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Macromolecules 55(19), 8757 - 8765 (2022). doi:10.1021/acs.macromol.2c01326, Dynamics of nanoparticles (NPs) in microscopic networks, in particular, localization and transport, play a key role in designing new functional nanocomposites and drug delivery systems. To this aim, it is crucial to understand the interplay between the network structure and dynamics on the microscopic scale which determines NP diffusion. Here, we study the localization and transport of spherical NPs in photorheological wormlike micellar nanocomposites where the mobility of the NPs is controlled by the network mesh size and the micelle length, which can be tuned by UV-illumination. The macroscopic viscoelastic properties are measured by classical rheology, while X-ray photon correlation spectroscopy and nanorheology provide information on the microscopic NP dynamics on length scales on the order of the network mesh size. On long time scales, the data reveal that transport through the network is determined by the ratio between the NP size and the network mesh size, while upon UV illumination, the NP mobility is drastically enhanced. On shorter time scales, the influence of the dynamical and structural micelle properties on the NP dynamics under confinement is explored and indicates an anomalous speed-up of the dynamics, which is discussed in the context of changes in the local structure and non-linear phenomena such as strain stiffening and hopping motion., Published by Soc., Washington, DC

Hydrated proteins undergo a transition in the deeply supercooled regime, which is attributed to rapid changes in hydration water and protein structural dynamics. Here, we investigate the nanoscale stress relaxation in hydrated lysozyme proteins stimulated and probed by X-ray Photon Correlation Spectroscopy (XPCS). This approach allows us to access the nanoscale dynamic response in the deeply supercooled regime (T = 180 K) which is typically not accessible through equilibrium methods. The relaxation time constants exhibit Arrhenius temperature dependence upon cooling with a minimum in the Kohlrausch-Williams-Watts exponent at T = 227 K. The observed minimum is attributed to an increase in dynamical heterogeneity, which coincides with enhanced fluctuations observed in the two-time correlation functions and a maximum in the dynamic susceptibility quantified by the normalised variance $\chi_T$. Our study provides new insights into X-ray stimulated stress relaxation and the underlying mechanisms behind spatio-temporal fluctuations in biological granular materials.

Chemistry of materials 13(16), 6553 – 6563 (2021). doi:10.1021/acs.chemmater.1c02159, During the self-organization of colloidal semiconductor nanoparticles by solvent evaporation, nanoparticle interactions are substantially determined by the organic ligands covering the inorganic core. However, the influence of the ligand grafting density on the assembly pathway is often not considered in experiments. Here, we carry out an in situ synchrotron small-angle X-ray scattering and X-ray cross-correlation analysis study of the real-time assembly of oleic acid-capped PbS nanocrystals at a low ligand coverage of 2.7 molecules/nm2. With high temporal and spatial resolution, we monitor the transitions from the colloidal suspension through the solvated superlattice states into the final dried superstructure. In a single in situ experiment, we observe a two-dimensional hexagonal, hexagonal close-packed, body-centered cubic, body-centered tetragonal (with different degrees of tetragonal distortion), and face-centered cubic superlattice phases. Our results are compared to the self-organization of PbS nanocrystals with a higher ligand coverage up to 4.5 molecules/nm2, revealing different assembly pathways. This highlights the importance of determining the ligand coverage in assembly experiments to approach a complete understanding of the assembly mechanism as well as to be able to predict and produce the targeted superstructures., Published by American Chemical Society, Washington, DC

The journal of physical chemistry letters 12(30), 7085 - 7090 (2021). doi:10.1021/acs.jpclett.1c01940, Microscopic dynamics of complex fluids in the early stage of spinodal decomposition (SD) is strongly intertwined with the kinetics of structural evolution, which makes a quantitative characterization challenging. In this work, we use X-ray photon correlation spectroscopy to study the dynamics and kinetics of a protein solution undergoing liquid���liquid phase separation (LLPS). We demonstrate that in the early stage of SD, the kinetics relaxation is up to 40 times slower than the dynamics and thus can be decoupled. The microscopic dynamics can be well described by hyper-diffusive ballistic motions with a relaxation time exponentially growing with time in the early stage followed by a power-law increase with fluctuations. These experimental results are further supported by simulations based on the Cahn���Hilliard equation. The established framework is applicable to other condensed matter and biological systems undergoing phase transitions and may also inspire further theoretical work., Published by ACS, Washington, DC

