Wide-angle X-ray Scattering Patterns Research Articles

In-operando X-ray scattering characterization of smectite swelling experiments

Swelling capacity of smectite was studied over decades regarding its application as barrier in disposal of nuclear wastes in geological repositories as well as the induced volume change potential in soils according to moisture. In order to improve our knowledge in the swelling capacity of smectite, a miniaturized oedometer was developed to combine swelling pressure measurement with wide angle X-ray scattering (WAXS) characterization in real time during hydration of smectite. This coupled set up allowed studying hydration of smectite up to saturation under confined condions and linking crystalline swelling to pressure at various densities. The modeling of the WAXS patterns gave also quantitative information about the relative proportion of the different interlayer water types at saturation. In situ and operando data were acquired for homo-ionic Na+- and Ca2+-exchanged smectite at two different densities (1.5 and 1.8 g/cm3). The results showed that the swelling pressure rise was correlated to a sequence of water layer type with the transition from 0W to interstratification of 2W/3W layers, depending on the density. The cation valency controlled the rate of hydration with faster hydration in the case of divalent exchanged smectite. At saturation, with increasing density, the amount of 3W layers decreased to the gain of 1W and 0W layers. Results also confirmed that at saturation and a density of 1.8 g/cm3, the interlayer porosity represented the total one. Finally, this development provided opportunity to improve our knowledge in the swelling mechanism of compacted swelling clay materials upon hydration.

Wide-angle X-ray scattering studies on contemporary and ancient bast fibres used in textiles \u2013 ultrastructural studies on stinging nettle

Stinging nettle (Urtica dioica) is a potential source material for industrial applications. However, systematic research on the ultrastructural properties of nettle fibres is lacking. Determining the ultrastructure of nettle and the other bast fibres also provides new insights into the studies of archaeological fibres and their usage. In this study, the nanostructure of modern and ancient nettle samples was studied using wide-angle X-ray scattering (WAXS) and compared to other bast fibres. The culturo-historical fibre samples consisted of nettle, flax, and hemp from White Karelian textiles collected 1894 as well as of 800–900-year-old archaeological textile fragments from Ravattula Ristimäki burial site, Finland. Using WAXS, the average cellulose crystallite widths, relative crystallinities and orientational order (including microfibril angle for the modern fibres) were determined and compared. The results also revealed the suitability of the WAXS analysis for fibre identification. The crystallite widths were of the similar size for all modern fibres (3.4–4.8 nm). Subtle differences in the relative crystallinities in descending order (from flax to nettle, and finally hemp) were observed. Also, subtle differences in the mean MFAs were observed (10 ± 1° for flax, 12 ± 1° for nettle, and 14 ± 1° for hemp). For the culturo-historical fibres, the values for crystallite widths and relative crystallinities were larger compared to the corresponding modern references. In addition, features due to the presence of non-cellulosic, crystalline substances (e.g., calcium oxalates) were detected in the WAXS patterns of all the modern nettle fibres. These features could potentially be used as a tool for identification purposes.Graphical abstract

The effect of annealing under acid or alkaline environment on the physicochemical and functional properties of wheat starch

The annealing of wheat starch was performed in dilute acid and alkaline media at 40 °C and 45 °C. To highlight the effect of these processes on wheat starch, the scanning electron microscopy and the optic microscopy under normal and polarized light, the Wide-Angle X-ray Scattering patterns and the colour parameters were analysed without revealing significant changes in comparison to the native wheat starch and samples submitted to the classical annealing process in pure water. Most striking changes induced were observed upon additional hydrothermal treatment above wheat starch gelatinization temperatures and when analysing the water-binding capacity and the solubility, the starch granules swelling kinetics, the pasting behaviour of starch-water dispersion as well as the flow properties of gels recovered. It is likely that the complementary changes induced by these variants of annealing are meanly related to the restructuration of the amorphous phase inside granules that modify irreversibly their swelling capacity as well as their susceptibility to collapse upon further hydrothermal treatments. Although the magnitude of the changes induced by these processes seems to depend on the incubation temperature, the same trends were observed when compared the results from the two incubation temperatures applied. Coupling the annealing process with incubation in diluted acid or alkaline media can be used as effective way to expand the possibilities of using wheat starches in various industries.

