Wide-angle X-ray Scattering Pattern Research Articles

Self-Assembly and Complexation of Cellulose/Ionic Liquid at High Cellulose Concentration: Anion Dependence

We investigated the state of cellulose that was dissolved in ionic liquid (IL) consisting of 1-methyl-3-propylimdiazolium cation ([C3mim]+) paired with acetate ([OAc]−), dimethylphospate ([DMP]−), or chloride (Cl–) anions using wide-angle X-ray scattering (WAXS), particularly focusing on the high cellulose concentration region (10–80 mol %). The anion species considerably altered the WAXS pattern of the cellulose/IL mixtures. [C3mim]­[OAc] deconstructed cellulose crystal structure up to the 40 mol % cellulose concentration. Similar to the previously reported cellulose/1-ethyl-3-methylimidazolium acetate system ([C2mim]­[OAc]), the mixtures of cellulose/[C3mim]­[OAc] at 25–60 mol % induced a low angle peak, which corresponds to the self-assembly of the system. For [C3mim]­[DMP] and [C3mim]Cl mixtures, sharp Bragg peaks were observed, which demonstrated the formation of the complex crystal of cellulose/IL. The presence of moisture eventually deconstructed these crystal structures; while for [C3mim]­Cl, an intermediate complex crystal containing H2O molecules emerged. This work contributes to understanding the cellulose state dissolved in IL at high concentrations and to the development of crystal engineering on this most abundant and recalcitrant biopolymer.

CarbX: a program for the evaluation of wide-angle X-ray scattering data of non-graphitic carbons

CarbX is an open-source program designed for the analysis of wide-angle X-ray scattering (WAXS) data of non-graphitic carbons (NGCs). As knowledge of their microstructure is crucial for tuning desired properties, an `easy-to-use' analysis tool is essential for effective research in this field. Using CarbX one can retrieve up to 14 microstructural parameters from a single WAXS pattern without having to master the associated complicated mathematics. CarbX was developed to serve as a convenient graphical user interface, translating a complex evaluation algorithm introduced by Ruland & Smarsly [J. Appl. Cryst. (2002), 35, 624–633] into software which can be operated by non-experts. Besides the core functionality of displaying data and manually fitting WAXS curves by user-editable parameters, CarbX offers additional features such as visualization of the deviation between data and fit, the possibility to choose the wavelength used in the measurement, and automatic fitting (using Wolfram Mathematica). One of the key features of the comfortable usability is the functionality to display templates. This allows the user to visually compare measurement data with typical types of NGC WAXS curves which are presented graphically around the measurement data. The authors believe that this program will provide a useful tool for scientists dealing with the characterization of NGCs.

The First 20 Hours of Geopolymerization: An in Situ WAXS Study of Flyash-Based Geopolymers

This study followed the first 20 h of flyash geopolymerization at 70 °C using time resolved Wide Angle X-ray Scattering (WAXS). The extent of dissolution of the amorphous phase of the flyash was determined to range from 29% to 54% for the different formulations trialed. The dissolution rate of the flyash significantly reduced after the first 5 h for all samples. During the formation stage of the geopolymer there were significant temporal variations in the chemistry of the dissolved solution due to the rate of flyash dissolution, with a relative standard deviation of 20%, 57% and 24% for the Si/Al, Na/Al and H/Si ratios, respectively. Utilizing the Power Law, scattering in the low angle region of the WAXS pattern combined with the geopolymer peak area yielded a measure which correlated with the compressive strength—providing a new method to measure the flyash dissolution and geopolymer formation processes independently. The evolution of several zeolite-like phases was followed, noting there are different formation mechanisms involved even within the same sample. Four samples were examined with compressive strengths ranging from 14(2)–50(9) MPa, each was synthesized with flyash from Collie Power Station (Western Australia) activated with sodium silicate solution of varying concentrations.

Structural Characterization of Lecithin-Stabilized Tetracosane Lipid Nanoparticles. Part II: Suspensions.

