Abstract
Neutron imaging and scattering give data of significantly different nature and traditional methods leave a gap of accessible structure sizes at around 10 micrometers. Only in recent years overlap in the probed size ranges could be achieved by independent application of high resolution scattering and imaging methods, however without providing full structural information when microstructures vary on a macroscopic scale. In this study we show how quantitative neutron dark-field imaging with a novel experimental approach provides both sub-pixel resolution with respect to microscopic correlation lengths and imaging of macroscopic variations of the microstructure. Thus it provides combined information on multiple length scales. A dispersion of micrometer sized polystyrene colloids was chosen as a model system to study gravity induced crystallisation of microspheres on a macro scale, including the identification of ordered as well as unordered phases. Our results pave the way to study heterogeneous systems locally in a previously impossible manner.
Highlights
Neutron imaging and scattering give data of significantly different nature and traditional methods leave a gap of accessible structure sizes at around 10 micrometers
In this article we introduce an advanced quantitative dark-field image (DFI) approach that is based on a modified neutron grating interferometry (nGI) enabling 2D sub-pixel resolution of autocorrelation lengths (ξ) on an extended microscopic range while maintaining the full spatial resolution capabilities in real space
The system used in ref. 18 is highly equivalent even though the colloids had to be modified with fluorescent molecules to enable fluorescent microscopy, which is not the case for the here presented study with ξDFI
Summary
Neutron grating interferometry (nGI)[15] is an imaging technique which simultaneously provides the conventional attenuation based transmission image (TI) and the scattering based dark-field image (DFI)[19,20,21]. Crystallisation and the corresponding ordering leads to a decreased inter particle distance as compared to isolated spheres, which can be detected and has significant impact on the recorded real-space scattering functions. The middle plot (purple dots) shows an increased concentration, to such extend that inter particle correlations are measured This can be seen by the increase in DFI signal for larger ξ-values. Gravitational acceleration g, colloidal Peclet number suggests a big influence of radius r, Boltzmann conbrownian motion, which supports crystallisation[36] The possibility for such interpretation was previously inaccessible with single sample-to-G2 distance measurements, as these could only indicate the amount of scattering present in the sample but not indicate a phase change
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