SIMULTANEOUS SAXS／WAXS／DSC STUDIES ON MICROSTRUCTURE OF CONVENTIONAL AND METALLOCENE-BASED ETHYLENE-BUTENE COPOLYMERS

The fractions of one metallocene-based (mPE) and one conventional (znPE) ethylene-butene copolymer eluted at 80-82℃ from temperature rising elution fractionation were selected for DSC and time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) characterization. The DSC and WAXS results show that two crystal structures exist in both mPE and znPE: structure A with higher melting temperature and structure B with lower melting temperature. It was found that original znPE (s-znPE) contains more highly ordered structure A than original mPE (s-mPE) in spite of the higher comonomer content of znPE. Another structure C is also identified because of higher crystallinity measured by WAXS than by DSC and is attributed to the interfacial region. The SAXS data were analyzed with correlation function and two maxima were observed in s-mPE and s-znPE, in agreement with the conclusion of two crystal populations drawn from DSC and WAXS results. These two crystal populatiorts have close long periods in s-mPE, but very different long periods in s-znPE. In contrast, freshly crystallized mPE and znPE (f-mPE and f-znPE) contain only a single crystal population with a broader distribution of long period     

In situ SAXS/WAXS of zeolite microwave synthesis: NaY, NaA, and beta zeolites.

A custom waveguide apparatus is constructed to study the microwave synthesis of zeolites by in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The WR-284 waveguide is used to heat precursor solutions using microwaves at a frequency of 2.45 GHz. The reaction vessels are designed to include sections of thin-walled glass, which permit X-rays to pass through the precursor solutions with minimal attenuation. Slots were machined into the waveguide to provide windows for X-ray energy to enter and scatter from solutions during microwave heating. The synthesis of zeolites with conventional heating is also studied using X-ray scattering in the same reactor. SAXS studies show that the crystallization of beta zeolite and NaY zeolite is preceded by a reorganization of nanosized particles in their precursor solutions or gels. The evolution of these particles during the nucleation and crystallization stages of zeolite formation depends on the properties of the precursor solution. The synthesis of NaA and NaX zeolites and sodalite from a single zeolite precursor is studied by microwave and conventional heating. Microwave heating shifts the selectivity of this synthesis in favor of NaA and NaX over sodalite; conventional heating leads to the formation of sodalite for synthesis from the same precursor. The use of microwave heating also led to a more rapid onset of NaA zeolite product crystallization compared to conventional heating. Pulsed and continuous microwave heating are compared for zeolite synthesis. The resulting rates of formation of the zeolite products, and the relative amounts of the products determined from the WAXS spectra, are similar when either pulsed or continuous microwave heating is applied in the reactor while maintaining the same synthesis temperature. The consequences of these results in terms of zeolite synthesis are discussed.     

利用小角/广角X射线散射联用及一维相关函数分析研究聚(ε-己内酯)片晶的形态

用小角/广角X射线散射(SAXS/WAXS)联用的实验方法考察了等温结晶温度(Tc)和等温时间对聚(ε-己内酯)(PCL)片晶形态的影响.根据WAXS数据计算了PCL的重量结晶度,进而求得其体积结晶度Vc(WAXS).在不同Tc下结晶的PCL样品的Vc(WAXS)均略高于50%.对SAXS谱线做一维相关函数(1DCF)分析,得到了PCL的片晶长周期(LP)和无定形层厚度(La).通过比较WAXS及SAXS的数据分析结果,认为PCL晶体需用"三相模型"予以描述,其过渡层厚度(E)约为LP的15%～18%,对片晶形态具有重要影响.随着Tc升高,PCL晶体的Lc、La及E均逐渐增大,但Lc的变化率最大,这使得结晶度上升.在50℃等温结晶不同时间,发现Lc随延长时间显著增加,而La及E则不断减小.等温10天后,PCL晶体的SAXS谱线上可观察到5级散射,表明片晶相当完善.     

Kinetics of fiber heat treatment. III Poly(butylene terephthalate) fibers

Small- and wide-angle X-ray scattering (SAXS and WAXS), shrinkage, and density experiments were performed on poly(butylene terephthalate) fibers which had been isothermally crystallized at different temperatures, and at constant tension, for times ranging from 100 to 1050 ms. A consistent correlation among WAXS, SAXS, and the kinetic results is demonstrated. Shrinkage results show that the crystallization process prevails over the chain-re-coiling process. Density measurements show that the rate of crystallization increases with temperature. Pinhole X-ray photos show that the orientation of the chains within the crystals remains constant with time and temperature. WAXS diffractometer scans show the development of wide-angle Bragg peaks. SAXS shows the development of small-angle Bragg peaks, as the annealing time is increased. The two-lobe arced pattern is the characteristic pattern. The value for long spacing ranged from 100 to 120 Å, increasing with temperature.     

