The effect of lowered pH on the thermal gelation behavior of hen egg yolk was investigated over the temperature range of 58-72 °C using low-dose X-ray photon correlation spectroscopy in ultra-small-angle X-ray scattering geometry. Progressive structural and dynamical alterations were observed at room temperature with decreasing pH, indicative of acid-induced protein denaturation, which correlates with an increase in yolk viscosity. Temperature- and pH-dependent structural and dynamic investigation suggests an acceleration in gel formation with decreasing pH. The time-temperature superposition relationship observed in all samples suggests an identical mechanism underlying protein aggregation-gelation with a temperature-dependent reaction rate. The sol-gel transition time extracted from kinetic and dynamic information follows Arrhenius behavior, with no significant change in the activation energy (450 ± 20 kJ/mol) of gelation. However, the prefactor A systematically decreases with decreasing pH, indicating that acidification accelerates gelation primarily by increasing the frequency of productive encounters without altering the fundamental energy barrier of the process.

Vapor-deposited amorphous ice, so-called amorphous solid water, exhibits complex structural and morphological transformations upon heating. A network of micropores, present at the deposition temperature (80 K), collapses at 100-145 K, and a glass transition takes place simultaneously above 120 K. Here, we separate the two processes by allowing the micropores to collapse upon heating, which is monitored by small-angle x-ray scattering experiments. The combined micropore collapse and glass transition dynamics are studied using x-ray photon correlation spectroscopy. After cooling back down and heating a second time, we see remaining pores collapsing only near T-g. Our analysis reveals both diffusive and ballistic processes attributed to pore collapse dynamics. Fast processes (similar to 100 & Aring;(2)/s) occur only when both micropore collapse and glass transition are simultaneously at play. In other words, both processes impact on each other and lead to a speed-up. The glass transition dynamics mainly features a slow diffusive process with a diffusion coefficient of around 1 & Aring;(2)/s and lower. This value is in nice agreement with other work on thin and on bulk samples.

Supercrystals of lead-halide perovskite nanocrystals combine the semiconducting properties of bulk perovskites with quantum confinement effects and extend them to the macroscopic scale. Supercrystals assembled via a two-layer phase diffusion process using an acetonitrile antisolvent were recently shown to be unusually robust. We investigate how the acetonitrile-assisted self-assembly process influences surface chemistry, the atomic lattice of nanocrystals, and the structure of the supercrystal. Using quantitative NMR spectroscopy, nanofocused X-ray diffraction, and optical spectroscopy, we show that a reduced density of the ligand shell caused by the exposure to acetonitrile in the assembly underlies the mechanical robustness of these supercrystals. Ligand stripping further drives a highly size-selecting lateral growth of the supercrystal and induces anisotropic relaxation of the nanocrystal atomic lattice while preserving the electronic coupling and robust light-emitting properties of the assembly. That enables the mechanical manipulation of supercrystals such as stacking, thereby opening new avenues for integration into optoelectronic devices.

Pressure provides a powerful parameter to control the protein conformation state, which at sufficiently high values can lead to unfolding. Here, we investigate the effects of increasing pressure up to 0.4 GPa on hydrated lysozyme proteins, by measuring the nanoscale stress relaxation induced and probed by X-rays. Structural and dynamical information at elevated pressures was obtained using X-ray photon correlation spectroscopy (XPCS) in combination with a diamond anvil cell (DAC). The dynamical analysis revealed a slowing down of the system up to 0.2 GPa, followed by a re-acceleration at 0.4 GPa. A similar non-monotonic behavior was observed both in the Porod and Kohlrausch-Williams-Watts (KWW) exponents, consistently indicating a crossover between 0.2 and 0.4 GPa. These findings suggest the presence of pressure-induced structural changes that impact protein collective stress-relaxation as the system transitions from a jammed state to an elastically driven regime. These results may be relevant for a deeper understanding of protein stability under compression as well as for practical high-pressure technologies, including food processing and pharmaceutical applications.

