Well-developed Crystalline Structure Research Articles

Effect of thermal history on the structure and mechanical properties of a thermoplastic polyester elastomer

An appropriate processing protocol was proposed to improve the rubber elasticity of a thermoplastic polyester elastomer (TPEE). Rheology measurements at the processing temperature and thermal measurements determined the critical temperature at which small numbers of crystals exist. It was found from dynamic mechanical analyses, wide- and small-angle X-ray measurements, and electron microscope observations that cooling from the critical temperature markedly promoted the crystallization of hard segments. Moreover, tensile tests revealed that the modulus and yield stress increased. Most importantly, compared with films obtained by cooling from high temperatures, the residual strain at a fixed stress was low—i.e., the rubber elasticity was improved owing to its well-developed crystalline structure. These effects were accelerated by a more optimized process—i.e., subsequent heating at slightly below the critical temperature. The technique is noteworthy because a TPEE with high modulus generally shows poor elasticity.

Ultrasonic irradiation as a green production route for coupling crystallinity and high specific surface area in iron nanomaterials

Coupling high crystallinity with high specific surface area in engineered nanomaterials is imperative whenever both chemical endurance regarding particle dissolution and a large specific surface area are needed for environmental clean-up purposes. Gathering both properties in the same particulate system is not trivial. In this work, A L-9 orthogonal array of experiments was used to assist a liquid-phase reduction method aiming to synthesize zero valent iron nanoparticles (nZVI) that could offer a large specific surface area while presenting a well-developed crystalline structure. The experimental variables included the reductant addition rate, the precursor (Fe+3) concentration, the (reductant/Fe3+) ratio, (R), and also the application of ultrasonic irradiation (UI) to the precipitating medium. The results show that NaBH4/FeCl3 ratio and Fe+3 concentration have opposite effects on the specific surface area of the synthesized particles whereas the effect of reductant addition rate is negligible. Moreover, the introduction of UI in the precipitation process benefits considerably the surface area of the particles while preserving or even enhancing the crystallinity of the precipitated nanomaterials. The effects of UI were interpreted in the frame work of the classical nucleation theory. This work raises the potential of UI as an environmentally friendly method to be applied to other precipitation systems which could end up in finer powder particles with better crystallinity.

Room temperature processed high mobility W-doped In2O3 electrodes coated via in-line arc plasma ion plating for flexible OLEDs and quantum dots LEDs

We fabricated W-doped In2O3 (IWO) films at room temperature on a flexible PET substrate using an in-line arc plasma ion plating system for application as flexible transparent conducting electrodes (FTCEs) in flexible organic light emitting diodes (OLEDs) and quantum dots light emitting diodes (QDLEDs). Due to the high-energy flux of the sublimated ions generated from the plasma region, the IWO films showed a well-developed crystalline structure with a low sheet resistance of 36.39 Ohm/square and an optical transmittance of 94.6% even though they were prepared at room temperature. The low sheet resistance of the IWO film processed at room temperature is attributed to the high mobility (59 cm2/V-s) in the well-developed crystalline structure of the ion-plated IWO film and screening effect of W dopants. In addition, the better adhesion of the ion-plated IWO film on the PET substrate led to small critical outer and inner bending radii of 6 and 3 mm, respectively, against substrate bending. Due to the low sheet resistance, high optical transmittance, better crystallinity, better adhesion, and outstanding flexibility of the ion-plated IWO films, the flexible OLEDs and QDLEDs with the IWO electrodes showed better performances than flexible OLEDs and QDLEDs with sputtered flexible ITO anodes. This indicates that in-line arc plasma ion plating is a promising large area coating technique to realize room temperature processed high-quality FTCEs for flexible OLEDs and QDLEDs.

