Synthesis and characterization of a copolymer: Poly(aniline‐co‐fluoroaniline)

In the present article, we report the chemical synthesis and characterization of poly(aniline‐co‐fluoroaniline) [poly(An‐FAn)]. The copolymerization of aniline and 2‐fluoroaniline was carried out by chemical method in acidic medium. The characterization of poly(aniline‐co‐fluoroaniline) was done using FTIR, UV‐visible spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron micrography (SEM), and a four‐points‐probe conductivity method. X‐ray diffraction (XRD) and SEM characterization reveal crystalline nature of doped copolymer compared to undoped copolymer. The observed decrease in the conductivity of the copolymer relative to polyaniline is attributed to the incorporation of the fluoro moieties into the polyaniline chain. The chemically synthesized copolymer shows good solubility in common organic solvents, and is, therefore, technological useful. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1460–1466, 2001     

In situ synthesis of Al2O3‐supported ZnCr2O4 nanoparticles for application as an activated photocatalyst

Zincochromite nanoparticles (NPs) were precipitated on surfaces of the as‐prepared Al₂O₃ micron‐sized particles by a heterogeneous precipitation technique using urea as a homogeneous precipitation agent. This procedure leads to decrease the pore diameter and increase the pore volume and specific surface area (a_s), realizing the potential access to ZnCr₂O₄ catalytic sites. Although the obtained band gap energy (E_g) of Al₂O₃‐ZnCr₂O₄ composite is about 2.3 eV (more than ZnCr₂O₄), the absorbance is enhanced about 1.5 orders of magnitude. These characteristics make it an effective photocatalyst of inorganic dyes from an aqueous media. Dye removal performance of the nanocomposite powder is higher than that of pure ZnCr₂O₄, which is attributed to an increase in the photocatalytic sites and the absorbance intensity. It was believed that the surface area created from Al₂O₃ support realized the potential access to ZnCr₂O₄ catalytic sites. To confirm these assertions, X‐ray diffractometry (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and N₂ adsorption‐desorption analysis were applied.     

Synthesis,structural characterization,and photoluminescence properties of TTB‐type PbTa2O6:Eu3+ phosphor

Undoped and Eu³⁺‐doped tetragonal tungsten bronze (TTB) PbTa₂O₆ phosphors were synthesized by using solid‐state reaction method. Synthesized samples were characterized by XRD, SEM‐EDS, and photoluminescence analyses. XRD results revealed TTB‐type crystal structure with single phase up to 10 mol% Eu³⁺ doping concentration. In SEM‐EDS analyses, elemental composition of Pb decreased with the increasing concentration of Eu³⁺. Emissions at the excitation wavelength of 398.5 nm were observed at 593.2 and 618.8 nm due to ⁵D₀→⁷F₁ transitions and ⁵D₀→⁷F₂ transitions, respectively. Emission increased with the increasing Eu³⁺ doping concentration up to 10 mol% and not observed concentration quenching.     

The fate of iron during the alkali‐activation of synthetic (CaO‐)FeOx‐SiO2 slags: An Fe K‐edge XANES study

Slags from the nonferrous metals industry have great potential to be used as feedstocks for the production of alkali‐activated materials. Until now, however, only very limited information has been available about the structural characteristics of these materials. In the work presented herein, synthetic slags in the CaO–FeO_x–SiO₂ system, representing typical compositions of Fe‐rich slags, and inorganic polymers (IPs) produced from the synthetic slags by activation with alkali silicate solutions have been studied by means of X‐ray absorption near‐edge structure (XANES) spectroscopy at the Fe K‐edge. The iron in the slags was largely Fe²⁺, with an average coordination number of approximately 5 for the iron in the amorphous fraction. The increase in average oxidation number after alkali‐activation was conceptualized as the consequence of slag dissolution and IP precipitation, and employed to calculate the degrees of reaction of the slags. The degree of reaction of the slags increased with increasing amorphous fraction. The iron in the IPs had an average coordination number of approximately 5; thus, IPs produced from the Fe‐rich slags studied here are not Fe‐analogs of aluminosilicate geopolymers, but differ significantly in terms of structure from the latter.     