Temperature dependent network properties of amorphous PCT during tensile stretching

Tensile deformation behavior of amorphous Poly (1,4-cyclohexylenedimethylene Terephthalate) (PCT) at 25 °C–108 °C was investigated by means of in situ synchrotron wide-angle X-ray scattering (WAXS). WAXS patterns were processed in a way that the scatterings from isotropic and anisotropic structures were separated. It turned out that the influences of temperature during deformation can be divided into three zones: below 80 °C, only molecular chains oriented; between 80 °C to 90 °C, very few imperfect crystals were induced by strain; above glass transition temperature (92 °C), the triclinic PCT crystalline structure began to form during deformation process. It was found that the Gaussian model of Haward and Thackray described the stress-strain behavior of the tensile stretched amorphous PCT very well. However, when being stretched above 80 °C, the system showed two characteristic network moduli because of strain-induced crystallization. The onset of change in network modulus occurred immediately after the formation of unoriented crystallites which served as physical cross-linking points to reinforce the material.

Destruction and Reorganization of Physically Cross-Linked Network of Thermoplastic Polyurethane Depending on Its Glass Transition Temperature

The mechanical behavior and morphological variation of thermoplastic polyurethanes (TPUs) with different hard segment contents (HSCs) deformed at different temperatures are investigated using tensile machine, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS) techniques. The average constraint molecular weight ⟨Mc⟩ between the hard domains, calculated from the stress–strain curve, increases with the increasing deformation temperature and decreases with the increasing HSC. The increased ⟨Mc⟩ is also confirmed by the increased long spacing calculated from the SAXS peak. The intensity increase of the SAXS peak at high deformation temperature indicates that the induced hard domains exhibit higher density. The WAXS patterns indicate the induction of crystal form III at the deformation temperature above the Tg of the hard domains. The starting true stress of the generation of form III lies in the interval between 20 and 35 MPa. The orientation degree of chain segments at high temperatur...

Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and wide-angle X-ray scattering (WAXS) of polypropylene (PP)/cyclic olefin copolymer (COC) blends for qualitative and quantitative analysis

In this study, polypropylene (PP), a versatile commodity thermoplastic, and cyclic olefin copolymer (COC), an amorphous engineering thermoplastic, were blended over full composition range by melt-mixing technique using a co-rotating twin-screw extruder. PP is likely to be compatible with COC due to its olefinic behaviour, and PP/COC blends provide significant promising properties. FTIR spectra, Raman spectra and wide-angle X-ray scattering (WAXS) patterns of polypropylene, cyclic olefin copolymer and its blends were recorded in solid phases and carried out qualitative and quantitative analysis in detail. The characteristic absorption peaks of PP, COC and PP/COC blends were determined and compared. PP/COC blends did not generate new chemical reactions, while the intensity of fundamental vibration peaks in the spectra tends to vary with respect to the component contents in the blends. The ratio of the integral intensities of polypropylene and cyclic olefin copolymer fundamental vibrations in the Raman spectra were used for the quantitative analysis of PP/COC blends, and the obtained results showed very good agreement with the experimental values. IR spectra, Raman spectra and WAXS patterns of PP/COC blends are useful to track the uniformity of blending and determine the blend composition.

Crystallization of hard segments in MDI/BD-based polyurethanes deformed at elevated temperature and their dependence on the MDI/BD content

Morphological variation of thermoplastic polyurethanes (TPUs) with different hard segment contents (HSCs) stretched at 100 °C higher than the Tg of hard domain was monitored by in-situ wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) techniques. WAXS patterns reveal that the crystalline modification of TPUs with high HSCs transforms from paracrystal (termed as form I) to form III of 4,4′-methylene diphenyl diisocyanate/1,4-butanediol (MDI/BD) segment, and TPUs with low HSCs show the direct transition from amorphous MDI/BD packing to form III packing. The form III crystals are fibrillar hard domains. Chord distribution functions (CDFs) computed from the SAXS patterns were employed to illustrate the domain topology. The streak-like CDF peaks off the meridian indicate the existence of cylindrical microfibrils which are composed of very low inhomogeneities between the destructured hard domains and stretched soft domains along the straining direction. These microfibrils of TPUs with low HSCs present a periodically lateral correlation. Interface distribution function (IDF) and chord length distribution (CLD) were computed from Bonart's longitudinal and transverse projection to quantify the domain stacking and microfibril arrangement respectively. The average size of hard domains increases up to a constant size with the increasing macroscopic strain which may be related to the maximal sequence length of hard segment. The average size of soft domain also reaches up to a constant size at large strain that is smaller than the fully-extended length of soft segment. The variation of domain size is different from deformation at room temperature. The HSC affects the behaviors of morphological evolution significantly.

Self-Associated Polyamide Alloys with Tailored Polymorphism Transition and Lamellar Thickening for Advanced Mechanical Application.

