| 1. |
- Begam, Nafisa, et al.
(författare)
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Effects of temperature and ionic strength on the microscopic structure and dynamics of egg white gels
- 2023
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 158:7
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Berkowicz, Sharon, 1994-, et al.
(författare)
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Resolving nanoscale dynamics during a liquid-liquid transition in supercooled glycerol-water solutions
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- It is proposed that a liquid-liquid transition (LLT), related to the hypothesized transition between high- and low-density liquids (HDL, LDL) in pure water, also exists in supercooled aqueous mixtures. However, experimental observations of the LLT in the supercooled solution is often complicated by the overlap with freezing. Here, we conducted an experiment probing the hypothesized LLT in deeply supercooled 16.5 mol% glycerol-water solution, combining X-ray photon correlation spectroscopy (XPCS), ultra small-angle X-ray scattering (USAXS) and wide-angle X-ray scattering (WAXS). This approach allows us to capture simultaneous, discontinuous structural and dynamic changes within the supercooled liquid following quenching to cryogenic temperatures (172-182 K). We observe changes in the inter-atomic liquid structure (from WAXS) as well as in the nanoscale structure and dynamics (from USAXS/XPCS), resembling a first-order LLT between HDL-like to LDL-like liquid. Importantly, we find that the LLT precedes the onset of ice crystalliization, which we can distinguish based on the advent of ice bragg peaks in WAXS. In addition, analysis of the two-time correlation (TTC) function from XPCS enables us to follow the dynamics during the LLT, which indicates super-diffusive ballistic-like motion and a gradual slowdown towards an arrested state upon freezing, consistent with an LLT via spinodal decomposition. We conclude that these results indicate the existence of a first-order LLT in supercooled glycerol-water solutions at intermediate glycerol concentrations, similar to that hypothesized for pure water at elevated pressures.
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| 3. |
- Bin, Maddalena, et al.
(författare)
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Coherent X-ray Scattering Reveals Nanoscale Fluctuations in Hydrated Proteins
- 2023
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 127:21, s. 4922-4930
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Tidskriftsartikel (refereegranskat)abstract
- 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 dynamics in the deeply supercooled regime (T = 180 K), which is typically not accessible through equilibrium methods. The observed stimulated dynamic response is attributed to collective stress-relaxation as the system transitions from a jammed granular state to an elastically driven regime. 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 normalized variance χT. The amplification of fluctuations is consistent with previous studies of hydrated proteins, which indicate the key role of density and enthalpy fluctuations in hydration water. Our study provides new insights into X-ray stimulated stress-relaxation and the underlying mechanisms behind spatiotemporal fluctuations in biological granular materials.
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| 4. |
- Kim, Young Yong, et al.
(författare)
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Synchrotron X-ray scattering and photon correlation spectroscopy studies on thin film morphology details and structural changes of an amorphous-crystalline brush diblock copolymer
- 2016
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 105, s. 472-486
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Tidskriftsartikel (refereegranskat)abstract
- We investigated structural details and temperature-induced structural changes of an amorphous-crystalline brush diblock copolymer, poly(3-((6-((7-(9H-carbazol-9-yl)heptanoyl)oxy)hexyl)thio)propylglycidyl ether)(60)-b-poly(glycidyl 12-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)oxy)-12oxododecanoate)(20) (PGK(60)-PGF(20)) in nanoscale thin films using synchrotron grazing incidence X-ray scattering (GIXS) and X-ray photon correlation spectroscopy (XPCS). Interestingly, the diblock copolymer was found to form a mixture of two different hexagonal cylinder structures (HEX1 and HEX2) where the PGF cylinders were aligned in the film plane. HEX1 was composed of PGF cylinders with higher population of crystals while HEX2 consisted of PGF cylinders with lower population of crystals. Surprisingly, the PGF block chains favorably self-assembled because of strong lateral interactions in the bristles, forming vertical multibilayer structure with partial interdigitation even in the highly confined cylindrical geometry. In heating run up to 340 K, some fraction of HEX2 was transformed to HEX1 via cold crystallization. In contrast, HEX1 was transformed to HEX2 above 340 K because of melting of the PGF crystals. The XPCS analysis found that the HEX structural changes associated with the cold crystallization in the PGF cylinder domains took place with relatively fast dynamics. The HEX structural changes associated with melting of the PGF crystals in the cylinder domains occurred with relatively slow dynamics; this unusual dynamics of structural changes might be attributed to a high energy melting process of PGF crystals against strong lateral interactions of the bristles.
