| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
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| 5. |
- Abrahamsson, Christoffer K., et al.
(författare)
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Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeability
- 2014
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 10:24, s. 4403-4412
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis, microstructure and mass transport properties of a colloidal hydrogel self-assembled from a mixture of colloidal silica and nontronite clay plates at different particle concentrations. The gel-structure had uniaxial long-range anisotropy caused by alignment of the clay particles in a strong external magnetic field. After gelation the colloidal silica covered the clay particle network, fixing the orientation of the clay plates. Comparing gels with a clay concentration between 0 and 0.7 vol%, the magnetically oriented gels had a maximum water permeability and self-diffusion coefficient at 0.3 and 0.7 vol% clay, respectively. Hence the specific clay concentration resulting in the highest liquid flux was pressure dependent. This study gives new insight into the effect of anisotropy, particle concentration and bound water on mass transport properties in nano/microporous materials. Such findings merit consideration when designing porous composite materials for use in for example fuel cell, chromatography and membrane technology.
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| 6. |
- Abrahamsson, Christoffer, 1984, et al.
(författare)
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Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeability
- 2014
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Ingår i: Soft Matter. - 1744-683X .- 1744-6848. ; 10:24, s. 4403-4412
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis, microstructure and mass transport properties of a colloidal hydrogel selfassembled from a mixture of colloidal silica and nontronite clay plates at different particle concentrations. The gel-structure had uniaxial long-range anisotropy caused by alignment of the clay particles in a strong external magnetic field. After gelation the colloidal silica covered the clay particle network, fixing the orientation of the clay plates. Comparing gels with a clay concentration between 0 and 0.7 vol%, the magnetically oriented gels had a maximum water permeability and self-diffusion coefficient at 0.3 and 0.7 vol% clay, respectively. Hence the specific clay concentration resulting in the highest liquid flux was pressure dependent. This study gives new insight into the effect of anisotropy, particle concentration and bound water on mass transport properties in nano/microporous materials. Such findings merit consideration when designing porous composite materials for use in for example fuel cell, chromatography and membrane technology.
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| 7. |
- Andersson, Markus, 1981, et al.
(författare)
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Coordination of Imidazoles by Cu(II) and Zn(II) as Studied by NMR Relaxometry, EPR, far-FTIR Vibrational Spectroscopy and Ab Initio Calculations: Effect of Methyl Substitution
- 2010
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 114:50, s. 13146-13153
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Tidskriftsartikel (refereegranskat)abstract
- Synthetic imidazole ligands are typically substituted at the N-1 ((1)-Im) position while natural imidazole ligands are substituted at the C-4 ((4)-Im) position. To outline the difference in coordination properties, the methyl-substituted imidazoles Me(4)-Im and Me(1)-Im were complexed with CuCl2 and ZnCl2 and investigated by NMR relaxometry, electron paramagnetic resonance, far-Fourier transform IR vibrational spectroscopy, and ab initio calculations. Me(4)-Im, Me(1)-Im, and Im in excess form the usual tetragonal D-4h [CuL4X2] complexes with CuCl2 whereas the methylated imidazoles form pseudotetrahedral C-2v, complexes instead of the usual octahedral O-h [ZnIm(6)](2+) complex. All imidazoles display a high degree of covalence in the M-L sigma- and pi-bonds and the pi-interaction strength affects the relative energies of complexation. Opportunities to tailor complexes by the chemical properties of the substituents are envisaged due to the role of the inductive and hyperconjugative effects, rather than position.
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| 8. |
- Andersson, Markus, 1981, et al.