Long chain polyamides with various number of methylene units in recurring amide groups, PA1012 and PA612, were blended to combine their unique advantages. The Brill transition and accompanied lamellar thickening were investigated by in situ wide angle X-ray scattering (WAXS) and small angle X-ray scattering. From WAXS patterns, the transformation from the α- to γ-crystalline phase, known as "Brill transition", can be independently observed in the constituent phases of the long chain polyamide alloys (LCPAs) during heating. A constant Tb (ca., 100 °C) irrespective of the blend composition and proportional variations of the phase content was obtained. Additionally, with elevated temperature, a gradual increase in both the crystalline layer (Lc) and amorphous layer (La) was detected in constituent polyamides. The compositional independence of the Brill transition in LCPAs and similar lamellar thickening originate from the complete immiscibility of both polyamides, which share stronger intramolecular rather than intermolecular hydrogen-bonding interaction and hence exhibit self-association. Contributed by the γ phase, with less extended structure and increased lamellar thickness with compact stacking, LCPAs with controlled strength and flexible features can be achieved, which can be utilized in advanced mechanical applications, particularly for hoses of automobiles. The unusually linear compositional dependence of mechanical parameters makes it possible to tailor the polymorphic and tensile properties.

Graphene nanoplatelets dispersion in poly(l-lactic acid): preparation method and its influence on electrical, crystallinity and thermomechanical properties

Poly(l-lactic acid) (PLLA)/graphene nanoplatelets (GnP) nanocomposites were prepared through solvent casting and coagulation methods. The better dispersion of graphene was achieved by ultrasounds and its effect on crystallinity, thermomechanical and electrical properties of PLLA were studied and compared in both methods. Differential scanning calorimetry (DSC) was used to investigate the crystallinity of PLLA and its composites. Field emission gun scanning electron microscope (FEG-SEM) and wide-angle X-ray scattering (WAXS) were employed to characterize the microstructure of PLLA crystallites. Dynamic mechanical thermal analysis (DMTA) was performed to study the thermomechanical properties of the nanocomposites. FEG-SEM images illustrated finer dispersion of GnP in samples obtained by coagulation method with respect to solvent casting method. Graphene imparted higher electrical conductivity to nanocomposites obtained by solvent casting under ultrasound due to better formation of graphene network. DSC thermograms and their resulting data showed positive effects of GnP on crystallization kinetics of PLLA in both methods enhanced by the nucleating effect of graphene particles. Meanwhile, the effect of GnP, as nucleating agent, was more prominent in samples produced by coagulation method without utilization of ultrasounds. WAXS patterns represented the same characteristic peaks of PLLA in nanocomposite specimens suggesting similar crystalline structure of PLLA in presence of graphene, and the intensified peaks of nanocomposites compared to neat PLLA confirmed the DSC results regarding its improved crystallinity. Graphene increased storage modulus in rubbery region and glass transition temperature of nanocomposites in the coagulation method due to restricted mobility of PLLA chains.

Implementation of in situ SAXS/WAXS characterization into silicon/glass microreactors.

A successful implementation of in situ X-ray scattering analysis of synthetized particle materials in silicon/glass microreactors is reported. Calcium carbonate (CaCO3) as a model material was precipitated inside the microchannels through the counter-injection of two aqueous solutions, containing carbonate ions and calcium ions, respectively. The synthesized calcite particles were analyzed in situ in aqueous media by combining Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) techniques at the ESRF ID02 beam line. At high wavevector transfer, WAXS patterns clearly exhibit different scattering features: broad scattering signals originating from the solvent and the glass lid of the chip, and narrow diffraction peaks coming from CaCO3 particles precipitated rapidly inside the microchannel. At low wavevector transfer, SAXS reveals the rhombohedral morphology of the calcite particles together with their micrometer size without any strong background, neither from the chip nor from the water. This study demonstrates that silicon/glass chips are potentially powerful tools for in situ SAXS/WAXS analysis and are promising for studying the structure and morphology of materials in non-conventional conditions like geological materials under high pressure and high temperature.

Determination of glass transitions in novel cellulose polymers by synchrotron wide-angle X-ray scattering

Synchrotron wide angle X-ray scattering (WAXS) was used to measure the glass-transition temperature (Tg) values for various cellulosic materials including a novel cellulose ester. WAXS patterns were obtained of films cast on silicon nitride windows. Two strong scattering peaks were observed that correlated with the intramolecular repeating anhydroglucose unit (d=10.6–14.3Å) and an intermolecular packing spacing (d=4.4–4.5Å). Real-time measurements were made during temperature cycling over a range of 80–160°C at 5°C/min. Significant shifts in position, width and area for the peak assigned to the intermolecular arrangement of the pseudo-linear cellulose mixed-ester chains were correlated with temperature. The calculated Tg mid-points correlated well with Tg values determined by differential scanning calorimetry (DSC). This application of temperature-dependent WAXS measurements shows promise for Tg determination in samples where shallow second-order transitions are observed by DSC and where other techniques are not applicable.

