Polyol-Mediated Synthesis of PbS Crystals: Shape Evolution and Growth Mechanism

An interesting shape evolution of. PbS crystals, that is, from cubes to (truncated) octahedra and finally to stable star-shaped multipods with six arms along the < 100 > directions is first realized via a facile polyol-mediated reaction between lead acetate and sulfur powder in the absence of surfactants. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) techniques were employed to characterize the samples. We elucidate the important parameters (including reaction temperature and sulfur sources) responsible for the shape-controlled synthesis of PbS crystals.

STRUCTURAL EVOLUTION AND COMPOSITION CHANGE IN THE SURFACE REGION OF POLYPROPYLENE/CLAY NANOCOMPOSITES ANNEALED AT HIGH TEMPERATURES

A model experiment was done to clear the formation mechanism of protective layers during combustion of polypropylene (PP)/organically modified montmorillonite (OMMT) nanocomposites. The investigation was focused on the effects of annealing temperature on the structural changes and protective layer formation. The decomposition of OMMT and degradation of PP/OMMT nanocomposites were characterized by means of thermogravimetric analysis (TGA). The structural evolution and composition change in the surface region of PP/OMMT nanocomposites during heating were monitored by means of X-ray photoelectron spectroscopy (XPS), ATR-FTIR and field emission scanning electron microscopy (FESEM).

Effects of Y2O3 addition on the phase evolution and thermophysical properties of lanthanum zirconate

Lanthanum zirconate (La2Zr2O7, LZ) powders with the addition of various Y2O3 contents for potential thermal barrier coatings (TBCs) application were synthesized by solid-state reaction. The structure evolution, sintering-resistance and thermophysical properties of the synthesized powders and sintered ceramics were systematically studied. X-ray diffraction (XRD) results indicate that LZ containing 3-12 wt.% Y2O3 mainly keeps a pyrochlore-type structure, and two new phases of LaYO3 and Y0.18Zr0.82O1.91 are also detected. Raman spectra confirm that the higher the Y2O3 content, the easier is the formation of LaYO3.

In Situ Observation of Tensile Deformation Processes of Soft Colloidal Crystalline Latex Fibers

The deformation mechanism or styrene/n-butyl acrylate copolymer latex films with fiber symmetric crystalline structure subjected to uniaxial stretching was studied using synchrotron small-angle X-ray scattering technique. The fibers were drawn at angles or 0, 35, and 55 degrees with respect to the Fiber axis. In all cases, the microscopic deformation within the crystallites was Found to deviate from affine deformation behavior with respect to the macroscopic deformation ratio. Moreover, the extent of this deviation is different in the three cases. This peculiar behavior can be attributed to the relative orientation of the (111) plane of the crystals, the plane of densest packing, with respect to the stretching direction in each case. When the stretching direction coincides with the crystallographic (111) plane, which is the case for stretching directions of 0 and 55 degrees with respect to the fiber axis, the microscopic deformation deviates less from affine behavior than when the stretching direction is arbitrarily oriented with respect to the crystallographic (111) plan.

Investigations of the properties of Mg-5Al-0.3Mn-xCe (x=0-3, wt.%) alloys

Mg-5Al-0.3Mn-xCe (x = 0-3, wt.%) alloys were prepared by metal mould casting method. The microstructures and mechanical properties were investigated. The results revealed that the main phases of as-cast Mg-5Al-0.3Mn alloy consist of alpha-Mg matrix and beta-Mg17Al12 phase. With the addition of Ce element, Al11Ce3 precipitates were formed and mainly aggregated along the grain boundaries. The amount of the Al11Ce3 precipitates increased with increasing addition of Ce, but the amount of beta-Mg17Al12 phase decreased. The highest tensile strength was obtained in Mg-5Al-0.3Mn-1.5Ce alloy. The ultimate tensile strength (UTS), yield strength (YS) and elongation at room temperature are 203 MPa, 88 MPa and 20%, separately.

Spectral and electrochemical detection of protonated triplex formation by a small-molecule anticancer agent

Triplex helical formation has been the focus of considerable interest because of possible applications in developing new molecular biology tools as well as therapeutic agents and the possible relevance of H-DNA structures in biology system. We report here that a small-molecule anticancer agent, coralyne, has binding preference to the less stable protonated triplex d(C+-T)(6):d(A-G)(6).d(C-T)(6) over duplex d(A-G)(6).d(C-T)(6) and shows different spectral and electrochemical characteristics when binding to triplex and duplex DNA, indicating that electrochemical technique can detect the less stable protonated triplex formation.

