Uniaxial deformation of overstretched polyethylene: In-situ synchrotron small angle X-ray scattering study

Synchrotron small angle X-ray scattering was used to study the deformation mechanism of high-density polyethylene that was stretched beyond the natural draw ratio. New insight into the cooperative deformational behavior being mediated via slippage of micro-fibrils was gained. The scattering data confirm on the one hand the model proposed by Peterlin on the static structure of oriented polyethylene being composed of oriented fibrils, which are built by bundles of micro-fibrils. On the other hand it was found that deformation is mediated by the slippage of the micro-fibrils and not the slippage of the fibrils. In the micro-fibrils, the polymer chains are highly oriented both in the crystalline and in the amorphous regions. When stretching beyond the natural draw ratio mainly slippage of micro-fibrils past each other takes place. The thickness of the interlamellar amorphous layers increases only slightly. The coupling force between micro-fibrils increases during stretching due to inter-microfibrillar polymer segments being stretched taut thus increasingly impeding further sliding of the micro-fibrils leading finally to slippage of the fibrils.

Structural evolution of tensile-deformed high-density polyethylene during annealing: Scanning synchrotron small-angle X-ray scattering study

The structural evolution of high-density polyethylene subjected to uniaxial tensile deformation was investigated as a function of strain and after annealing at different temperatures using a scanning synchrotron small-angle X-ray scattering (SAXS) technique. The results confirm that in the course of tensile deformation intralamellar block slips were activated at small deformations followed by a stress-induced fragmentation and recrystallization process yielding thinner lamellae with their normal parallel to the stretching direction. The original sheared lamellae underwent severe internal deformation so that they were even less stable than the newly developed thinner lamellae. Accordingly, annealing results in a melting of the original crystallites even at moderate strains where the stress-induced fragmentation and recrystallization just sets in and generates a distinctly different form of lamellar stacks aligned along the drawing direction. It was found that the lamellae newly formed during stretching at moderate strains remain stable at lower temperature. Only at a very high annealing temperature of 120 degrees C can they be melted, leading to an isotropic distribution of the lamellar structure.

Determination of degree of crystallinity of Nylon 1212 by wide-angle X-ray diffraction

Based on the X-ray scattering intensity theory and using the approximate expression for the atomic scattering factor, the correction factors for three crystalline peaks and an amorphous peak of Nylon 1212 were calculated and the formula of degree of crystallinity of Nylon 1212 was derived by a graphic multipeak resolution method. The degree of crystallinity calculated from the WARD method is compatible with those obtained by density and calorimetry methods.

Self-immobilized titanium and zirconium catalysts with phenoxy-imine ligands for ethylene polymerization. X-ray crystal structure of bis(N-(3-tert-butylsalicylidene)-4 '-allyloxyanilinato) zirconium(IV) dichloride

Four self-immobilized FI catalysts with allyl substituted phenoxy-imine ligands [{4-(CH2=CHCH2O)C6H5N=CH-C6H3(3-tert-C4H9)O}(2) MCl2] (1: M = Ti: 2: M = Zr), [{3-(CH2=CHCH2O)C6H5N=CH-C6H3(3-tert-C4H9)O}(2)MCl2] (3: M = Zr), [{4-(CH2=CHCH2-2,6-(iso-C3H7)(2))C6H5N=CH-C6H3(3,5-(NO2)(2))O}(2)MCl2] (4: M = Zr) have been synthesized and characterized. The molecular structure of 2 has been determined by X-ray crystallographic analysis. The results of ethylene polymerization showed that the self-immobilized titanium (IV) and zirconium (IV) catalysts 1-3 kept high activity for ethylene polymerization and 4 showed no activity. SEM showed the immobilization effect could greatly improve the morphology of polymer particles to afford micron-granula polyolefin as supported catalysts.