Bicellar systems as vehicle for the treatment of impaired skin

This study assesses the potential usefulness of bicellar systems to retard the penetration of drugs into damaged skin. The active compound used in this study was diclofenac diethylamine (DDEA). Initially, physicochemical characterisation of the DDEA bicellar systems was performed at different temperatures by small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) techniques. Subsequently, in vitro percutaneous absorption of bicellar systems into in vitro damaged skin was studied.SAXS results indicated a slight decrease in the width of their bilayers with increasing temperature, with no apparent stacking in those systems. WAXS patterns were compatible with an orthorhombic lateral packing of the nanoaggregates. The thermogram obtained by DSC indicated a decrease in gel-to-liquid crystalline transition temperature (Tm) when the drug was included into bicellar systems. A retardation effect for DDEA was detected by in vitro percutaneous absorption studies when DDEA was vehiculised in the bicellar systems with respect to an aqueous solution of the drug. It seems that the use of bicellar systems as a vehicle for topical application of DDEA on skin with an impaired barrier function may inhibit the penetration of DDEA to the systemic level. Such systems may consequently repair stratum corneum barrier function to some extent. The use of these systems could be considered a new alternative strategy to treat topically pathological skin with different drugs.

Microstructural change of degummed Bombyx mori silk: An in situ stretching wide-angle X-ray-scattering study

The microstructural change of degummed Bombyx mori silk was examined by in situ wide-angle X-ray-scattering (WAXS) with applied stretching force. WAXS patterns confirmed that the crystalline and amorphous regions coexist in the silk fibers. The crystallites with β-sheet structure have an orthorhombic unit cell with lattice parameters: a=9.10Å, b=9.71Å and c=6.80Å. The crystallite size, crystallite orientation and crystallinity were also estimated based on the WAXS patterns. The results demonstrate that the crystallite size is almost unchanged with the stretching strain. The crystallinity is approximately linearly increasing with the applied stretching force. However, the change of the unit-cell orientation degree with c-axis along the fiber axis behaves as a fast stage and an approximately unchanged stage during the in situ stretching process. All these experimental phenomena confirm that the microstructure of the degummed silk fibers can be well explained by the model of oriented β-sheet structure with a banded feature.

Characterizing the Structure of Organic Molecules of Intrinsic Microporosity by Molecular Simulations and X-ray Scattering

The design of a new class of materials, called organic molecules of intrinsic microporosity (OMIMs), incorporates awkward, concave shapes to prevent efficient packing of molecules, resulting in microporosity. This work presents predictive molecular simulations and experimental wide-angle X-ray scattering (WAXS) for a series of biphenyl-core OMIMs with varying end-group geometries. Development of the utilized simulation protocol was based on comparison of several simulation methods to WAXS patterns. In addition, examination of the simulated structures has facilitated the assignment of WAXS features to specific intra- and intermolecular distances, making this a useful tool for characterizing the packing behavior of this class of materials. Analysis of the simulations suggested that OMIMs had greater microporosity when the molecules were the most shape-persistent, which required rigid structures and bulky end groups. The simulation protocol presented here allows for predictive, presynthesis screening of OMIMs and similar complex molecules to enhance understanding of their structures and aid in future design efforts.

Molecular packing in highly stable glasses of vapor-deposited tris-naphthylbenzene isomers

Physical vapor deposition of organic molecules can produce glasses with high kinetic stability and low enthalpy. Previous experiments utilizing wide-angle x-ray scattering (WAXS) have shown that, relative to the ordinary glasses prepared by cooling the supercooled liquid, such glasses exhibit excess scattering characteristic of anisotropic packing. We have used vapor deposition to prepare glasses of four isomers of tris-naphthylbenzene (TNB), and measured both the WAXS patterns and the kinetic stability. While vapor-deposited glasses of all four TNB isomers exhibit high and nearly uniform kinetic stability, the level of excess scattering varies significantly. In addition, for α,α,β-TNB, glasses of essentially identical kinetic stability can have excess scattering levels that vary by a factor of two. These results indicate that anisotropic packing is not the source of kinetic stability in vapor-deposited glasses but rather a secondary feature that depends upon the chemical structure of the glass-forming molecules. We also show that the time required for these stable vapor-deposited glasses to transform into the supercooled liquid greatly exceeds the structural relaxation time τ(α) of the liquid and scales approximately as τ(α) (0.6). The kinetic stability of the vapor-deposited TNB glasses matches that expected for ordinary glasses that have been aged for 10(2) to 10(7) years.

