Site-resolved X-ray scattering studies,II the morphology in injection-molded PP foams

PP-structural foam moldings, composed of three co-axial cylinders were produced on an on-line injection molding machine in a pre-pressurized mold cavity by the classical low-pressure process and an alternative low-pressure process. Melt temperature, injection direction and sprue diameter were varied. Cross-sections cut from the middle of the small cylinder in longitudinal orientation were investigated by site-resolved X-ray scattering techniques in three different experiments: (i) wide-angle scans of the cross-sections, resulting in two-dimensional intensity maps; (ii) measurements of azimuthal intensity distributions of the principal PP reflections, for selected positions in the cross-sections; (iii) again for selected positions, small-angle measurements interpreted in terms of long periods. The comparison of the results derived from the different samples in the different experiments allows far-reaching statements about the influence of melt temperature, sprue dimension and position, and the type of process on the morphology and texture in the smallest cylinder of the moldings.     

Small angle X-ray scattering investigations on vinylpyridine-butadiene rubbers

Methylvinylpyridine-butadiene copolymers vulcanized by various α, ω dibromo-alkanes were investigated by X-ray small angle scattering. In these systems, employing the Hosemann-Joerchel analysis, only one cluster dimension of about 45 Å has been found with a polydispersity not exceeding 35 per cent. Stretched rubbers show interference effects both in the meridional and equatorial directions.     

Small-angle X-ray scattering studies on the X-ray induced aggregation of malate synthase I. Structural and kinetic studies

Small-angle X-ray scattering measurements on malate synthase in aqueous solution revealed a continuous increase of the intensity in the innermost portion of the scattering curve with increasing measuring time. We have definite evidence that this increase reflects an X-ray induced aggregation of the enzyme particles in the course of the small-angle X-ray scattering experiment. Obviously this aggregation is a consequence of a radiation damage of the particles by the primary beam used in the scattering experiment.The aggregation process of malate synthase was monitoredin situ by smallangle X-ray scattering. For this purpose scattering curves were taken at various stages of aggregation. The analysis of these curves established the increase of the particle dimensions, the retention of the pseudo thickness factor of the native enzyme and the occurrence of one and later on of two pseudo cross-section factors. These results suggest the way how the aggregation might proceed. The results led to a tentative model of the aggregation process in which a one-dimensional side-by-side association of the oblate enzyme particles is followed by a two-dimensional aggregation. An aggregation in the third dimension was not observed during the time covered by our experiment.The time dependence of molecular parameters, for instance of the apparent mean radius of gyration, was used to compare the aggregation of enzyme samples that were irradiated under different experimental conditions. The addition of dithiothreitol to the enzyme solutions as well as the presence of the substrates or of a substrate analogue or of ethanol were found to reduce the rate of aggregation.

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Röntgenkleinwinkeluntersuchungen der durch Röntgenstrahlen induzierten Aggregation der Malatsynthase. I. Strukturuntersuchungen und kinetische Messungen

Zusammenfassung Röntgenkleinwinkeluntersuchungen an wäßrigen Lösungen von Malatsynthase zeigten eine mit der Meßdauer ansteigende Zunahme der Streuintensität im Innenteil der Streukurve. Dieser Intensitätsanstieg spiegelt zweifelsohne eine durch die Röntgenbestrahlung induzierte Aggregation der Enzymteilchen während der Röntgenkleinwinkelmessung wider. Diese Aggregation ist offensichtlich auf einen durch die Primärstrahlung verursachten Strahlenschaden zurückzuführen.Das Fortschreiten der Aggregation der Malatsynthase wurde mit Hilfe der Röntgenkleinwinkelstreuungin situ verfolgt. Zu diesem Zweck wurden Streukurven bei verschiedenen Aggregationsstadien aufgenommen. Die Analyse dieser Kurven zeigte die Zunahme der Teilchendimensionen, das Beibehalten des Pseudodickenfaktors des nativen Enzyms und das Auftreten eines und später zweier Pseudoquerschnittsfaktoren an. Diese Ergebnisse lieferten Hinweise, wie die Aggregation ablaufen könnte, und führten zu einem möglichen Modell für den Aggregationsvorgang. Demnach sollte auf eine eindimensionale, laterale Aggregation der oblaten Enzymteilchen eine zweidimensionale Aggregation folgen. Ein Fortschreiten der Aggregation in der dritten Dimension konnte während der Dauer des Experimentes nicht beobachtet werden.Die zeitliche Abhängigkeit molekularer Parameter, z. B. des apparenten mittleren Streumassenradius, wurde für den Vergleich der Aggregation von Enzymproben, die unter verschiedenen experimentellen Bedingungen bestrahlt wurden, herangezogen. Durch Zugabe von Dithiothreitol oder Ethanol zu den Enzymlösungen oder durch die Anwesenheit der Substrate oder eines Substratanalogen konnte die Aggregationsgeschwindigkeit herabgesetzt werden.

