Varying Degrees Of Crystallinity Research Articles

The role of lamellar morphology on the post-irradiation oxidative degradation of ultra-high molecular weight polyethylene

Post-irradiation oxidative degradation of ultra-high molecular weight polyethylene (UHMWPE) has drawn much attention due to the well-known effects of the long term-degradation of mechanical and wear properties after gamma-radiation induced sterilization of orthopedic implant components. While the chemistry of oxidation, associated morphological changes and consequence of the effects of post-gamma radiation aging on the properties of UHMWPE components have been extensively studied in both laboratory fabricated components and explants, there have been no systematic studies on the effects of the lamellar morphology of post-radiation aging of PE. In this study, high-pressure crystallization was used to produce UHMWPE with various degrees of crystallinity and lamellar thickness, subjected to the same 50 kGy dose of gamma radiation, accelerated aged and then subjected to Fourier Transform Infrared Spectroscopy which, combined with ultra-small angle x-ray scattering, was used to draw quantitative correlations between morphological parameters and oxidative degradation. Lamellar thickness was shown to monotonically increase post-radiation oxidation.

Effects of Synthesis Parameters on Crystallization Behavior of K-MER Zeolite and Its Morphological Properties on Catalytic Cyanoethylation Reaction

MER-type zeolite is an interesting microporous material that has been widely used in catalysis and separation. By carefully controlling the synthesis parameters, a procedure to synthesize K-MER zeolite crystals with various morphologies has been developed. The silica, water and mineralizer content in the synthesis gel, as well as crystallization time and temperature, have a profound impact on the crystallization kinetics, resulting in zeolite solids with various degrees of crystallinity, crystal sizes and shapes. K-MER zeolite crystals with nanorod, bullet-like, prismatic and wheatsheaf-like morphologies have been successfully obtained. The catalytic performances of the K-MER zeolites in cyanoethylation of methanol, under novel non-microwave instant heating, have been investigated. The zeolite in nanosize form shows the best catalytic performance (94.1% conversion, 100% selectivity) while the bullet-like zeolite gives poorest catalytic performance (44.2% conversion, 100% selectivity).

Experimental and theoretical studies on isatin-Schiff bases and their copper(II)-complexes: Syntheses, spectroscopy, tautomerism, redox potentials, EPR, PXRD and DFT/TDDFT

Abstract The isatin-Schiff bases 3-(o/p-tolylimino)indolin-2-one (HL1 and HL2) react with the copper(II) acetate or nitrate to give the bis[3-(o/p-tolylimino)indole-2-olato-κ2N,O]copper(II) (1 and 2) via lactam (L)- to enol (E)-tautomerism in solution. IR spectra show solely the L-tautomer at solid state, while both tautomers in solution. 1H NMR results indicate a dynamic tautomerization equilibria between the L- and E-tautomers in solution with varying ratios of ca. 83/17, 60/40 and 54/46 (L/E) within 0.5, 5 and 24 h, respectively. Cyclic voltammograms demonstrate two quasi reversible one electron charge transfer processes for the Cu(II)/Cu(I) and Cu(I)/Cu(0) couples in acetonitrile, respectively. PXRD patterns at 5–50° (2θ) correspond well to the crystalline nature with various degrees of crystallinity for the ligands and complexes. X-band EPR spectrum shows an intense broad band at relatively high field region with isotropic nature. Magnetic moment values (μeff. = 1.56–1.63 μB) indicate paramagnetic nature of the copper(II)-complexes with one unpaired electron in methanol. Optimized structures by DFT show the L-form relatively stable than the E-form by 19.76 kcal/mol, while compounds HL2 and 2 are slightly stable than HL1 and 1 by 0.35 and 0.79 kcal/mol, respectively. Electronic spectra by TDDFT strongly support the experimental results in methanol.