Using photon correlation spectroscopy, transmission electron microscopy, microcalorimetry, wide-angle X-ray scattering (WAXS), and small-angle X-ray and neutron scattering (SAXS, SANS), the structure of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-stabilized colloidal tetracosane suspensions was studied from the molecular level to the microscopic scale as a function of the temperature. The platelike nanocrystals exhibit for tetracosane an unusual orthorhombic low-temperature crystal structure. The corresponding WAXS pattern can be reproduced with a predicted orthorhombic unit cell (space group Pca21), which usually occurs only for much longer even-numbered n-alkanes. Special emphasis was placed on the structure of the DMPC stabilizer layer covering the nanocrystals. Their structure was investigated by SAXS and SANS, using suspensions with different neutron scattering contrasts. As for the emulsions in Part I , the crystallized nanoparticles are covered by a DMPC monolayer. Their significant smaller thickness of 10.5 Å (for the emulsions in Part I : 16 Å) could be related to a more tilted orientation of the DMPC molecules to cover the expanded surface of the crystallized nanoparticles.

Modulation of HIV protease flexibility by the T80N mutation.

The flexibility of HIV protease (HIVp) plays a critical role in enabling enzymatic activity and is required for substrate access to the active site. While the importance of flexibility in the flaps that cover the active site is well known, flexibility in other parts of the enzyme is also critical for function. One key region is a loop containing Thr 80, which forms the walls of the active site. Although not situated within the active site, amino acid Thr80 is absolutely conserved. The mutation T80N preserves the structure of the enzyme but catalytic activity is completely lost. To investigate the potential influence of the T80N mutation on HIVp flexibility, wide-angle X-ray scattering (WAXS) data was measured for a series of HIVp variants. Starting with a calculated WAXS pattern from a rigid atomic model, the modulations in the intensity distribution caused by structural fluctuations in the protein were predicted by simple analytic methods and compared with the experimental data. An analysis of T80N WAXS data shows that this variant is significantly more rigid than the WT across all length scales. The effects of this single point mutation extend throughout the protein, to alter the mobility of amino acids in the enzymatic core. These results support the contentions that significant protein flexibility extends throughout HIVp and is critical to catalytic function.

Solid phase helical and crystal structures of poly(phenylacetylene)s with para-oligo ethylene oxy methylether moieties prepared with an organorhodium catalyst in ethanol

The stereoregular polymerization of phenylacetylenes with a para-(ethylene oxide)-methylether: p-O(CH2CH2O)mCH3 (m=1 and 2) using a [Rh(norbornadine)Cl]2 – triethylamine catalyst was performed at 25°C for 0.5h to afford the corresponding helical bright-yellow and dark-violet polymers, P1Y and P2V, respectively. The diffuse reflective UV–vis spectra of P1Y exhibited a λmax at 470nm, unlike the broad peak of P2V. The wide angle X-ray scattering (WAXS) pattern of P1Y was assigned to the columnar hexagonal crystals (CHC)s on which the stretched cis–transoid helices of P1Y are packed. The bent position of the 2CO bond in p-O1CH22CH2O3CH3 was deduced from these crystals. In contrast, the WAXS pattern of P2V demonstrated the formation of a CHC with contracted cis–cisoid helices. The small peak at d=3.4Å for P2V was assigned to a π-stacking between each benzene ring and/or helical backbone. Their stable geometrical structures, helical diameters, and bent position calculated using the MMFF94 program agreed with those estimated using WAXS.

Lamellar cluster structure formation resulting from interchain interaction in a novel aromatic polyimide based on PMDA monomer

The aggregation structure of a novel polyimide (PIM-6) with six methylene flexible spacing groups in biphenyl side chain synthesized by the traditional two-step imidisation process was investigated by polarized light microscope (PLM), small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), and molecular simulation approach. The agreement between the experimental data and simulation result reveals that due to the predominant interchain interaction, each three backbones stack together to form a distinct lamellar cluster with side chains packed inside dispersedly. The thickness of the lamellar cluster is about 16.0 A°, corresponding to a strong peak at 5.5° in SAXS pattern. As the backbone is not perfectly parallel to each other in each lamellar cluster, the distance between each backbone ranges from 5.8 to 8.8 A° possibly relating to the weak peak at 9.8° in WAXS pattern. Meanwhile, no birefringence or apparent phase texture has been observed by PLM indicating an amorphous nature in this film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Crystalline β‐structure of PHBV grown epitaxially on silicate layers of MMT