Self-immobilized metallocene catalysts bearing an allyl group for ethylene polymerization, X-ray crystal structure of [(CH2=CHCH2)CH3Si(C13H8)(2)]ZrCl2

A series of ansa-metallocene complexes with an allyl substituted silane bridge [(CH =CHCH2)CH3Si(C5H4)(2)]TiCl2 (1), [(CH2=CHCH2)CH3Si(C9H6)(2)]MCl2 [M = Ti (2), Zr (3), Hf (4)] and [(CH2=CHCH2)CH3Si(C13H8)(2)]ZrCl2 (6) have been synthesized and characterized. The molecular structure of 6 has been determined by X-ray crystallographic analysis. Complexes 1-4, 6 bearing allyl groups have been investigated as self-immobilized catalysts for ethylene polymerization in the presence of MMAO. The results showed that the self-immobilized catalysts 1-4, 6 kept high ethylene polymerization activities of ca. 10(6) g PE mol(-1) M h(-1) and high molecular weight (M-w approximate to 10(5)) of polyethylene.

Non-affine structural evolution of soft colloidal crystalline latex films under stretching as observed via synchrotron X-ray scattering

A polymer dispersion consisting of soft latex spheres with a diameter of 135 nm was used to produce a crystalline film with face-centered cubic (fcc) packing of the spheres. Different from conventional small-molecule and hardsphere colloidal crystals, the crystalline latex film in the present case is soft (i.e., easily deformable). The structural evolution of this soft colloidal latex film under stretching was investigated by in-situ synchrotron ultra-small-angle X-ray scattering. The film exhibits polycrystalline scattering behavior corresponding to fcc structure. Stretching results not only in a large deformation of the crystallographic structure but also in considerable nonaffine deformation at high draw ratios. The unexpected nonaffine deformation was attributed to slippage between rows of particles and crystalline grain boundaries. The crystalline structure remains intact even at high deformation, suggesting that directional anisotropic colloidal crystallites can be easily produced.

Photochemical synthesis, characterization and X-ray crystal structure of dodecamolybdophosphate tetrabutylammonium heteropoly blue (Bu4N)(4)[PMo12O40]center dot 2DMF center dot H2O

In this paper, we will report the preparation of a mixed-valence polyoxometalate compound (Bu4N)(4)[PMo12O40].2DMF.H2O (TBA = tetrabutylammonium; DMF = N,N-dimethyl formamide). The title compound has been photochemically synthesized and characterized by using elemental analysis, IR, solid diffusion reflectance electronic spectra, ESR spectra, XPS, CV and X-ray single-crystal analysis. The crystal lographic data are as follows: monoclinic, P2(1)/c, a = 14.124(3), b = 17.481(4), c = 22.744(5) Angstrom, beta = 101.66(3)degrees, V = 5500(2) Angstrom(3), C70H160Mo12N6O43P, M-r = 2956.29, Z = 2, D-c = 1.785 g/cm(3), F(000) = 2970 and mu(MoKalpha) = 1.412 mm(-1). The structure has been refined to R = 0.0638 and wR = 0.1975 by full-matrix least-squares methods. The title compound is composed of four tetrabutylammonium cations, one [(PMoMo11O40)-Mo-V](4-) heteropoly anion, two N,N-dimethyl formamide and one H2O molecule.

In situ study of nanostructure and morphological development during the crystal-mesophase transition of poly(di-n-hexylsilane) and poly(di-n-butylsilane) by X-ray and hot-stage AFM

Nanostructure and morphology and their development of poly(di-n-hexylsilane) (PDHS) and poly(di-n-butylsilane) (PDBS) during the crystal-mesophase transition are investigated using small angle X-ray scattering (SAXS), wide angle X-ray diffraction and hot-stage atomic force microscopy. At room temperature, PDHS consists of stacks of lamellae separated by mesophase layers, which can be well accounted using an ideal two-phase model. During the crystal-mesophase transition, obvious morphological changes are observed due to the marked changes in main chain conformation and intermolecular distances between crystalline phase and mesophase. In contrast to PDHS, the lamellae in PDBS barely show anisotropy in dimensions at room temperature. The nonperiodic structure and rather small electronic density fluctuation in PDBS lead to the much weak SAXS. The nonperiodic structure is preserved during the crystal-mesophase transition because of the similarity of main chain conformation and intermolecular distances between crystalline phase and mesophase.