Carbon nanosheets by the graphenization of ungraphitizable isotropic pitch molecules

We report a tremendous structural evolution of carbon nanosheets (CNSs) through the graphenization of isotropic pitches prepared by reforming commercially available naphtha cracking bottom oil. CNSs with thicknesses of 2–13 nm were prepared by spin-coating on quartz substrates directly without a catalytic material, followed by two successive thermal treatments consisting of stabilization at 270 °C in air and carbonization at up to 1200 °C in H2/Ar. The development of well-ordered graphene layers around pebble-like structures with increasing carbonization temperature was observed in only the 13-nm thick CNSs by transmission electron microscopy, whereas thin CNSs did not reveal well-developed fringe growth. In addition, Raman, UV–vis, and X-ray photoelectron spectroscopies along with mass spectrometry unanimously showed clear evidence indicating that unusually well-developed crystalline structure was formed in the thick CNSs. It should be noted that isotropic pitches, which are intrinsically non-graphitizable carbon sources, evolved into highly ordered structures at a relatively low carbonization temperature (1200 °C). We believe that the graphenization of spin-coated films of pitch molecules resulted from the condensation of small pitch molecules and their self-assembled structure during carbonization under the anisotropic pressure induced by significant shrinkage in the vertical axis.

Role of ethanol concentration on drawing and infusion behavior of poly(ethylene terephthalate) filaments upon cold drawing

This paper describes the drawing and concomitant infusion behavior in low oriented PET filament drawn at room temperature in ethanol/water solution of various ethanol concentrations. Increasing concentration of ethanol greatly increased the number of necks on filament, and reduced the yield and drawing stresses. With increasing concentration of ethanol the infusion of ethanol into filament was increased, and a well-developed crystalline structure was formed. Shrinkage reduction of filament with increasing ethanol concentration was also investigated. Infusion of dye molecules in filament was also increased with raising of ethanol concentration. Color spectrum study confirmed that dye molecules infused only in drawn parts of filament and undrawn parts showed 100% transmittance.

High-yield synthesis of single-crystal silicon nanoparticles as anode materials of lithium ion batteries via photosensitizer-assisted laser pyrolysis

Single crystal silicon nanoparticles (Si-NPs) of 20 nm were produced via laser pyrolysis with a virtually complete conversion from SiH4 to Si-NPs. SF6 was used as the photosensitizer to transfer laser beam energy to silicon precursors, dramatically enhancing crystallinity of Si-NPs and their production efficiency. By using their well-developed crystalline structure, the directional volume expansion of Si-NPs was confirmed during lithiation. Lithiation/delithiation kinetics of our Si-NPs was superior to that of their amorphous counterparts due to the footprinted Li+ pathways formed during amorphization.

Investigation of Pseudocapacitive Charge-Storage Behavior in Highly Conductive Ordered Mesoporous Tungsten Oxide Electrodes

Herein, a pseudocapacitive charging behavior of highly conductive ordered mesoporous tungsten oxide (m-WO3-X) is investigated. For this purpose, various electrochemical analysis methods such as cyclic voltammetry (CV), galvanostatic charge–discharge experiment and electrochemical impedance spectroscopy (EIS) were employed. From CV experiment, a relationship analysis between voltammetric charge and scan rate resulted in total (67 C g–1), outer (61 C g–1) and inner charge (6 C g–1), which was related with the well-developed crystalline structure of m-WO3-X. In galvanostatic charge–discharge profiles with change of applied current, a more severe decrease of cathodic capacity than the anodic one was observed, which was attributed to larger cathodic resistance. This resistance dependency on potential was clarified with EIS fitting analysis. Here, the charge transfer resistance and Warburg diffusion resistance became larger with increasing potential, which was relevant to the change of oxidation state during re...

Characterization of BiFeO 3 nanopowder obtained by mechanochemical synthesis

Bismuth ferrite nanopowders have been obtained by mechanochemical synthesis. The materials were characterized by high resolution electron microscopy, X-ray diffraction and NIR Raman scattering. The XRD pattern of the powder consists of reflections, characteristic of BiFeO 3 perovskite structure, superimposed on broad maxima that can be ascribed to an amorphous/disordered phase. The analysis of the two broad bands at low 2 θ angle yields mean distances of about 3 and 1.8 Å which may be related to Bi O and Fe O bonds, respectively. The powder consists of loosely packed grains with a broad distribution of sizes between a few nm and 45 nm. The grains of sizes larger than about 30 nm exhibit well-developed crystalline structure.

