Thermally stimulated current study on flexible siloxane-modified epoxy sheets

Copolymers prepared from the epoxy resin of ALBIFLEX and PMPS oligomer were evaluated with IR, ¹H-and ¹³C NMRs for structural determinations. The flexible epoxy resin as a model compound was examined by TSC with variations on the operational parameters t_p and V_p. Transitions denoted as T_g,δ, T_g,γ, T_g,β, T_g,α and T_g,ρ in increasing order of temperature were observed for these copolymers. As an example, ESAF-7430 copolymer showed these transitions at −138, −84, 26, 87, and 110 °C, respectively. Each transition except the T_g,ρ at 110 °C, has been correlated to a segment in the copolymeric structure. The result indicates that TSC provides clear molecular transitions at the temperature of the transition. The molecular transition of the grafted PMPS-siloxane segment in an epoxy matrix appeared at the −45 °C region as a broad, nearly flat peak as it filled the concave part of the TSC curve of the unmodified resin. The flexibility that the modified copolymers retained may be attributed to these sub-T_g transitions as observed in the TSC spectrum.     

β-Phase Morphology in Ordered Poly(9,9-dioctylfluorene) Nanopillars by Template Wetting Method

An efficient method based in template wetting is applied for fabrication of ordered Poly(9,9-dioctylfluorene) (PFO) nanopillars with β-phase morphology. In this process, nanoporous alumina obtained by anodization process is used as template. PFO nanostructures are prepared under ambient conditions via infiltration of the polymeric solution into the pores of the alumina with an average pore diameter of 225 nm and a pore depth of 500 nm. The geometric features of the resulting structures are characterized with environmental scanning electron microscopy (ESEM), luminescence fluorimeter (PL) and micro μ-X-ray diffractometer (μ-XRD). The characterization demonstrates the β-phase of the PFO in the nanopillars fabricated. Furthermore, the PFO nanopillars are characterized by Raman spectroscopy to study the polymer conformation. These ordered nanostructures can be used in optoelectronic applications such as polymer light-emitting diodes, sensors and organic solar cells.     

The effects of vibration field on crystal structures and orientation of isotactic polypropylene injection samples

In this study, isotactic polypropylene (iPP) samples were prepared by self-made pressure vibration injection device, in which a periodical shear field was imposed on the iPP melt during the filling and packing stages. The crystal structures and orientation of samples were investigated by wide-angle X-ray diffraction and polarizing light microscopy (PLM). The β form and γ form were found in vibration injection molding samples. Compared with the static samples, the orientation of iPP chains within lamellae was observed in the transition layer (at the depth of 1.5 mm from the surface) of the vibration injection molding samples, and the orientation was found even in the core layer. The PLM observation indicates the β form exists in the transition and core region of the vibration sample. Besides, two types of β-PP could be observed simultaneously in the core region under high magnification. The bright β crystallites (β_III) are fan-shaped and lie perpendicularly to the flow direction. In the other hand, the ringed β crystallites (β_IV) almost remain their spherulite shape. Moreover, fiber crystal was observed in vibration sample, even in the core region. Some fiber crystals in the transition region reappeared in the cooling circle after the sample was held at 180 °C for 2 min. This could be explained in structure memory effect and its high thermal stability.     

Facile synthesis of water-soluble luminescent mesoporous Tb(OH)3@SiO2 core-shell nanospheres