X-ray study of microstructure of slightly plasticized poly-(vinylchloride) (PVC)

Small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) as well as transmission electron microscopy (TEM) techniques have been applied to investigate the microstructure of a number of commercial poly-(vinylchloride) (PVC) samples, stretched 200% and annealed for 1 h at 110 °C. From SAXS analysis, the microstructure is described as an ensemble of quasi-spherical particles one-dimensionally ordered (in the fiber axis direction) and with large distance fluctuations in the equatorial plane. The superstructure is described as fibrillar or nematic-like. TEM micrographs confirm the SAXS data.SAXS meridional patterns present 001 and 003 reflections of Ca-stearate added as stabilizer to the samples, while WAXS profiles do not show any crystalline reflection of Castearate.An interaction of Ca-stearate molecules with PVC chains is postulated, which could partially account for the phenomenon called antiplasticization of PVC.     

Kinetics of fiber heat treatment. II. Poly(ethylene terephthalate) fibers

Microstructural changes occurring during the process of crystallization in as-spun poly(ethylene terephthalate) (PET) have been monitored using wide- and small-angle X-ray scattering, optical birefringence, shrinkage measurements, and specific gravity. Shrinkage and birefringence results show a competition between two processes: chain re-coiling on the one hand and crystallization on the other hand. A consistent correlation among WAXS, SAXS, shrinkage, and birefringence results is demonstrated. SAXS data show a fibrillar morphology. On the basis of WAXS results, the crystallization is envisioned as a two stage process: first, the formation of defective fibrils, and then the formation of more perfect crystals. WAXS results also demonstrate a remelting phenomenon in samples which have experienced positive shrinking.     

The short-lived signaling state of the photoactive yellow protein photoreceptor revealed by combined structural probes

The signaling state of the photoactive yellow protein (PYP) photoreceptor is transiently developed via isomerization of its blue-light-absorbing chromophore. The associated structural rearrangements have large amplitude but, due to its transient nature and chemical exchange reactions that complicate NMR detection, its accurate three-dimensional structure in solution has been elusive. Here we report on direct structural observation of the transient signaling state by combining double electron electron resonance spectroscopy (DEER), NMR, and time-resolved pump-probe X-ray solution scattering (TR-SAXS/WAXS). Measurement of distance distributions for doubly spin-labeled photoreceptor constructs using DEER spectroscopy suggests that the signaling state is well ordered and shows that interspin-label distances change reversibly up to 19 ? upon illumination. The SAXS/WAXS difference signal for the signaling state relative to the ground state indicates the transient formation of an ordered and rearranged conformation, which has an increased radius of gyration, an increased maximum dimension, and a reduced excluded volume. Dynamical annealing calculations using the DEER derived long-range distance restraints in combination with short-range distance information from (1)H-(15)N HSQC perturbation spectroscopy give strong indication for a rearrangement that places part of the N-terminal domain in contact with the exposed chromophore binding cleft while the terminal residues extend away from the core. Time-resolved global structural information from pump-probe TR-SAXS/WAXS data supports this conformation and allows subsequent structural refinement that includes the combined energy terms from DEER, NMR, and SAXS/WAXS together. The resulting ensemble simultaneously satisfies all restraints, and the inclusion of TR-SAXS/WAXS effectively reduces the uncertainty arising from the possible spin-label orientations. The observations are essentially compatible with reduced folding of the I(2)' state (also referred to as the 'pB' state) that is widely reported, but indicates it to be relatively ordered and rearranged. Furthermore, there is direct evidence for the repositioning of the N-terminal region in the I(2)' state, which is structurally modeled by dynamical annealing and refinement calculations.     

Rapid internal bubble formation in a microwave heated polymer observed in real-time by X-ray scattering

A combined study of small-angle and wide-angle X-ray scattering (SAXS/WAXS) of the melting of a nylon-6 sample by localized microwave radiation has shown that this method can reveal the presence of bubbles forming and disappearing rapidly in real time in the interior of the sample due to its thermal decomposition.     