Structure and magnetic properties of CoFe2O4 and Fe3O4 nanoparticles

The Fe3O4 and CoFe2O4 nanoparticles of radius 3.2±0.3 and 3.8±0.3 nm, respectively, were synthesized by the high-temperature solution phase reaction of metal acetylacetonates. Nanoparticles with the spherical shape and well-developed crystalline structure are superparamagnetic at room temperature. The CoFe2O4 showed high coercivity up to 1.7 T at low temperatures and a step-like change of magnetization at 138 K, which might point at the Verwey transition.

Characterization of PbTiO3 Nanopowders Obtained by Room Temperature Synthesis

Lead titanate nanopowders were fabricated by mechanochemical synthesis. The obtained materials were characterized by high resolution electron microscopy, X-ray excited photoelectron spectroscopy and NIR Raman scattering. The powder consists of loosely packed grains with a broad distribution of sizes between a few nm and 45 nm. The grains of sizes larger than about 30 nm exhibit well-developed crystalline structure. All grains have a shell of thin disordered/amorphous layer which was investigated by XPS. The Raman spectroscopy showed slight differences in Raman spectra of nanopowder in comparison to the bulk material: the lines related to A1(1TO), E(2TO) and A 1 (3TO) modes are shifted to lower frequencies and their spectral linewidth increase.

Low Temperature Catalytic Pyrolysis for the Synthesis of High Surface Area, Nanostructured Graphitic Carbon

High surface area graphitic carbons are of great interest in emerging applications including catalysis and energy storage because of the well-developed crystalline structure, high electronic conductivity and thermal stability, and satisfactory oxidation resistance at low temperature. We have developed the synthesis of porous graphitic carbon with a large and accessible surface area via synthesis of carboxyl-containing polymer particles, followed by ion exchange and pyrolysis at low temperature (850 °C). The evolution of the graphitic structure together with mesoporosity is temperature dependent, as revealed from the results of X-ray diffraction, transmission electron microscopy, and nitrogen sorption measurement. Specifically, the development of mesoporosity resulting from continuously catalyzed carbonization by the in situ formed cobalt nanoparticles can be clearly recognized. Further nitric acid oxidation leads to an increase of the pore volume due to the removal of cobalt nanoparticles and opening of closed pore entrances. Moreover, the use of silica as the isolating shell facilitates the formation of high surface area graphitic carbon. Magnetization measurements show that the graphitic carbon/cobalt composites exhibit ferromagnetic properties, and the cobalt nanoparticles are stable under air for more than 10 months without degradation of their magnetic properties.

Hydrothermal synthesis and characterization of CNT@MoS 2 nanotubes

CNT@MoS 2 nanotubes were prepared by a hydrothermal method. The products were characterized by HRTEM, EDX and XRD. The results demonstrated that the MoS 2 layers coated on CNTs have a well-developed crystalline structure. CNTs can provide a topological and structural template for the nucleation and growth of the tubular MoS 2 layers.

Holocene Soil Development on Till and Outwash Inferred from Lake-Sediment Geochemistry in Michigan and Wisconsin

Two geochemical techniques from soil mineralogy were used with lake sediment to reconstruct soil development in the catchments of two lakes—one on outwash and the other on till—in the Great Lakes region. A sodium pyrophosphate extraction provides information about leaching of exchangeable and organically complexed cations from terrestrial sources, while an acidified ammonium oxalate extraction removes mineral materials without well-developed crystalline structure that are indicative of podzolization. More evidence of pedogenesis is preserved in sediment of the lake on outwash—likely a result of greater retention of material within the soil profile in the catchment on till. This difference between the records suggests that excessively well-drained (leaky) catchments may provide better records of soil development than those with higher water-holding capacity. Evidence of acidification and podzolization appeared first at the lake on till and 4500 years later at the lake on outwash. Both records reveal a late Holocene intensification of weathering that coincided with a regional climatic change to greater moisture availability. The variability in weathering rates observed presents a more complex picture of weathering than the simple exponential functions often assumed in chronosequence studies. Use of lake sediment records provides better temporal resolution of significant events in soil formation than could be achieved using a chronosequence approach.