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| 5. |
- Ladd-Parada, Marjorie, et al.
(författare)
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Using coherent X-rays to follow dynamics in amorphous ices
- 2022
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Ingår i: Environmental Science. - : Royal Society of Chemistry (RSC). - 2634-3606. ; 2:6, s. 1314-1323
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous solid water plays an important role in our overall understanding of water's phase diagram. X-ray scattering is an important tool for characterising the different states of water, and modern storage ring and XFEL facilities have opened up new pathways to simultaneously study structure and dynamics. Here, X-ray photon correlation spectroscopy (XPCS) was used to study the dynamics of high-density amorphous (HDA) ice upon heating. We follow the structural transition from HDA to low-density amorphous (LDA) ice, by using wide-angle X-ray scattering (WAXS), for different heating rates. We used a new type of sample preparation, which allowed us to study μm-sized ice layers rather than powdered bulk samples. The study focuses on the non-equilibrium dynamics during fast heating, spontaneous transformation and crystallization. Performing the XPCS study at ultra-small angle (USAXS) geometry allows us to characterize the transition dynamics at length scales ranging from 60 nm–800 nm. For the HDA-LDA transition we observe a clear separation in three dynamical regimes, which show different dynamical crossovers at different length scales. The crystallization from LDA, instead, is observed to appear homogenously throughout the studied length scales.
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| 6. |
- Lazarev, Sergey, et al.
(författare)
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Influence of contacts and applied voltage on a structure of a single GaN nanowire
- 2021
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 11:20
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires (NWs) have a broad range of applications for nano-and optoelectronics. The strain field of gallium nitride (GaN) NWs could be significantly changed when contacts are applied to them to form a final device, especially considering the piezoelectric properties of GaN. Investigation of influence of the metallic contacts on the structure of the NWs is of high importance for their applications in real devices. We have studied a series of different type of contacts and influence of the applied voltage bias on the contacted GaN NWs with the length of about 3 to 4 micrometers and with two different diameters of 200 nm and 350 nm. It was demonstrated that the NWs with the diameter of 200 nm are bend already by the interaction with the substrate. For all GaN NWs, significant structural changes were revealed after the contacts deposition. The results of our research may contribute to the future optoelectronic applications of the GaN nanowires.
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| 7. |
- Lazarev, Sergey, et al.
(författare)
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Structural Changes in a Single GaN Nanowire under Applied Voltage Bias
- 2018
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:9, s. 5446-5452
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Tidskriftsartikel (refereegranskat)abstract
- GaN nanowires (NWs) are promising building blocks for future optoelectronic devices and nanoelectronics. They exhibit stronger piezoelectric properties than bulk GaN. This phenomena may be crucial for applications of NWs and makes their study highly important. We report on an investigation of the structure evolution of a single GaN NW under an applied voltage bias along polar [0001] crystallographic direction until its mechanical break. The structural changes were investigated using coherent X-ray Bragg diffraction. The three-dimensional (3D) intensity distributions of the NWs without metal contacts, with contacts, and under applied voltage bias in opposite polar directions were analyzed. Coherent X-ray Bragg diffraction revealed the presence of significant bending of the NWs already after metal contacts deposition, which was increased at applied voltage bias. Employing analytical simulations based on elasticity theory and a finite element method (FEM) approach, we developed a 3D model of the NW bending under applied voltage. From this model and our experimental data, we determined the piezoelectric constant of the GaN NW to be about 7.7 pm/V in [0001] crystallographic direction. The ultimate tensile strength of the GaN NW was obtained to be about 1.22 GPa. Our work demonstrates the power of in operando X-ray structural studies of single NWs for their effective design and implementation with desired functional properties.