Luminescent mesoporous Tb(OH)₃@SiO₂ core-shell nanospheres were synthesized through W/O microemulsion process at ambient temperature. The negatively charged silica favors a coating of the positively charged Tb³⁺ composite. Thus, silicon layer was adsorbed on the surface of Tb(OH)₃ groups to form Tb-O-Si through electrostatic interaction. X-ray diffraction, field emission transmission electron microscopy (FE-TEM), energy-dispersive X-ray spectrometry, and Fourier transform infrared, UV/Visible, and photoluminescence spectroscopies were applied to examine the phase purity, crystallinity, surface morphology, and optical properties of the core-shell nanospheres. The FE-TEM results have revealed typically ordered mesoporous characteristics of the material with monodisperse spherical morphology in a narrow size distribution. The luminescent mesoporous core-shell nanospheres exposed remarkable splitting with broadening in the emission transition ⁵D₄ → ⁷F₅ (543 nm). In addition, the luminescent mesoporous core-shell nanospheres emit strong green fluorescence (from Tb³⁺) in the middle of the visible region under 325 nm (3.8) excitation. The luminescent mesoporous Tb(OH)₃@SiO₂ core-shell nanospheres can therefore be exploited as fluorescent probes in biomarkers or biolabeling, optical sensing, and drug delivery system. Further, these nanospheres could have potential use as scattering layers in dye-sensitized solar cells.     

Computer modeling ofα- toβ′- form phase transitions using theoretical triglyceride structures

Intermolecular energy calculations were performed on theoretical triarachidinα-form structures as selected bond rotations converted them intoβ′-forms with a chain-tilt change in the glycerol region. Interactions across the methyl gaps amounted to only 2-3% of the total energy in initialα- and finalβ′-forms, but computer generated energy profiles duringα- toβ′-phase transitions revealed highly repulsive regions due to the close approach of methyl groups. This methyl gap interaction, plus additional repulsive interactions in the lateral packing of molecules during rigid chain rotations, necessitated modification of certain chain movements during phase transition to reduce excessive repulsive energy. These results suggest that phase transitions proceed in a particular sequence of events that either distribute energy to promote further phase excitation or that lead to collapse into the stable polymorphic form. Phase transition energy curves also reveal that secondaryα- andβ′-forms are possible and are dependent on the startingα-forms, the direction of chain rotation and the subcell arrangement.     

Hydrothermal synthesis of vanadium pentoxide nanostructures and their morphology control

Different morphologies of vanadium pentoxide (V₂O₅) from 1D to 3D, including nanospheres, nanowires, urchin-like and flower-like nanostructures, have been synthetized by a simple hydrothermal method. Some parameters, such as the reaction temperature, the volume of polyvinyl pyrrolidone (PVP) and possible formation mechanisms of different V₂O₅ nanostructures were discussed. The results demonstrate that PVP and the reaction temperature play a critical role on the morphology of vanadium pentoxide.     

Optical characterizations of GaN nanorods fabricated by natural lithography

We fabricated GaN/Sapphire nanorods by nanosphere lithography (NSL) using SiO₂ nanospheres. Arrays of SiO₂ nanospheres were packed on GaN, followed by dry-etching via inductively coupled plasma (ICP) etching. SiO₂ nanospheres served as the etching mask under our etching conditions. Finally, a sapphire substrate under GaN was exposed by dry-etching. A significant blue shift was observed in the room temperature photoluminescence (PL) spectrum from GaN/Sapphire nanorods when the underlying Al₂O₃ was exposed. GaN nanorods were fabricated by simple and reproducible methods, where SiO₂ nanospheres were successfully used as the etching mask. In addition, a blueshift in PL by the band-filling effect was observed due to the GaN nanostructures.     

The zirconium/hydrogen system as the solid-state reference of a high-temperature proton conductor-based hydrogen sensor

A new solid-state hydrogen reference electrode has been developed that is based on the two-component two-phase mixture of β-zirconium and δ-zirconium hydride, and is suitable for use in conjunction with the high-temperature proton-conducting CaZr_0.9In_0.1O_3−δ solid electrolyte. Coulometric titration studies have confirmed the presence of a true two-phase plateau, existing over a wide composition range, which may be exploited as a precision thermodynamic buffer for reference hydrogen partial pressure. Cell voltage measurements have demonstrated that potentiometric hydrogen sensors incorporating this reference electrode exhibit Nernstian response over a broad range of temperature and hydrogen partial pressure, as well as excellent thermal cycling and long-term stability. The new solid-state hydrogen reference electrode is of considerable technological relevance and has already found application in a commercialised sensor unit.     