Proceedings of the National Academy of Sciences of the United States of America 119(12), e2109717119 (2022). doi:10.1073/pnas.2109717119, Neural mechanisms behind stereopsis, which requires simultaneous disparity inputs from two eyes, have remained mysterious. Here we show how ultrafast mirror-symmetric photomechanical contractions in the frontal forward-facing left and right eye photoreceptors give Drosophila superresolution three-dimensional (3D) vision. By interlinking multiscale in vivo assays with multiscale simulations, we reveal how these photoreceptor microsaccades—by verging, diverging, and narrowing the eyes’ overlapping receptive fields—channel depth information, as phasic binocular image motion disparity signals in time. We further show how peripherally, outside stereopsis, microsaccadic sampling tracks a flying fly’s optic flow field to better resolve the world in motion. These results change our understanding of how insect compound eyes work and suggest a general dynamic stereo-information sampling strategy for animals, robots, and sensors., Published by National Acad. of Sciences, Washington, DC

SignificanceTo move efficiently, animals must continuously work out their x,y,z positions with respect to real-world objects, and many animals have a pair of eyes to achieve this. How photoreceptors actively sample the eyes' optical image disparity is not understood because this fundamental information-limiting step has not been investigated in vivo over the eyes' whole sampling matrix. This integrative multiscale study will advance our current understanding of stereopsis from static image disparity comparison to a morphodynamic active sampling theory. It shows how photomechanical photoreceptor microsaccades enable

We are currently witnessing fast development of diverse methods for imaging at modern 3rd-generation X-ray synchrotron sources [1]. One of the recently developed approaches in imaging is to use the...

Small 18(37), 2201324 (2022). doi:10.1002/smll.202201324, X-ray photon correlation spectroscopy (XPCS), a synchrotron source-based technique to measure sample dynamics, is used to determine hydrodynamic diameters of gold nanoparticles (Au NPs) of different sizes in biological environments. In situ determined hydrodynamic diameters are benchmarked with values obtained by dynamic light scattering. The technique is then applied to analyze the behavior of the Au NPs in a biological environment. First, a concentration-dependent agglomeration in the presence of NaCl is determined. Second, concentration-dependent increase in hydrodynamic diameter of the Au NPs upon the presence of proteins is determined. As X-rays in the used energy range are barely scattered by biological matter, dynamics of the Au NPs can be also detected in situ in complex biological environments, such as blood. These measurements demonstrate the possibility of XPCS for in situ analytics of nanoparticles (NPs) in biological environments where similar detection techniques based on visible light would severely suffer from scattering, absorption, and reflection effects., Published by Wiley-VCH, Weinheim

Journal of applied crystallography 55(4), 751 - 757 (2022). doi:10.1107/S1600576722004435, Machine learning methods are used for an automated classification of experimental two-time X-ray photon correlation maps from an arrested liquid–liquid phase separation of a protein solution. The correlation maps are matched with correlation maps generated with Cahn–Hilliard-type simulations of liquid–liquid phase separations according to two simulation parameters and in the last step interpreted in the framework of the simulation. The matching routine employs an auto-encoder network and a differential evolution based algorithm. The method presented here is a first step towards handling large amounts of dynamic data measured at high-brilliance synchrotron and X-ray free-electron laser sources, facilitating fast comparison with phase field models of phase separation., Published by Wiley-Blackwell, [S.l.]