High-spin bis[(S or R)-N-1-(Ar)ethyl-salicylaldiminato-κ2N,O]-Λ/Δ-iron(II): Combined studies of syntheses, spectroscopy, diastereoselection, electrochemistry, paramagnetic, thermal, PXRD and DFT/TDDFT

The enantiopure Schiff bases (S or R)-N-1-(Ar)ethyl-salicylaldimine (S or R-HL) react with the iron(II) chloride to give high-spin bis[(S or R)-N-1-(Ar)ethyl-salicylaldiminato-κ2N,O]-Λ/Δ-iron(II) {Ar = C6H5 (FeSL1 or FeRL1), p-OMeC6H4 (FeSL2 or FeRL2) and p-BrC6H4 (FeSL3 or FeRL3)}. ECD spectra show expected mirror-image relationship for the enantiomeric pairs and confirm the enantiopurity of the complexes in methanol. The electronic spectra calculated by DFT/TDDFT fit well to the experimental spectra. Comparisons of experimental ECD spectra for FeRL2 (or FeSL2) with those of the calculated spectra for Λ-FeRL2/Δ-FeRL2 (or Δ-FeSL2/Λ-FeSL2) exhibit diastereoselection and induced chirality (Λ vs. Δ) at-metal centre by R- or S-ligand and prefer formation of Δ-FeRL2 (or Λ-FeSL2) in solution. CV results demonstrate three redox peaks associated to the FeI/0, FeII/I and FeIII/II couples, respectively in acetonitrile. Thermal analyses by DSC suggest an irreversible phase transformation from solid to isotropic-liquid phase. Variable temperature magnetic measurements show relatively high magnetic moment values (i.e., μeff. = 4.6–5.0 μB), correspond to the tetrahedral high-spin iron(II)-Schiff bases complexes in methanol. Fair matching between experimental and simulated PXRD patterns indicates the ligands and complexes having well define crystalline nature with various degrees of crystallinity.

Interphase Development in Polyacrylonitrile/SWNT Nanocomposite and Its Effect on Cyclization and Carbonization for Tuning Carbon Structures

In this study, the self-stiffening behavior of polyacrylonitrile (PAN)/carbon nanotube (CNT) nanocomposites is used to develop the interphase structure. Instead of multi-walled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs) were used, since they provide much more interfacial area with PAN matrix. The effects of SWNT content (0–1.5 wt %) and temperature on the structural development of PAN/SWNT nanocomposites during dynamic straining were compared for processing optimization. Using this unique dynamic straining method, we were able to tune the structures, especially the interphase of PAN/SWNT nanocomposites. The degree of crystallinity of nanocomposite could be improved from 54.3 to 58.5% after dynamic straining for 12 h, and the activation of the PAN glass transition increased from 434 to 1192 kJ/mol. The thermal behaviors of PAN and PAN/SWNT films with various degrees of crystallinity were compared by differential scanning calorimeter and thermal gravimetric analysis. The relationships ...

The Impact of Crystallinity on Mesoporous TiO2 Nanoparticle Electrode for Li- and Na- Ion Batteries

Demands for rechargeable batteries have been significantly increasing not only in portable electronics (e.g. cell phones and laptops), but also in large-scale energy storage systems (e.g. grids).1-3 TiO2 as anode materials is electrochemically active in both lithium and sodium ion batteries. It has drawn significant attentions due to its nontoxicity, stability, low production cost and high capacity. Indeed, many works have been conducted to study the impact of morphology, particle size, facet control and electronic structure manipulation on the electrochemical performance of TiO2 materials in either lithium or sodium ion batteries.4-9 In addition, in terms of crystalline structures, TiO2 materials with various polymorphs, for example, anatase (tetragonal, I41/amd), rutile (tetragonal, P42/mnm), TiO2-B (monoclinic, C2/m), brookite (orthorhombic, Pbcv) and amorphous TiO2 have been extensively investigated.10-14 Previously, Xiong et al. observed a phase transformation from amorphous to face-centered cubic phase when the amorphous TiO2 nanotube electrode first discharged under 1 V vs. Li/Li+, significantly self-improving the long-term reversibility and specific capacity.15 Xiong et al. also investigated the electrochemical performance of amorphous TiO2 nanotubes as anode materials in sodium cell.14Though capacity increased gradually with charge-discharge cycling, the phase transition from amorphous to cubic phase was not observed. Herein, we demonstrate the impact of various degree of crystallinity on pure TiO2 anode materials for both Li and Na ion batteries. XRD, Raman, selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) were conducted to confirm the gradually crystalized TiO2 nanoparticles. Electrochemical performance of TiO2 nanoparticles was tested by voltage profile, rate capability, cycle life, cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). Structure evolution during cycling was tested by ex situRaman spectroscopy and soft XAS.