Microstructures, mechanical properties and corrosion behavior of high-pressure die-cast Mg-4Al-0.4Mn-xPr (x=1, 2, 4, 6) alloys

Mg-4Al-0.4Mn-xPr (x = 1, 2, 4 and 6 wt.%) magnesium alloys were prepared successfully by the high-pressure die-casting technique. The microstructures, mechanical properties, corrosion behavior as well as strengthening mechanism were investigated. The die-cast alloys were mainly composed of small equiaxed dendrites and the matrix. The fine rigid skin region was related to the high cooling rate and the aggregation of alloying elements, such as Pr. With the Pr content increasing, the alpha-Mg grain sizes were reduced gradually and the amounts of the Al2Pr phase and All, Pr-3 phase which mainly concentrated along the grain boundaries were increased and the relative volume ratio of above two phases was changed. Considering the performance-price ratio, the Pr content added around 4 wt.% was suitable to obtain the optimal mechanical properties which can keep well until 200 degrees C as well as good corrosion resistance. The outstanding mechanical properties were mainly attributed to the rigid casting surface layer, grain refinement, grain boundary strengthening obtained by an amount of precipitates as well as solid solution strengthening.

Preparation and electrical properties of new oxide ion conductors Ce6-xDyxMoO15-delta (0.0 <= x <= 1.8)

Ce6-xDyxMoO15-delta (0.0 <= x <= 1.8) were synthesized by modified sol-gel method. Structural and electrical properties were investigated by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The XRD patterns showed that the materials were single phase with a cubic fluorite structure. Impedance spectroscopy measurement in the temperature range between 350 degrees C and 800 degrees C indicated a sharp increase in conductivity for the system containing small amount of Dy2O3. The Ce5.6Dy0.4MoO15-delta detected to be the best conducting phase with the highest conductivity (sigma(t) = 8.93 x 10(-3) S cm(-1)) is higher than that of Ce5.6Sm0.4MoO15-delta (sigma(t) = 2.93 x 10(-3) S cm(-1)) at 800 degrees C, and the corresponding activation energy of Ce5.6Dy0.4MoO15-delta (0.994 eV) is lower than that of Ce5.6Sm0.4MoO15-delta (1.002 eV).

Computer simulation of the damage evolution of fiber-reinforced polypropylene-matrix composites with matrix defects

The damage evolution of fiber-reinforced polypropylene-matrix composites with matrix defects was studied via a Monte Carlo technique combined with a finite element method. A finite element model was constructed to predict the effects of various matrix defect shapes on the stress distributions. The results indicated that a small matrix defect had almost no effect on fiber stress distributions other than interfacial shear stress distributions. Then, a finite element model with a statistical distribution of the fiber strength was constructed to investigate the influences of the spatial distribution and the volume fraction of matrix defects on composite failure. The results showed that it was accurate to use the shear-lag models and Green's function methods to predict the tensile strength of composites even though the axial stresses in the matrix were neglected.

Surface plasmon resonance and electrochemistry for detection of small molecules using catalyzed deposition of metal ions on gold substrate

Small molecules are difficult to detect by conventional surface plasmon resonance (SPR) spectroscopy due to the fact that the changes in the refractive index resulted from the binding process of small biomolecules are quite small. Here, we report a simple and effective method to detect small biomolecule using SPR spectroscopy and electrochemistry by catalyzed deposition of metal ions on SPR gold film. As an example, the ascorbic acid-mediated deposition of Ag on gold film was monitored by in situ SPR spectrum. The deposition of Ag atom on gold film resulted in an obvious decrease of depth in SPR angular scan curves of reflectance intensity and minimum reflectivity angle. The depth change of the SPR reflectance intensity and minimum reflectivity angle curves mainly relied on the amount of Ag atom deposited on gold film that can be controlled by the concentration of ascorbic acid. By monitoring the deposition of Ag atom on gold film, ascorbic acid was detected in the concentration range of 2 x 10(-5) M to 1 x 10(-3) M. After each of detections, the SPR sensor surface was completely regenerated by a potential step that stripped off the Ag atom. Furthermore, the regeneration process of the sensor surface provides the feasibility for detecting the concentration of ascorbic acid by electrochemical method.