Carbon/carbon composites derived from poly(ethylene oxide)‐modified novolac‐type phenolic resin: Microstructure and physical,and morphological properties

A poly(ethylene oxide) (PEO) novolac‐type phenolic resin blend was prepared by the physical blending method. The modified novolac‐type phenolic resin with various PEO contents was used as a matrix precursor to fabricate carbon/carbon composites. The effect of the PEO/phenolic resin mixing ratio on the change of the density and of the porosity was studied. The flexural strength and interlaminar shear strength of the PEO/phenolic resin blend‐derived carbon/carbon composites were also investigated. The results show that the density of the PEO/phenolic resin blend‐derived carbon/carbon composites decreases with the PEO content. The X‐ray diffraction and Raman spectra studies showed that the carbon fiber in the samples will affect the growth of the ordered carbon structure. From SEM morphological observation, it is shown that the fracture surface of specimens is smooth. Also, there is less fiber pull‐out and fiber breakage on the fracture surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1609–1619, 2002; DOI 10.1002/app.10407     

Local structure of the MgxNixCoxCuxZnxO(x=0.2) entropy‐stabilized oxide: An EXAFS study

Entropy‐stabilized oxides (ESOs) provide an alternative route to novel materials discovery and synthesis. It is, however, a challenge to demonstrate that the constituent elements in an entropy‐stabilized crystal are homogeneously and randomly dispersed among a particular sublattice, resulting in a true solid solution with no evidence of local order or clustering. In this work, we present the application and analysis of extended X‐ray absorption fine structure (EXAFS) on the prototype ESO composition Mg_xNi_xCo_xCu_xZn_xO (x=0.2). In so doing, we can quantify the local atomic structure on an element‐by‐element basis. We conclude that local bond lengths between metal and oxygen vary around each absorbing cation, with notable distortion around the Cu–O polyhedra. By the second near neighbor (i.e., the cation‐cation pair), interatomic distances are uniform to the extent that the collected data can resolve. Crystal models that best fit the experimental scattering data include cations that are distributed randomly on an FCC sublattice with minimal positional disorder, with an interleaved FCC anion sublattice with oxygen ions displaced from the ideal locations to accommodate the distortions in the cation polyhedra. Density functional theory calculations of the ESO system yield a significant broadening in the positional distribution for the oxygen sublattice compared to that for the cation sublattice for all peaks, showing consistency with the conclusion from the experimental data that the distortion from an ideal rock salt structure occurs primarily through disorder in the oxygen sublattice.     

Crystallization,melting behavior,and wettability of poly(ε‐caprolactone) and poly(ε‐caprolactone)/ poly(N‐vinylpyrrolidone) blends

Both wettability and crystallizability control poly(ε‐caprolactone)'s (PCL) further applications as biomaterial. The wettability is an important property that is governed by both chemical composition and surface structure. In this study, we prepared the PCL/poly(N‐vinylpyrrolidone) (PVP) blends via successive in situ polymerization steps aiming for improving the wettability and decreasing crystallizability of PCL. The isothermal crystallization of PCL/PVP at different PVP concentrations was carried out. The equilibrium melting point (T), crystallization rate, and the melting behavior after isothermal crystallization were investigated using differential scanning calorimetry (DSC). The Avrami equation was used to fit the isothermal crystallization. The DSC results showed that PVP had restraining effect on the crystallizability of PCL, and the crystallization rate of PCL decreased clearly with the increase of PVP content in the blends. The X‐ray diffraction analysis (WAXD) results agreed with that. Water absorptivity and contact angle tests showed that the hydrophilic properties were improved with the increasing content of PVP in blends. The coefficient for the water diffusion into PCL/PVP blends showed to be non‐Fickian in character. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structural properties of CrF3‐ and MnCl2‐filled poly(vinyl alcohol) films

Poly(vinyl alcohol) (PVA) films filled with different amounts of CrF₃ and MnCl₂ were prepared by the casting method. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) analysis were used to study the changes in the structure properties that occurred because of filling. The changes occurring in the measured parameters with increasing filler contents were interpreted in terms of the structural modification of the PVA matrix. All the studied samples had a main melting temperature due to the main crystalline phase of PVA. The intensity and position of this peak depended on the filling level. However, the samples of CrF₃‐filled PVA films with a filling level greater than or equal to 10 wt % revealed another melting temperature, which indicated the presence of a new crystalline phase in addition to the main crystalline phase. The changes that occurred in the degree of crystallinity of the studied samples were examined. The calculated degree of crystallinity was formulated numerically to be an exponential function of the filling level. The XRD patterns of the studied samples confirmed the DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1115–1120, 2003     

Mullite‐glass and mullite‐mullite interfaces: Analysis by molecular dynamics (MD) simulation and high‐resolution TEM

The properties of mullite‐glass and mullite‐mullite interfaces have been investigated at 1800 K by molecular dynamics (MD) simulation and high‐resolution TEM. The simulation showed that mullite‐glass interfaces typically have much lower interfacial energies than mullite‐mullite interfaces, which results from the structural flexibility of the glass and associated accommodation of interfacial mismatch. The (110)‐glass interface has the lowest energy of all interfaces studied, which is consistent with the observed dominance of this interface in experimental mullite‐glass samples examined by TEM. The simulation shows that the interfacial energies of the (100)‐glass and (010)‐glass interfaces are higher than that those of the (001)‐glass interface, so [100] and [010] would be expected to be the dominant growth directions. However, the growth of mullite in glass occurs predominantly in the [001] direction. This apparent discrepancy can be explained by the fact that growth in the [100] and [010] directions is limited by the slow growth of (110) plane (i.e., [110] direction), which facilitates [001] growth, which is confirmed by the TEM data.     

