Wide Angle X-ray Scattering Technique Research Articles

Implications of size dispersion on X-ray scattering of crystalline nanoparticles: CeO2 as a case study

Controlling the shape and size dispersivity and crystallinity of nanoparticles (NPs) has been a challenge in identifying these parameters' role in the physical and chemical properties of NPs. The need for reliable quantitative tools for analyzing the dispersivity and crystallinity of NPs is a considerable problem in optimizing scalable synthesis routes capable of controlling NP properties. The most common tools are electron microscopy (EM) and X-ray scattering techniques. However, each technique has different susceptibility to these parameters, implying that more than one technique is necessary to characterize NP systems with maximum reliability. Wide-angle X-ray scattering (WAXS) is mandatory to access information on crystallinity. In contrast, EM or small-angle X-ray scattering (SAXS) is required to access information on whole NP sizes. EM provides average values on relatively small ensembles in contrast to the bulk values accessed by X-ray techniques. Besides the fact that the SAXS and WAXS techniques have different susceptibilities to size distributions, SAXS is easily affected by NP–NP interaction distances. Because of all the variables involved, there have yet to be proposed methodologies for cross-analyzing data from two techniques that can provide reliable quantitative results of dispersivity and crystallinity. In this work, a SAXS/WAXS-based methodology is proposed for simultaneously quantifying size distribution and degree of crystallinity of NPs. The most reliable easy-to-access size result for each technique is demonstrated by computer simulation. Strategies on how to compare these results and how to identify NP–NP interaction effects underneath the SAXS intensity curve are presented. Experimental results are shown for cubic-like CeO2 NPs. WAXS size results from two analytical procedures are compared, line-profile fitting of individual diffraction peaks in opposition to whole pattern fitting. The impact of shape dispersivity is also evaluated. Extension of the proposed methodology for cross-analyzing EM and WAXS data is possible.

Monitoring the Particle Size Distribution, Phase Quantification and Chemical Composition of Acid-Leached PtCo Electrocatalyst Under Start-up/Shut-Down Conditions Probed By in-Situ SAXS and WAXS Techniques