AbstractThe poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/montmorillonite(MMT) nanocomposites were investigated by wide‐angle X‐ray scattering (WAXS). The aim of the investigation was solution intercalation of MMT with PHBV. Beside the usual orthorhombic unit cell, a stable pseudohexagonal β‐structure of PHBV was obtained. Well known β‐structure has one common WAXS reflection (d = 0.480 nm), which corresponds to the mean distance of PHBV chains in the pseudohexagonal structure. The new β‐structure has two diffraction peaks in the WAXS pattern. It is a three‐dimensionally ordered crystalline structure oriented in parallel with the silica layers of MMT. The new polymorphic form is supposed to be growing on the layers of MMT. Its layers serve as primary nucleation centers for epitaxial growth of the β‐structure. After annealing, this polymorphic form of PHBV disappears and it is transformed into the more stable α‐form leading to an enhanced total crystallinity of the polymer comprised in the nanocomposite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 751–755, 2009

Order Parameters and Areas in Fluid-Phase Oriented Lipid Membranes Using Wide Angle X-Ray Scattering

We used wide angle x-ray scattering (WAXS) from stacks of oriented lipid bilayers to measure chain orientational order parameters and lipid areas in model membranes consisting of mixtures of 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC)/cholesterol and 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC)/cholesterol in fluid phases. The addition of 40% cholesterol to either DOPC or DPPC changes the WAXS pattern due to an increase in acyl chain orientational order, which is one of the main properties distinguishing the cholesterol-rich liquid-ordered (Lo) phase from the liquid-disordered (Ld) phase. In contrast, powder x-ray data from multilamellar vesicles does not yield information about orientational order, and the scattering from the Lo and Ld phases looks similar. An analytical model to describe the relationship between the chain orientational distribution and WAXS data was used to obtain an average orientational order parameter, S x-ray. When 40% cholesterol is added to either DOPC or DPPC, S x-ray more than doubles, consistent with previous NMR order parameter measurements. By combining information about the average chain orientation with the chain-chain correlation spacing, we extended a commonly used method for calculating areas for gel-phase lipids to fluid-phase lipids and obtained agreement to within 5% of literature values.

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.

Processing of mica/epoxy nanocomposites by ultrasound mixing

AbstractRubbery mica/epoxy nanocomposites are synthetized by in situ polymerization, and their morphology, mechanical, and viscoelastic properties were investigated by wide angle X‐ray scattering (WAXS), transmission electron microscopy (TEM), tensile testing, and dynamic mechanical thermal analysis (DMTA). Ultrasonicator was used as a means of applying external shearing forces to disperse the silicate clay layers in the epoxy matrix. The first step of the nanocomposite preparation consisted of swelling the mica in a curing agent, i.e., aliphatic diamine based on polyoxypropylene backbone having a low viscosity for better diffusion into the intragalleries. Then, the epoxy prepolymer was added into the mixture. It was expected to have better dispersion and intercalation of the nanoclay in the matrix. The study showed that the organomodification of mica with octadecylammonium ions leads to an increase in the initial d‐spacing ([d001] peak) from 12.3 to 28.1 Å, determined by WAXS, indicating the occurrence of an intercalation. The addition of 5 per hundred resin (phr) of MICAC18 into the epoxy matrix resulted in finer dispersion as evidenced by both the disappearance of the diffraction peak in the WAXS pattern and TEM images. The mechanical and viscoelastic properties were improved for both MICA and MICAC18 nanocomposites, however, more pronounced for the modified ones. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Morphology and mechanical and viscoelastic properties of rubbery epoxy/organoclay montmorillonite nanocomposites