Study of the photoinduced degradation of tandem photovoltaic converters based on a-Si:H/μc-Si:H

The photoinduced degradation of photovoltaic converters based on an a-Si:H/µc-Si:H tandem structure under a standard illuminance of 1000 W/m2 is studied. The spectral and current–voltage characteristics of specially fabricated samples with various degrees of crystallinity of the intrinsic layer in the lower (microcrystalline) cascade are measured in the course of the tests.

Nanomineralogy in the real world: A perspective on nanoparticles in the environmental impacts of coal fire.

Detailed geochemistry similarities between the burning coal cleaning rejects (BCCRs) and non-anthropogenic geological environments are outlined here. While no visible flames were detected, this research revealed that auto-combustion existed in the studied area for many years. The occurrence of several amorphous phases, mullite, hematite and many other Al/Fe-minerals formed by high temperature was found. Bad disposal of coal-dump wastes represents significant environmental concerns due to their potential influence on atmosphere, river sediments, soils and as well as on the surface and groundwater in the surroundings of these areas. The present work using multi-analytical techniques were performed to provide an improved understanding of the complex processes related with sulphide-rich coal waste oxidation, spontaneous combustion and newmineral creation. It recording huge numbers of rare minerals with alunite, montmorillonite, szmolnockite, halotrichite, coquimbite and copiapite at the BCCRs. The information presented the presence of abundant amorphous Si-Al-Fe-Ti as (oxy-)hydroxides and Fe-hydro/oxides with goethite and hematite with various degrees of crystallinity, containing potential hazardous elements (PHEs), such as Cu, Cr, Hf, Hg, Mo, Ni, Se, Pb, Th, U, Zr, and others. Most of the nano-particles and ultra-fine particles found in the burned coal-dump wastes are the same as those commonly associated with coal cleaning rejects, in which oxidation of sulphides plays an important impact to environment and subsequently animal and human health.

The properties of the nano-minerals and hazardous elements: Potential environmental impacts of Brazilian coal waste fire

Brazilian coal area (South Brazil) impacted the environment by means of a large number of coal waste piles emplaced over the old mine sites and the adjacent areas of the Criciúma, Urussanga, and Siderópolis cities. The area studied here was abandoned and after almost 30years (smokeless visual) some companies use the actual minerals derived from burning coal cleaning rejects (BCCRs) complied in the mentioned area for industry tiles or refractory bricks. Mineralogical and geochemical similarities between the BCCRs and non-anthropogenic geological environments are outlined here. Although no visible flames were observed, this study revealed that auto-combustion existed in the studied area for many years. The presence of amorphous phases, mullite, hematite and other Fe-minerals formed by high temperature was found. There is also pyrite, Fe-sulphates (eg. jarosite) and unburnt coal present, which are useful for comparison purposes. Bad disposal of coal-dump wastes represents significant environmental concerns due to their potential influence on atmosphere, river sediments, soils and as well as on the surface and groundwater in the surroundings of these areas. The present study using advanced analytical techniques were performed to provide an improved understanding of the complex processes related with sulphide-rich coal waste oxidation, spontaneous combustion and mineral formation. It is reporting huge numbers of rare minerals with alunite, montmorillonite, szomolnokite, halotrichite, coquimbite and copiapite at the BCCRs. The data showed the presence of abundant amorphous Si–Al–Fe–Ti as (oxy-)hydroxides and Fe-hydro/oxides with goethite and hematite with various degrees of crystallinity, containing hazardous elements, such as Cu, Cr, Hf, Hg, Mo, Ni, Se, Pb, Th, U, Zr, and others. By Principal Component Analysis (PCA), the mineralogical composition was related with the range of elemental concentration of each sample. Most of the nano-minerals and ultra-fine particles found in the burned coal-dump wastes are the same as those commonly associated with coal cleaning rejects, in which oxidation of sulphides plays an important role to environment and human health.

