A Shielding Topology Stabilizes the Early Stage Protein–Mineral Complexes of Fetuin‐A and Calcium Phosphate: A Time‐Resolved Small‐Angle X‐ray Study

Biomineralization mechanisms : The serum protein α₂‐HS glycoprotein/fetuin‐A is an important inhibitor that prevents pathological mineralization of calcium phosphate in soft tissues and in the extracellular fluid. TR‐SAXS and stopped‐flow analysis were used to monitor the growth of protein mineral particles nucleating from supersaturated salt solutions in the presence of the protein. It was found that fetuin‐A did not influence the formation of mineral nuclei, but did prevent the aggregation of nuclei and thus mineral precipitation.

     

X‐ray diffraction studies on reverse‐annealed polyethylenes

Linear low and high density polyethylene sheets were compression molded and crystallized at a 5–10°C/min cooling rate. Parts of the sheets were annealed at different temperatures up to 2°C below the melting temperature. The small angle X‐ray scattering (SAXS) and the wide angle X‐ray scattering intensities of the annealed samples were studied. SAXS intensities showed particle scattering with a bimodal size distribution. The estimated radii of gyration were 15–17 nm and 5–7 nm, respectively. The crystallinity and the radius of gyration increased slightly with increasing annealing temperature for some samples; others did not show any change. No peaks characteristic of intercorrelated lamellar crystallinity in the SAXS intensities developed during the annealing. The original broad peak of high density polyethylene disappeared from the SAXS recordings on annealing. The length of the perfect chain versus melting temperature was calculated by the Thomson‐Gibbs formula and Flory's concept of melting temperature depression where methyl groups and tertiary carbon atoms at the branches were regarded as second components (solvent). Linear relationships were found for both cases. Experimental data for a linear low density polyethylene obtained from the literature were in between the two functions. A lamellar model of crystallization corresponding to the data is proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 340–349, 2001     

Kinetics of Multi‐Step Redox Processes by Time‐Resolved In Situ X‐ray Diffraction

The kinetics of redox reactions of iron oxide in oxygen carrier 50Fe₂O₃/MgAl₂O₄ are examined using different time‐resolved techniques. Reduction kinetics are studied by H₂ temperature‐programmed reduction (H₂‐TPR) monitored by time‐resolved in situ XRD. In contrast to conventional TPR, in situ XRD distinguishes the three‐stage reduction of Fe₂O₃ → Fe₃O₄ → FeO → Fe. It also shows that the oxidation of Fe → Fe₃O₄ by CO₂ has no intermediate crystalline phases, explaining why its kinetics can easily be investigated by conventional CO₂ temperature‐programmed oxidation (CO₂‐TPO). A shrinking core model which takes into account solid state diffusion allows describing the experimental data.     

Oligolactate‐grafted dextran hydrogels: Detection of stereocomplex crosslinks by X‐ray diffraction

Physically crosslinked hydrogels are formed upon mixing equal amounts of aqueous solutions of dextran grafted with L ‐lactic acid oligomers and dextran grafted with D ‐lactic acid oligomers. In this paper, the dex‐lactate hydrogels are analyzed by X‐ray diffraction to provide evidence that hydrogel formation occurred through stereocomplex formation. First, the stereocomplex formation of monodisperse lactic acid oligomers was studied and comparison with published results of poly(lactic acid) was made. It was clearly demonstrated that stereocomplexes were formed between oligomers of opposite chirality. The data for these monodisperse lactic acid oligomers were used to interpret the results obtained with the dex‐lactate hydrogels. X‐ray diffraction measurements demonstrated that in the hydrogels stereocomplexes were formed between the lactic acid oligomers of opposite chirality. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 289–293, 2002     

Recent developments in polymer applications of synchrotron small‐angle X‐ray scattering

Synchrotron radiation facilities have been established and become very familiar in the polymer community not only from academic but also industrial viewpoints. It is not so unusual now to conduct simultaneous measurements of small‐angle X‐ray scattering (SAXS) with other techniques such as wide‐angle X‐ray scattering, stress–strain, light scattering, and so forth. New techniques have also been established and have become more familiar in recent years. In this review, recent developments in polymer applications of synchrotron SAXS are summarized. Instrumental developments and progress in data analyses are reviewed from the following aspects: ultra‐small‐angle X‐ray scattering, anomalous SAXS, X‐ray photon correlation spectroscopy, new types of simultaneous measurements, grazing‐incidence SAXS, new trends in nanoparticle analyses and industrial applications. © 2016 Society of Chemical Industry     

X‐ray diffractometric study of microcrystallite size of naturally colored cottons