(författare)
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Vinylimidazole copolymers: coordination chemistry, solubility, and cross-linking as function of Cu2+ and Zn2+ complexation
- 2011
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Ingår i: Colloid and Polymer Science. - : Springer Science and Business Media LLC. - 0303-402X .- 1435-1536. ; 289:12, s. 1361-1372
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Tidskriftsartikel (refereegranskat)abstract
- P(1-VIm-co-MMA) copolymers with 4 or 44 wt.% 1-VIm (abbreviated PVM-4 and PVM-44) where polymerized from 1-VIm (1-vinylimidazole) and methylmethacrylate with azobisisobutyronitrile as initiator and reacted with either Cu(2+) or Zn(2+). The resulting coordinated polymer complexes were studied using ICP-AES, CP/MAS (13)C NMR, conductivity measurements, vibrational spectroscopy (mid-FTIR and far-FTIR), DSC, and EPR. It was established by ICP-AES, CP/MAS (13)C NMR, conductivity, mid-FTIR and EPR measurements that the transition metal ions in the complexes were exclusively coordinated by the imidazole ligand. The coordination geometry is square planar with regard to Cu(II) complexes. The strong interaction between the polymeric imidazole ligand and the transition metal ion cross-links the system, resulting in augmentation of T (g) (the glass transition temperature), especially for copolymers with high relative amount of 1-VIm. The effect of changing metal ion is more complicated and depends on both the strength of the coordinate interaction as well as the coordination number. The solubility of the coordinate polymer complex in conventional solvents is low due to the coordinate cross-links. However, the coordinate polymer complexes are soluble in strongly coordinating solvents such as acetonitrile and dimethylsulfoxide.
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| 9. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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Charged microcapsules for controlled release of hydrophobic actives. Part 1: encapsulation methodology and interfacial properties
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:5, s. 1468-1477
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Tidskriftsartikel (refereegranskat)abstract
- Highly charged microcapsules have been prepared using the internal phase separation technique. The charges are introduced by using ionic dispersants, which have been characterized with respect to surface activity with a quartz crystal microbalance with dissipation monitoring and with optical tensiometry. The long-term stability of the microcapsule suspension without excess dispersant, as well as the stability at high ionic strength, have been investigated. Three types of ionic dispersants have been evaluated: a weak polyacid (poly(methacrylic acid)), a small set of ionic amphiphilic block copolymers of poly(methyl methacrylate)-block-poly(sodium (meth) acrylate) type and an oil-soluble anionic surfactant, sodium 1,5-dioxo-1,5-bis(3,5,5-trimethylhexyloxy)-3-((3,5,5-trimethylhexyloxy)carbonyl)pentane-2-sulfonate, in combination with a water-soluble polycation, poly(diallyldimethylammonium chloride). The block copolymer based microcapsule suspension is characterized by a long-term stability, even at high ionic strength, provided by electrostatic and steric stabilization. The weak polyacid based microcapsule suspension is stable for a few weeks, after which aggregation starts due to desorption of the dispersant. The surfactant-polycation based microcapsules appear to have a multicore morphology in contrast to the weak polyacid or block copolymer based microcapsules, which are core-shell particles.
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| 10. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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Charged microcapsules for controlled release of hydrophobic actives Part II: Surface modification by LbL adsorption and lipid bilayer formation on properly anchored dispersant layers
- 2013
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 409, s. 8-17
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Tidskriftsartikel (refereegranskat)abstract
- Charge microcapsules with a dodecane core and a poly(methyl methacrylate) (PMMA) shell have been prepared via the internal phase separation method using ionic dispersants. The microcapsules have subsequently been surface modified with polyelectrolyte multilayers and lipid bilayers. Two types of ionic dispersant systems have been investigated: a small set of ionic amphiphilic block copolymers of poly(methyl methacrylate)-block-poly(sodium (meth)acrylate) type and an oil-soluble anionic surfactant, sodium 1,5-dioxo-1,5-bis(3,5,5-trimethylhexyloxy)-3((3,5,5trimethylhexyloxy)car bonyl)pentane-2-sulfonate, in combination with a water-soluble polycation, poly(diallyldimethylammonium chloride). The Layer-by-Layer adsorption of the polyelectrolyte pair poly(diallydimethylammonium chloride) (350,000 g/mol) and poly(sodium methacrylate) (15,000 g/mol) was successfully made on both microcapsule systems with the formation of very thin multilayers as indicated with quartz crystal microbalance with dissipation monitoring (QCM-D) measurements on model surfaces. Formation of a lipid bilayer on the surface of the microcapsules from liposomes with a charge opposite that of the capsule surface was also proven to be successful as indicated by the C-potential of the microcapsules, the characteristic frequency shift as measured with QCM-D and fluorescence recovery after photobleaching (FRAP) on model systems. However, the proper anchorage of the dispersants in the underlying PMMA surface was key for the successful surface modification.
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