| 1. |
- Adlmann, Franz A., et al.
(author)
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Towards neutron scattering experiments with sub-millisecond time resolution
- 2015
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In: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 48, s. 220-226
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Journal article (peer-reviewed)abstract
- Neutron scattering techniques offer several unique opportunities in materials research. However, most neutron scattering experiments suffer from the limited flux available at current facilities. This limitation becomes even more severe if time-resolved or kinetic experiments are performed. A new method has been developed which overcomes these limitations when a reversible process is studied, without any compromise on resolution or beam intensity. It is demonstrated that, by recording in absolute time the neutron detector events linked to an excitation, information can be resolved on sub-millisecond timescales. Specifically, the concept of the method is demonstrated by neutron reflectivity measurements in time-of-flight mode at the Liquids Reflectometer located at the Spallation Neutron Source, Oak Ridge National Laboratory, Tennessee, USA, combined with in situ rheometry. The opportunities and limitations of this new technique are evaluated by investigations of a micellar polymer solution offering excellent scattering contrast combined with high sensitivity to shear.
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| 2. |
- Bergendal, Erik, et al.
(author)
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Tuneable interfacial surfactant aggregates mimic lyotropic phases and facilitate large scale nanopatterning
- 2021
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In: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 13:1, s. 371-379
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Journal article (peer-reviewed)abstract
- It is shown that the air-liquid interface can be made to display the same rich curvature phenomena as common lyotropic liquid crystal systems. Through mixing an insoluble, naturally occurring, branched fatty acid, with an unbranched fatty acid of the same length, systematic variation in the packing constraints at the air-water interface could be obtained. The combination of atomic force microscopy and neutron reflectometry is used to demonstrate that the water surface exhibits significant tuneable topography. By systematic variation of the two fatty acid proportions, ordered arrays of monodisperse spherical caps, cylindrical sections, and a mesh phase are all observed, as well as the expected lamellar structure. The tuneable deformability of the air-water interface permits this hitherto unexplored topological diversity, which is analogous to the phase elaboration displayed by amphiphiles in solution. It offers a wealth of novel possibilities for the tailoring of nanostructure
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| 3. |
- Moulin, M., et al.
(author)
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Towards a molecular understanding of the water purification properties of Moringa seed proteins
- 2019
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 554, s. 296-304
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Journal article (peer-reviewed)abstract
- Seed extracts from Moringa oleifera are of wide interest for use in water purification where they can play an important role in flocculation; they also have potential as anti-microbial agents. Previous work has focused on the crude protein extract. Here we describe the detailed biophysical characterization of individual proteins from these seeds. The results provide new insights relating to the active compounds involved. One fraction, designated Mo-CBP3, has been characterized at a molecular level using a range of biochemical and biophysical techniques including liquid chromatography, X-ray diffraction, mass spectrometry, and neutron reflection. The interfacial behavior is of particular interest in considering water purification applications and interactions with both charged (e.g. silica) and uncharged (alumina) surfaces were studied. The reflection studies show that, in marked contrast to the crude extract, only a single layer of the purified Mo-CBP3 binds to a silica interface and that there is no binding to an alumina interface. These observations are consistent with the crystallographic structure of Mo-CBP3-4, which is one of the main isoforms of the Mo-CBP3 fraction. The results are put in context of previous studies of the properties of the crude extract. This work shows possible routes to development of separation processes that would be based on the specific properties of individual proteins.
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| 4. |
- Piscitelli, Francesco, et al.
(author)
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Neutron reflectometry on highly absorbing films and its application to (B4C)-B-10-based neutron detectors
- 2016
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In: Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 472:2185
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Journal article (peer-reviewed)abstract
- Neutron reflectometry is a powerful tool used for studies of surfaces and interfaces. The absorption in the typical studied materials is neglected and this technique is limited only to the reflectivity measurement. For strongly absorbing nuclei, the absorption can be directly measured by using the neutron-induced fluorescence technique which exploits the prompt particle emission of absorbing isotopes. This technique is emerging from soft matter and biology where highly absorbing nuclei, in very small quantities, are used as a label for buried layers. Nowadays, the importance of absorbing layers is rapidly increasing, partially because of their application in neutron detection; a field that has become more active also due to the He-3-shortage. We extend the neutron-induced fluorescence technique to the study of layers of highly absorbing materials, in particular (B4C)-B-10. The theory of neutron reflectometry is a commonly studied topic; however, when a strong absorption is present the subtle relationship between the reflection and the absorption of neutrons is not widely known. The theory for a general stack of absorbing layers has been developed and compared to measurements. We also report on the requirements that a (B4C)-B-10 layer must fulfil in order to be employed as a converter in neutron detection.
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| 5. |
- Adlmann, Franz A., et al.