Large progress has been made towards commercialization of polymer electrolyte membrane fuel cells (PEMFCs) through the development of highly active and robust Pt-Co alloy catalysts for oxygen reduction reaction (ORR).[1,2] However, most ORR catalyst materials suffer from the extremely corrosive conditions occurring during start-up/shut-down (SUSD).[3] Consequently, understanding the degradation mechanisms during SUSD is highly crucial for designing new catalyst materials with enhanced ORR activity and long-term durability.In this work, we show a comprehensive and complementary combination of different advanced techniques such as in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) as well as ex-situ scanning transmission electron microscopy in combination with electron energy loss spectroscopy (STEM-EELS) to provide deeper insights into the degradation processes of acid-leached Pt-Co catalyst under SUSD conditions.Firstly, Pt-Co nanoparticles supported on high surface area carbon (HSAC) were synthesized using wet impregnation – freeze-drying – thermal annealing method.[4] Compared to our previous works [4-6], an acid-leaching (1 M H2SO4, 15 °C, 2 h) was applied to dissolve the less noble metal from the surface of alloy nanoparticles forming a Pt-enriched skin. STEM-EELS data has also confirmed the formation of the Pt-enriched skin. In addition, ex-situ WAXS data signifies that the acid-leached PtCo catalyst consists of two face-centered cubic (fcc) disordered crystal phases: Pt90Co10 phase with a crystallite size of 3.6 ± 0.4 nm and Pt70Co30 phase with 4.2 ± 0.4 nm size.In terms of ORR performance, the acid-leached PtCo catalyst exhibits a 2.5- & 2-times higher mass activity (0.61 ± 0.12 A mgPt -1) and a 3.5- and 1.3-times higher specific activity (665 ± 84 µA cmPt -2) at 0.9 VRHE compared to commercial ~2 nm Pt/C (0.24 ± 0.05 A mgPt -1, 187 ± 29 µA cmPt -2) and heat-treated 4-5 nm Pt/HSAC (0.30 ± 0.04 A mgPt -1, 297 ± 42 µA cmPt -2), respectively. After SUSD experiments (800 cycles, 0.5 - 1.5 VRHE, 50 mV s-1, 0.1 M HClO4), the mass activity decreases to 0.21 ± 0.06 A mgPt -1 (-65 %) and 0.15 ± 0.03 A mgPt -1 (-38 %) for the acid-leached PtCo catalyst and commercial Pt/C, respectively.To monitor the potential-dependent changes in particle/crystallite size, phase quantification and chemical composition of the acid-leached PtCo catalyst under the SUSD conditions, in-situ SAXS and WAXS experiments were simultaneously performed at the beamline ID31 at European Synchrotron Radiation Facility (ESRF).In-situ WAXS analysis reveals that the lattice parameter of both Pt90Co10 and Pt70Co30 phases increases as a function of the SUSD cycle number, signifying the successive depletion of cobalt mainly from the Pt70Co30 phase. More precisely, the lattice parameter changed from 3.819 ± 0.004 Å (Pt70Co30) to 3.829 ± 0.004 Å (Pt76Co24) during the first 150 SUSD cycles. Only a slight change in lattice parameter for Pt90Co10 phase is observed during the SUSD protocol. Based on the Rietveld quantification, the amount of the Pt70Co30 phase decreases from 61 ± 2 wt.% to 47 ± 2 wt.% during the first 150 SUSD cycles. Afterwards, the Co depletion from this phase is less pronounced with additional cycle number. Furthermore, STEM-EELS investigations on acid-leached PtCo catalyst after first 150 SUSD cycles has confirmed the drastic Co depletion within the nanoparticles. After the SUSD protocol, the chemical composition of the acid-leached PtCo catalyst alters from Pt67±3Co33±3 to Pt81±3Co19±3 (-42 at.%) obtained from the bulk techniques like EDX and µ-XRF.In addition, the Rietveld refinement reveals an increase in crystallite sizes for both Pt-Co crystal phases over the course of the SUSD protocol which is in excellent agreement to the in-situ SAXS and ex-situ TEM results (from 4.1 ± 1.0 nm to 5.2 ± 0.8 nm, +27 %). In detail, the initial larger Pt70Co30 phase shows only a small increase in crystallite size (from 4.3 ± 0.4 nm to 4.8 ± 0.4 nm, +12 %), whereas for the initial smaller Pt90Co10 phase a gradual increase from 3.2 ± 0.3 nm to 4.5 ± 0.4 nm (+41 %) is observed during the SUSD experiment.Based on the in-situ SAXS/WAXS and the ex-situ STEM-EELS data, the Co depletion is the dominant degradation mechanism for the disordered fcc Pt70Co30 phase during the first 150 SUSD cycles. With increasing SUSD cycle number, the particle growth via Ostwald ripening and particle coalescence predominates. Our degradation model can be used to further improve the ORR performance and durability of acid-leached Pt-Co catalysts under the SUSD conditions.Literature:[1] L.R.Borup et al.,Curr.Opin.Electrochem.,2020,21,192-200.[2] C.Wang et al.,Energies,2016,9,603-642.[3] Y.Yu, et al.,J.Power Sources,2012,205,10-23.[4] M.Oezaslan et al.,J.Electrochem.Soc.,2012,159,B394-B405.[5] D.J.Weber et al.,J.Mater.Chem.A,2021,9,15415-15431.[6] P.Weber et al.,ACS Catal.,2022,12,6394-6408.

A Life-Cycle of Ni in Proton Exchange Membrane Fuel Cells

The usage of Proton Exchange Membrane Fuel Cells (PEMFCs) in the automotive industry is currently limited by the price, performance, and durability of a platinum catalyst. Alloying with nickel provides lower cost and enhances activity. However, the membrane electrode assembly (MEA) performance is, in practice, much lower than expected from liquid laboratory experiments on the catalyst layer. One of the identified issues is Ni leaching from nanoparticles (NPs) and subsequent Ni poisoning of the Nafion membrane.Here, we use Wide-Angle X-ray Scattering (WAXS) and X-ray Absorption Near-Edge Structure (XANES) to follow Ni dissolution from the catalyst layer and its movement in the MEA. We shine (synchrotron) light on the full life cycle of Ni, starting from (i) characterization of the catalyst powder, followed by (ii) the changes in catalyst composition during the ink-making process and (iii) membrane coating and finishing with (iv) NP characterization and Ni tracking during the operation of MEAs.Proper incorporation of PtNi catalyst requires modification of all the aforementioned steps that are otherwise well optimized for pure Pt catalyst. It is even more critical for shape-controlled octahedra (oh) PtNi NPs as their activity is closely related to their structure [1]. Highly active oh-PtNi NPs are usually made from precursors such as Nickel(II) bis(acetylacetonate). Using EDX, we find precursor residues in catalyst powders that dissolve upon further processing and add to membrane poisoning. We conclude that we need to develop a cleaning protocol that would remove all Ni residue while retaining the nanoparticle shape.During ink-making, high ionomer concentrations and elevated temperatures promote Ni dissolution from the catalyst, which can, in turn, poison the membrane even before the MEA is put in use. With the WAXS technique, we track the dissolution during ink-making and MEA operation by following changes in lattice parameter, showing the dynamics and the extent of Ni dissolution in each step of aging.Furthermore, we use angle-resolved XANES to track the movement of dissolved Ni. We show that Ni ions are getting reduced back to metallic form within the MEA, likely due to hydrogen crossover. The presence of such a metal band in the membrane blocks proton conductivity and decreases performance [2]. That is why it is crucial to set manufacturing and operational boundaries to prevent dissolution.For this reason, we follow WAXS total scattering intensity during oxidation and reduction cycles to understand the Ni dissolution dynamics during operation. We find that limiting both upper and lower potential cycling limits greatly reduces the redox extent and subsequent dissolution. It is, therefore, possible to find and understand the trade-off between high power density and dissolution in operational cells.Even though this work looks at the Ni life cycle, the presented techniques and conclusions are transferable to all multimetallic high-performance PEMFC catalysts.