     

Small-angle X-ray scattering studies on plastically deformed rubber-modified polystyrene

The deformation process of blends of polystyrene (PS) and rubbery block copolymers based on polystyrene and hydrogenated polybutadiene (SEBS, Shell Kraton G1651)was studied by Transmission Electron Microscopy (TEM) and Small-angle X-ray Scattering (SAXS) on deformed tensile samples, under loaded conditions. When the rubber concentration is increased the impact toughness as well as the elongation at break Increases while the SAXS studies show that the amount of crazing decreases. TEM studies suggest that the main deformation mechanism in these materials is cavitation-induced shearing. When a crazing agent is incorporated in the disperse phase of rubber-modified PS the amount of crazing increases more than four times, but the toughness decreases dramatically.     

X-ray scattering studies of surfaces and interfaces

Here we shall briefly review the basics and some applications of x-ray specular reflectivity and diffuse scattering techniques. These x-ray scattering techniques are uniquely suited to study of the structure of surfaces and interfaces at atomic resolutions as they are nondestructive and can probe even interfaces which are buried. The study of structure of surfaces and interfaces is not only required in understanding physics in reduced dimensions but is also essential in developing technologically important materials.     

Small angle X-ray scattering investigations of thermodynamic properties of fluid mixtures

Absolute small angle X-ray studies of concentration fluctuations were performed in order to determine thermodynamic properties of a model blend, consisting ofn-hexane and perfluoro-n-hexane. The quantities which we determined were the second derivate of the Gibbs free energy of mixing with respect to the concentration of the components, the location of the spinodal, interaction and solubility parameters, the energy gradient density coefficient as well as the correlation length of the fluctuations at various compositions and temperatures, particularly in the neighbourhood of the spinodal and the critical point. The data obtained were compared with those obtainable from the well known location of the binodal, to test the reliability of the scattering method.     

Small-angle X-ray scattering and structural modeling of full-length: cellobiohydrolase I from Trichoderma harzianum

Cellobiohydrolases hydrolyze cellulose releasing cellobiose units. They are very important for a number of biotechnological applications, such as, for example, production of cellulosic ethanol and cotton fiber processing. The Trichoderma cellobiohydrolase I (CBH1 or Cel7A) is an industrially important exocellulase. It exhibits a typical two domain architecture, with a small C-terminal cellulose-binding domain and a large N-terminal catalytic core domain, connected by an O-glycosylated linker peptide. The mechanism by which the linker mediates the concerted action of the two domains remains a conundrum. Here, we probe the protein shape and domain organization of the CBH1 of Trichoderma harzianum (ThCel7A) by small angle X-ray scattering (SAXS) and structural modeling. Our SAXS data shows that ThCel7A linker is partially-extended in solution. Structural modeling suggests that this linker conformation is stabilized by inter- and intra-molecular interactions involving the linker peptide and its O-glycosylations.     

On the structure of glassy polymers. I. Small-angle X-ray scattering from polycarbonate

The small-angle x-ray scattering (SAXS) from glassy bisphenol-A polycarbonate has been measured using a Bonse–Hart system. The data cover the angular range (2θ) between 20 sec and 2 deg. After correcting for absorption, background, and vertical beam divergence, they have been placed on an absolute basis by comparison with the scattering from a standard silica suspension. The corrected absolute intensity decreases strongly with increasing angle over the range between 20 sec and 30 min, and is nearly constant between 30 min and 2 deg. The magnitude of the scattering in the constant range, 0.44 (electrons)² Å^?3, is well represented by the thermodynamic theory for fluids applied at the glass-transition temperature. The increase in intensity at smaller angles cannot be described by structures on the scale of the nodules reported in this material (50–200 Å), but can be well represented by a small concentration of heterogeneities (0.04% by volume or less), several thousand angstrom units in size, superimposed on the thermal density fluctuations frozen in at the glass transition. It is suggested that the nodular features reported for this material are not representative of bulk material but should be associated with surface effects. The bulk structure can—as far as the SAXS is concerned—be well described as a random amorphous solid, containing simple thermal fluctuations and a small concentration of relatively large heterogeneities.     