The journal of chemical physics 158(7), 074903 (2023). doi:10.1063/5.0130758, We investigate the thermal gelation of egg white proteins at different temperatures with varying salt concentrations using x-ray photon correlation spectroscopy in the geometry of ultra-small angle x-ray scattering. Temperature-dependent structural investigation suggests a faster network formation with increasing temperature, and the gel adopts a more compact network, which is inconsistent with the conventional understanding of thermal aggregation. The resulting gel network shows a fractal dimension δ, ranging from 1.5 to 2.2. The values of δ display a non-monotonic behavior with increasing amount of salt. The corresponding dynamics in the q range of 0.002–0.1 nm−1 is observable after major change of the gel structure. The extracted relaxation time exhibits a two-step power law growth in dynamics as a function of waiting time. In the first regime, the dynamics is associated with structural growth, whereas the second regime is associated with the aging of the gel, which is directly linked with its compactness, as quantified by the fractal dimension. The gel dynamics is characterized by a compressed exponential relaxation with a ballistic-type of motion. The addition of salt gradually makes the early stage dynamics faster. Both gelation kinetics and microscopic dynamics show that the activation energy barrier in the system systematically decreases with increasing salt concentration., Published by American Institute of Physics, Melville, NY

With the advent of next-generation X-ray detectors with large sensor areas and high sampling rates, photon science experiments are now having to deal with a data explosion. We present a scalable, near real-time data processing toolkit developed to address this challenge at PETRA III, which is currently in use at the coherence applications beamline P10 and at the macromolecular crystallography beamline P11. This toolkit runs automated analysis pipelines on high-volume data concurrently with data acquisition, thus providing quick feedback during experiments at the beamlines. Named mento (Maxwell-Enhanced Near real-Time Online analysis), the toolkit leverages the computing resources of the in-house HPC cluster ‘Maxwell’ to enhance analysis performance, and additionally takes advantage of the available distributed data storage to provide analysis results directly back to the experimenter with minimal delay. mento works seamlessly with the experiment control mechanisms used at P10, P11, and other PETRA III beamlines, and ensures that analysis on the HPC cluster is triggered automatically during data acquisition at the beamline, and that results are available for visualization at the beamline control hutch even though the analysis itself is performed remotely. mento thus helps the human-in-the-loop concentrate on novel science aspects of the experiment, without needing to manage the computational workload in a high data-rate regime. mento has been used with both in-house and commercial analysis software to achieve speedups of 50x-100x relative to the existing analysis pipelines, thus proving its utility for different kinds of experiments at PETRA III. The source code for mento is available at https://gitlab.desy.de/fs-sc/mento.

Soft matter 18, 1591 - 1602 (2022). doi:10.1039/D1SM01537K, Depending on the volume fraction and interparticle interactions, colloidal suspensions can form different phases, rangingfrom fluids, crystals, and glasses to gels. For soft microgels that are made from thermoresponsive polymers, the volumefraction can be tuned by temperature, making them excellent systems to experimentally study phase transitions in densecolloidal suspensions. However, investigations of phase transitions at high particle concentration and across the volumephase transition temperature in particular, are challenging due to the deformability and possibility for interpenetrationbetween microgels. Here, we investigate the dense phases of composite core-shell microgels that have a small gold coreand a thermoresponsive microgel shell. Employing Ultra Small Angle X-ray Scattering, we make use of the strong scatteringsignal from the gold cores with respect to the almost negligible signal from the shells. By changing the temperature we studythe freezing and melting transitions of the system in-situ. Using Bragg peak analysis and the Williamson-Hall method, wecharacterize the phase transitions in detail. We show that the system crystallizes into an rhcp structure with differentdegrees of in-plane and out-of-plane stacking disorder that increase upon particle swelling. We further find that the meltingprocess is distinctly different, where the system separates into two different crystal phases with different meltingtemperatures and interparticle interactions., Published by Royal Soc. of Chemistry, London