Multiaxial deformation of polyethylene and polyethylene/clay nanocomposites: in situ synchrotron small angle and wide angle X‐ray scattering study

AbstractA unique in situ multiaxial deformation device has been designed and built specifically for simultaneous synchrotron small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) measurements. SAXS and WAXS patterns of high‐density polyethylene (HDPE) and HDPE/clay nanocomposites were measured in real time during in situ multiaxial deformation at room temperature and at 55 °C. It was observed that the morphological evolution of polyethylene is affected by the existence of clay platelets as well as the deformation temperature and strain rate. Martensitic transformation of orthorhombic into monoclinic crystal phases was observed under strain in HDPE, which is delayed and hindered in the presence of clay nanoplatelets. From the SAXS measurements, it was observed that the thickness of the interlamellar amorphous region increased with increasing strain, which is due to elongation of the amorphous chains. The increase in amorphous layer thickness is slightly higher for the nanocomposites compared to the neat polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

X‐ray scattering experiments on sputtered titanium dioxide coatings onto PVDF polymers for self‐cleaning applications

AbstractThe performance of active polymer substrates used in sensor and actuator or tactile display applications can be hindered by the inevitable soiling of their surface. A possible approach to overcome this problem is to deposit a self‐cleaning coating onto the polymer surface, taking care that the layer underneath withholds its intrinsic properties. In this work, titanium dioxide, TiO2, was naturally chosen for coating material due to its inherent photocatalytic properties. Thus, TiO2 thin films were deposited by reactive magnetron sputtering on poly(vinilydene fluoride) ‐ (PVDF) substrates, in its α‐ (nonelectroactive) and β‐ (electroactive) phases. Wide angle x‐ray scattering (WAXS) experiments in a synchrotron were performed to monitor the crystalline structure of the polymer substrates upon thin film deposition and also to assess the crystalline structure of the TiO2 coating at different temperatures. In the WAXS patterns of the coated α‐PVDF, the TiO2 polymorph anatase phase can be distinguished. At the same time, no explicit diffraction peaks for anatase were detected in the coated β‐PVDF. Fourier transform infrared spectroscopy evidenced that the chemical structure of PVDF is unaffected by the coating deposition process. These structural results have been correlated with the photocatalytic properties of the TiO2 coatings. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Micromechanical behavior related to the nanostructure of biodegradable polyesters

AbstractThe microhardness of a series of biodegradable polyesters was determined. The nanostructural features of these materials were studied by wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering (SAXS), and differential scanning calorimetry. Analysis of the SAXS and WAXS patterns allowed direct derivation of the degree of crystallinity and crystal thickness values, and correlations of the micromechanical properties are presented. The differences in the thermal and mechanical properties exhibited by the studied systems and the ones found in other aromatic polyesters are explained as due to the different chemical natures of the monomeric units. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Microstructure and dynamic mechanical analysis of extruded layered silicate PVC nanocomposites

AbstractThe nanostructure and dynamic mechanical properties of polyvinyl chloride (PVC) and the bentonite nanocomposites have been investigated. Nanocomposites with 5 wt% concentration of bentonite were prepared by melt extrusion followed by two‐roll‐milled processing. Atomic force microscopy (AFM) and wide‐angle X‐ray scattering (WAXS) were utilized to study the micro and nanostructure of the two‐roll‐milled sheets. The nanocomposites were compounded with two types of coupling agents: KZTPP® and Tamol 2001®. Optical microscopy showed that the materials remained optically transparent, i.e. they did not show evidence of nanoclay agglomeration. The WAXS patterns of PVC‐bentonite‐KZTPP nanocomposite were anisotropic, suggesting flow‐induced preferred orientation of the nanoplates. Moreover, the 001 reflection of the bentonite was shifted toward smaller angles, suggesting that the nanoplates were intercalated by the macromolecules. On the other hand, the WAXS patterns of PVC‐bentonite‐Tamol 2001 nanocomposite remained isotropic and did not show evidence of bentonite, suggesting exfoliation of the nanoplates. The nanocomposites showed an increase in glass transition temperature Tg, with the sequence Tg,PVC < Tg,KZTPP < Tg,Tamol 2001. Moreover, dynamic mechanical analysis (DMA) showed an increase in mechanical moduli and activation energy (and a decrease in the intensity of the mechanical damping Tan δ) following the same sequence. Interestingly, the improvement in mechanical moduli became more pronounced above the glass transition temperature. Copyright © 2008 John Wiley & Sons, Ltd.

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.