Structural studies of bleached melanin by synchrotron small-angle X-ray scattering

Small-angle X-ray scattering was used to measure the effects of chemical bleaching on the size and morphology of tyrosine-derived synthetic melanin dispersed in aqueous media. The average size as measured by the radius of gyration of the melanin particles in solution, at neutral to mildly basic pH, decreases from 16.5 to 12.5 angstroms with increased bleaching. The melanin particles exhibit scattering characteristic of sheet-like structures with a thickness of approximately 11 angstroms at all but the highest levels of bleaching. The scattering data are well described by the form factor for scattering from a pancake-like circular cylinder. These data are consistent with the hypothesis that unbleached melanin, at neutral to mildly basic pH, is a planar aggregate of 6- to 10-nm-sized melanin protomolecules, hydrogen bonded through their quinone and phenolic perimeters. The observed decrease in melanin particle size with increased bleaching is interpreted as evidence for deaggregation, most probably the result of oxidative disruption of hydrogen bonds and an increase in the number of charged, carboxylic acid groups, whereby the melanin aggregates disassociate into units composed of decreasing numbers of protomolecules.     

Raman and X-ray scattering studies of high-pressure phases of urea

Single-crystal and polycrystalline urea samples were compressed to 12 GPa in a diamond-anvil cell. Raman-scattering measurements indicate a sequence of four structural phases occurring over this pressure range at room temperature. The transitions to the high-pressure phases take place at pressures near 0.5 GPa (phase I --> II), 5.0 GPa (II --> III), and 8.0 GPa (III --> IV). Lattice parameters in phase I (tetragonal, with 2 molecules per unit cell, space group P42(1)m (D3(2d))) and phase II (orthorhombic, 4 molecules per unit cell, space group P2(1)2(1)2(1) (D2(4))) were determined using angle-dispersive X-ray diffraction experiments. For phases III and IV, the combined Raman and diffraction data indicate that the unit cells are likely orthorhombic with four molecules per unit cell. Spatially resolved Raman measurements on single-crystal samples in phases III and IV reveal the coexistence of two domains with distinct spectral features. Physical origins of the spatial domains in phases III and IV are examined and discussed.     

X-ray scattering studies of the structure of aqueous hydroxy-propylcellulose solutions

X-ray diffraction studies have been undertaken on aqueous solutions of hydroxy propylcellulose (HPC) over a wide range of the scattering vector Q. The experiments revealed only modest differences in local structure on a distance scale ca. 5–300 Å despite the fact that they covered concentrations generally interpreted as ranging from the isotropic (35.1 wt %) to the anisotropic liquid crystalline (LC) phase (53.5 wt %). Several models were used to interpret the small-angle scattering data, and each gave similar structural parameters and extrapolated intensities ( Q → 0) for both solutions. Peaks were observed with d-spacings ca. 12–17 Å in both materials. Wide-angle x-ray scattering (WAXS) showed slightly increased local order over a size range ca. 5–20 Å for the anisotropic solution, and this is consistent with a greater intensity of the 13 Å peak in this material. It is difficult to reconcile these findings with an interpretation of the LC state involving major differences with the isotropic phase and a high degree of orientational order extending over long length scales.     

Oscillatory diffuse X-ray scattering from lead chalcogenides

New inorganic compounds having the general formula (Bi₂O₃)_1−x (Lu₂O₃) _x (x ranges from 0.1 to 0.5) displaying orange colours have been synthesized by traditional solid-state route, as viable alternatives to lead, cadmium and chromium based yellow toxic inorganic pigments. The host lattice of these pigments is Bi₂O₃ that is doped by Lu³⁺ ions. The goal was to develop conditions for the synthesis of these compounds and to determine the influence of calcination temperature and lutetium content on their colouring effects. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. The pigments were also evaluated from the standpoint of their structure and particle sizes.     

X-ray scattering studies of fatty acid films on water and on Cdcl2 solutions

X-ray diffraction methods for Langmuir films on the surface of water are briefly presented, together with recent results for docosanoic acid monolayers on pure water and for eicosanoic acid monolayers on an ionic subphase.     

