding up with increasing water concentration, while it is basically concentration independent in the confinement. From the NMR measurements, it was also possible to conclude that the a-relaxation of the confined solutions is composed of a number of consecutive small-angle elementary rotational jumps, and that the beta-process is related to a spatially restricted motion.
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| 2. |
- Shojaatalhoseini, Mansoureh, 1981, et al.
(author)
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Conductivity-Relaxation Relations in Nanocomposite Polymer Electrolytes Containing Ionic Liquid
- 2017
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 121:41, s. 9699-9707
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Journal article (peer-reviewed)abstract
- In this study, we have used nanocomposite polymer electrolytes, consisting of poly(ethylene oxide) (PEO), delta-Al2O3 nanoparticles, and lithium bis(trifluoromethanesolfonyl)imide (LiTFSI) salt (with 4 wt % delta-Al2O3 and PEO:Li ratios of 16:1 and 8:1), and added different amounts of the ionic liquid 1-butyl-3-methylimidazo- 0) hum bis(trifluoromethanesolfonyl)imide (BMITFSI). The aim was to m elucidate whether the ionic liquid is able to dissociate the Li-ions from the ether oxygens and thereby decouple the ionic conductivity from the segmental polymer dynamics. The results from DSC and dielectric spectroscopy show that the ionic liquid speeds up both the segmental polymer dynamics and the motion of the Le ions. However, a close comparison between the structural (a) relaxation process, given by the segmental polymer dynamics, and the ionic conductivity shows that the Motion of the Li+ ions decouples from the segmental polymer dynamics at higher concentrations of the ionic liquid (>= 20 wt %) and instead becomes more related to the viscosity of the ionic liquid. This decoupling increases with decreasing temperature. In addition to the structural. alpha-relaxation, two more local relaxation processes, denoted)6 and y, are observed. The fi-relaxation becomes slightly faster at the highest concentration of the ionic liquid (at least for the lower salt concentration), whereas the y -relaxation is unaffected by the ionic liquid, over the whole concentration range 0-40 wt %.
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