Cellulose crystallite sizes of naturally green and brown cottons as well as of white undyed and dyed cotton were studied by using X‐ray diffractometry. Data were analyzed both by a peak stripping method using the program WinFit and by whole profile matching using the FullProf program. The fit obtained with WinFit agreed with the results from the FullProf except for a small difference centered on the 002 reflection. Crystallite sizes of white and colored cottons were estimated by the full‐width‐at‐ half‐minimum (FWHM) method, and the results showed that compared to the white cotton, the crystallite sizes of green and brown cottons based on the 101 and 002 reflections were found to be comparable, whereas smaller 101¯ crystallite sizes were observed. After dyeing, the crystallite size of dyed brown cotton displayed a slight increase in the 002 crystallite size compared to that of the undyed white cottons. The average crystallite size of 101, 101¯, and 002 for each cotton determined by the WinFit program was comparable to that estimated by the FullProf program. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1466–1471, 2000     

The Tyrosine Gate of the Bacterial Lectin FimH: A Conformational Analysis by NMR Spectroscopy and X‐ray Crystallography

Urinary tract infections caused by uropathogenic E. coli are among the most prevalent infectious diseases. The mannose‐specific lectin FimH mediates the adhesion of the bacteria to the urothelium, thus enabling host cell invasion and recurrent infections. An attractive alternative to antibiotic treatment is the development of FimH antagonists that mimic the physiological ligand. A large variety of candidate drugs have been developed and characterized by means of in vitro studies and animal models. Here we present the X‐ray co‐crystal structures of FimH with members of four antagonist classes. In three of these cases no structural data had previously been available. We used NMR spectroscopy to characterize FimH–antagonist interactions further by chemical shift perturbation. The analysis allowed a clear determination of the conformation of the tyrosine gate motif that is crucial for the interaction with aglycone moieties and was not obvious from X‐ray structural data alone. Finally, ITC experiments provided insight into the thermodynamics of antagonist binding. In conjunction with the structural information from X‐ray and NMR experiments the results provide a mechanism for the often‐observed enthalpy–entropy compensation of FimH antagonists that plays a role in fine‐tuning of the interaction.     

Peak‐fitting analysis of cotton fiber powder X‐ray diffraction spectra

The precision and accuracy of diffraction peak positions resolved from the powder X‐ray diffraction spectra of cotton fibers by means of the residuals peak‐fitting procedure of a commercial peak‐fitting software package (PeakFit®) was investigated to explore the potential of such programs in providing reliable data that are not readily apparent in diffuse X‐ray spectra. Each intensity spectrum was fitted by employing a Gaussian function as the peak profile. The precision of 15 pairs of the resolved diffraction peaks is 0.0017 mm; 9 of the 15 pairs fall into the 99% confidence interval. The precision in 2θ of four commonly identified peaks through four independent fittings is from 0.002 to 0.014°. The 2θ accuracy of the resolved peaks is good in comparison to data calculated for both the traditionally accepted and the more recently revised concepts of the cellulose I crystal structure. A peak resolved at about 15.3° may be attributed to the triclinic crystal structure component of cellulose I. Although distinct peaks are not readily apparent in the diffuse spectrum of cellulose, peak‐fitting procedures may provide additional data for structure determination. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2019–2024, 2004     

In Situ X‐Ray Diffraction and Stress Analysis of Solid Oxide Fuel Cells

To increase the long term stability and performance of solid oxide fuel cell (SOFC) materials, it is important to understand the main degradation processes in their functional layers. In this work, the interface between electrolyte and anode material was investigated by in situ X‐ray diffraction (XRD) stress and phase analysis. It has been found that the determining process for the initial degradation of SOFC is the reduction of the anode material with hydrogen. During this process a tensile strength of 600–700 MPa is measured. These stresses are induced in the electrolyte material and produce crack networks. The reduction from nickel oxide to pure nickel was monitored by in situ phase analysis. This reaction induces tensile stress at the interface between electrolyte and anode. The stress produced in the electrolyte material was also confirmed by the observation of crack networks detected using scanning electron microscopy (SEM). Finally, the reducing process was optimized using different process gases, decreasing the destructive tensile stress level.     