Production of Amorphous and Nanocrystalline Silicon Films by the Hot-Wire Activation Method

Thin films of amorphous silicon with inclusions of a nanocrystalline silicon phase have been obtained by the method of gas-phase chemical deposition with hot-wire activation of the precursor. The influence of the gas pressure and of the hydrogen–monosilane ratio on the rate of growth and the degree of crystallinity of the deposited silicon has been investigated. Characteristic values of the synthesis parameters for obtaining silicon films of various degrees of crystallinity have been established.

Design of Multistimuli-Responsive Shape-Memory Polymer Materials by Reactive Extrusion

Shape-memory polymers (SMPs) are a class of stimuli-responsive materials that have attracted tremendous attention in various applications, especially in the medical field. While most SMPs are thermally actuated, relating to a change of thermal transition (e.g., melting temperature), SMPs that can be actuated upon exposure to light are emerging. Recently, there has been new interest into multiple stimuli-responsive SMPs in order to cover the range of applications for these smart materials. In this work, poly(ester-urethane)s (PURs) made of heating-responsive poly(e-caprolactone) (PCL) segments of various degrees of crystallinity and photoresponsive N,N-bis(2-hydroxyethyl) cinnamide (BHECA) monomer were successfully prepared using reactive extrusion technology to design dual-stimuli-responsive SMPs (DSRSMP). In order to tune the SMP properties (temperature or light), the crystallinity of the PCL segment was finely adjusted by the copolymerization of e-caprolactone with para-dioxanone in bulk at 160 °C using...

Effect of the crystallinity of indium tin oxide on the charge transfer at the interfaces and the performances of flexible organic light emitting diodes

In this study, we investigated the factors that determine the efficiency of flexible organic light emitting diodes (f-OLEDs) in relation to transparent conductive electrodes (TCE). Indium tin oxide (ITO) was selected as the TCE and was deposited on polyimide substrates. Controlling the sputtering conditions, ITOs with various degrees of crystallinity were made. Flexible OLEDs (f-OLED) were fabricated on the ITOs, and the current density (J)–luminescence (L)–voltage (V) characteristics of the f-OLEDs were evaluated. The experimental results revealed that the sheet carrier density and surface roughness of ITO are significantly increased and reduced, respectively, as the film crystallinity increased over a certain degree. Based on our X-ray photoelectron spectroscopy (XPS) analysis, chemical bonds formed between the mostly crystallized ITO and a hole transfer layer (HTL) in f-OLEDs, deposited on ITO. To the contrary, In and Sn of the less crystallized ITO diffused into HTL with no formation of interfacial bonds, which may become barriers to carrier flows through HTL. The f-OLED on the mostly crystalline ITO showed significantly better J–L–V characteristics than on the less crystallized ITO, which proved that the crystallinity of ITO is the critical factor that determines the performance of the flexible organic devices constructed on the ITO.

Nanominerals and ultrafine particles from coal fires from Santa Catarina, South Brazil

Coal mining in Santa Catarina, South Brazil, impacted the environment by means of a large number of coal waste piles emplaced over the old mine sites and the adjacent areas of the Criciúma, Urussanga, and Siderópolis. Poor disposal of coal cleaning rejects represents significant environmental concerns due to their potential influence on soils and river sediments, as well as on the surface and groundwater in the surroundings of these zones. In this research advanced analytical techniques were performed to provide an improved understanding of the complex processes related with sulfide-rich coal waste oxidation, spontaneous combustion, sequences of mineral formation, and the transport mechanisms of hazardous elements by neoformed soluble nanominerals and ultrafine particles. The results showed the presence of massive amorphous Si–Al–Fe–Ti–Zr (oxy-) hydroxides and Fe-hydr/oxides with goethite and hematite with various degrees of crystallinity, containing hazardous elements, such as Cr, Hf, Hg, Mo, Ni, Se, Pb, Th, U, Zr, and others. Several of the neoformed nanominerals found in the burned coal rejects are the same as those commonly associated with coal mine drainage, in which oxidation of sulfides plays an important role to environment and human health. This is the first Brazilian coal spontaneous combustion research.

