Towards the optimization of carbon nanotube properties via <Emphasis Type="Italic">in situ</Emphasis> and <Emphasis Type="Italic">ex situ</Emphasis> studies of the growth mechanism

The synthesis conditions of multi-walled carbon nanotubes (MWCNTs) indirectly determine their application potential through the decisive role in the characteristics of individual tubes: diameter distribution, structure and defectiveness of graphene walls, the amount of metal impurities and amorphous carbon. In the present work, we have studied the influence of the catalyst composition and synthesis conditions on the diameter distribution and the structure of nanotube walls. We have observed the influence of the particle size for MWCNT synthesis (i.e. size effect) on catalytic activity by ex situ and in situ techniques: in situ X-ray diffraction on synchrotron radiation (SRXRD), gas chromatography, and ex situ transmission electron microscopy. The data obtained by in situ SRXRD are in agreement with the results collected using laboratory tubular fix-bed catalytic reactor allowing thereby extending the applicability of the approach. For the first time we have shown the increase of the fraction of graphene walls in the total MWCNT diameter with time.     

A universal blown film apparatus for <Emphasis Type="Italic">in situ</Emphasis> X-ray measurements

A setup of blown film machine combined with in situ synchrotron radiation X-ray diffraction measurements and infrared temperature testing is reported to study the structure evolution of polymers during film blowing. Two homemade auto-lifters are constructed and placed under the blown machine at each end of the beamline platform which move up and down with a speed of 0.05 mm/s bearing the 200 kg weight machine. Therefore, structure development and temperature changes as a function of position on the film bubble can be obtained. The blown film machine is customized to be conveniently installed with precise servo motors and can adjust the processing parameters in a wide range. Meanwhile, the air ring has been redesigned in order to track the structure information of the film bubble immediately after the melt being extruded out from the die exit. Polyethylene (PE) is selected as a model system to verify the feasibility of the apparatus and the in situ experimental techniques. Combining structure information provided by the WAXD and SAXS and the actual temperature obtained from the infrared probe, a full roadmap of structure development during film blowing is constructed and it is helpful to explore the molecular mechanism of structure evolution behind the film blowing processing, which is expected to lead to a better understanding of the physics in polymer processing.     

In Situ Synchrotron Radiation Techniques: Watching Deformation-induced Structural Evolutions of Polymers

Synchrotron radiation(SR) provides highly brilliant light with tunable wavelength from hard X-ray to far infrared, on which scattering, spectroscopy and imaging techniques with high time and spatial resolutions have been developed for in situ study on biological system and materials like polymer. With examples on flow-induced crystallization of polymer, deformation of nanoparticle filler network in rubber composite and necking propagation in tensile stretch, current work attempts to demonstrate the advantages of in situ synchrotron radiation X-ray scattering, X-ray nano-CT and infrared imaging in the study of deformation-induced multi-scale structural evolutions of polymers. With time resolution up to sub-ms, synchrotron radiation is expected to play a great role in understanding non-equilibrium polymer physics under processing and service conditions, while high-throughput characterization platform based on synchrotron radiation opens the possibility to establish polymer Materials Genome database in processing parameter space within reasonable time, which can serve as the roadmap for industrial polymer processing and accelerate material innovation.     

Circular dichroism of photoemission of Fe<Subscript>1/4</Subscript>TiTe<Subscript>2</Subscript>

High-resolution ARPES has been employed for examination of angular distribution of valence band photoelectrons emitted by a Fe_1/4TiTe₂ single crystal near the point Γ of the Brillouin zone in the most symmetrical directions ΓK (A-H) and ΓM (A-L) under excitation with synchrotron radiation (21.5 eV, He I) at 50 K. It has been found out that excitation with circular polarized synchrotron radiation results in essential circular dichroism in angular dependence of valence band photoemission of Fe_1/4TiTe₂. Analysis of entire experimental data has revealed that the dichroic effect is also related to the chiral geometry of the experiment. The decrease in symmetry induces dichroism, thus allowing determination of electron states at intercalant atoms.     

Using <Emphasis Type="Italic">ex situ</Emphasis> X-ray powder diffraction at synchrotron radiation to follow changes in the phase composition of perovskite-like strontium cobaltites

Precision X-ray diffraction at synchrotron radiation was used to reveal the separation of perovskite-like oxides SrCo_0.8-x Fe_0.2Nb _x O_3-z (x = 0.2 and 0.3) into two phases of a similar structure identical to initial perovskite structure, but having different unit cell parameters and supposedly different oxygen deficiency. The structural transformation is accompanied by oxygen outlet from the structure. The study of oxygen atoms intercalation from air into the oxygen-deficient structure showed that the structural changes are reversible: heating to 400°C in air restores the initial state of samples.     