(author)
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Överlåtaren : a fast way to transfer and orthogonalize two-dimensional off-specular reflectivity data
- 2016
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In: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 49, s. 2091-2099
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Journal article (peer-reviewed)abstract
- Reflectivity measurements offer unique opportunities for the study of surfaces and interfaces, and specular reflectometry has become a standard tool in materials science to resolve structures normal to the surface of a thin film. Off-specular scattering, which probes lateral structures, is more difficult to analyse, because the Fourier space being probed is highly anisotropic and the scattering pattern is truncated by the interface. As a result, scattering patterns collected with (especially time-of-flight) neutron reflectometers are difficult to transform into reciprocal space for comparison with model calculations. A program package is presented for a generic two-dimensional transformation of reflectometry data into q space and back. The data are represented on an orthogonal grid, allowing cuts along directions relevant for theoretical modelling. This treatment includes background subtraction as well as a full characterization of the resolution function. The method is optimized for computational performance using repeatable operations and standardized instrument settings.
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| 6. |
- Kawecki, Maciej, et al.
(author)
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Probing the dynamics of high-viscosity entangled polymers under shear using Neutron Spin Echo spectroscopy
- 2016
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In: VI European Conference On Neutron Scattering (ECNS2015). - : IOP Publishing.
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Conference paper (peer-reviewed)abstract
- Neutron Spin Echo spectroscopy provides unique insight into molecular and submolecular dynamics as well as intra-and inter-molecular interactions in soft matter. These dynamics may change drastically under shear flow. In particular in polymer physics a stress plateau is observed, which might be explained by an entanglement-disentanglement transition. However, such a transition is difficult to identify directly by experiments. Neutron Spin Echo has been proven to provide information about entanglement length and degree by probing the local dynamics of the polymer chains. Combining shear experiments and neutron spin echo is challenging since, first the beam polarisation has to be preserved during scattering and second, Doppler scattered neutrons may cause inelastic scattering. In this paper we present a new shear device adapted for these needs. We demonstrate that a high beam polarisation can be preserved and present first data on an entangled polymer solution under shear. To complement the experiments on the dynamics we present novel SANS data revealing shear-induced conformational changes in highly entangled polymers.
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| 7. |
- Theis-Broehl, Katharina, et al.
(author)
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Self assembly of magnetic nanoparticles at silicon surfaces
- 2015
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 11:23, s. 4695-4704
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Journal article (peer-reviewed)abstract
- Neutron reflectometry was used to study the assembly of magnetite nanoparticles in a water-based ferrofluid close to a silicon surface. Under three conditions, static, under shear and with a magnetic field, the depth profile is extracted. The particles have an average diameter of 11 nm and a volume density of 5% in a D2O-H2O mixture. They are surrounded by a 4 nm thick bilayer of carboxylic acid for steric repulsion. The reflectivity data were fitted to a model using a least square routine based on the Parratt formalism. From the scattering length density depth profiles the following behavior is concluded: the fits indicate that excess carboxylic acid covers the silicon surface and almost eliminates the water in the densely packed wetting layer that forms close to the silicon surface. Under constant shear the wetting layer persists but a depletion layer forms between the wetting layer and the moving ferrofluid. Once the flow is stopped, the wetting layer becomes more pronounced with dense packing and is accompanied by a looser packed second layer. In the case of an applied magnetic field the prolate particles experience a torque and align with their long axes along the silicon surface which leads to a higher particle density.
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| 8. |
- Wolff, Max, et al.
(author)
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Combined neutron reflectometry and rheology
- 2013
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In: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 46:Part 6, s. 1729-1733
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Journal article (peer-reviewed)abstract
- Neutron reflectometry has been combined with rheology in order to investigate the solid boundary of liquids and polymers under shear deformation. This approach allows one to apply a controlled stress to a material while resolving the structural arrangements on the sub-nanometre length scale with neutron reflectivity, off-specular scattering and small-angle scattering at the same time. The specularly reflected neutron intensity of a 20% by weight solution of Pluronic F127 in deuterated water in contact with an octadecyl trichlorosilane-covered and a piranha-treated silicon wafer is evaluated. A pronounced difference is found in the structure formed by the polymer micelles at the two surfaces, which is explained by the difference in the affinity of the micellar shell to the solid interfaces. Under deformation, the near interface structure changes at deformations of about 2, 30 and 900%. The structural changes are correlated with changes in the storage and loss modulus of the polymer solution, revealing a transition from more solid to more liquid like properties.
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| 9. |
- Wolff, Max, et al.
(author)
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Depth-resolved grazing-incidence time-of-flight neutron scattering from a solid-liquid interface
- 2014
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In: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 47, s. 130-135
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Journal article (peer-reviewed)abstract
- Small-angle scattering in grazing-incidence beam geometry has been applied on a time-of-flight neutron instrument to investigate a solid-liquid boundary. Owing to the broad wavelength distribution provided for a specific incident beam angle, the penetration depth of the neutron beam is varied over a wide range in a single measurement. The near surface structures of block copolymer micelles close to silicon substrates with distinct surface energies are resolved. It is observed that the very near surface structure strongly depends on the surface coating, whereas further away from the surface, bulk-like ordering is found.
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