| 1. |
- Svenningsson, Leo, 1990, et al.
(författare)
-
Molecular Orientation Distribution of Regenerated Cellulose Fibers Investigated with Polarized Raman Spectroscopy
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 52:10, s. 3918-3924
-
Tidskriftsartikel (refereegranskat)abstract
- The molecular orientation distribution of polymeric fibers influences physical properties. We present a novel method of analyzing polarized Raman experiments to determine molecular orientation, which is based on exchanging the Legendre polynomial approach with a wrapped Lorentzian function, as determined from a prescreening of X-ray scattering patterns. This method removes the need for performing right angle scattering experiments while avoiding common approximations. The molecular orientation of regenerated cellulose fibers, using the presented method, is shown to correlate well with X-ray scattering and an analogous experiment using solid-state NMR spectroscopy. Challenges of quantitatively measuring molecular anisotropy occur with semi-crystalline, partially modified, or composite materials. As such, a plethora of techniques, each with a unique chemical selectivity, is paramount for material characterization.
|
|
| 2. |
- Garaga Nagendrachar, Mounesha, 1985, et al.
(författare)
-
A long-chain protic ionic liquid inside silica nanopores: Enhanced proton mobility due to efficient self-assembly and decoupled proton transport
- 2018
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 10:26, s. 12337-12348
-
Tidskriftsartikel (refereegranskat)abstract
- We report enhanced protonic and ionic dynamics in an imidazole/protic ionic liquid mixture confined within the nanopores of silica particles. The ionic liquid is 1-octylimidazolium bis(trifluoromethanesulfonyl)imide ([HC8Im][TFSI]), while the silica particles are microsized and characterized by internal well connected nanopores. We demonstrate that the addition of imidazole is crucial to promote a proton motion decoupled from molecular diffusion, which occurs due to the establishment of new N-H⋯N hydrogen bonds and fast proton exchange events in the ionic domains, as evidenced by both infrared and1H NMR spectroscopy. An additional reason for the decoupled motion of protons is the nanosegregated structure adopted by the liquid imidazole/[HC8Im][TFSI] mixture, with segregated polar and non-polar nano-domains, as clearly shown by WAXS data. This arrangement, promoted by the length of the octyl group and thus by significant chain-chain interactions, reduces the mobility of molecules (Dmol) more than that of protons (DH), which is manifested by DH/Dmolratios greater than three. Once included into the nanopores of hydrophobic silica microparticles, the nanostructure of the liquid mixture is preserved with slightly larger ionic domains, but effects on the non-polar ones are unclear. This results in a further enhancement of proton motion with localised paths of conduction. These findings demonstrate significant progress in the design of proton conducting materials via tailor-made molecular structures as well as by smart exploitation of confinement effects. Compared to other imidazole-based proton conducting materials that are crystalline up to 90 °C or above, the gel materials that we propose are useful for applications at room temperature, and can thus find applications in e.g. intermediate temperature proton exchange fuel cells.
|
|
| 3. |
- Hasani, Mohammad, 1985, et al.
(författare)
-
Molecular dynamics involving proton exchange of a protic ionic liquid-water mixture studied by NMR spectroscopy
- 2019
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 21:39, s. 22014-22021
-
Tidskriftsartikel (refereegranskat)abstract
- Protic ionic liquids (PILs) are proposed as alternative anhydrous proton conducting electrolytes for intermediate temperature fuel cells. One of the key factors in their performance as electrolytes, as far as charge transport is concerned, is their proton conductivity. Noting the success of water-containing electrolytes and recognising faster proton mobility than structural relaxation (via mechanisms such as Grotthuss) as their advantage, such an advantage is envisaged for PILs and in some cases deduced. As extended hydrogen bond networks and proton exchange are at the heart of these mechanisms, here we report our results on a prototypical characterisation of proton exchange in a PIL (C2HimNTf2)-water mixture. NMR lineshape analysis and exchange spectroscopy (EXSY) are used to quantify the proton exchange rate. The obtained exchange rate is then used to explain the diffusion behaviour of the exchangeable proton as measured by pulse field gradient NMR methods; a marginal anomaly in the translational dynamics of the exchangeable proton in the form of a faster NH proton is observed. As far as we know this is the first report on systematic characterisation of proton exchange in PILs with the aim of understanding its effect on translational motion as a way of discerning exchange related mobility anomalies.
|
|
| 4. |
- Martinelli, Anna, 1978, et al.
(författare)
-
An investigation of the sol-gel process in ionic liquid/silica gels by time resolved Raman and 1H NMR spectroscopy
- 2012
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 14:38, s. 13216-13223
-
Tidskriftsartikel (refereegranskat)abstract
- We report, by employing time resolved Raman and nuclear magnetic resonance (NMR) spectroscopy, on the gelation process in ionogels. These are prepared from a non-aqueous sol–gel reaction in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C1C6ImTFSI). Raman and NMR spectroscopies are complementarily used to decipher the chemical reactions that occur during synthesis and to clarify the state of the ionic liquid up to, and well beyond, gelation. We find that the ionic liquid concentration affects both the reaction rate and the gelation time (tgel). In addition, NMR and Raman data reveal inherently different roles of the cation and the anion in the gelation process. While the oscillating behavior of the TFSI Raman signature at 740 cm−1 is mainly an effect of solvation and chemical composition, the evolution of the relative chemical shifts (Δδ) of different hydrogen atoms on the imidazolium correlates with gelation, as does the width of the chemical shift of –OH containing groups (δOH). We also observe that in the confined state the TFSI anion preferably adopts the cisoid conformation and experiences a stronger ion–ion interaction.
|
|
| 5. |
- Yaghini, Negin, 1976, et al.
(författare)
-
Effect of water on the transport properties of protic and aprotic imidazolium ionic liquids - an analysis of self-diffusivity, conductivity, and proton exchange mechanism
- 2014
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 16:20, s. 9266-9275
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we report on the transport properties of protic and aprotic ionic liquids of the imidazolium cation (C(2)C(1)Im(+) or C(2)HIm(+)) and the TFSI- or TfO- anion as a function of added water. We observe that the self-diffusion coefficient of the ionic species increases upon addition of water, and that the cation diffuses faster than the anion in the entire water concentration range investigated. We also observe that the overall increase of anionic and cationic diffusion coefficients is significant for C(2)HImTfO while it is rather weak for C(2)C(1)ImTFSI, the former being more hydrophilic. Moreover, the difference between cationic and anionic self-diffusivity specifically depends on the structure of the ionic liquid's ions. The degree of ion-ion association has been investigated by comparing the molar conductivity obtained by impedance measurements with the molar conductivity calculated from NMR data using the Nernst-Einstein equation. Our data indicate that the ions are partly dissociated (A(imp)/A(NMR) in the range 0.45-0.75) but also that the degree of association decreases in the order C(2)HImTfO > C(2)HImTFSI approximate to C(2)C(1)ImTfO > C(2)C(1)ImTFSI. From these results, it seems that water finds different sites of interaction in the protic and aprotic ionic liquids, with a strong preference for hydrogen bonding to the -NH group (when available) and a stronger affinity to the TfO anion as compared to the TFSI. For the protic ionic liquids, the analysis of H-1 NMR chemical shifts (upon addition of H2O and D2O, respectively) indicates a water-cation interaction of hydrogen bonding nature. In addition, we could probe proton exchange between the -NH group and deuterated water for the protic cation, which occurs at a significantly faster rate if associated with the TfO anion as compared to the TFSI.
|
|