Revisiting Surface-Enhanced Raman Scattering on Realistic Lithographic Gold Nanostripes

In this article, we investigate the Surface-Enhanced Raman Scattering (SERS) efficiency of methylene blue (MB) molecules deposited on gold nanostripes which, due to their fabrication by electron beam lithography and thermal evaporation, present various degrees of crystallinity and nanoscale surface roughness (NSR). By comparing gold nanostructures with different degrees of roughness and crystallinity, we show that the NSR has a strong effect on the SERS intensity of MB probe molecules. In particular, the NSR features of the lithographic structures significantly enhance the Raman signal of MB molecules, even when the excitation wavelength lies far from the localized surface plasmon resonance (LSPR) of the stripes. These results are in very good agreement with numerical calculations of the SERS gain obtained using the discrete dipole approximation (DDA). The influence of NSR on the optical near-field response of lithographic structures thus appears crucial since they are widely used in the context of nano-optics or/and molecular sensing.

Mineral speciation and fate of some hazardous contaminants in coal waste pile from anthracite mining in Portugal

The coal (anthracite A) in Douro Coalfield (NW of Portugal) has been exploited for many years and has been mainly used as fuel supply by a thermal power plant. The mining activities inevitably impacted the environment, which includes a large number of coal waste piles emplaced over the old mine sites and adjacent areas of the Douro Coalfield. The disposal of coal mining residues represents significant environmental concerns due to their potential influence on soils and sediments, as well as on the surface and groundwater of the surrounding areas. In the present study, the development of sequential extraction combined with various advanced analytical techniques was performed to provide an improved understanding of the complex processes related with sulfide-rich coal waste oxidation, sequences of mineral formation, and the transport mechanisms of hazardous elements by specific neoformed soluble minerals. The results showed the presence of amorphous iron (oxy-) hydroxides and goethite with various degrees of crystallinity, containing hazardous elements, such as As, Cr, Hg, Mo, Se, Pb, U, and others. Some of the neoformed minerals found in the coal waste material are the same as those commonly associated with coal acid drainage, in which oxidation of sulfides plays an important role. The precipitated neoformed minerals include pickeringite, blödite, and a mixture of epsomite, pickeringite, and hexahydrite. As these sulfates may dissolve after the first rain, they may release above-mentioned elements into surrounding water bodies.

Resistive switching in hafnium dioxide layers: Local phenomenon at grain boundaries

Overcoming challenges associated with implementation of resistive random access memory technology for non-volatile information storage requires identifying the material characteristics responsible for resistive switching. In order to connect the switching phenomenon to the nano-scale morphological features of the dielectrics employed in memory cells, we applied the enhanced conductive atomic force microscopy technique for in situ analysis of the simultaneously collected electrical and topographical data on HfO2 stacks of various degrees of crystallinity. We demonstrate that the resistive switching is a local phenomenon associated with the formation of a conductive filament with a sufficiently small cross-section, which is determined by the maximum passing current. Switchable filament is found to be formed at the dielectric sites where the forming voltages were sufficiently small, which, in the case of the stoichiometric HfO2, is observed exclusively at the grain boundary regions representing low resistant conductive paths through the dielectric film.