The journal of chemical physics 157(18), 184901 (2022). doi:10.1063/5.0123118, The gelation of PEGylated gold nanoparticles dispersed in a glycerol–water mixture is probed in situ by x-ray photon correlation spectroscopy. Following the evolution of structure and dynamics over 10$^4$ s, a three-step gelation process is found. First, a simultaneous increase of the Ornstein–Zernike length $ξ$ and slowdown of dynamics is characterized by an anomalous q-dependence of the relaxation times of $τ ∝ q^{−6}$ and strongly stretched intermediate scattering functions. After the structure of the gel network has been established, evidenced by a constant $ξ$, the dynamics show aging during the second gelation step accompanied by a change toward ballistic dynamics with $τ ∝ q^{−1}$ and compressed correlation functions. In the third step, aging continues after the arrest of particle motion. Our observations further suggest that gelation is characterized by stress release as evidenced by anisotropic dynamics once gelation sets in., Published by American Institute of Physics, Melville, NY

In this study, faceted mesocrystals have been assembled from the dispersion of truncated cubic-shaped iron oxide nanoparticles stabilized by oleic acid (OA) molecules using the non-solvent “gas phase diffusion technique” into an organic solvent. The effects of synthesis conditions as well as of the nanoparticle size and shape on the structure and morphogenesis of mesocrystals were examined. The interactions of OA capped iron oxide nanoparticles with solvent molecules were probed by analytical ultracentrifugation and double difference pair distribution function analysis. It was shown that the structure of the organic shell significantly depends on the nature and polarity of solvent molecules.

In this study, faceted mesocrystals have been assembled from the dispersion of truncated cubic-shaped iron oxide nanoparticles stabilized by oleic acid (OA) molecules using the non-solvent “gas phase diffusion technique” into an organic solvent. The effects of synthesis conditions as well as of the nanoparticle size and shape on the structure and morphogenesis of mesocrystals were examined. The interactions of OA capped iron oxide nanoparticles with solvent molecules were probed by analytical ultracentrifugation and double difference pair distribution function analysis. It was shown that the structure of the organic shell significantly depends on the nature and polarity of solvent molecules.

Neural mechanisms behind stereopsis, which requires simultaneous disparity inputs from two eyes, have remained mysterious. Here we show how ultrafast mirror-symmetric photomechanical contractions in the frontal forward-facing left and right eye photoreceptors giveDrosophilasuper-resolution 3D-vision. By interlinking multiscalein vivoassays with multiscale simulations, we reveal how these photoreceptor microsaccades - by verging, diverging and narrowing the eyes’ overlapping receptive fields - channel depth information, as phasic binocular image motion disparity signals in time. We further show how peripherally, outside stereopsis, microsaccadic sampling tracks a flying fly’s optic flow field to better resolve the world in motion. These results change our understanding of how insect compound eyes work and suggest a general dynamic stereo-information sampling strategy for animals, robots and sensors.Significance statementTo move efficiently, animals must continuously work out their x,y,z-positions in respect to real-world objects, and many animals have a pair of eyes to achieve this. How photoreceptors actively sample the eyes’ optical image disparity is not understood because this fundamental information-limiting step has not been investigatedin vivoover the eyes’ whole sampling matrix. This integrative multiscale study will advance our current understanding of stereopsis from static image disparity comparison to a new morphodynamic active sampling theory. It shows how photomechanical photoreceptor microsaccades enableDrosophilasuper-resolution 3D-vision and proposes neural computations for accurately predicting these flies’ depth-perception dynamics, limits, and visual behaviors.

Physical review / E 104, L012602 (1-7) (2021). doi:10.1103/PhysRevE.104.L012602, We study the structure and dynamics of colloidal particles with a spherical hard core and a thermo-responsive soft shell over the whole phase diagram by means of small-angle x-ray scattering and x-ray photon correlation spectroscopy. By changing the effective volume fraction by temperature and particle concentration, liquid, repulsive glass. and attractive gel phases are observed. The dynamics slow down with increasing volume fraction in the liquid phase and reflect a Vogel-Fulcher-Tamann behavior known for fragile glass formers. We find a liquid-glass transition above 50 vol.% that is independent of the particles' concentration and temperature. In an overpacked state at effective volume fractions above 1, the dispersion does not show a liquid phase but undergoes a gel-glass transition at an effective volume fraction of 34 vol.%. At the same concentration, extrema of subdiffusive dynamics are found in the liquid phase at lower weight fractions. We interpret this as dynamic precursors of the glass-gel transition., Published by Inst., Woodbury, NY