X-ray spectral study of a material containing BN nanostructures

The multicomponent substance obtained by laser evaporation of the BN target under nitrogen was studied by X-ray fluorescence and X-ray absorption spectroscopy. The BK _α spectra of the substance and boroncontaining compounds rh-BN, B₂O₃, and α-B were measured on a laboratory instrument using an ethyleneglycol distearate crystal as an analytical element; X-ray absorption spectra near the boron and nitrogen K edge were recorded on a BESSY synchrotron radiation station. The contents of the components in the synthesized substance were evaluated by decomposing the BK _α spectrum into the spectra of the test boron-containing compounds. A comparison of the X-ray absorption spectra near the NK edge of the substance and rh-BN revealed that BN nanostructures obtained by laser evaporation were defective.     

Mechanistic insights into the shear effects on isotactic polypropylene crystallization containing <Emphasis Type="Italic">β</Emphasis>-nucleating agent

The crystalline structures and crystallization behaviors of iPP containing β nucleation agent TMB-5 (iPP/TMB-5) were investigated by synchrotron radiation wide angel X-ray diffraction (SR-WAXD), differential scanning calorimeter (DSC) and polarized light microscope (PLM). It was found that α-crystallization lagged behind β-crystallization at normal temperatures, but the discrepancy reduced with increasing temperature. TMB-5 could not induce β-iPP when the nucleation agent is wrapped up with α-crystal that crystallized at high temperatures. The polymorphic composition of iPP/TMB-5 was susceptible to the introductory moment of shear. New crystallization process of β-nucleated iPP was proposed to understand the experimental phenomena which could not be explained by those reported in the literature. It was supposed that polymer crystallization initiated from mesophase, and the formations of iPP crystals involved the organization of helical conformation ordering within mesophase. It was proposed that the iPP melt contained mesophases with stereocomplex-type ordering of right-handed and left-handed helical chains which could be disturbed by shear or TMB-5, leading to different polymorphic structures.     

Structure of nanocomposites based on lead sulfide and poly-<Emphasis Type="Italic">p</Emphasis>-xylylene

Nanocomposites containing controlled (in the course of synthesis) concentrations of lead sulfide nanoparticles dispersed in the polymer matrix were prepared by the method of gas-phase polymerization on the surface of an active monomer, paracyclophane, which was codeposited with lead sulfide molecules. According to wide-angle X-ray diffraction measurements, the prepared nanocomposites contain lead sulfide clusters of 4 nm size, which are localized in the amorphous regions of poly-p-xylylene. Size distribution curves for lead sulfide particles as calculated on the basis of the Fourier analysis of crystallographic X-ray reflections and the volume distributions functions of particles as determined from small-angle X-ray scattering data are reported. A mechanism for the formation of lead sulfide nanoparticles in the poly-p-xylylene matrix is proposed on the basis of analysis of the X-ray scattering curves.     

Thermoresponsive behavior of water-salt solutions of a graft copolymer with a main polyimide chain and side poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylamino-2-ethyl methacrylate) side chains

The water-salt solutions of the graft copolymer bearing a polyimide main chain and poly(N,N-dimethylamino-2-ethyl methacrylate) side chains (M = 4.7 × 10⁵, the density of grafting with side chains z = 0.44) are studied by static and dynamic light scattering and turbidimetry. The solutions are investigated in a tenfold range of NaCl concentrations (from 0.015 to 0.15 mol/L) at the polymer concentration from 0.002 to 0.015 g/cm³ and pH from 8 to 12. The temperature dependences of the intensity of scattered light, optical transmission, hydrodynamic radius of scattering objects, and their concentrations in solutions are derived. The temperatures of phase separation onset T ₁ and end T ₂ are determined. It is shown that an increase in the salt content in solution leads to reduction in the polymer solubility and in temperatures T ₁ and T ₂. The watersalt solutions retain all the regularities of phase-separation temperature variation observed for aqueous solutions with change in the concentration of solution and pH of a medium: the values of T ₁ and T ₂ increase upon dilution and growth of acidity.     

Crystal structure of a cobalt oxide LuBaCo<Subscript>4</Subscript>O<Subscript>7</Subscript>

Crystals of LuBaCo₄O_7+δ (114Lu) have been obtained by spontaneous crystallization of slowly cooled nonstoichiometric melt of the system Lu-Ba-Co-O. The crystals have been characterized by EDX microprobe and synchrotron radiation powder diffraction. Structure refinement has been carried out (automated diffractometer Bruker X8 APEX with a CCD detector, MoK _α, graphite monochromator, ?_max = 32.54°). Parameters of the hexagonal unit cell: space group P6₃ mc, a = 6.2601(1) Å c = 10.2017(3) Å V = 346.23(1) Å₃, Z = 2, d _calc = 6.331 g/cm₃. Framework structure of the wurtzite type has been refined anisotropically to R-factor 0.0174. Charge balance in the compound and geometrical matching of structural fragments are discussed.     