Correlation among Structure, Microstructure, and Electrochemical Properties of NiAl–CO3Layered Double Hydroxide Thin Films

We studied a series of NiAl–CO3 layered double hydroxides (LDHs) of various degrees of crystallinity prepared by a glycine-assisted hydrothermal method. The structures and the microstructures were determined by Rietveld refinement with a spherical harmonic-implemented algorithm using high-resolution synchrotron powder X-ray diffraction (XRD) data. These XRD results combined with transmission electron microscopy (TEM) observations indicate that the broadening of 00l diffraction lines is mainly due to size effects, while both size and strain effects contribute to the anisotropic broadening of the other hkl reflections. The in-plane TEM dimensions of LDH platelets are found larger than the coherent lengths in the 110 direction, indicating a noncoherent coalescence of domains during crystal growth. The DIFFaX program was also used to model structural defects, i.e., CO32–/SO42– interstratification and intergrowth between rhombohedral 3R1 and hexagonal 2H1 polytypes. Furthermore, the distribution of the cations...

The influence of crystallinity on radiation stability of UHMWPE

The influence of ionizing radiation on ultra high molecular weight polyethylene (UHMWPE) was studied using EPR spectroscopy and GC. Two samples of various degree of crystallinity, 85% and 53%, were investigated upon exposure to electron beam. In this study it was found that radicals generated following irradiation decay much faster in amorphous than in crystalline phase. The primary product generated in both phases is second ordered alkyl radical. EPR spectra detected for the sample containing 85% crystalline regions revealed a quintet of hyperfine splitting about 2.28mT and the signal was tentatively assigned to the product of β-fragmentation. The radiation yield of hydrogen for two studied samples of various crystallinity was similar.

Effect of phosphorylation of the maize starch on thermal generation of stable and short‐living radicals

AbstractEffect of hydrolysis, phosphorylation and treatment with high hydrostatic pressure on thermal generation of stable and short‐living radicals in maize starch was studied by X‐ray diffraction (XRD), electron paramagnetic resonance (EPR) spectroscopy, differential scanning calorimetry and polarized light microscopy. Phosphorus was introduced into maize starch as mono‐ and distarch phosphates. XRD indicated localization of phosphate groups in amorphous part of the granule whereas calorimetric data suggested some cross‐linking of the distarch phosphates. Stable and short‐living radicals with unpaired electron localized at carbon atom were generated in all investigated samples in the temperature range commonly used for processing food. The number of detected short‐living radicals, stabilized by a spin trap, is of two orders of magnitude greater than that of the stable radical species. Hydrolysis and phosphorylation strongly increase the number of stable radicals while pretreatment of the starch with high hydrostatic pressure diminishes their amount. The EPR spectra of stable radicals consist of two components, single line and another one with hyperfine structure, indicating interaction of unpaired electron with neighboring hydrogen atom. The EPR spectra of the spin trap adducts with short‐living radicals contain three components from species differing in their dynamic properties depending on localization in zones of various degree of crystallinity.

Organo‐ and Hydrogelators Based on Luminescent Monocationic Terpyridyl Platinum(II) Complexes with Biphenylacetylide Ligands

A series of phosphorescent terpyridyl platinum(II) complexes with ancillary biphenylacetylide ligands, namely, [(R(3)tpy)PtC≡C(biphenyl)]X (R=tBu, H, or Et(2)N; tpy=2,2';6',2''-terpyridyl; X is an anion) were synthesized and structurally characterized by various spectroscopic techniques and X-ray diffraction methods. Despite a lack of long alkyl chain(s) or hydrogen-bonding motif(s), complexes [(tpy)PtC≡C(biphenyl)]Cl and [(tBu(3)tpy)PtC≡C(biphenyl)]X (X=Cl, ClO(4), PF(6), or BF(4)) were found to gelate water and organic solvents, respectively. The self-aggregation of these complexes in solutions and the resulting gels were investigated with variable-temperature (VT) (1)H NMR spectroscopy, polarized optical microscopy, and absorption/emission spectroscopy. SEM micrographs on dry gels revealed entangled nanofibers with diameters of 20-40 nm and lengths of tens of micrometers. Powder X-ray diffraction (PXRD) study revealed various degrees of crystallinity of these fibrillar nanostructures. The substituents on both the terpyridyl and acetylide ligands and counterion of these complexes play a profound but concerted role in tuning the intermolecular metal···metal and/or π-π interactions, and hence the gelation properties.