Bubble size and radial gas hold‐up distributions in a slurry bubble column using ultrafast electron beam X‐ray tomography

Gas hold‐up and bubble size distribution in a slurry bubble column (SBC) were measured using the advanced noninvasive ultrafast electron beam X‐ray tomography technique. Experiments have been performed in a cylindrical column (D_T = 0.07 m) with air and water as the gas and liquid phase and spherical glass particles (d_P = 100 μm) as solids. The effects of solid concentration (0 ≤ C_s ≤ 0.36) and superficial gas velocity (0.02 ≤ U_G ≤ 0.05 m/s) on the flow structure, radial gas hold‐up profile and approximate bubble size distribution at different column heights in a SBC were studied. Bubble coalescence regime was observed with addition of solid particles; however, at higher solid concentrations, larger bubble slugs were found to break‐up. The approximate bubble size distribution and radial gas hold‐up was found to be dependent on U_G and C_s. The average bubble diameter calculated from the approximate bubble size distribution was increasing with increase of U_G. The average gas hold‐up was calculated as a function of U_G and agrees satisfactorily with previously published findings. The average gas hold‐up was also predicted as a function of C_s and agrees well for low C_s and disagrees for high C_s with findings of previous literature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1709–1722, 2013     

A Single‐Phase Phosphor NaLa9 (GeO4)6O2: Tm3+, Dy3+ for Near Ultraviolet‐White LED and Field‐Emission Display

Single‐phase white‐light‐emitting phosphors NaLa_9(1?x?y) (GeO₄)₆O₂: xTm³⁺, yDy³⁺ (NLGO: xTm³⁺, yDy³⁺) have been synthesized by a traditional solid‐state reaction method. The powder X‐ray diffraction (XRD), photoluminescence (PL), PL excitation (PLE) spectra, fluorescence decay curves, chromaticity coordinates, correlated color temperature (CCT), and the cathodoluminescence (CL) properties of the obtained phosphors are measured and discussed in detail. It is discovered that the series samples could be color‐tunable (from blue to yellow) by tuning the doping content of Dy³⁺ with a fixed Tm³⁺ content excited at 357 nm and white light (0.341, 0.324) could be obtained with the CCT of 5079 K. A NLGO: 0.01Tm³⁺, 0.02Dy³⁺ is studied carefully as representative. The main emissions of Tm³⁺ (453 nm, ¹D₂–³F₄) and Dy³⁺ (478 nm, ⁴F_9/2–⁶H_15/2; 572 nm, ⁴F_9/2–⁶H_13/2) make it emit white light with good thermal stability (67% of the initial till 523 K). The energy transfer from Tm³⁺ to Dy³⁺ is noticed and further research has been done to explain the enhancement of Dy³⁺ emission and the excellent thermal stability. It also keeps stable under continuous electron bombardment with high intensity. All of these indicate that it could be a suitable candidate for white‐emitting phosphor applied for near ultraviolet‐white light‐emitting diode (NUV‐WLED) and field‐emission display (FED).     

Strong magnetoelectric effect in pulse laser deposited [Ba(Zr0.2Ti0.8)O3‐0.5(Ba0.7Ca0.3)TiO3]/CoFe2O4 bilayer thin film

Polycrystalline bilayer thin film of multiferroic [Ba(Zr_0.2Ti_0.8)O₃‐0.5(Ba_0.7Ca_0.3)TiO₃]/CoFe₂O₄([BZT‐0.5BCT]/CFO) has been deposited on Pt/Si (100) substrate using a pulsed laser deposition technique. The dielectric analysis reveals a significant change in the dielectric constant (~39% at a typical frequency of 100 Hz) at room temperature when a magnetic field is applied, in addition to a substantial improvement in the saturation polarization. A low leakage current density (~ 5 × 10^?7 A/cm²) and a high magnetoelectric coupling coefficient (α_E) both in the transverse (~2.085 V/Oe cm) as well as in the longitudinal (~0.708 V/cm Oe) directions, indicate in‐principle usability of this system for multifunctional device applications in thin film form.     