About the Lorentz correction used in interpretation of small‐angle X‐ray scattering data of semicrystalline polymers

Lorentz correction is used to correct the intensities of X‐ray scattering of single‐crystal diffractometry in order to recalculate intensities to obtain structure factors. This correction reduces the intensities to zero at zero diffraction angle. Small‐angle scattering is used to study the dimensions of heterogeneities in polymeric materials. The scattering intensities at a near to zero scattering angle originate partly from periodic systems (reciprocal lattice) and partly from dispersed particle systems. Periodic systems should result in individual Gaussian or Lorentzian peaks with the position of a peak maximum depending on the length of the periodicity. Particle scattering results in a Gaussian peak centered at zero scattering angle. The effect of the Lorentz correction on the interpretation of small‐angle X‐ray scattering data is shown for some semicrystalline polyethylenes (high‐density, linear low‐density, and low‐molecular‐weight waxy polyethylenes). The data are compared to those for amorphous block copolymers (styrene–butadiene), in which there is a periodic system with homogeneous lamellar thickness. Lorentz correction destroys the characteristics of the particle scattering and can be applied only for periodic systems. It should not be used to produce a peak on scattering data, which do not show periodicity (peaks) without correction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 358–366, 2001     

Study of the degree of crystallinity in eudragit/poly(methyl methacrylate) polyblends by X‐ray diffraction

Plaques of blends of Eudragit RL 100 (EU) and poly(methyl methacrylate) (PMMA) with different weight‐per‐weight ratios were prepared by compression molding at 150°C. The X‐ray diffraction profiles of the blends were studied and compared, and the interplanar distance, crystallite size, and crystallinity were computed for various peaks. The Eu/PMMA blend with a 70:30 (w/w) ratio had the maximum crystallinity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1835–1838, 2005     

Method for Direct Determination of Glassy Phase Dissolution in Hydrating Fly Ash‐Cement System Using X‐ray Diffraction

A method for quantitative X‐ray diffraction analysis is developed for direct determination of the glassy phase content of fly ash in a hydrating binary blend of cement and low‐calcium, siliceous fly ash. The intensity contributions of the unhydrated glassy phase of fly ash and the amorphous reaction products to the intensity pattern of the total amorphous phase in the hydrating binary blend are obtained by decomposition of the total intensity signature as a sum of component pseudo Voigt (PV) peaks. An experimental program involving binary blends with three different low calcium siliceous fly ashes and two different curing temperatures is reported. The centers of the component PV peaks of the fly ash glassy phase fitted to the overall intensity pattern are found to be invariant. The glassy phase content of hydrating binary blends determined from the XRD method were found to agree well with the values obtained from a selective dissolution method.     

Design of an X‐Ray Powder Diffraction Probe for Multi‐Channel Application: Proof of Principle

The design of an X‐ray powder diffraction probe and its integration with a multi‐channel reactor system for potential application in high‐throughput experimentation is presented. The working principle of the apparatus is exemplified by measurements of corundum and of the phase change observed when oxidizing vanadium(III) oxide (V₂O₃) in air during heating up to 450 °C. The phase transformations of the parent material were monitored by phase identification of the crystalline intermediate vanadium(IV) oxide (VO₂) and the final product vanadium(V) oxide (V₂O₅).     

Sillimanite‐mullite transformation observed in synchrotron X‐ray diffraction experiments

High‐resolution synchrotron powder X‐ray diffraction (XRD) experiments were conducted to clarify the transformation of sillimanite to mullite (mullitization) and determine the mullitization temperature (T_c). We were able to distinguish sillimanite and mullite in the XRD patterns, despite their very similar crystallographic parameters, and to detect the appearance of small mullite peaks among sillimanite peaks. Analysis of the Johnson‐Mehl‐Avrami (JMA) equation for mullitization ratio (ζ) revealed that at temperatures T≥1240°C the mullitization had the same kinetics. The activation energy E at T≥1240°C obtained from the Arrhenius plot was 679.8 kJ mol^?1. In analysis using a time‐temperature‐transformation diagram for mullitization, a mullitization curve of ζ=1% can be described as where t is time, n is a reaction‐mechanism‐dependent parameter determined as 0.324 by JMA‐analysis, k₀ is the frequency factor, E_A is the activation energy for atomic diffusion, and represents the activation energy for nucleation. The results of fitting the data to this equation were T_c=1199°C, A=3.9×10⁶ kJ mol^?1 K^?2, E_A=605 kJ mol^?1, and k₀=3.65×10¹⁵. We conclude that the boundary between sillimanite and mullite+SiO₂ in the phase diagram is ~1200°C.     