AbstractThe morphology and mechanical and viscoelastic properties of rubbery epoxy/organoclay montmorillonite (MMT) nanocomposites were investigated with wide‐angle X‐ray scattering (WAXS), transmission electron microscopy (TEM), tensile testing, and dynamic mechanical thermal analysis. An ultrasonicator was used to apply external shearing forces to disperse the silicate clay layers in the epoxy matrix. The first step of the nanocomposite preparation consisted of swelling MMT in a curing agent, that is, an aliphatic diamine based on a polyoxypropylene backbone with a low viscosity for better diffusion into the intragalleries. Then, the epoxy prepolymer was added to the mixture. Better dispersion and intercalation of the nanoclay in the matrix were expected. The organic modification of MMT with octadecylammonium ions led to an increase in the initial d‐spacing (the [d001] peak) from 14.4 to 28.5 Å, as determined by WAXS; this indicated the occurrence of an intercalation. The addition of 5 phr MMTC18 (MMT after the modification) to the epoxy matrix resulted in a finer dispersion, as evidenced by the disappearance of the diffraction peak in the WAXS pattern and TEM images. The mechanical and viscoelastic properties were improved for both MMT and MMTC18 nanocomposites, but they were more pronounced for the modified ones. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 103: 3547–3552, 2007

Calculation of mesophase percentage of polymer fibers from 2D wide-angle X-ray scattering patterns

A computational method is developed to evaluate the relative amount of mesophase of polymer fibers from their two-dimensional (2D) wide-angle X-ray scattering (WAXS) patterns. This is achieved by first evaluating the percentage of oriented phases (POPs) from a 2D WAXS pattern. If there exists a crystalline phase, crystallinity is subtracted from the POPs to obtain the mesophase percentage. If no crystalline phase is observed from a WAXS pattern, the POPs is the mesophase percentage. To increase the computation accuracy, a center search algorithm is developed and a Fourier filter is adapted to perform data smoothing. The Bresenham midpoint circle algorithm is applied to accelerate the computation. This method is applied to compute the mesophase percentages of poly(trimethylene terephthalate) (PTT) fibers of take-up speeds ranging from 970 to 4185 m/min. Our results indicate that the mesophase percentage increases with take-up speeds up to 2550 m/min. With further increase in take-up speeds, the mesophase percentage begins to drop. This is because the mesophase is precursory to the crystalline phase and is depleted by the formation of the crystalline phase during spin-line stress-induced crystallization in the take-up speed range of 3050 to 4185 m/min. This finding is consistent with results on PET fibers.

Thermal stabilization of polyacrylonitrile fibres

A polyacrylonitrile (PAN) fibre, Dralon T (DT), and a copolymer manufactured as a carbon fibre precursor, Special Acrylic Fibre (SAF), were studied as received and after heat-treatment in air at various temperatures up to 300°C. Wide angle X-ray scattering (WAXS) was undertaken on single fibres, fibre bundles and films, utilizing both conventional and synchrotron sources. With a conventional source, the normal WAXS pattern was observed for both polymers, i.e. two main equatorial reflections, a diffuse equatorial reflection and a diffuse off-equatorial reflection. With a synchrotron source, seven equatorial WAXS reflections could be detected in DT. Also, a sharp, meridional reflection was observed in SAF as received and in DT after stretching at 100°C. Unpolarized and polarized infra-red spectra were obtained from single fibres and films by FTIR microscopy. A measure of the extent of reaction (EOR) following heat-treatment was derived from the intensity of the nitrile absorption and the intensity of absorption at 1600 cm −1: EOR=[ I 1600/( I CN+ I 1600)]. Two complementary measures of orientation were used to follow changes on heat-treatment: the peak width at half-height of an azimuthal plot of the most intense WAXS reflection and the nitrile dichroic ratio from FTIR microscopy. For fibres held under tension during heat-treatment, the degree of orientation by either measure did not decrease until the EOR exceeded 0.5. Solid-state 13C NMR, together with IR results, indicated that at least three chemical processes occurred on heat-treatment: nitrile reaction, conjugated C=C formation and oxidation.

Influence of glass bead fillers on phase transitions of syndiotactic polypropene

The influence of glass beads on the phase transition of syndiotactic polypropene has been investigated. The glass transition at 4°C, detected by means of dynamic mechanical analysis, and multiple melt behaviour, detected by means of differential scanning calorimetry (DSC), does not depend upon the presence of glass bead fillers. However, dynamic mechanical analysis shows an unexpected phase transition at 55°C. This transition, which is not found for neat syndiotactic polypropene, can be also detected by DSC and pressure–volume–temperature (PVT) measurements. The signal detected by PVT appears at higher temperatures, due to higher pressure during measurement. Wide angle X-ray scattering (WAXS) measurements reveal that neat syndiotactic polypropene crystallizes in unit cell II, whereas glass bead-filled syndiotactic polypropene crystallizes in unit cells I and II. Glass bead-filled syndiotactic polypropene, heated up above 60°C, shows a WAXS pattern corresponding to unit cell II. From these results, it can be concluded, that glass beads can nucleate the formation of unit cell type I, which transforms into unit cell type II upon heating at 55°C.