Improved fitting of solution X-ray scattering data to macromolecular structures and structural ensembles by explicit water modeling

A new procedure, AXES, is introduced for fitting small-angle X-ray scattering (SAXS) data to macromolecular structures and ensembles of structures. By using explicit water models to account for the effect of solvent, and by restricting the adjustable fitting parameters to those that dominate experimental uncertainties, including sample/buffer rescaling, detector dark current, and, within a narrow range, hydration layer density, superior fits between experimental high resolution structures and SAXS data are obtained. AXES results are found to be more discriminating than standard Crysol fitting of SAXS data when evaluating poorly or incorrectly modeled protein structures. AXES results for ensembles of structures previously generated for ubiquitin show improved fits over fitting of the individual members of these ensembles, indicating these ensembles capture the dynamic behavior of proteins in solution.     

Physicochemical investigation of a lipid with a new core structure for gene transfection: 2-amino-3-hexadecyloxy-2-(hexadecyloxymethyl)propan-1-ol

Cationic liposomes/DNA complexes can be used as nonviral vectors for direct delivery of DNA-based biopharmaceuticals to damaged cells and tissues. In order to obtain more effective and safer liposome-based gene transfection systems, the new cationic lipid 2-amino-3-hexadecyloxy-2-(hexadecyloxymethyl)propan-1-ol (AHHP) was synthesized. In this paper we report on the synthesis of AHHP and investigations of its physical-chemical properties. Langmuir monolayers of AHHP were studied at the air/buffer interface by film balance measurements, grazing incidence X-ray diffraction (GIXD), and infrared reflection absorption spectroscopy (IRRAS). Structure and thermotropic phase behavior of AHHP in aqueous dispersion were examined by small-angle and wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). The results show clear differences in structure and phase behavior of AHHP, both in the monolayer system and in aqueous dispersions, in dependence on the subphase pH due to protonation or deprotonation of the primary amine in the lipid head group. Thermodynamic data derived from pi-A isotherms provide information about the critical temperature (Tc), which is in rough agreement with the temperature of the lipid phase transition from gel to fluid state (Tm) found by X-ray and calorimetry studies of AHHP aqueous dispersions. The packing properties of the molecules in mono- and bilayer systems are very similar. DNA couples to the monolayer of the new lipid at low as well as at high pH but in different amounts. The DNA coupling leads to an alignment of adsorbed DNA strands indicated by the appearance of a Bragg peak. The distance between aligned DNA strands does not change much with increasing monolayer pressure.     

Effects of processing on the structure of zein/oleic Acid films investigated by x-ray diffraction

Zein films plasticized with oleic acid were formed by solution casting, by the stretching of moldable resins, and by blown film extrusion. The effects of the forming process on film structure were investigated by X-ray diffraction. Wide-angle X-ray scattering (WAXS) patterns showed d-spacings at 4.5 and 10 A, which were attributed to the zein alpha-helix backbone and inter-helix packing, respectively. The 4.5 A d-spacing remained stable under processing while the 10 A d-spacing varied with processing treatment. Small-angle X-ray scattering (SAXS) detected a long-range periodicity for the formed films but not for unprocessed zein, which suggests that the forming process-promoted film structure development is possibly aided by oleic acid. The SAXS d-spacing varied among the samples (130-238 A) according to zein origin and film-forming method. X-ray scattering data suggest that the zein molecular structure resists processing but the zein supramolecular arrangements in the formed films are dependent on processing methods. Structural model for a zein molecular aggregate (based on Matsushima et al.10). Rectangular prisms of individual zein molecules are hexagonally aligned parallel to each other.     

Microfibril diameter in celery collenchyma cellulose: X-ray scattering and NMR evidence