Synthesis and characterization of biodegradable polyethylene by graft copolymerization of starch using glucose–Ce(IV) redox system

Graft copolymerization of low‐density polyethylene (LDPE) onto starch was carried out with glucose–cerium(IV) redox initiator in an aqueous sulfuric acid medium under nitrogen atmosphere. The graft yield was influenced by various parameters like reaction time, temperature, and concentrations of acid, glucose, polyethylene (PE), starch, and initiator. A maximum graft yield of 85.66% was obtained at a temperature of 50°C and at higher concentration of starch. Effect of grafting on crystallinity, morphology, and thermal properties of modified PE has been evaluated using X‐ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA/DTA). Biodegradability of starch‐grafted PE has been tested applying soil‐burial test. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3229–3239, 2006     

Cationic copolymers of α,β‐poly‐(N‐2‐hydroxyethyl)‐DL‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy): synthesis and characterization

In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry     

Microwave‐assisted YBa2Cu3O7 precursors: A fast and reliable method towards chemical precursors for superconducting films

Highly stable, pure, and anhydrous organometallic YBa₂Cu₃O_7‐δ (YBCO) precursor solutions were prepared by dissolving commercial YBCO powder in acetone by trifluoroacetic anhydride (TFAA) or a mixture of TFAA with propionic acid for low fluorine precursors. It is shown that compared to conventional oil bath heating reported in literature, the reaction to produce YBCO precursor occurs 72 times faster by microwave heating. More importantly, the formation of byproducts is suppressed, as shown by nuclear magnetic resonance (NMR) and mass spectrometry (MS). This approach allows a highly reproducible preparation of superconducting coatings which is of interest for low‐cost manufacturing processes capable of large‐scale production of the coated conductors via chemical solution deposition (CSD). This technology requires reliable and stable precursor solutions for continuous deposition. In this work, we obtained YBCO thin films on single‐crystal substrates ((100)‐LaAlO₃) with a high critical current density (J_c) of 3‐4 MA/cm² in self‐field at 77 K using TFA‐based YBCO precursors and J_c of 5‐6 MA/cm² using low fluorine YBCO precursors.     

Structure and high‐resolution thermogravimetry of liquid‐crystalline copoly(p‐oxybenzoate‐ethylene terephthalate‐p‐benzamide)

Thermotropic liquid‐crystalline copoly(ester‐amide)s consisting of three units of p‐oxybenzoate (B), ethylene terephthalate (E) and p‐benzamide (A) were studied by proton nuclear magnetic resonance at 200 and 400 MHz, wide‐angle X‐ray diffraction, and high‐resolution thermogravimetry to ascertain their molecular and supermolecular structures, thermostability and kinetics parameters of thermal decomposition in both nitrogen and air. The assignments of all resonance peaks of [¹H]NMR spectra for the copoly(ester‐amide)s are given and the characteristics of X‐ray equatorial and meridional scans are discussed. Overall activation energy data of the first major decomposition have been evaluated through three calculating techniques. The thermal degradation occurs in three steps in nitrogen and air. The degradation temperatures are higher than 447 °C in nitrogen and 440 °C in air and increase with increasing B‐unit content at a fixed A‐unit content of 5 mol%. The temperatures at the first maximum weight‐loss rate are higher than 455 °C in nitrogen and 445 °C in air and also increase with an increase in B‐unit content. The first maximum weight‐loss rates range between 11.1 and 14.5%min⁻¹ in nitrogen and between 11.9 and 13.5%min⁻¹ in air. The char yields at 500 °C in both nitrogen and air range from 45.8 to 54.3 wt% and increase with increasing B‐unit content. But the char yields at 800 °C in nitrogen and air are quite irregular with the variation of copolymer composition and testing atmosphere. The activation energy and Ln (pre‐exponential factor) for the first major decomposition are usually higher in nitrogen than in air and increase slightly with an increase in B‐unit content at a given A‐unit content of 5 mol%. The activation energy, decomposition order, and Ln (pre‐exponential factor) of the thermal degradation for the copoly(ester‐amide)s in two testing atmospheres, are situated in the ranges of 210–292 kJmol⁻¹, 2.0–2.8, 33–46 min⁻¹, respectively. The three kinetic parameters of the thermal degradation for the aromatic copoly(ester‐amide)s obtained by high‐resolution thermogravimetry at a variable heating rate are almost the same as those by traditional thermogravimetry at constant heating rate, suggesting good applicability of kinetic methods developed for constant heating rate to the variable heating‐rate method. These results indicate that the copoly(ester‐amide)s exhibit high thermostability. The isothermal decomposition kinetics of the copoly(ester‐amide)s at 450 and 420 °C are also discussed and compared with the results obtained based on non‐isothermal high‐resolution thermogravimetry. © 1999 Society of Chemical Industry