Here we report on recent progress in X-ray waveguide optics for full-field coherent imaging at the Göttingen Instrument for Nano-Imaging with X-rays (GINIX), installed at the P10 coherence beamline of the PETRA III storage ring at DESY, Hamburg. We describe fabrication methods including new materials and the corresponding characterization in terms of transmission, exit intensity distribution, far-field intensity distribution and coherence properties. In addition to single channels, which are currently used for holographic imaging, we include results on tapered waveguides and off-axis waveguide interferometers. We also address optimization of waveguide optics with respect to the novel super-resolution holography method presented by Soltau et al. [Optica (2021), 8, 818–823]. Finally, we discuss the further development of high-resolution nano-holography in view of the planned storage ring upgrade to PETRA IV.

Wetting of solid surfaces by a liquid is important for many natural and industrial processes, such as printing, painting, and coating. However, a quantitative description of the dynamic receding and advancing contact angle is still debated, in particular for aqueous solutions. One reason for our lack of quantitative understanding is the limited spatial resolution of currently used optical methods. We therefore present a new approach to access the submicroscopic region. We use X-ray phase contrast imaging to measure the dynamic receding contact angle on a moving glass fiber of 17 μm diameter. The fiber was pulled out of a liquid bath, which was filled with a mixture of glycerol and Milli-Q water. The dynamic receding contact angle decreased with increasing contact line velocity for all mixtures. In the holograms, we achieved a resolution of 50 nm/pixel with a spatial error of 450 nm. This spatial error is due to an extended surface region of the fiber and the liquid surface in the holograms. Our results demonstrate the feasibility of X-ray holography as a method to investigate dynamic contact angle phenomena and thereby open pathways to higher spatial and temporal resolution.

The localization of polymer-grafted nanoparticles (GNPs) at the interface between immiscible polymers can significantly alter their phase separation kinetics. However, modifying the role of GNP surface activity has not been explored in this context. Using in situ atomic force microscopy and grazing-incidence X-ray photon correlation spectroscopy, we reveal how subtle variations in the entropic and enthalpic interactions between the GNPs and the blend polymers can result in dramatic differences in phase separation kinetics. We use a bilayer geometry of polystyrene (PS, molecular weight ≈ 50 kDa) and poly(vinyl methyl ether) (PVME, molecular weight ≈ 80 kDa), with GNPs bearing PS chains of different molecular weights incorporated in the PS layer. While the GNPs grafted with shorter PS chains (3 kDa) should prefer the interface due to entropic effects, the gold GNP cores have a strong enthalpic preference for the PVME phase (even though the PS grafts themselves do not enthalpically prefer the PVME). As a result, these GNPs do not localize and jam the interface and blends do not show arrested phase separation. In contrast, GNPs grafted with longer PS chains (20 kDa), which do not experience such favorable enthalpic effects with the PVME due to screening of the enthalpic interactions between the core and PVME, are interfacially localized leading to a strong arrest of phase separation. These results establish that the coevolution of GNP segregation and phase separation is the decisive factor in stabilizing polymer blends, offering a new design principle for GNP-polymer composites under nonequilibrium conditions.

Dynamic properties of nanoparticles under high pressure are poorly understood due to experimental challenges. Here, we use X-ray photon correlation spectroscopy (XPCS) to investigate the diffusion dynamics of polyethylene glycol (PEG)-functionalized gold nanoparticles dispersed in water at pressures up to 6 kbar. Complementary small-angle X-ray scattering reveals no measurable pressure-induced changes in the gold core size, confirming structural stability across the studied pressure range. XPCS measurements show a systematic slowing down of nanoparticle dynamics with increasing pressure, with relaxation rates retaining the expected q2-dependence characteristic of Brownian motion. The extracted diffusion coefficients decrease continuously with pressure and align with predictions based on the pressure-dependent viscosity of water and the Stokes-Einstein relation, assuming a constant hydrodynamic particle size. Within experimental uncertainty, no additional contribution from pressure-induced ligand-shell modifications is observed in these dilute dispersions.

We compare the fluorescence properties of CsPbBr2Cl nanocrystals, obtained via two distinct synthetic procedures and self-assembled into supercrystals using the same antisolvent crystallization technique. By spatially resolved fluorescence (lifetime) measurements we demonstrate that the optical properties of the supercrystals depend on the specific synthesis conditions of the constituting nanocrystals. Using scanning electron microscopy, small-angle X-ray scattering, and nuclear magnetic resonance spectroscopy, we find evidence that spatial fluctuations in the supercrystal fluorescence correlate with the ligand sphere of the nanocrystals. Specifically, homogeneous surface passivation of the nanocrystals leads to consistent interparticle distances and increased structural order within the supercrystals, resulting in a uniform fluorescence center wavelength and lifetime. The results of this study emphasize the importance of the relationship between crystalline structure and ligand configuration in controlling the optical properties of lead halide perovskite supercrystals.