Macromolecules 54(5), 2551 - 2560 (2021). doi:10.1021/acs.macromol.0c02818, Studies of glass transition under confinement frequently employ supported polymer thin films, which are known to exhibit different transition temperature T$_g$ close to and far from the interface. Various techniques can selectively probe interfaces, however, often at the expense of sample designs very specific to a single experiment. Here, we show how to translate results on confined thin film T$_g$ to a “nacre-mimetic” clay/polymer Bragg stack, where periodicity allows to limit and tune the number of polymer layers to either one or two. Exceptional lattice coherence multiplies signal manifold, allowing for interface studies with both standard T$_g$ and broadband dynamic measurements. For the monolayer, we not only observe a dramatic increase in T$_g$ (∼ 100 K) but also use X-ray photon correlation spectroscopy (XPCS) to probe platelet dynamics, originating from interfacial slowdown. This is confirmed from the bilayer, which comprises both “bulk-like” and clay/polymer interface contributions, as manifested in two distinct T$_g$ processes. Because the platelet dynamics of monolayers and bilayers are similar, while the segmental dynamics of the latter are found to be much faster, we conclude that XPCS is sensitive to the clay/polymer interface. Thus, large T$_g$ shifts can be engineered and studied once lattice spacing approaches interfacial layer dimensions., Published by Soc., Washington, DC

New journal of physics 23(9), 093041 (2021). doi:10.1088/1367-2630/ac2594, We demonstrate the successful application of x-ray speckle visibility spectroscopy (XSVS) experiments to study the dynamics of radiation sensitive, biological samples with unprecedented small x-ray doses of 45 Gy and below. Using XSVS, we track the dynamics of casein micelles in native, concentrated, and acidified solution conditions, while substantially reducing the deposited dose as compared to alternative techniques like sequential x-ray photon correlation spectroscopy. The Brownian motion in a skim milk sample yields the hydrodynamic radius of the casein micelles while deviations from Brownian motion with a characteristic q-dependent diffusion coefficient D(q) can be observed in more concentrated solution conditions. The low dose applied in our experiments allows the observation of static, frozen speckle patterns from gelled acidic milk. We show that the XSVS technique is especially suitable for tracking dynamics of radiation sensitive samples in combination with the improved coherent properties of new generation x-ray sources, emphasizing the great potential for further investigations of protein dynamics using fourth generation synchrotrons and free electron lasers., Published by IOP, [London]

Studies of glass transition under confinement frequently employ supported polymer thin films, which are known to exhibit different transition temperature Tg close to and far from the interface. Various techniques can selectively probe interfaces, however, often at the expense of sample designs very specific to a single experiment. Here, we show how to translate results on confined thin film Tg to a “nacre-mimetic” clay/polymer Bragg stack, where periodicity allows to limit and tune the number of polymer layers to either one or two. Exceptional lattice coherence multiplies signal manifold, allowing for interface studies with both standard Tg and broadband dynamic measurements. For the monolayer, we not only observe a dramatic increase in Tg (∼ 100 K) but also use X-ray photon correlation spectroscopy (XPCS) to probe platelet dynamics, originating from interfacial slowdown. This is confirmed from the bilayer, which comprises both “bulk-like” and clay/polymer interface contributions, as manifested in two distinct Tg processes. Because the platelet dynamics of monolayers and bilayers are similar, while the segmental dynamics of the latter are found to be much faster, we conclude that XPCS is sensitive to the clay/polymer interface. Thus, large Tg shifts can be engineered and studied once lattice spacing approaches interfacial layer dimensions.