Water sorption behaviors of the BPDA-based polyimide films depending upon the structural isomers of diamine

For the biphenyltetracarboxylic dianhydride (BPDA)-based polyimide thin films, the water sorption behaviors were gravimetrically investigated by using a thin film diffusion analyzer. The water sorption behaviors of the polyimide thin films are quite different and strongly dependent upon the sort of polyimide. The diffusion coefficients of the polyimide thin films vary in the range of 1.6 × 10−10 to 12.4 × 10−10cm2/s and the water uptakes vary from 1.52 to 5.25 wt %. Both the diffusion coefficient and water uptake of the polyimide thin films are in the increasing order: BPDA-pPDA < BPDA-p,p′ODA < BPDA-p,m′ODA < BPDA-mPDA ∼ BPDA-p,p′DDS < BPDA-m,m′DDS. Specifically, the polyimide films with para-oriented linkages in backbone structure showed relatively lower diffusion coefficient and water uptake than the corresponding polyimide films with meta-oriented linkages because of the well-developed crystalline structure and good intermolecular chain ordering. In addition, the polyimide thin films having higher chain order showed relatively lower diffusion coefficient and water uptake. The crystallinity and intermolecular chain ordering in the morphological structure are critical parameters in controlling the water sorption behaviors of the polyimide thin films. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2121–2127, 2001

Residual stress behaviour of isomeric PMDA-ODA polyimides

Poly(3,4′-oxydiphenylene pyromellitimide) (PMDA-3,4′-ODA), an isomer of poly(4,4′-oxydiphenylene pyromellitimide) (PMDA-4,4′-ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4′-oxydiphenylene diamine (3,4′-ODA). For these two polyimide isomers and their poly(amic acid) precursors in the condensed state on Si wafers, residual stress behaviour over the range 25–400°C was investigated by the dynamic measurement of wafer bending. During thermal imidization both isomers did not show any difference in stress versus temperature behaviour. Once imidized, however, one isomer exhibited a quite different stress behaviour from that of the other during cool-down: the stress of PMDA-3,4′-ODA increased rapidly from zero at 400°C to ≈45 MPa at 40°C, whereas that of PMDA-4,4′-ODA rose gradually from zero to ≈27 MPa. For both cured isomers, stress-temperature profile on heating was the same as that on cooling, with some deviation due to moisture uptake over the temperature range 25–150°C, indicating that their stresses were insensitive to thermal cycling or thermal annealing. From independently measured properties (thermal expansion coefficient, modulus, Poisson's ratio of 0.34) of both polyimides, the thermal stresses were calculated and compared with the measured overall stresses. It is concluded that for both polyimides the overall residual stress results primarily from the thermal stress. In comparison with PMDA-4,4′-ODA, PMDA-3,4′-ODA showed a much higher stress despite its slightly lower thermal expansion coefficient. This leads to the conclusion that the large difference between the stresses of the isomers results from the large difference in their moduli (5.0 GPa for PMDA-3,4′-ODA and 3.0 GPa for PMDA-4,4′-ODA). This behaviour is further supported by the difference in morphological structures of these two isomers as determined by wide-angle X-ray diffraction: PMDA-3,4′-ODA showed a well-developed crystalline structure, whereas the PMDA-4,4′-ODA did not. In addition, the interfacial adhesion between polyimide film and Si wafer primed with A1100 was investigated.