Dynamics, morphology, and structure of glassy water are highly relevant for cryochemical techniques, in particular for cryo-electron microscopy. Here, we study the structural dynamics of a deposit consisting of thousands of micrometer-sized glassy water droplets during and after droplet coalescence using x-ray photon correlation spectroscopy at the micro- and meso-scale. We cover the temperature range from 94 to 161 K, encompassing droplet coalescence, the glass transition, and crystallization to ice I. Our experimental protocol involves heating beyond the coalescence regime, followed by recooling and reheating beyond crystallization, which allows us to disentangle the dynamics of coalescence from those associated with the glass transition. During coalescence, we observe an irreversible ballistic process in the temperature range between 130 and 145 K, with characteristic velocities of ∼0.1-0.2 Å s-1. In addition, samples that are not annealed below 125 K exhibit a q-independent mode (q0) at 130-145 K, which only appears while coalescence is progressing. We regard this to be a collective relaxation connected to a mobile surface layer at the droplet interfaces. After coalescence is complete, we observe significant diffusive dynamics. In particular, we find a sharp increase in diffusivity to ∼2 Å2 s-1 at around 148 K, indicating the onset of pronounced diffusive motion. From these results, we conclude droplet coalescence is primarily governed by ballistic, non-diffusive dynamics below ∼136 K, whereas strongly heterogeneous diffusive dynamics emerge at higher temperatures. We associate the abrupt increase in diffusivity after coalescence with the bulk glass-to-liquid transition.

When a liquid is cooled down to temperatures close to the glass transition, the relaxation dynamics are characterized by two timescales associated with the structural relaxation and a secondary process known as the Johari-Goldstein (JG) or slow β relaxation. The JG relaxation is related to many crucial properties of glasses, such as their plastic response, and is here investigated using fast-scanning calorimetry in high-enthalpy GeSe3 glasses. High-enthalpy states are reached by two methods: (1) increasing the cooling rate used to quench the melt and (2) irradiating the glass with X-rays. Both methods make the JG relaxation visible in the calorimetric traces, where it appears as an exothermic signal at temperatures below the glass transition. The JG relaxation can be associated with mobile regions produced by quenching or defect regions produced by irradiation. These findings strongly support a general connection between the JG relaxation and local defect regions in the glass network and offer a new strategy to control via X-ray irradiation a key feature of the glass transition and, thereby, the related mechanical properties of the glass.

Understanding the structural evolution of supercooled water-glycerol solutions is important for cryopreservation, yet distinguishing liquid-state transformations from ice crystallization remains challenging. Here, we investigate a deeply supercooled water-glycerol solution by X-ray photon correlation spectroscopy (XPCS) in ultra-small-angle X-ray scattering (USAXS) geometry, combined with wide-angle X-ray scattering (WAXS). This combination simultaneously captures the structural and dynamical evolution of the supercooled liquid upon quenching to cryogenic temperatures (172 K). We observe discontinuous changes in the liquid structure on molecular length scales and formation of microscale domains. The dynamics slow down during this stage and exhibit hyper-diffusive, ballistic-like relaxation. This transformation precedes ice crystallization, which we identify from the emergence of ice Bragg peaks in WAXS, allowing the two processes to be temporally separated. Phase-field (Cahn-Hilliard) simulations qualitatively reproduce the experimental observations and show that a spinodal-decomposition scenario is consistent with the measured scattering evolution. These findings are consistent with a liquid-liquid phase separation scenario preceding ice crystallization and provide a route to disentangle the two processes in supercooled aqueous systems.