Physical review letters 126(13), 138004 (2021). doi:10.1103/PhysRevLett.126.138004, While the interplay between liquid-liquid phase separation (LLPS) and glass formation in biological systems is highly relevant for their structure formation and thus function, the exact underlying mechanisms are not well known. The kinetic arrest originates from the slowdown at the molecular level, but how this propagates to the dynamics of microscopic phase domains is not clear. Since with diffusion, viscoelasticity, and hydrodynamics, distinctly different mechanisms are at play, the dynamics needs to be monitored on the relevant time and length scales and compared to theories of phase separation. Using x-ray photon correlation spectroscopy, we determine the LLPS dynamics of a model protein solution upon low temperature quenches and find distinctly different dynamical regimes. We observe that the early stage LLPS is driven by the curvature of the free energy and speeds up upon increasing quench depth. In contrast, the late stage dynamics slows down with increasing quench depth, fingerprinting a nearby glass transition. The dynamics observed shows a ballistic type of motion, implying that viscoelasticity plays an important role during LLPS. We explore possible explanations based on the Cahn-Hilliard theory with nontrivial mobility parameters and find that these can only partially explain our findings., Published by APS, College Park, Md.

Nature Communications 11, 3821 (2020). doi:10.1038/s41467-020-17632-4, The assembly of plasmonic nanoparticles into ordered 2D- and 3D-superlattices could pave the way towards new tailored materials for plasmonic sensing, photocatalysis and manipulation of light on the nanoscale. The properties of such materials strongly depend on their geometry, and accordingly straightforward protocols to obtain precise plasmonic superlattices are highly desirable. Here, we synthesize large areas of crystalline mono-, bi- and multilayers of gold nanoparticles >20 nm with a small number of defects. The superlattices can be described as hexagonal crystals with standard deviations of the lattice parameter below 1%. The periodic arrangement within the superlattices leads to new well-defined collective plasmon-polariton modes. The general level of achieved superlattice quality will be of benefit for a broad range of applications, ranging from fundamental studies of light–matter interaction to optical metamaterials and substrates for surface-enhanced spectroscopies., Published by Nature Publishing Group UK, [London]

The journal of physical chemistry / C 124(46), 25645 - 25656 (2020). doi:10.1021/acs.jpcc.0c08670, Amorphous calcium carbonate (ACC) is an essential component present during the early stages of biomineralization of many calcifying organisms, which is used as a precursor of crystalline calcium carbonate phases. Here, we performed X-ray photon correlation spectroscopy experiments on ACC which show that the amount of adsorbed water has a strong control over its diffusive dynamics. Results of crystallization experiments under conditions of controlled humidity indicate that the adsorbed water is enough to spark crystallization of calcite. A direct proportionality is found between the relative humidity of the environment and the final size of the calcite crystals. Different hypotheses are made to explain this result, with the confinement within the amorphous matrix being the main suspect of controlling the size of the crystallites. Control of water activity and water content is, therefore, a possible way to regulate biomineral crystallinity both in nature and for the design of functional biomimetic materials., Published by Soc., Washington, DC

We present a three-dimensional (3D) approach for virtual histology and histopathology based on multi-scale phase contrast x-ray tomography, and use this to investigate the parenchymal architecture of unstained lung tissue from patients who succumbed to Covid-19. Based on this first proof-of-concept study, we propose multi-scale phase contrast x-ray tomography as a tool to unravel the pathophysiology of Covid-19, extending conventional histology by a third dimension and allowing for full quantification of tissue remodeling. By combining parallel and cone beam geometry, autopsy samples with a maximum cross section of 8 mm are scanned and reconstructed at a resolution and image quality, which allows for the segmentation of individual cells. Using the zoom capability of the cone beam geometry, regions-of-interest are reconstructed with a minimum voxel size of 167 nm. We exemplify the capability of this approach by 3D visualization of diffuse alveolar damage (DAD) with its prominent hyaline membrane formation, by mapping the 3D distribution and density of lymphocytes infiltrating the tissue, and by providing histograms of characteristic distances from tissue interior to the closest air compartment. Open-Access-Publikationsfonds 2020 peerReviewed