Confined intra-molecular clustering in orientated polyethylene after annealing

Deuterated polyethylene tracer molecules with small amount of branches (12 C2H5- branches per 1000 backbone carbon atoms) were blended with a hydrogenated polyethylene matrix to form a homogenous mixture. The conformational evolution of the deuterated chains in a stretched semi-cry stall me film was observed via online small angle neutron scattering measurements during annealing at high temperatures close to the melting point. Because the sample was annealed at a temperature closely below its melting point, the crystalline lamellae were only partially molten and the system could not fully relax. The global chain dimensions were preserved during annealing. Recrystallization of released polymeric chain segments allows for local phase separation thus driving the deuterated chain segments into the confining interlamellar amorphous layers giving rise to an interesting intra-molecular clustering effect of the long deuterated chain. This clustering is deduced from characteristic small angle neutron scattering patterns. The confined phase separation has its origin in primarily the small amount of the branches on the deuterated polymers which impede the crystallization of the deuterated chain segments.

Transformation from ordered islands to holes in phase-separating P2VP/PS blend films by adding triton X-100

Our previous investigation showed that the ordered hexagonal island pattern in the phase-separating polymeric blend films of polystyrene and poly(2-vinylpyridine) (PS/P2VP) formed due to the convection effect by proper control of PS molecular weight, solvent evaporation rate, and the weight ratio of PS to P2VP. In this paper, we further illustrate that, by adding a proper amount of the surfactant Triton X-100 to the PS/P2VP toluene solution, the ordered hexagonal island pattern can be transformed to the ordered honeycomb pattern. The effects of the amount of Triton X-100 on the surface morphology evolution and the pattern transformation are discussed in terms of the collapse of Triton X-100, phase separation between Triton X-100/P2VP and PS, the interfacial interaction between Triton X-100/P2VP and the mica substrate, and the Benard-Marangoni convection.

Surface morphology evolution of poly (styrene-block-4-vinylpyridine) (PS-b-P4VP)(H+) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA) supramolecular film

Well-ordered nanostructured polymeric supramolecular thin films were fabricated from the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP)(H+) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA). A depression Of cylindrical nanodomains was formed by the block of P4VP(H+) and PMCMA associates surrounded by PS. The repulsive force aroused from the incompatibility between the block of P4VP(H+) and PMCMA was varied through changing the molecule weight (M-w) of PMCMA, the volume fraction of the block of P4VP(H+), and annealing the film at high temperature. Increasing the repulsive force led to a change of overall morphology from ordered nanoporous to featureless structures. The effects of solvent nature and evaporation rate on the film morphology were also investigated. Further evolution of surface morphologies from nanoporous to featureless to nanoporous structures was observed upon exposure to carbon bisulfide vapors for different treatment periods. The wettability of the film surface was changed from hydrophilicity to hydrophobicity due to the changes of the film surface microscopic composition.

Structural and magnetic properties of Sr2Fe1−xGaxMoO6 (0≤x≤0.25)

We have investigated the structure, magnetization and magnetoresistance (MR) of the double perovskite compounds Sr2Fe1−xGaxMoO6 (0≤x≤0.25). Rietveld refinement results show that the anti-site defects (ASDs) concentration increases with x, giving rise to highly disordered samples at the B/B positions, for the highest doping levels. The evolution of bond lengths and ions oxidation states could be understood by the distribution of trivalent Ga ions at the B/B positions, which leads to the formation of more disorder structure. The saturation magnetization and Curie temperature decreased with the Ga content increases in the samples, and their origin was found that the cations disorder for the Ga-doped compounds is annihilating double exchange mechanism due to the presence of significant amounts of Fe and Ga cations on the B site. The low-field magnetoresistance of Sr2FeMoO6 (SFMO) can be greatly enhanced by replacing the Fe by the nonmagnetic Ga ion up to a temperature of 300 K,since Ga ions may act as a barrier for electron transport along the chain in the ferromagnetic segregation and weaken the ferromagnetic exchange.