Model of partial crystallization and melting derived from small-angle X-ray scattering and electron microscopic studies on low-density polyethylene

A temperature-dependent small-angle x-ray scattering and electron microscopic study on a sample of low-density polyethylene affords a determination of the structure changes in a heating and cooling cycle and suggests a new model of partial crystallization and melting. The analysis of SAXS data is based upon some general properties of the electron-density correlation function. Electron micrographs are obtained from stained sections γ irradiated at elevated temperatures and are analyzed quantitatively by statistical means. According to the model proposed here the thickness distribution in the amorphous layers, rather than that of the crystalline regions, is the essential factor governing the crystallization and melting behavior. The temperature-dependent changes in this thickness distribution provide a natural explanation for the large reversible changes in long-spacing.     

A Study on the ordering of intercalated solvents in poly-benzyl-l-glutamate; In-situ raman and X-ray scattering investigations

A polymer/solvent system can form a gel due to specific interactions between the polymer and the solvent. For poly-benzyl-L-glutamate/solvent systems, gelation can be based on carbonyl or phenyl ring interactions, depending on the solvent. The present paper describes X-ray scattering and Raman investigations on cast films of poly-benzyl-L-glutamate (PBLG) and benzylmethacrylate (BzMA). The studies indicate that in the cast samples separate zones of PBLG and BzMA are present. Upon heating, the system homogenises and the PBLG molecules pack in a pseudo hexagonal lattice. At approximately 150°C a new reflection at 11.4 Å in the WAXS pattern arises. This reflection is attributed to structural ordering of the solvent, due to intercalation of the solvent molecules within the helices of PBLG. The observed changes in the WAXS pattern upon heating are supported by Raman experiments.     

Ternary systems of nonionic surfactant Brij 35, water and various simple alcohols: Structural investigations by small-angle X-ray scattering and dynamic light scattering

Structural properties of ternary systems composed of nonionic surfactant dodecyl-poly(ethylene oxide-23) ether (C12E23, commercial name: Brij 35), water and various alcohols from ethanol to 1-decanol have been investigated using small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques. All measurements were performed at the temperature 25 degrees C. SAXS experimental data were put on absolute scale using water as a secondary standard. The data of water-rich mixtures at low to moderate surfactant concentrations were evaluated using the generalized indirect Fourier transformation method (GIFT), which is based on the simultaneous determination of the intra- and inter-particle scattering contributions. In this way, the size and the shape of interacting scattering particles in real space could be deduced. The systems with a relatively low surfactant concentration (5 mass%) were studied most extensively. In these cases, the water-rich regions of the phase diagrams could be investigated into more detail, since in the alcohol-rich regions problems with the GIFT evaluation of the SAXS data were encountered. The presented results demonstrate the level of structural details that can be obtained on the basis of scattering methods and point out the specific stages of data evaluation and interpretation where one must be extremely precautious. As such they reveal the inner structuration of the complex ternary systems of our present interest. In parallel, they also indicate that the longer chain alcohols actually behave as real oil phases in the studied systems, as one might expect, and also confirm the well-known properties of different short to medium chain alcohols that act as co-solvents and/or co-surfactants in microemulsion systems depending on their chain length.     

Small-angle X-ray scattering studies on the X-ray induced aggregation of malate synthase II. Inactivation and aggregation experiments

The X-ray induced inactivation and aggregation of the enzyme malate synthase in aqueous solution were investigated by small-angle X-ray scattering and enzymic tests.Enzymic activity decreases about exponentially with increasing dose. The rate of inactivation depends linearly on the dose rate; the extrapolation to zero dose rate yielded a finite limiting value of the rate constant of inactivation. The inactivation doseD ₃₇ is a linear function of enzyme concentration.Enzymic tests and small-angle X-ray scattering on samples, which had been X-irradiated before the measurements, showed no direct relation between aggregation and inactivation. The substrates glyoxylate and acetyl-CoA and the substrate analogue pyruvate are able to protect the enzyme against radiation damage, however to a different extent against aggregation (pyruvate > glyoxylate > acetyl-CoA) or inactivation (glyoxylate > pyruvate acetyl-CoA; the latter showed no effect). These findings and the protective effect of dithiothreitol against aggregation and inactivation of the enzyme are discussed in context with the formation of hydrogen peroxide. A possible shielding of radiosensitive groups of the enzyme by the substrates and scavenging are also taken into consideration as explanations for the protective effects.While the novel application of small-angle X-ray scattering in the field of radiation biology delivers information on X-ray induced structural changes of biopolymers and on their kinetics, the occurrence of radiation damages in conventional small-angle X-ray scattering measurements on biopolymers can be reduced by a variety of precautions.

