| 1. |
- Hallberg, Fredrik, et al.
(författare)
-
Electrokinetic transport of water and methanol in Nafion membranes as observed by NMR spectroscopy
- 2010
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 55:10, s. 3542-3549
-
Tidskriftsartikel (refereegranskat)abstract
- Electrophoretic NMR (eNMR) and pulsed-field-gradient NMR (PFG-NMR) methods were used to study transport processes in situ and in a chemically resolved manner in the electrolyte of an experimental direct methanol fuel cell (DMFC) setup, constituted of several layers of Nation 117. The measurements were conducted at room temperature for membranes fully swollen by methanol-water mixtures over a wide concentration interval. The experimental setup and the experimental protocol for the eNMR experiments are discussed in detail. The magnitude of the water and methanol self-diffusion coefficients show a good agreement with previously published data while the ratio of the two self-diffusion coefficients may indicate an imperfect mixing of the two solvent molecules. On the molecular level, the drag of water and methanol molecules by protons is roughly of the same magnitude, with the drag of methanol molecules increasing with increasing methanol content. The electro-osmotic drag defined on mass-flow basis increased for methanol from a low level with increasing methanol concentration while that of water remained roughly constant. (C) 2010 Elsevier Ltd. All rights reserved.
|
|
| 2. |
- Hallberg, Fredrik, et al.
(författare)
-
Molecular complexation and binding studied by electrophoretic NMR spectroscopy
- 2008
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 130:24, s. 7550-
-
Tidskriftsartikel (refereegranskat)abstract
- Electrophoretic mobilities obtained on a molecularly selective manner by electrophoretic NMR can be used to proved a quantitative characterization of the composition and stoichiometry of molecular complexes. This is demonstrated in complexes formed by uncharge cyclodextrins which attain an electrophoretic mobility upon inclusion of charged surfactants.
|
|
| 3. |
- Pettersson Thyboll, Erik, et al.
(författare)
-
On experimental aspects of electrophoretic NMR
- 2004
-
Ingår i: Concepts in magnetic resonance. Bridging education and research. - : Wiley. - 1546-6086 .- 1552-5023. ; 22:2, s. 61-68
-
Tidskriftsartikel (refereegranskat)abstract
- Artefacts in electrophoretic NMR experiments are investigated in detail. We identify electroosmosis, sample heating, and gas development on the electrodes as main error sources and suggest experimental strategies and setups to suppress their influence on the monitored electrophoretic mobilities. We hereby demonstrate essentially artefact-free experiments up to currents and electric fields 3 mA and 70 V/cm, respectively.
|
|
| 4. |
- Smith, Kevin W., et al.
(författare)
-
Slow recrystallization of tripaimitoylglycerol from MCT oil observed by H-2 NMR
- 2007
-
Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 55:21, s. 8585-8588
-
Tidskriftsartikel (refereegranskat)abstract
- The crystallization and recrystallization of fats have a significant impact on the properties and quality of many food products. While crystallization has been the subject of a number of studies using pure triacylglycerols (TAG), recrystallization in similarly pure systems is rarely studied. In this work, percleuterated tripalmitoylglycerol (H-2-PPP) was dissolved in medium chain triacylglycerol oil (MCT) to yield a saturated solution. The solution was heated to cause partial melting of the solid and dissolution of the molten fraction of H-2-PPP in MCT and was then cooled to the original temperature to induce recrystallization from the supersaturated solution. H-2 NMR was used to monitor the disappearance of H-2-PPP from the solution and showed that recrystallization occurred in two steps. The first step was rapid, taking place over a few minutes, and accounted for more than two-thirds of the total recrystallization. The second step was much slower, taking place over a remarkably long timescale of hours to days. It is proposed that dissolution occurs from all parts of the crystals, leaving an etched and pitted surface. The first step of crystallization is the infilling of these pits, while the second step is the continued growth on the smoothed crystal faces.
|
|