Magnetic Field Orientation of Liquid Crystalline Epoxy Thermosets.

The effect of magnetic fields on the orientation and properties of 4,4'-bis(2,3-epoxypropoxy)-alpha-methylstilbene cured with sulfanilamide has been studied. This epoxy system is initially isotropic and forms a smectic A phase upon curing. A magnetic field was applied during the cure reaction, resulting in alignment of the molecules along the direction of the applied field. Measurement of the orientation parameter of the fully cured material by wide-angle X-ray scattering (WAXS) showed that orientation improved with an increase in field strength. The orientation parameters of the smectic layer normals calculated from the inner reflection of the WAXS pattern attained a maximum level of approximately 0.8 at a field strength of approximately 12 T. The orientation parameters calculated from the outer reflection of the WAXS pattern were considerably lower, possibly due to the presence of amorphous regions associated with domain boundaries or the loss of molecular alignment within the smectic layers due to topological restrictions of the cross-linking sites. Orientation resulted in an anisotropic linear thermal expansion coefficient after curing, although the overall volumetric expansion was constant. The elastic tensile modulus increased with the square of the orientation parameter, attaining a maximum value of 8.1 GPa, compared to 3.1 GPa for the unoriented material. The change in modulus with orientation could be fit with a simple model for the modulus of anisotropic materials.

The Use of Small-Angle Light-Scattering (SALS) to Examine the Structure of Fibers 1

The small-angle light-scattering (SALS) patterns of a wide range of polypropylene, nylon 6, and polyethylene ter ephthalate (PET) fibers have been examined so as to investigate the level of superstructural (>500 nm) ordering present within them. Many samples that were highly-disordered at a microstructural level, as evidenced by their wide-angle x-ray scattering (WAXS) patterns, showed evidence of extensive superstructural ordering. For example, a rapidly- quenched polypropylene fiber, which exhibited a "smectic" WAXS pattern, had a SALS pattern characteristic of spheru lites about 6 μm in diameter. Brief annealing of this sample produced the conventional monoclinic polypropylene WAXS pattern but did not noticeably change the size or shape of the SALS pattern. The usefulness and limitations of SALS for examining sheath-core effects and for demonstrating the existence of distorted spherulites is also discussed.

On the source of X‐ray small angle scattering in rubbers vulcanized with methacrylic acid salts

AbstractStyrene‐butadiene rubber (SBR) is mixed with zinc methacrylate (ZnM) powder SBR: ZnM = 5:1 by weight. Wide angle X‐ray diffraction proves that the ZnM crystallites are larger than 240Å. The pure SBR and the SBR‐ZnM mixture exhibit the same small angle X‐ray pattern, indicating particle sizes for SBR and ZnM beyond the resolving power. After annealing the SBR‐ZnM mixture for 30min at 155°C a weak small angle X‐ray scattering (SAXS) pattern appears which indicates particles of 160Å diameter with a polydispersity of gy = 0,2. The same particle size is found from wide angle X‐ray scattering (WAXS) which proves that these particles are ZnM microcrystals and split from the larger crystals. Heating the mixture SBR‐ZnM (100 parts by weight) with 0,8 parts by weight dicumylperoxide, (bis(1‐methyl‐1‐phenylethyl)peroxide) for 30min at 155°C gives rise to a seven times stronger WAXS pattern with the same particle dimension 160Å and polydispersity gy = 0,2. The particle scattering is superimposed by a paracrystalline interference which indicates that the ZnM particles have a mean distance of 250Å and hence are homogeneously spread over the SBR matrix. The ZnM particles have lost their innercrystalline structure, since the WAXS reflection has become very diffuse. Striking similarities to the graft copolymerization of styrene on polyethylene are discussed.