Specific detection and effective inhibition of a single bacterial species <Emphasis Type="Italic">in situ</Emphasis> using peptide mineralized Au cluster probes

Increasingly serious microbial infections call for the development of new simpler methods for the precise diagnosis and specific inhibition of such pathogens. In this work, a peptide mineralized Au cluster probe was applied as a new simplified strategy to both recognize and inhibit a single bacteria species of Staphylococcus aureus (S. aureus) simultaneously. The probes are composed of peptides and Au clusters. Moreover, the peptides specifically target S. aureus cells and the Au clusters provide fluorescent imaging and have an antibacterial effect. These new probes enable the simultaneous specific detection and effective destruction S. aureus cells in situ.     

Rheological behavior and reversible swelling of pH sensitive poly(acrylamide-<Emphasis Type="Italic">co</Emphasis>-itaconic acid) hydrogels

The study involved preparation of poly(acrylamide-co-itaconic acid) hydrogels by radical cross-linking copolymerization. The copolymer hydrogels were characterized through infrared spectroscopy, thermal analysis, swelling measurements and in oscillatory and steady shear rheology. Results showed that more stable copolymers were formed due to the strong interaction in the hydrogels. These hydrogels have shown substantial percent swelling in water and shrinking in saline solution and acidic buffers. The rheological properties were described by the Herschel-Bulkley and power-law models to explore their non-Newtonian behavior. The results showed that higher itaconic acid content raised the polymer viscosity; the degree of shear-thinning and polymer elasticity (G′) were also increased. The transition from the viscous (G′ < G″) to the predominant viscoelastic behavior (G′ > G″) occurs at a crossover frequency ranged from 17.8 rad/s for polyacrylamide to 15.7, 12.8 and 12.5 rad/s for copolymers.     

An <Emphasis Type="Italic">in situ</Emphasis> cell for investigation of the catalyst structure using synchrotron radiation

Design of a cell for in situ characterization of heterogeneous catalysts by X-ray absorption spectroscopy EXAFS/XANES and X-ray diffraction on synchrotron radiation at high temperatures in a controllable gas medium, which was implemented at the Structural Materials Science end-station installed at KCSRNT, is presented. First results on nanostructural evolution of Pt/γ-Al₂O₃, Pd/γ-Al₂O₃ and other catalysts during various treatments — oxidation in oxygen, reduction in H₂/N₂, and annealing in vacuum — are reported.     

Solvothermal synthesis and crystal structure of a 1d coordination polymer: [Ni(1,4-BDC)(N-MIM)<Subscript>2</Subscript>]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (1,4-BDC = 1,4-benzenedicarboxylic acid,N-MIM = <Emphasis Type="Italic">N</Emphasis>-methylimidazole)

A new metal-organic coordination polymer, namely [Ni(1,4-BDC)(N-MIM)₂] _n (I) (1,4-BDC = 1,4-benzenedicarboxylic acid and N-MIM = N-methylimidazole), has been synthesized under solvothermal conditions by using N-MIM as solvent and characterized by elemental analysis, IR, and X-ray single-crystal diffraction. The X-ray diffraction analysis reveals that I crystallizes in the monoclinic system, space group C2/c. The 1,4-BDC ligand adopts a bis(bidentate) chelating mode to connect two adjacent Ni(II) centers to form a one-dimensional (1D) zigzag chain. The adjacent chains are further linked through hydrogen bonds and π-π stacking interactions, forming a three-dimensional (3D) supramolecular framework. The unit cell parameters for I: a = 17.250(10), b = 7.214(4), c = 16.506(7)Å, β = 125.53(4)°, V = 1671.6(15)ų, Z = 4.     

A study of structural non-stoichiometry with respect to oxygen in <Emphasis Type="Italic">R</Emphasis>BaCo<Subscript>4</Subscript>O<Subscript>7+<Emphasis Type="Italic">x</Emphasis></Subscript> single crystals

Impurity-free RBaCo₄O_7+x (R = Y, Lu) crystals are grown and the evolution of their structure with varying oxygen concentration in the range 0 ≤ x ≤ 1.3 is studied. The structural features of the studied samples required to develop an extended strategy of the X-ray crystallographic experiment, which made it possible to obtain more accurate data on unit cell parameters and additional information on the features of superstructure modulation and diffuse scattering, along with the phase composition of crystalline samples. A crystal chemical analysis of the known structural models of RBaCo₄O_7+x is performed and suggestions are made about possible structural changes occurring when the oxygen concentration increases up to the limit.     

