| 1. |
- MacGregor-Ramiasa, M., et al.
(författare)
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Magnetic alignment of nontronite dispersions
- 2015
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Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317. ; 116-117, s. 167-174
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Tidskriftsartikel (refereegranskat)abstract
- The time dependent alignment of exfoliated nontronite dispersions subjected to moderate magnetic field strengths (B.
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| 2. |
- Nordin, Matias, 1981, et al.
(författare)
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Estimation of mass thickness response of embedded aggregated silica nanospheres from high angle annular dark-field scanning transmission electron micrographs
- 2014
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 253:2, s. 166-170
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the functional behaviour of the intensity in high-angle annular dark field scanning transmission electron micrograph images. The model material is a silica particle (20 nm) gel at 5 wt%. By assuming that the intensity response is monotonically increasing with increasing mass thickness of silica, an estimate of the functional form is calculated using a maximum likelihood approach. We conclude that a linear functional form of the intensity provides a fair estimate but that a power function is significantly better for estimating the amount of silica in the z-direction. The work adds to the development of quantifying material properties from electron micrographs, especially in the field of tomography methods and three-dimensional quantitative structural characterization from a scanning transmission electron micrograph. It also provides means for direct three-dimensional quantitative structural characterization from a scanning transmission electron micrograph.
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| 3. |
- Rosén, Olof, et al.
(författare)
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Anomalous surfactant diffusion in a gel of chemically cross-linked ethyl(hydroxyethyl) cellulose
- 2003
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 107:17, s. 4074-4079
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Tidskriftsartikel (refereegranskat)abstract
- The interactions of sodium dodecyl sulfate (SDS) with chemically cross-linked gels of ethyl(hydroxyethyl) cellulose (EHEC) were studied. Above the so-called critical association concentration (cac), binding of SDS gives rise to an increased swelling of the EHEC gels. The binding of SDS to the gels was measured with flame emission analysis of the sodium ion. The self-diffusion of the surfactant ion (DS) in the gels was studied by the NMR pulsed field gradient spin-echo technique. Both experiments were performed on gels swollen to equilibrium in SDS solutions of varying concentrations. Comparisons with the DS diffusion in a solution of non-crosslinked EHEC were also made. In the EHEC solutions the observed spin-echo decays for DS were always describable in terms of a single surfactant diffusion coefficient (Gaussian diffusion). In contrast, the DS diffusion in the gels above the cac (SDS) was clearly non-Gaussian, or anomalous. The echo decays in the gels could be fitte to a log-normal distribution of diffusion coefficients. When the time during which the diffusion was measured was increased, the width of the distribution increased, while the average diffusion coefficient remained constant. An increase in the width of distribution was also seen when the SDS concentration was increased. The anomalous diffusion is ascribed to inhomogeneities in the gel.
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| 4. |
- Röding, Magnus, 1984, et al.
(författare)
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The gamma distribution model for pulsed-field gradient NMR studies of molecular-weight distributions of polymers
- 2012
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Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 222, s. 105-111
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Tidskriftsartikel (refereegranskat)abstract
- Self-diffusion in polymer solutions studied with pulsed-field gradient nuclear magnetic resonance (PFG NMR) is typically based either on a single self-diffusion coefficient, or a log-normal distribution of self-diffusion coefficients, or in some cases mixtures of these. Experimental data on polyethylene glycol (PEG) solutions and simulations were used to compare a model based on a gamma distribution of self-diffusion coefficients to more established models such as the single exponential, the stretched exponential, and the log-normal distribution model with regard to performance and consistency. Even though the gamma distribution is very similar to the log-normal distribution, its NMR signal attenuation can be written in a closed form and therefore opens up for increased computational speed. Estimates of the mean self-diffusion coefficient, the spread, and the polydispersity index that were obtained using the gamma model were in excellent agreement with estimates obtained using the log-normal model. Furthermore, we demonstrate that the gamma distribution is by far superior to the log-normal, and comparable to the two other models, in terms of computational speed. This effect is particularly striking for multi-component signal attenuation. Additionally, the gamma distribution as well as the log-normal distribution incorporates explicitly a physically plausible model for polydispersity and spread, in contrast to the single exponential and the stretched exponential. Therefore, the gamma distribution model should be preferred in many experimental situations.
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| 5. |
- Röding, Magnus, et al.
(författare)
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The power of heterogeneity : Parameter relationships from distributions
- 2016
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- Complex scientific data is becoming the norm, many disciplines are growing immensely data-rich, and higher-dimensional measurements are performed to resolve complex relationships between parameters. Inherently multi-dimensional measurements can directly provide information on both the distributions of individual parameters and the relationships between them, such as in nuclear magnetic resonance and optical spectroscopy. However, when data originates from different measurements and comes in different forms, resolving parameter relationships is a matter of data analysis rather than experiment. We present a method for resolving relationships between parameters that are distributed individually and also correlated. In two case studies, we model the relationships between diameter and luminescence properties of quantum dots and the relationship between molecular weight and diffusion coefficient for polymers. Although it is expected that resolving complicated correlated relationships require inherently multi-dimensional measurements, our method constitutes a useful contribution to the modelling of quantitative relationships between correlated parameters and measurements. We emphasise the general applicability of the method in fields where heterogeneity and complex distributions of parameters are obstacles to scientific insight.
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| 6. |
- Steglich, Thomas, 1983, et al.