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| 8. |
- Li, Hailong, et al.
(författare)
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Intrinsic Dynamics of Amorphous Ice Revealed by a Heterodyne Signal in X-ray Photon Correlation Spectroscopy Experiments
- 2023
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 14:49, s. 10999-11007
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Tidskriftsartikel (refereegranskat)abstract
- Unraveling the mechanism of water's glass transition and the interconnection between amorphous ices and liquid water plays an important role in our overall understanding of water. X-ray photon correlation spectroscopy (XPCS) experiments were conducted to study the dynamics and the complex interplay between the hypothesized glass transition in high-density amorphous ice (HDA) and the subsequent transition to low-density amorphous ice (LDA). Our XPCS experiments demonstrate that a heterodyne signal appears in the correlation function. Such a signal is known to originate from the interplay of a static component and a dynamic component. Quantitative analysis was performed on this heterodyne signal to extract the intrinsic dynamics of amorphous ice during the HDA-LDA transition. An angular dependence indicates non-isotropic, heterogeneous dynamics in the sample. Using the Stokes-Einstein relation to extract diffusion coefficients, the data are consistent with the scenario of static LDA islands floating within a diffusive matrix of high-density liquid water.
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| 9. |
- Osterhoff, Markus, et al.
(författare)
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Progress on multi-order hard x-ray imaging with multilayer zone plates
- 2015
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Ingår i: X-Ray Nanoimaging : Instruments and Methods II - Instruments and Methods II. - : SPIE. - 9781628417586 ; 9592
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Konferensbidrag (refereegranskat)abstract
- Hard x-ray focusing and imaging on the few nano metre scale has gained a lot of attraction in the last couple of years. Thanks to new developments in fabrication and inspection of high-N.A. optics, focusing of hard x-rays has caught up with the focusing performance for soft x-rays. Here we review the latest imaging experiments of the Göttinger Multilayer zone plate collaboration, summarising our route from 1D to 2D lenses for different hard x-ray energies, and recapitulate recent progress on a journey from focusing to imaging.
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| 10. |
- Perakis, Fivos, et al.
(författare)
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Diffusive dynamics during the high-to-low density transition in amorphous ice
- 2017
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 114:31, s. 8193-8198
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Tidskriftsartikel (refereegranskat)abstract
- Water exists in high- and low-density amorphous ice forms (HDA and LDA), which could correspond to the glassy states of high(HDL) and low-density liquid (LDL) in the metastable part of the phase diagram. However, the nature of both the glass transition and the high-to-low-density transition are debated and new experimental evidence is needed. Here we combine wide-angle X-ray scattering (WAXS) with X-ray photon-correlation spectroscopy (XPCS) in the small-angle X-ray scattering (SAXS) geometry to probe both the structural and dynamical properties during the high-to-low-density transition in amorphous ice at 1 bar. By analyzing the structure factor and the radial distribution function, the coexistence of two structurally distinct domains is observed at T = 125 K. XPCS probes the dynamics in momentum space, which in the SAXS geometry reflects structural relaxation on the nanometer length scale. The dynamics of HDA are characterized by a slow component with a large time constant, arising from viscoelastic relaxation and stress release from nanometer-sized heterogeneities. Above 110 K a faster, strongly temperature-dependent component appears, with momentum transfer dependence pointing toward nanoscale diffusion. This dynamical component slows down after transition into the low-density form at 130 K, but remains diffusive. The diffusive character of both the high- and low-density forms is discussed among different interpretations and the results are most consistent with the hypothesis of a liquid-liquid transition in the ultraviscous regime.
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