A combined experimental and theoretical approach to quantitative assessment of microstructure in PLA/PP/Organo-Clay nanocomposites; wide-angle x-ray scattering and rheological analysis

Abstract A rheological study and morphological investigation using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and wide angle x-ray scattering (WAXS) techniques were performed on the single step melt processed poly (lactic acid) (PLA)/polypropylene (PP)/organoclay counterpart blend nanocomposites prepared via a micro-compounder. Two types of organoclay, Cloisite 30B and 15A were used for the preparation of the nanocomposites. Using a thermodynamic approach and with the aid of experimental techniques, it was indicated that both types of organoclay tend to localize within the PLA phase. Accordingly, in PLA-rich blends, 30B organoclay was localized in the matrix while in the PP-rich system the organoclay (15A) was mainly concentrated within the dispersed phase and also at the interface. In analyzing the WAXS results, two quantities, derived from Bragg and Scherrer's equations, in order to quantify the extent of interaction of organoclay with the different media and also partitioning of clay within the blend components. By that means, it was indicated that WAXS technique owns a great potential to predict organoclay morphology within the blend nanocomposites. Using the weighted relaxation spectrum of blends and implementation of Palierne emulsion model the interfacial tension of PLA/PP counterpart blends was determined. Despite the weak interaction of organoclay with the PP and also the low content of PLA in the PP-rich blend, the 25/75 PLA/PP blend represented substantial enhancement in elasticity as a result of organoclay loading. This behavior was attributed to the created network-like structure of organoclay platelets around the dispersed particles of PLA. Moreover, the applicability of fractional Zener model, to get the best fit to the melt rheological material functions using the genetic algorithm approach, and dependency of the fitting parameter of that model to the blend ratio and organoclay content, were evaluated.

Effect of microwave radiation on hydroxy propyl methyl cellulose polymer films and HPMC/poly(vinylpyrrolidone) polymer blend films using the wide-angle X-ray technique

The changes in the microstructural parameters of microwave-irradiated hydroxy propyl methyl cellulose (HPMC) and HPMC/PVP (poly(vinylpyrrolidone)) blend films have been studied using the Wide Angle X-Ray Scattering Technique (WAXS) method. The crystal imperfection parameters, such as lattice strain (g%), the average number of unit cells ⟨ N ⟩ counted in a direction perpendicular to Bragg's plane (hkl), spacing of (hkl planes dhkl, crystallite size ⟨ Ds ⟩, distortion width, standard deviation, stacking faults, twin faults, were computed by the whole pattern fitting method. The obtained results were quantified in terms of the radiation dosage given to the samples. X-ray analysis reveals that there is a decrease in the crystallite size with the increase in the radiation dosage. Fourier transform Infra-Red (FTIR) analysis has been also carried out for both the unirradiated and irradiated films to study the effect of microwave radiation on HPMC and HPMC/PVP polymer blend films. The scanning electron microscope study is also carried out to know the surface morphology of these blend films.