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Röntgenkleinwinkeluntersuchungen der durch Röntgenstrahlen induzierten Aggregation der Malatsynthase. II. Inaktivierungs- und Aggregationsexperimente

Zusammenfassung Die durch Röntgenbestrahlung in wäßriger Lösung induzierte Inaktivierung und Aggregation des Enzyms Malatsynthase wurden mit der Methode der Röntgenkleinwinkelstreuung und mit Enzymtests untersucht.Die Enzymaktivität nimmt mit zunehmender Dosis annähernd exponentiell ab. Die Inaktivierungsgeschwindigkeit hängt linear von der Dosisleistung ab; die Extrapolation auf Dosisleistung null ergab einen endlichen Grenzwert der Inaktivierungsgeschwindigkeitskonstante. Die InaktivierungsdosisD ₃₇ ist eine lineare Funktion der Enzymkonzentration.Enzymtests und Röntgenkleinwinkelstreuexperimente an Proben, welche vorher bereits bestrahlt worden waren, zeigten keinen direkten Zusammenhang zwischen Aggregation und Inaktivierung. Die Substrate Glyoxylat und Acetyl-CoA sowie das Substratanaloge Pyruvat vermögen das Enzym gegen Strahlenschäden zu schützen, jedoch in unterschiedlichem Ausmß gegen Aggregation (Pyruvat > Glyoxylat > Acetyl-CoA) oder Inaktivierung (Glyoxylat > Pyruvat Acetyl-CoA; letzteres zeigte keinen Effekt). Diese Befunde und die Schutzwirkung von Dithiothreitol gegen die Aggregation und Inaktivierung des Enzyms werden in Zusammenhang mit der Bildung von Wasserstoffperoxid diskutiert. Als weitere Erklärungen für die Schutzwirkungen werden die mögliche Abschirmung strahlenempfindlicher Gruppen des Enzyms durch die Substrate und der Einfang von Radikalen in Erwägung gezogen.Während die neuartige Anwendung der Röntgenkleinwinkelstreuung auf dem Gebiet der Radiobiologie Aufschluß über strahleninduzierte Strukturänderungen von Biopolymeren und deren Kinetik gibt, läßt sich das Auftreten von Strahlenschäden bei konventionellen Röntgenkleinwinkelmessungen an Biopolymeren durch verschiedene Vorkehrungen reduzieren.

     

Light scattering from swollen textured polymer network composites

Light scattering from a swollen textured heterogeneous polymer network is discussed using example of a network composite filled by spherical inclusions anisotropically distributed in the matrix. The dependence of the scattering intensity on the Fourier transform of the correlation function dry-state shear moduli fluctuations has been established. H_v scattering patterns from uniaxial textures and their ratio with the composite anisotropy parameter are analyzed. The sensitivity of the H_v scattering pattern on restrictions during the swelling is emphasized. © 1993 John Wiley & Sons, Inc.     

Small-angle X-ray scattering studies of microdomain structure in segmented polyurethane elastomers

The small-angle x-ray scattering (SAXS) technique has been used to characterize the detailed microphase structure of two crosslinked segmented polyurethane elastomers. Both copolymers contain trifunctional polypropylene ether triols in the rubbery elastomeric block, but are synthesized with different hard segments: a symmetric 4,4′-diphenylmethane diisocyanate (MDI) chain extended with butanediol (BD); and an 80/20 mixture of asymmetric 2,4-toluene diisocyanate (TDI) and symmetric 2,6-toluene diisocyanate (TDI) chain extended with ethylene glycol (EG). Calculations of SAXS invariants and determinations of deviations from Porod's law are used to examine the degree of phase segregation of the hard- and soft-segment domains. Results show that the overall degree of phase separation is poorer in the asymmetric TDI/EG-based copolymer than in the symmetric MDI/BD-based copolymer. Determination of diffuse phase boundary thicknesses, however, reveals that the domain boundaries are sharper in the asymmetric TDI/EG system. The contrasting morphologies found in the two systems are interpreted in terms of differences in hard-soft segment compatibility, diisocyanate symmetry, and diisocyanate length. Coupled with conformational considerations, this information is used to construct a new model for polyurethane hard-segment microdomain structure. Important features of the model are that it takes into account the effects of hard-segment sequence length distribution and allows for folding of the longer hard-segment sequences back into the hard-segment domain.