Physical review letters 125(5), 055701 (2020). doi:10.1103/PhysRevLett.125.055701, We present a detailed investigation of the wave-vector dependence of collective atomic motion in Au$_{49}$Cu$_{26.9}$Si$_{16.3}$Ag$_{5.5}$Pd$_{2.3}$ and Pd$_{42.5}$Cu$_{27}$Ni$_{9.5}$P$_{21}$ supercooled liquids close to the glass transition temperature. Using x-ray photon correlation spectroscopy in a previously uncovered spatial range of only a few interatomic distances, we show that the microscopic structural relaxation process mimics the structure and presents a marked slowing down at the main average interparticle distance. This behavior is accompanied by dramatic changes in the shape of the intermediate scattering functions, which suggest the presence of large dynamical heterogeneities at length scales corresponding to a few particle diameters. A ballisticlike mechanism of particle motion seems to govern the structural relaxation of the two systems in the highly viscous phase, likely associated with hopping of caged particles in agreement with theoretical studies., Published by APS, College Park, Md.

Journal of synchrotron radiation 23(6), 1401 - 1408(2016). doi:10.1107/S1600577516012613, Combining microfluidics with coherent X-ray illumination offers the possibilityto not only measure the structure but also the dynamics of flowing samples in asingle-scattering experiment. Here, the power of this combination is demon-strated by studying the advective and Brownian dynamics of colloidalsuspensions in microflow of different geometries. Using an experimental setupwith a fast two-dimensional detector and performing X-ray correlationspectroscopy by calculating two-dimensional maps of the intensity auto-correlation functions, it was possible to evaluate the sample structure andfurthermore to characterize the detailed flow behavior, including flow geometry,main flow directions, advective flow velocities and diffusive dynamics. Byscanning a microfocused X-ray beam over a microfluidic device, the anisotropicauto-correlation functions of driven colloidal suspensions in straight, curved andconstricted microchannels were mapped with the spatial resolution of the X-raybeam. This method has not only a huge potential for studying flow patternsin complex fluids but also to generally characterize anisotropic dynamicsin materials., Published by IUCr, Chester

Structural distortion and relaxation are central to any liquid flow. Their full understanding requires simultaneous probing of the mechanical as well as structural and dynamical response. We provide the first full dynamical measurement of the transient structure using combined coherent X-ray scattering and rheology on electrostatically interacting colloidal fluids. We find a stress overshoot during the start-up of shear which is due to the strong anisotropic overstretching and compression of nearest-neighbor distances. The rheological response is reflected in uncorrelated entropy-driven intensity fluctuations. While the structural distortion under steady shear is well described by Smoluchowski theory, we find an increase of the particle dynamics beyond the trivial contribution of flow. After the cessation of shear, the full fluid microstructure and dynamics are restored, both on the structural relaxation timescale. We thus find unique structure-dynamics relations in liquid flow, responsible for the macroscopic rheological behavior of the system. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 10 July 2015; Accepted 26 September 2015; Advance Article published 9 October 2015; Version of Record published 16 December 2015 ispartof: Soft Matter vol:12 issue:1 pages:171-180 ispartof: location:England status: published

Advanced materials interfaces 7(19), 1-9 (2020). doi:10.1002/admi.202000919, Supercrystals composed of plasmonic nanoparticles constitute a promising material platform for tailored light‐matter interactions. The optimization of their optical properties requires precise syntheses and a detailed structural characterization that addresses not only the basic geometrical parameters but also the degree of order. Herein, plasmonic supercrystals with a well‐defined layered structure are studied by a combined transmission electron microscopy, small‐angle X‐ray scattering and X‐ray cross‐correlation analysis (TEM‐SAXS‐XCCA) approach. It is demonstrated that scanning small‐angle x‐ray scattering (SAXS) data can unambiguously be assigned to the number of crystalline layers by comparison with complementary transmission electron microscopy (TEM) experiments on the same regions of interest. A small but significant increase of the lattice constant with increasing number of layers and a high degree of orientational order irrespective of the number of layers is found. This points to specifics of the supercrystal formation mechanism that could be utilized to improve the control of self‐assembly for supercrystal geometries with subnanometer precision., Published by Wiley-VCH, Weinheim