Structure property relations in polyethylene oxide/starch blended films using WAXS techniques

AbstractA series of polyethylene oxide (PEO)/starch blends were prepared by extrusion and their films were prepared by compression molding. It was observed that the presence of characteristic peaks of PEO and starch at 845 and 1643.7 cm−1, respectively, in FTIR spectra of PEO/starch blends favors the blending of PEO/starch. The physicomechanical and optical properties of PEO/starch‐blended films were measured. The tensile strength of the blended films decreased, whereas the haze values increased with an enhanced starch concentration in PEO/starch blends. The results obtained were correlated with microstructural parameters such as, crystallite size and lattice strain determined using wide angle X‐ray scattering (WAXS) data. The X‐ray line profile analysis shows that the crystallite shape area is maximum in PEO and decreases with the addition of starch. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preliminary study of human breast tissue using synchrotron radiation combining WAXS and SAXS techniques

Using synchrotron radiation, we combined simultaneously wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) techniques to obtain the scattering profiles of normal and neoplastic breast tissues samples at the momentum transfer range 6.28 nm(-1)<or=Q(=4pi x sin(theta/2)/lambda)<or=50.26 nm(-1) and 0.15 nm(-1)<or=Q<or=1.90 nm(-1), respectively. The results obtained show considerable differences between the scattering profiles of these tissues. We verified that the combination of some parameters (ratio between glandular and adipose peak intensity and third-order axial peak intensity) extracted from scattering profiles can be used for identifying breast cancer.

Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sites.

Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the program GASBOR at 5 A resolution (q(max) = 1.25 A(-1)) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8 A resolution from the correctly positioned envelope; four distinct peaks at the 3.2sigma level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (q(max) = 0.25 A(-1)). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination of FSEARCH and WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement.

Regulation and action of the bacterial enhancer-binding protein AAA+ domains

Bacterial EBPs (enhancer-binding proteins) play crucial roles in regulating cellular responses to environmental changes, in part by providing efficient control over sigma(54)-dependent gene transcription. The AAA+ (ATPase associated with various cellular activites) domain of the EBPs, when assembled into a ring, uses energy from ATP binding, hydrolysis and product release to remodel the sigma(54)-RNAP (RNA polymerase) holoenzyme so that it can transition from closed to open form at promoter DNA. The assembly, and hence activity, of these ATPases are regulated by many different signal transduction mechanisms. Recent advances in solution scattering techniques, when combined with high-resolution structures and biochemical data, have enabled us to obtain mechanistic insights into the regulation and action of a subset of these sigma(54) activators: those whose assembly into ring form is controlled by two-component signal transduction. We review (i) experimental considerations of applying the SAXS (small-angle X-ray scattering)/WAXS (wide-angle X-ray scattering) technique, (ii) distinct regulation mechanisms of the AAA+ domains of three EBPs by similar two-component signal transduction receiver domains, and (iii) major conformational changes and correlated sigma(54)-binding activity of an isolated EBP AAA+ domain in the ATP hydrolysis cycle.

Electric-field induced phase transition in a near-surface layer of a PbMg0.33Nb0.67O3-28% PbTiO3 (001) single-crystalline plate

Abstract An (001) single-crystal plate of a solid solution of PbMg1/3Nb2/3O3-28 mol.% PbTiO3 was investigated by Wide-Angle X-ray Scattering techniques at room temperature in situ under the influence of an external static electric field (field strength E up to 13 kV cm−1) applied along the [001] direction of the wafer. Structural changes attributed to a reversible phase transition between ferroelectric modifications of the solid solution in a near electrode region of about 1 mm depth are found. Part of the near-electrode layer (of about 5 vol.% at E = 4.5 kV cm−1 and about 15 vol.% at 13 kV cm−1) transforms from the initial rhombohedral structure to another one, most probably, the monoclinic Mb phase. Changes of the profile shape of X-ray rocking curves suggest possible technical use of the electric-field induced phase transition for adaptive X-ray optics.

Structure and Drug Release in a Crosslinked Poly(Ethylene Oxide) Hydrogel

Hydrogels are a continuously expanding class of pharmaceutical polymers designed for sustained or controlled drug release. The structure and intermolecular interactions in such systems define their macroscopic properties. The aim of this study was to investigate the mechanism of swelling, drug impregnation, and drug release from poly(ethylene oxide) (PEO) gel crosslinked by urethane bonds. A combination of SAXS/WAXS/SANS techniques enabled us to determine the phase transition between lamellar and extended gel network, and to apply different descriptions of crystallinity, based on lamellar and crystal lattice structures. It is shown that even low (1-7% w/w) loading of model drugs acetaminophen and caffeine, produced significant disorder in the polymer matrix. This effect was particularly pronounced for acetaminophen due to its specific ability to form complexes with PEO. The drug-release profiles were analyzed using a general cubic equation, proposed for this work, which allowed us to determine the gel hydration velocity. The results indicate that the release profiles correlate inversely with the polymer crystallinity.