Cellulose isolated from celery collenchyma is typical of the low-crystallinity celluloses that can be isolated from primary cell-walls of higher plants, except that it is oriented with high uniformity. The diameter of the microfibrils of celery collenchyma cellulose was estimated by three separate approaches: ¹³C NMR measurement of the ratio of surface to interior chains; estimation of the dimensions of the crystalline lattice from wide angle X-ray scattering (WAXS) measurements using the Scherrer equation; and the observation that microfibrils of this form of cellulose have the unusual property of packing into an irregular array from which small angle X-ray scattering (SAXS) shows features of both form and interference functions. The interference function contributing to the SAXS pattern implied a mean microfibril centre-to-centre distance of 3.6 nm, providing an upper limit for the diameter. However modelling of the scattering pattern from an irregular array of microfibrils showed that the observed scattering curve could be matched at a range of diameters down to 2.4 nm, with the intervening space more or less sparsely occupied by hemicellulose chains. The lateral extent of the crystalline lattice normal to the 200 plane was estimated as a minimum of 2.4 nm by WAXS through the Scherrer equation, and a diameter of 2.6 nm was implied by the surface: volume ratio determined by ¹³C NMR. The WAXS and NMR measurements both depended on the assumption that the surface chains were positioned within an extension of the crystalline lattice. The reliability of this assumption is uncertain. If the surface chains deviated from the lattice, both the WAXS and the NMR data would imply larger microfibril diameters within the range consistent with the SAXS pattern. The evidence presented is therefore all consistent with microfibril diameters from about 2.4 to 3.6 nm, larger than has previously been suggested for primary-wall cellulose. Some degree of aggregation may have occurred during the isolation of the cellulose, but the larger microfibril diameters within the range proposed are a consequence of the novel interpretation of the experimental data from WAXS and NMR and are consistent with previously published data if these are similarly interpreted.     

Comparative structural analysis of a histone-like protein from Spiroplasma melliferum in the crystalline state and in solution

A solution of a histone-like protein from Spiroplasma melliferum (HUSpm) was examined by small-angle X-ray scattering (SAXS). The experimental SAXS curve was compared with those calculated for the HUSpm structures from the PDB databank obtained by both X-ray diffraction analysis and nuclear magnetic resonance spectroscopy. The model of the HUSpm structure in solution, which best agrees with the experimental SAXS data, has a shorter distance between the centers of mass of the HUSpm monomers compared to the crystal structure, indicating that the HUSpm monomers can be located closer to each other in solution than in the crystalline state.     

In situ observation of homogeneous nucleation of nanosized zeolite A

The formation of zeolite A (LTA) in the presence of tetramethylammonium cations is studied using in situ small angle and wide angle X-ray scattering (SAXS/WAXS) techniques. The SAXS measurements show the formation of homogeneous precursors 10 nm in size prior to the crystallization of LTA which were consumed during the crystallization. The crystal size is estimated by fitting the SAXS patterns with an equation for a cubic particle, and it is revealed that the final crystal size of the LTA depends on the synthesis temperature. However, although such temperature dependence is noted for the final crystal size, the initial precursor particles size appears to be closely similar (ca. 10 nm) irrespective of the synthesis temperature.     

Watching nanoparticles form: an in situ (small-/wide-angle X-ray scattering/total scattering) study of the growth of yttria-stabilised zirconia in supercritical fluids

Understanding nanoparticle-formation reactions requires multi-technique in situ characterisation, since no single characterisation technique provides adequate information. Here, the first combined small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering (WAXS)/total-scattering study of nanoparticle formation is presented. We report on the formation and growth of yttria-stabilised zirconia (YSZ) under the extreme conditions of supercritical methanol for particles with Y(2)O(3) equivalent molar fractions of 0, 4, 8, 12 and 25 %. Simultaneous in situ SAXS and WAXS reveals a quick formation (seconds) of sub-nanometre amorphous material forming larger agglomerates with subsequent slow crystallisation (minutes) into nanocrystallites. The amount of yttria dopant is shown to strongly affect the crystallite size and unit-cell dimensions. At yttria-doping levels larger than 8 %, which is known to be the stoichiometry with maximum ionic conductivity, the strain on the crystal lattice is significantly increased. Time-resolved nanoparticle size distributions are calculated based on whole-powder-pattern modelling of the WAXS data, which reveals that concurrent with increasing average particle sizes, a broadening of the particle-size distributions occur. In situ total scattering provides structural insight into the sub-nanometre amorphous phase prior to crystallite growth, and the data reveal an atomic rearrangement from six-coordinated zirconium atoms in the initial amorphous clusters to eight-coordinated zirconia atoms in stable crystallites. Representative samples prepared ex situ and investigated by transmission electron microscopy confirm a transformation from an amorphous material to crystalline nanoparticles upon increased synthesis duration.     

Phase transitions in poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate). SAXS,WAXS and DSC study

The main-chain thermotropic liquid-crystalline poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate) (P7MB) was investigated by time-resolved small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and differential scanning calorimerty (DSC). Nonisothermal crystallisation with different rates of cooling and heating was used. On cooling, two phase transitions are observed, isotropic melt - smectic (I-Sm) and Sm- three-dimensional crystalline structure (Sm-Cr), whereas on heating only one transition is observed, Cr-I transition. The transition enthalpies were calculated. Temperature dependences of d-spacings of all crystalline peaks and of the peak observed at high values of scattering vector in the SAXS region were derived. The temperature dependence of the degree of crystallinity was established, based on the integrated intensities of the crystalline peaks and amorphous halo in WAXS.     