This paper reports on coherent scattering experiments in the low-count regime with less than one photon per pixel per acquisition on average, conducted with two detectors based on the Eiger single-photon-counting chip. The obtained photon-count distributions show systematic deviations from the expected Poisson–gamma distribution, which result in a strong overestimation of the measured speckle contrast. It is shown that these deviations originate from an artificial increase of double-photon events, which is proportional to the detected intensity and inversely proportional to the exposure time. The observed miscounting effect may have important implications for new coherent scattering experiments emerging with the advent of high-brilliance X-ray sources. Different correction schemes are discussed in order to obtain the correct photon distributions from the data. A successful correction is demonstrated with the measurement of Brownian motion from colloidal particles using X-ray speckle visibility spectroscopy.

We report on high pressure small angle x-ray scattering on suspensions of colloidal crystallites in water. The crystallites made out of charge-stabilized poly-acrylate particles exhibit a complex pressure dependence which is based on the specific pressure properties of the suspending medium water. The dominant effect is a compression of the crystallites caused by the compression of the water. In addition, we find indications that also the electrostatic properties of the system, i.e. the particle charge and the dissociation of ions, might play a role for the pressure dependence of the samples. The data further suggest that crystallites in a metastable state induced by shear-induced melting can relax to a similar structural state upon the application of pressure and dilution with water. X-ray cross correlation analysis of the two-dimensional scattering patterns indicates a pressure-dependent increase of the orientational order of the crystallites correlated with growth of these in the suspension. This study underlines the potential of pressure as a very relevant parameter to understand colloidal crystallite systems in aqueous suspension.

We report on a nano-beam small angle X-ray scattering study on densely-packed, dried binary films made out of spherical silica particles with radii of 11.2 and 19.3 nm. For these three-dimensional thin films prepared by drop casting, only a finite number of colloidal particles contributes to the scattering signal due to the small beam size of 400 × 400 nm2. By scanning the samples, the structure and composition of the silica particle films are determined spatially resolved revealing spatial heterogeneities in the films. Three different types of domains were identified: regions containing mainly large particles, regions containing mainly small particles, and regions where both particle species are mixed. Using the new angular X-ray cross-correlations analysis (XCCA) approach, spatial maps of the local type and degree of orientational order within the silica particle films are obtained. Whereas the mixed regions have dominant two-fold order, weaker four-fold and marginal six-fold order, regions made out of large particles are characterized by an overall reduced orientational order. Regions of small particles are highly ordered showing actually crystalline order. Distinct differences in the local particle order are observed by analyzing sections through the intensity and XCCA maps. The different degree of order can be understood by the different particle size polydispersities. Moreover, we show that preferential orientations of the particle domains can be studied by cross-correlation analysis yielding information on particle film formation. We find patches of preferential order with an average size of 8–10 μm. Thus, by this combined X-ray cross-correlation microscopy (XCCM) approach the structure and orientational order of films made out of nanometer sized colloids can be determined. This method will allow to reveal the local structure and order of self-assembled structures with different degree of order in general.

We report x-ray photon correlation spectroscopy experiments on the dynamics of the glass-former polypropylene glycol covering a temperature range from room temperature to the glass transition at Tg = 205 K using silica tracer particles. Three temperature regimes are identified: At high temperatures, Brownian motion of the tracer particles is observed. Near Tg, the dynamics is hyperdiffusive and ballistic. Around 1.12Tg, we observe an intermediate regime. Here the stretching exponent of the Kohlrausch-Williams-Watts function becomes q dependent. By analyzing higher-order correlations in the scattering data, we find that dynamical heterogeneities dramatically increase in this intermediate-temperature regime. This leads to two effects: increasing heterogeneous dynamics and correlated motion at temperatures close to and below 1.12Tg.