Initial-Stage Growth Controlled Crystal Orientations in Nanoconfined Lamellae of a Self-Assembled Crystalline−Amorphous Diblock Copolymer

Crystallization temperature (Tc)-dependent crystal orientations within nanoconfined lamellae have been studied in a self-assembled poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer. The copolymer possesses number-average molecular weights of M̄nPEO = 8.7K and M̄nPS = 9.2K, and it forms a microphase-separated lamellar structure in the melt. It has been found that the PEO crystal (the c axis) orientations are determined by only varying the Tc.1 Based on real-time simultaneous two-dimensional (2D) small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) experiments, the formation of crystal orientation is found in an early stage of PEO crystallization confined between the PS lamellae. To understand whether the crystal orientation is determined during the primary nucleation or crystal growth step, specifically designed self-seeded crystallization experiments are carried out using 2D SAXS and WAXS techniques. Experimental results suggest that primary nuclei (self-seeds) do not possess specific orientation with respect to the PS lamellar surface normal, disregarding the history of crystal orientation in the samples generated before the self-seeding process. It is found that the initial stage of crystal growth determines the final crystal orientation in the nanoconfined lamellae. Studies of the correlation lengths (apparent crystallite sizes) along both [120] directions of the PEO crystals with various crystal orientations indicate that the PEO crystals formed in nanoconfined lamellae undergo a change from a one-dimensional to a two-dimensional growth with increasing Tc.

Structure Development during the Melt Spinning of Polyethylene and Poly(vinylidene fluoride) Fibers by in Situ Synchrotron Small- and Wide-Angle X-ray Scattering Techniques

In the present study, the structural and morphological development during melt spinning of polyethylene and poly(vinylidene fluoride) fibers was studied using simultaneous in-situ synchrotron small...

Ionic conduction of lithium and magnesium salts within laminar arrays in a smectic liquid-crystal polymer electrolyte

Three polymers having the structure shown below where R =–C16H33 or –C12H25 and n= 5 or 6 (coded C16O5, C16O6 and C12O6), have been synthesised and their complexes with LiClO4, LiBF4, LiCF3SO3, LiBr and Mg(ClO4)2 have been prepared. [graphic omitted] Using thermal analysis, polarised light microscopy, small-angle (SAXS) and wide-angle X-ray scattering techniques (WAXS) techniques and energy-minimised modelling it is shown that the complexes having 0.5 mol salt per polymer repeating unit form smectic liquid-crystal structures above the side-chain melting temperatures [e.g. 43.5 °C for C16O5-LiClO4(1 : 1)]. The salt is complexed to the two-dimensional helical polyether backbone layers which are separated by hydrocarbon layers. In contrast to expectation from conventional polymer electrolyte behaviour, the ionic conductivities of the lithium salt complexes in the liquid-crystal phases are greatest for systems having the most extensive two-dimensional organisation and follow the sequence C16O5 > C16O6 > C12O6. Mg(ClO4)2 complexes with C16O5 and C16O6 are similarly organised in two dimensions. The results suggests that ionic mobility is most extensive within the plane of the polyether layers and there is no evidence for ‘tunnelling’ through the hydrocarbon material.

STRUCTURE INVESTIGATIONS ON HALIDE GLASSES (MnF2)x(BaCl2)100-x WITH THE EXAFS AND WAXS TECHNIQUES

A short range structure investigation of halide glasses (MnF2)x(BaCl2)100-x(x = 65, 60, 55) has been made using the extended X-ray absorption fine structure (EXAFS) and the wide angle X-ray scattering (WAXS) techniques. The local structure information around the Mn is derived from the study of the MnK absorption edge EXAFS and the X-ray scattering intensity of the materials, respectively. The results show that the F and Cl atoms in the first neighbour shell of the Mn atom construct a octahedra (MnCl2F4) with the bond-length rMn-Cl = 0.246 nm and rMn-F= 0.200 nm in the glass of x = 65, which share the atom F with the neighbouring one to form zigzag chains linked by Ba atoms distributed between them. With decreasing of the amount of MnF2 below x = 65, the bond-length rMn-Cl and the Debye-Waller factor σMn-Cl2 of Mn-Cl increase, and that of Mn-F is almost invariant. The disappearance of the Mn-Mn peak has been found from x = 60 to x = 55 with an abrupt increase in rMn-Cl and σMn-Cl2, which can be explained as the chains being broken to form the solitude octahc-dra (MnCl2F4).