Multiple endothermic peaks resulted from different crystal structures in an isomorphous copolymer poly(3-hydroxybutyrate-<Emphasis Type="Italic">co</Emphasis>-3-hydroxyvalerate)

The multiple endothermic peaks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) in differential scanning calorimetry (DSC) results, as one representative phenomenon of polymer with unique cocrystallization behavior, were generally considered as the results of melting/recrystallization. In this study, wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) experiments were conducted to analyze the phenomena of multiple endothermic peaks in DSC results. The results of these analyses indicated that the multiple endotherms were mainly caused by different lamellae structures. For P(HB-co-HV) with lower HV content, it was comprised of two structures of HV total exclusion and HV partial inclusion in the crystal lamellae. For P(HB-co-HV) with higher HV content, it was also comprised of two structures of HV total inclusion and HV partial inclusion in the crystal lamellae. However, only structure with HV partial inclusion in the crystal lamellae remained existing after first melting peak for all samples.     

Preparation and characterization of poly(amide-imide)/ZnO nanocomposites containing pendent benzoxazole and benzimidazole segments

In the present investigation, novel poly(amid-imide)/zinc oxide nanocomposites (PAI/ZnO NCs) containing benzoxazole and benzimidazole pendent groups with different amounts of modified zinc oxide nanoparticles (ZnO NPs) were successfully prepared via the ex situ method. Poly(amid-imide) (PAI) was prepared by direct polycondensation of 2-[3,5- bis(N-trimellitimidoyl)phenyl]benzoxazole (DCA) with 5-(2-benzimidazole)-1,3-phenylenediamine (DAMI) and provided the polymeric matrix with well-designed groups. The surface of ZnO NPs was functionalized with 3-aminopropyltriethoxysilane (APS) coupling agent to have a better dispersion and enhancing possible interactions of NPs with functional groups of polymer matrix. The amount of APS bonded to the ZnO surface was determined by thermogravimetric analysis. PAI/ZnO nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). SEM analysis showed that the modified ZnO nanoparticles were homogeneously dispersed in polymer matrix. In addition, TGA data indicated an enhancement of thermal stability of the nanocomposite compared with the neat polymer.     

Synthesis,structure, and properties of the thermolysis products of [Os(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>Cl][ReCl<Subscript>6</Subscript>]

The crystal structure of [Os(NH₃)₅Cl][ReCl₆] has been refined by X-ray powder analysis: a = 11.645(3) Å, b = 8.3788(2) Å, c = 15.277(4) Å, β = 91.029(6)°, V = 1490(1) ų, d _x = 3.163 g/cm³, space group P2₁/m, Z = 4. The thermolysis product of the salt in a hydrogen atmosphere is a solid substitution solution Os_0.5Re_0.5: a = 2.753(2) Å, c = 4.366(3) Å, space group P6₃/mmc; coherent scattering region (CSR) is ～230 Å.     

Analysis of the fine structure of XANES spectra over Ni<Emphasis Type="Italic">K</Emphasis> edge in Ni(EtOCS<Subscript>2</Subscript>)<Subscript>2</Subscript>

The NiK edge X-ray absorption near edge spectra (XANES) of the Ni(EtOCS₂)₂ complex were measured. The theoretical NiK edge XANES spectra were calculated by the total multiple scattering and finite difference methods; the potential was calculated with a muffin-tin approximation and without it. It is shown that inclusion of the non-muffin-tin effects is important for modeling the NiK XANES spectrum for the Ni(EtOCS₂)₂ complex; good agreement with experiment was achieved only in the calculations with the total potential (without the muffin-tin approximation for the shape of the potential).     

A new 1D chiral metal-organic coordination polymer constructed by Cu(II) with L-3-Cyanophenylalanine

A new 1D chiral metal-organic coordination polymer [Cu(Cphe)₂] · 3H₂O (I) (HCphe = L-3-Cyanophenylalanine) has been synthesized in an aqueous solution and characterized by elemental analysis, thermogravimetric analysis (TGA), X-ray powder diffraction (XRPD), infrared spectroscopy (IR) and single crystal X-ray diffraction. The X-ray diffraction analysis reveals that I crystallizes in the monoclinic space group P2₁. The adjacent copper(II) atoms are linked by Cphe ligands to form a 1D zigzag chain, which is further connected via strong hydrogen bonds to form a 3D supramolecular framework. The unit cell parameters for I are: a = 12.0201(8), b = 6.1495(4), c = 14.8576(10) Å, β = 94.1720(10)°, V = 1095.00(13) ų, and Z = 2.