| 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. |
- Adlmann, Franz, et al.
(author)
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Normalization of stroboscopic neutron scattering experiments
- 2018
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 434, s. 61-65
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Journal article (peer-reviewed)abstract
- Neutron scattering studies of kinetic processes are often flux limited. For processes which can be repeated many times, this can be mitigated by stroboscopic reintegration. The recorded scattering events are assigned to different time slices of the process and corresponding slices from all repetitions are summed up. The normalization of such data with respect to the incident beam spectrum can be challenging since the incident neutron flux may not necessarily be evenly distributed over all time slices. In this paper, we discuss how this can result in misleading information and we expand on a technique to amend these issues.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Hillborg, H., et al.
(author)
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Crosslinked polydimethylsiloxane exposed to oxygen plasma studied by neutron reflectometry and other surface specific techniques
- 2000
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In: Polymer. - 0032-3861 .- 1873-2291. ; 41:18, s. 6851-6863
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Journal article (peer-reviewed)abstract
- Spin-coated specimens of crosslinked polydimethylsiloxane (PDMS) exposed to radio-frequency (RF) and microwave (MW) oxygen plasma were studied by specular neutron reflectometry, X-ray photoelectron spectroscopy (XPS), Wilhelmy balance, contact angle measurements, scanning electron microscopy and atomic force microscopy. Neutron reflectometry and XPS showed that the oxygen plasma led to the formation of a smooth (<10 nm), oxidised surface layer with a thickness of 130-160 nm. The oxidised layer contained a mixture of the original polymer and silicon bonded to three or four oxygen atoms (SiOx). The oxidised layer was thinner after longer plasma exposure, indicating a decrease in specific volume due to a conversion of the polymer structure to an inorganic SiOx-rich structure. The formation of the SiOx-containing layer with low segmental mobility was further confirmed by the small hysteresis in the Wilhelmy balance measurements. The similarity in the hydrophobicity recovery kinetics of specimens aged in dry air, dry argon and vacuum and XPS data showed that the hydrophobicity recovery is not due to contamination through adsorption from the atmosphere but due to migration of low molar mass PDMS species to the surface. Scanning electron microscopy also showed the presence of surface cracks in heavily oxidised specimens.
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