Nanoparticle (NP) self-assembly is a promising tool for the straightforward preparation of complex materials without lithography. Self-assembly on liquid subphases is established for the preparation of thin NP films with quasicrystalline order on large scales. Small-angle X-ray scattering (SAXS) at synchrotron radiation sources is in particular advantageous to study self-assembly in situ, providing detailed structural information with high temporal resolution. Here we present a new experimental setup that allows measuring SAXS in a vertical geometry. This way it is possible to study the self-assembly of nanoparticles on liquid subphases in situ as demonstrated with gold nanoparticles. In contrast to measurements with grazing incidence (GISAXS), spatial resolution in the µm range and sampling of the volume material is possible. Integration of optical microscopy allows observing the measurement position and formation of supercrystal flakes. The setup can be used to study self-assembly of various nanoparticles on liquid subphases but is not limited to such studies. It was realized at the beamline P10 at PETRA III (Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany).

Wetting of solid surfaces by a liquid is important for many natural and industrial processes such as printing, painting and coating. However, a quantitative description of the dynamic receding and advancing contact angle is still debated, in particular for aqueous solutions. One reason for our lack of quantitative understanding is the limited spatial resolution of currently used optical methods. We therefore present a new approach to access the sub-microscopic region. We use X-ray phase contrast imaging to measure the dynamic receding contact angle on a moving glass fiber of 17 um diameter. The fiber was pulled out of a liquid bath which was filled with a mixture of glycerol and Milli-Q water. The dynamic receding contact angle decreased with increasing contact line velocity for all mixtures. In the holograms we achieved a resolution of 50 nm/pixel with a spatial error of 450 nm. This spatial error is due to an extended surface region of the fiber and the liquid surface in the holograms. Our results demonstrate the feasibility of X-ray holography as a method to investigate dynamic contact angle phenomena and thereby opening pathways to higher spatial and temporal resolution.

Supercrystalline nanocomposites (SCNCs) are nanostructured hybrid materials with a variety of unique functional properties. Given their periodically arranged building blocks, they also offer interesting parallels with crystalline materials. They can be processed in multiple forms and at different scales, and cross-linking their organic ligands via heat treatment leads to a boost of their mechanical properties. This study shows, via X-ray and in situ scanning transmission electron microscopy (STEM) analyses, how each of these processing steps plays a distinct role in the generation, migration, interaction, and healing of supercrystalline defects. Pressing of SCNCs into bulk pellets leads to a distortion of the otherwise fcc superlattice, while emulsion-templated self-assembly yields supraparticles (SPs) with stacking faults and size-dependent symmetries. Heat treatment at the same temperatures as those applied for the organic cross-linking has significant effects on planar defects. Stacking faults migrate and get healed, as also confirmed via molecular dynamics simulations, and intersupercrystalline "grain" boundaries migrate via anisotropic motion of disconnections. These rearrangements of defects at the supercrystalline scale (tens of nanometers) in nanocomposites with high mechanical properties (compressive strength of 100-500 MPa) provide insights into the formation and evolution of ordered assemblies of functionalized nanoparticles.

The structure and dynamics of concentrated silica-PNIPAm (poly-N-iso-prop-yl-acrylamide) nanogels are studied as a function of hydrostatic pressure up to 3500 bar. A combination of X-ray photon correlation spectroscopy and small-angle X-ray scattering shows similar characteristics of the dynamics for both temperature- and pressure-induced volume phase transitions of PNIPAm nanogels. Upon increasing the pressure and depending on the initial particle volume fraction, a transition from a liquid or glass state to a colloidal gel is observed for pressures p ≃ 1500 bar at a temperature of 293 K. Time-dependent analysis of the dynamics shows aging in glass and gel samples which is absent in the liquid state. This indicates stress-dominated dynamics upon pressure changes that equilibrate after a few hundred seconds.

Low-dose X-ray photon correlation spectroscopy experiments on biological samples can be used to investigate the structure formation and underlying dynamics during phase separation, denaturation, and gelation. However, the use of intensive X-ray beams as an investigative tool is limited due to the susceptibility of biological samples to radiation-induced changes. XPCS in particular requires recording a series of high-frame-rate images to capture fast dynamics. In such cases, a fast X-ray shutter system is required to minimize beam damage to the samples by allowing a flexible delay between two images. Here we show how a fast (250 Hz) X-ray shutter system, built by the University of Siegen in close collaboration with DESY, improves low-dose XPCS capabilities at the P10 beamline at PETRA III. We found that by employing this shutter system in a logarithmic sampling scheme, the absorbed X-ray dose on the samples could be significantly decreased.