Synthesis, properties and X-ray crystal structure of a new heteropolyacid supermolecular charge-transfer complex [(VB1)(2)DMFHPMo12O40 center dot 5DMF]

The title complex [(VB1)(2)DMFHPMo12O40.5DMF, VB1 = vitamin B-1 (thiamine chloride), DMF = N,N-dimethylformamide] has been synthesized and characterized by elemental analysis, IR, UV-Vis, electron spin resonance, X-ray photoelectron spectroscopy and cyclic voltammetry methods. The X-ray crystal structure revealed that there is one independent molecule in the unit cell of the title complex that contains one mixed-valence heteropolyanion, two VB1+ cations and six DMF molecules. The title complex possesses a centrosymmetrical arrangement in the unit cell, with the P atom at the symmetry center of the heteropolyanion and with eight O atoms surrounding the central P atom, such that two sets of PO4 tetrahedra are formed. The PO4 tetrahedra and MoO66-(7-) octahedra are disordered in the heteropolyanion. The bond distances of P-O-a and Mo=O-d are in the ranges 1.57 (4)-1.70 (4) Angstrom and 1.61 (2)-1.67 (2) Angstrom, respectively.

High-temperature X-ray diffraction studies on polyamide6/clay nanocomposites upon annealing

The influence of nanodispersed clay on the alpha crystalline structure of polyamide 6 (PA6) was examined in-situ with X-ray diffraction (XRD) between room temperature and melting. In pure PA6 upon annealing the alpha crystalline phase was substituted by an unstable pseudohexagonal phase at 150degreesC, then it transformed into a new stable crystalline structure - high temperature alpha' phase above the transition temperature. However, in PA6/clay nanocomposite (PA6CN), the alpha phase did not present crystalline phase transition on heating. The increase in the annealing temperature only led to continuous intensity variation. The different behaviors were caused by the confined spaces formed by silicate layers, which constrained the mobility of the polymer chains in-between.

Characterization of organic-inorganic multilayer films by cyclic voltammetry, UV-Vis spectrometry, X-ray photoelectron spectroscopy, small-angle X-ray diffraction and electrochemical impedance spectroscopy

We have employed several techniques, including cyclic voltammetry, UV-Vis spectrometry, small-angle X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy, to characterize the formation processes and interfacial features of ultrathin multilayer films of silicotungstate and a cationic redox polymer on cysteamine-coated Au electrodes self-assembled monolayers. All of these techniques confirm that the multilayer films are built up stepwise as well as uniformly in a layer-by-layer fashion. In particular, the electrochemical impedance spectroscopy is successfully used to monitor the multilayer deposition processes. It has been proved that the electrochemical impedance spectroscopy is a very useful technique in characterization of multilayer films because it provides valuable information about the interfacial impedance features.

Hydrothermal synthesis and X-ray single crystal structure of bimetallic cluster complex [{Co(phen)(2)}(2)V4O12]center dot H2O

A new bimetallic cluster complex with the formula [{Co(phen)(2)}(2)V4O12](H2O)-H-. was synthesized from the hydrothermal reaction of V2O5, H2C2O4, Co(NO3)(2), 1,10-phenanthroline (phen), (C4H9)(4)NOH and water. The compound crystallizes in an orthorhombic system with space group Pbcn and unit cell parameters a = 19.106(3) Angstrom, b = 15.250(3) Angstrom, c = 16.321(2) Angstrom, V = 4755.4(13) Angstrom(3), Z = 4 and R = 0.0318. The bimetallic cluster complex [{Co(phen)(2)}(2)V4O12](H2O)-H-. is composed of a discrete V4O124- cluster eovalently attached to two [Co(phen)(2)](2+) fragments and the discrete hexanuclear bimetallic clusters of [{Co(phen)(2)}(V4O12)-V-2](H2O)-H-. are further extended into interesting three-dimensional supermolecular arrays via pi-pi stacking interactions of phen groups. Other characterizations by elemental analysis, IR, and thermal analysis are also described.