(författare)
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Microstructure and water distribution of commercial pasta studied by microscopy and 3D magnetic resonance imaging
- 2014
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Ingår i: Food Research International. - : Elsevier BV. - 0963-9969 .- 1873-7145. ; 62, s. 644-652
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Tidskriftsartikel (refereegranskat)abstract
- Manufacturing pasta is a rather well known process, but it is still challenging to tailor pasta products with new raw materials. In this study, we evaluated the effects of raw materials on the microstructure and water distribution in cooked pasta using H-1 magnetic resonance imaging (MRI) as well as bright field and polarized light microscopy. The MRI parameters initial intensity (I-0) and transverse dephasing time (T-2*) serve as indicators of the local water concentration and water-macromolecule interactions through chemical exchange, respectively. These parameters were mapped throughout the whole pasta volume with a spatial resolution of 78 mu m in all three dimensions. MRI was combined with light microscopy to link I-0 and T-2* to microstructure components such as fiber particles and the extent of starch gelatinization. Four commercial spaghetti samples were analyzed which were made of durum wheat flour, both plain and enriched with wheat fiber, as well as with wholegrain and soft wheat flour. Although all pasta samples showed similar macroscopic water absorption as measured by weight increase, the sample structures differed at the microscopic scale. Compared to durum wheat spaghetti, the presence of fiber particles decreased T-2*, while spaghetti enriched with soft wheat flour increased T-2*. In addition, light microscopy showed that large fiber particles partly acted as barriers against water migration and protected starch granules from swelling. Smaller wheat fiber particles did not affect local starch swelling. Thus, the combination of light microscopy and MRI is a powerful tool to study the microstructure and water distribution in pasta.
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| 7. |
- Williamson, Nathan H., et al.
(författare)
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Obtaining T1-T2 distribution functions from 1-dimensional T1 and T2 measurements : The pseudo 2-D relaxation model
- 2016
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 269, s. 186-195
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Tidskriftsartikel (refereegranskat)abstract
- We present the pseudo 2-D relaxation model (P2DRM), a method to estimate multidimensional probability distributions of material parameters from independent 1-D measurements. We illustrate its use on 1-D T1 and T2 relaxation measurements of saturated rock and evaluate it on both simulated and experimental T1-T2 correlation measurement data sets. Results were in excellent agreement with the actual, known 2-D distribution in the case of the simulated data set. In both the simulated and experimental case, the functional relationships between T1 and T2 were in good agreement with the T1-T2 correlation maps from the 2-D inverse Laplace transform of the full 2-D data sets. When a 1-D CPMG experiment is combined with a rapid T1 measurement, the P2DRM provides a double-shot method for obtaining a T1-T2 relationship, with significantly decreased experimental time in comparison to the full T1-T2 correlation measurement.
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| 8. |
- Williamson, Nathan H., et al.
(författare)
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Scaling exponent and dispersity of polymers in solution by diffusion NMR
- 2017
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 493, s. 393-397
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Tidskriftsartikel (refereegranskat)abstract
- Molecular mass distribution measurements by pulsed gradient spin echo nuclear magnetic resonance (PGSE NMR) spectroscopy currently require prior knowledge of scaling parameters to convert from polymer self-diffusion coefficient to molecular mass. Reversing the problem, we utilize the scaling relation as prior knowledge to uncover the scaling exponent from within the PGSE data. Thus, the scaling exponent—a measure of polymer conformation and solvent quality—and the dispersity (Mw/Mn) are obtainable from one simple PGSE experiment. The method utilizes constraints and parametric distribution models in a two-step fitting routine involving first the mass-weighted signal and second the number-weighted signal. The method is developed using lognormal and gamma distribution models and tested on experimental PGSE attenuation of the terminal methylene signal and on the sum of all methylene signals of polyethylene glycol in D2O. Scaling exponent and dispersity estimates agree with known values in the majority of instances, leading to the potential application of the method to polymers for which characterization is not possible with alternative techniques.
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| 9. |
- Williamson, Nathan H., et al.
(författare)
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The lognormal and gamma distribution models for estimating molecular weight distributions of polymers using PGSE NMR
- 2016
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Ingår i: Journal of magnetic resonance. - : Academic Press. - 1090-7807 .- 1096-0856. ; 267, s. 54-62
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Tidskriftsartikel (refereegranskat)abstract
- We present comprehensive derivations for the statistical models and methods for the use of pulsed gradient spin echo (PGSE) NMR to characterize the molecular weight distribution of polymers via the well-known scaling law relating diffusion coefficients and molecular weights. We cover the lognormal and gamma distribution models and linear combinations of these distributions. Although the focus is on methodology, we illustrate the use experimentally with three polystyrene samples, comparing the NMR results to gel permeation chromatography (GPC) measurements, test the accuracy and noise-sensitivity on simulated data, and provide code for implementation.
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| 10. |
- Williamson, Nathan H., et al.
(författare)
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The pseudo 2-D relaxation model for obtaining T1-T2 relationships from 1-D T1 and T2 measurements of fluid in porous media
- 2018
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 269, s. 191-194
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Tidskriftsartikel (refereegranskat)abstract
- NMR spin-lattice (T1) and spin-spin (T2) relaxation times and their inter-relation possess information on fluid behaviour in porous media. To elicit this information we utilize the pseudo 2-D relaxation model (P2DRM), which deduces the T1-T2 functional relationship from independent 1-D T1 and T2 measurements. Through model simulations we show empirically that the P2DRM accurately estimates T1-T2 relationships even when the marginal distributions of the true joint T1-T2 distribution are unknown or cannot be modeled. Estimates of the T1:. T2 ratio for fluid interacting with pore surfaces remain robust when the P2DRM is applied to simulations of rapidly acquired data. Therefore, the P2DRM can be useful in situations where experimental time is limited.
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