Early oriented isothermal crystallization of polyethylene studied by high-time-resolution SAXS/WAXS

During cooling from the quiescent melt of a highly oriented polyethylene rod, highly oriented proto-lamellae are formed first, which are not crystalline. This is shown in scattering data which are recorded on two-dimensional detectors with a cycle time of 1 s and an exposure of 0.1 s. In the experiments small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) are registered simultaneously during the first 3 min after quenching to a crystallization temperature. A non-uniform thickness between 20 and 100 nm is characteristic for the ensemble of proto-lamellae. During the first minute of isothermal treatment the number of proto-lamellae slowly increases without a change of the thickness distribution. As crystallization starts, the crystallites are not oriented in contrast to the proto-lamellae. During crystallization the layer thickness distribution narrows. The number of lamellae rapidly increases during the following 2 min of isothermal treatment (at 128 °C and 124 °C). The results are obtained by interpretation of the WAXS and of the multidimensional chord distribution function (CDF), a model-free real-space visualization of the nanostructure information contained in the SAXS data. Dedicated to Prof. Dr. F. J. Baltá Calleja on the occasion of his 70th birthday.     

Probing the structure of the crystalline core of field-aligned, monodisperse, cylindrical polyisoprene-block-polyferrocenylsilane micelles in solution using synchrotron small- and wide-angle X-ray scattering

The self-assembly of block copolymers in selective solvents represents a powerful approach to functional core-shell nanoparticles. Crystallization of the core can play a critical role in directing self-assembly toward desirable, nonspherical morphologies with low mean interfacial curvature. Moreover, epitaxial growth processes have been implicated in recent advances that permit access to monodisperse cylinders, cylindrical block comicelles with segmented cores and/or coronas, and complex hierarchical architectures. However, how the core-forming block crystallizes in an inherently curved nanoscopic environment has not been resolved. Herein we report the results of synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) studies of well-defined, monodisperse crystalline-coil polyisoprene-block-polyferrocenylsilane cylindrical micelles aligned in an electric field. WAXS studies of the aligned cylinders have provided key structural information on the nature of the PFS micelle core together with insight into the role of polymer crystallinity in the self-assembly of these and potentially related crystalline-coil block copolymers.     

Wide and small-angle X-ray scattering study of isotactic polypropylene gamma irradiated in bulk

Gamma irradiated isotactic polypropylene (IPP) has been studied by means of wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). The skin layer has been investigated by WAXS reflection mode while the core layer underwent WAXS studies by transmission mode. β-IPP has been found solely in the skin layer. An increase in the β-phase has been observed as result of the irradiation. A phase transitions and decrease of crystallite sizes have been also observed. All of the parameters show a sharp change at a critical dose of 100 kGy. At this point the system parameters reverse. Radiation processes proceeding up to 100 kGy called radiation annealing are related to the improved crystallite perfection and thus emphasize the phase boundary. The processes provoke at higher radiation doses, up to 2000 kGy, damage in both crystal and amorphous lamellar parts. The values of the crystal and amorphous densities get closer and the process is similar to the partial radiation melting.     

Density minimum of confined water at low temperatures: a combined study by small-angle scattering of X-rays and neutrons

A simple explanation is given for the low-temperature density minimum of water confined within cylindrical pores of ordered nanoporous materials of different pore size. The experimental evidence is based on combined data from in-situ small-angle scattering of X-rays (SAXS) and neutrons (SANS), corroborated by additional wide-angle X-ray scattering (WAXS). The combined scattering data cannot be described by a homogeneous density distribution of water within the pores, as was originally suggested from SANS data alone. A two-step density model reveals a wall layer covering approximately two layers of water molecules with higher density than the residual core water in the central part of the pores. The temperature-induced changes of the scattering signal from both X-rays and neutrons are consistent with a minimum of the average water density. We show that the temperature at which this minimum occurs depends monotonically on the pore size. Therefore we attribute this minimum to a liquid-solid transition of water influenced by confinement. For water confined in the smallest pores of only 2 nm in diameter, the density minimum is explained in terms of a structural transition of the surface water layer closest to the hydrophilic pore walls.