| 1. |
- Frise, Anton, et al.
(författare)
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Polymer binding to carbon nanotubes in aqueous dispersions : Residence time on the nanotube surface As Obtained by NMR diffusometry
- 2012
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 116:9, s. 2635-2642
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Tidskriftsartikel (refereegranskat)abstract
- The binding of block copolymer Pluronic F-127 in aqueous dispersions of single- (SWCNT) and multiwalled (MWCNT) carbon nanotubes has been studied by pulsed-field-gradient (PFG) 1H NMR spectroscopy. We show that a major fraction of polymers exist as a free species while a minor fraction is bound to the carbon nanotubes (CNT). The polymers exchange between these two states with residence times on the nanotube surface of 24 ± 5 ms for SWCNT and of 54 ± 11 ms for MWCNT. The CNT concentration in the solution was determined by improved thermal gravimetric analysis (TGA) indicating that the concentration of SWCNT dispersed by F-127 was significantly higher than that for MWCNT. For SWCNT, the area per adsorbed Pluronic F-127 molecule is estimated to be about 40 nm 2.
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| 2. |
- Frise, Anton, et al.
(författare)
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Polymer Binding to Carbon Nanotubes in Aqueous DispersionsStudied by NMR Diffusometry
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The diffusion behavior of block copolymer Pluronic F-127 in aqueous dispersions of single-walled (SW) and multi-walled (MW) carbon nanotubes (CNT) has been studied by pulsed-field-gradient (PFG) 1H NMR spectroscopy. We show that the polymers are either free monomers or bound to the CNT and exchange between these two states. The residence times and relative populations in those states could also be obtained. For both classes of CNT, the residence time in the bound state was found to be similar and in the order of 10-100 milliseconds. Thermal gravimetric analysis (TGA) showed that the SWCNT concentration dispersed by F-127 was higher than that for MWCNT.
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| 3. |
- Pagès, Guilhem, et al.
(författare)
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Suppressing magnetization exchange effects in stimulated-echo diffusion experiments
- 2013
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 234, s. 35-43
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Tidskriftsartikel (refereegranskat)abstract
- Exchange of nuclear magnetization between spin pools, either by chemical exchange or by cross-relaxation or both, has a significant influence on the signal attenuation in stimulated-echo-type pulsed field gradient experiments. Hence, in such cases the obtained molecular self-diffusion coefficients can carry a large systematic error. We propose a modified stimulated echo pulse sequence that contains T-2-filters during the z-magnetization store period. We demonstrate, using a common theoretical description for chemical exchange and cross-relaxation, that these filters suppress the effects of exchange on the diffusional decay in that frequent case where one of the participating spin pools is immobile and exhibits a short T-2. We demonstrate the performance of this experiment in an agarose/water gel. We posit that this new experiment has advantages over other approaches hitherto used, such as that consisting of measuring separately the magnetization exchange rate, if suitable by Goldman-Shen type experiments, and then correcting for exchange effects within the framework of a two-site exchange model. We also propose experiments based on selective decoupling and applicable in systems with no large T-2 difference between the different spin pools. (C) 2013 The Authors. Published by Elsevier Inc. All rights reserved.
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| 4. |
- Pagès, Guilhem, et al.
(författare)
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Vegetable oil reactions within wood studied by direct 13C excitation with 1H decoupling and magic-angle sample spinning (MAS) NMR
- 2012
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Ingår i: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 75:3, s. 259-263
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Forskningsöversikt (refereegranskat)abstract
- Despite having been used for ages to protect wood against the influence of outdoor elements, the chemistry of vegetable oils within wood is poorly known. We propose a method based on solid-state magic-angle sample spinning NMR to in situ characterize oil oxidation as well as its immobilization. To eliminate signal coming from wood molecules but to keep signal from the oil, direct 13C excitation is performed with low-power 1H decoupling during signal acquisition. To suppress the effect of anisotropic spin-interactions and magnetic field inhomogeneity, the sample is spun at the magic-angle. Mono- and polyunsaturated fatty acid derivatives show a difference in their oxidation process: the monounsaturated methyl oleate reacts with wood components and becomes immobilized while the polyunsaturated methyl linoleate becomes oxidized and form oligomers but does not seem to bind to wood. Linola ® oil behaves as would be expected on the basis of its composition by monounsaturated and polyunsaturated chains. This method can be generalized to all coating treatments to characterize chemical pathways and reactions. A better understanding of coating effects on wood is a crucial step to design more efficient protective mixtures.
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| 5. |
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| 6. |
- Salehi Muhaved, Alireza, et al.
(författare)
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Oxidation of methyl linoleate in the presence of lignin
- 2011
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Ingår i: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 72:3, s. 325-333
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Tidskriftsartikel (refereegranskat)abstract
- The overall aim of this study is to develop new wood modifications using vegetable oils to obtain improved durability of wood materials in an environmentally friendly way. Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopies were used to study oxidation and possible chemical coupling reactions between polyunsaturated fatty acids and model lignin compounds in order to better understand the interactions between oxidatively drying systems such as vegetable oils or alkyds with the lignin part in wood. This was done by studying mixtures of different model lignin compounds and methyl linoleate. The oxidation process was analyzed at 70 °C both in methyl linoleate alone and in combination with 20 wt% of lignin model compounds. The effects of those compounds on the oil polymerization processes were monitored by NMR (both 13C and 1H experiments) and the domain specific reactivity and patterning were then combined with FT-IR data. No covalent bonds having formed between the oil and the model compounds were detected by combination of several 13C/1H 2D NMR methods. From the spectra, the oxidation degrees of model compounds were calculated, and for some lignin model compounds alcohols were oxidized to carbonyls during the process. Those results were in excellent agreement with FT-IR data and oxidation mechanisms were proposed. The combination of both analytical techniques was necessary to have a better understanding of these systems: NMR demonstrated the absence of chemical bond and quantified oxidation degree of model lignin molecules while FT-IR focused on oil oxidation.
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| 7. |
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