Bubbles in a fluidized bed: A fast X‐ray scanner

We present experiments on a bubble train in a 23‐cm‐diameter fluidized bed of a Geldart B powder. The bubbles are injected via a single capillary inserted in the bed. We use our double X‐ray tomographic scanner to measure the solids distribution in two parallel cross sections of the bed. We report data for four different heights of the measuring planes above the capillary outlet. The velocity of individual bubbles is found from the time of flight from the lower to the upper plane. We have done separate calibration experiments for the velocity. In this article, we present data for the size and velocity of individual bubbles. From the bubble velocity, we could obtain the vertical dimension of the bubbles. This makes it possible to measure the volume of each bubble. The results show that our scanner is capable of measuring properties of bubbles with a size of 2.5 cm and above. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

In Situ Soft X‐ray Microscopy Study of Fe Interconnect Corrosion in Ionic Liquid‐Based Nano‐PEMFC Half‐Cells

This in situ soft X‐ray scanning microscopy electrochemical study of model proton exchange cathodic and anodic nano‐fuel cells is exploring the evolving structure and chemical composition of key cell components represented by Au and Fe electrodes in contact with Nafion‐ionic liquid composite electrolyte containing Pt black catalyst particles. Morphological and chemical changes of the electrodes as well as the chemical state and fate of the Fe species released into the electrolyte are monitored in short circuit and with applied cathodic or anodic polarization. The in situ X‐ray absorption images of the cathodic cell fed with 2.5 × 10^–5 mbar O₂ have revealed corrosion‐induced morphology changes in the Fe electrode, being more pronounced in the vicinity of Pt‐black particles, and deposition of the Fe species released into the electrolyte, onto the intact Au counter electrode upon cathodic polarization. The Fe electrodes of the anodic cell containing NaBH₄ in the electrolyte appear relatively more corrosion resistant. The Fe L₃ absorption spectra taken in different locations within the Fe electrode have shown lateral variations in the relative ratio between Fe²⁺ and Fe^3&4+ oxidation states, whereas the Fe species released into the RTIL electrolyte are only in the high Fe^3&4+ oxidation states.     

X‐ray diffraction studies and phase volume determinations in poly(ethylene glycol)–montmorillonite nanocomposites

Poly(ethylene glycol)–montmorillonite nanocomposites were prepared by both solution and melt intercalation methods with a range of polymer molecular weights and at a range of polymer loadings. Particular attention was given to the reliability of low‐angle X‐ray diffraction results for basal plane spacing and a sound correlation between three diffractometers was obtained (±0.005 nm). Expansion of the basal plane spacing from 1.23 nm to 1.82 nm by solution intercalation was independent of polymer molecular weight in the range 300–20 000. Furthermore, the clay expansion was independent of the method of intercalation; melt intercalation also gave d₀₀₁ = 1.82 nm irrespective of polymer molecular weight. The maximum amount of polymer intercalated by clay and the maximum loading of clay that polymer can sustain were also studied for the determination of nanocomposite formulations. The confined polymer exerts a reduced effective density (670 kg m^?3) in the galleries. Copyright © 2005 Society of Chemical Industry     

X‐ray pole figures to assess orientation in PVC sheets

A series of X‐ray pole figures were obtained from oriented and unoriented rigid polyvinyl chloride sheets. From these, information about crystallite orientation in uniaxially and biaxially drawn sheets stretched at 90°C was obtained. Uniaxial orientation produced two crystallite orientations with the extent of orientation increasing with draw ratio; for biaxial samples the chain direction (c) was distributed uniformly in the plane of the sheet, with the planar orientation improving as draw ratio increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 528–535, 2007     

X‐ray diffraction characterization of the structure of zein–Oleic acid films

Wide‐angle (WAXS) and small‐angle X‐ray scattering (SAXS) studies of dry granular zein, zein fibers, zein–oleic acid resin, and zein–oleic acid films are reported. WAXS patterns showed two diffuse rings for these samples indicative of noncrystalline structures. Measured d‐spacings of ∼ 4.6 Å and ∼ 10.5 Å were found for zein–oleic acid resins and films, consistent with the presence of α‐helical segments. The granular zein and zein fibers had ∼ 4.6‐Å and ∼ 9.5‐Å spacings. Neither the films nor the fibers showed evidence of orientation of the molecular axes. SAXS studies of zein–oleic acid films indicated that the structure of the films was affected by preparation method. Biaxially drawn resin films showed periodicities of ∼ 170 Å along the film surface direction and ∼ 135 Å in the thickness direction, while the cast films had weaker intensity periodicities of ca. 80 Å for all beam directions; a weak, diffuse 45‐Å spacing was also observed for both samples. The 170‐Å periodicity was present in the resin before deformation and following uniaxial deformation. No SAXS periodicity was observed for the granular zein or zein fibers. Several structural models are presented for the resin films that are consistent with reports in the literature that zein, in solution, consist of prism‐like particles consisting of four or more molecules. ? 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1267‐1281, 1999