α-Melt-mediated crystallization of 1-palmitoyl-2-oleoyl-3-stearoyl-sn-glycerol

The α-melt-mediated crystallization of 1-palmitoyl-2-oleoyl-3-stearoyl-sn-glycerol (POS) has been investigated by differential scanning calorimetry (DSC), combined with polarized-light microscopy. Starting from a completely liquid state, the melt was first cooled down and maintained at a temperature, T ₁, during a time, t ₁, where the α-phase formed. Then it was heated to a temperature, T ₂, above the melting point of α for isothermal solidification into a solid phase, which was identified as δ. Based upon DSC solidification peaks, the time-temperature-transformation (TTT) diagram of POS was constructed for these solidification conditions and was compared with the TTT diagram of direct crystallization from the melt. The α-melt-mediated solidification showed accelerated kinetics of the δ-phase. The effects of T ₁ and t ₁ were also studied: at short t ₁, crystallization was faster with a decreasing value of T ₁, whereas the opposite trend was observed for a longer plateau at T ₁. These tendencies were interpreted in terms of three competing phenomena: the density of δ-nuclei that can form during the plateau at T ₁, α-δ solid-state transformation, and memory effects of molecule arrangements in the α-remelted phase.     

The selective formation of unsaturated alcohols by hydrogenation of α,β-unsaturated aldehydes in supercritical carbon dioxide using unpromoted Pt/Al2O3 catalyst

When α,β-unsaturated aldehydes are reduced by hydrogen in supercritical carbon dioxide using an unmodified Pt/Al₂O₃ catalyst, unsaturated alcohols are highly selectively produced, in contrast to previous results with organic solvents in which such a selective hydrogenation is difficult to achieve with monometallic Pt catalysts. The selectivity of unsaturated alcohols depends mainly on pressure of carbon dioxide while the conversion depends on both carbon dioxide and hydrogen pressures. The selectivity increases with increasing pressure and then does not change so much at higher pressures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Facile Synthesis and Tensile Behavior of TiO<Subscript>2</Subscript> One-Dimensional Nanostructures

High-yield synthesis of TiO₂ one-dimensional (1D) nanostructures was realized by a simple annealing of Ni-coated Ti grids in an argon atmosphere at 950 °C and 760 torr. The as-synthesized 1D nanostructures were single crystalline rutile TiO₂ with the preferred growth direction close to [210]. The growth of these nanostructures was enhanced by using catalytic materials, higher reaction temperature, and longer reaction time. Nanoscale tensile testing performed on individual 1D nanostructures showed that the nanostructures appeared to fracture in a brittle manner. The measured Young’s modulus and fracture strength are ~56.3 and 1.4 GPa, respectively.     

Selective propene formation in periodic flow reactor: reducibility and catalytic activity of Ni–Mo–O system

Oxidative dehydrogenation (ODH) of propane with lattice oxygen of α-, α'- and β-NiMoO₄ phases has been studied. Reduction tests of the different phases were performed by TG analysis under hydrogen at different temperatures. Under isothermal conditions lattice-oxygen-consumption rate was found to be higher on the β-phase with respect to the α- and α'-phases. TG analyses showed the existence of different sources of lattice oxygen in the catalyst, depending on the NiMoO₄ phase. Catalytic activity was measured under steady state conditions, using a periodic flow reactor and it was then correlated to the reduction curve. It was found that the activation energy for ODH reaction over NiMoO₄ of 54.3–62.7 kJ/mol is nearly identical to that obtained for the catalyst reduction under hydrogen (46–50.2 kJ/mol). The correlation between the activation energy of the reaction in a periodic operating system (POS) and that of solid reduction under hydrogen suggests that the reaction obeys a red–ox mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrothermal synthesis of titanate nanostructures with high UV absorption characteristics

The titanate nanostructures with high UV absorption characteristics could be fabricated by hydrothermal method within a temperature range of 90–150 °C. TEM, XRD, BET analyses, and UV–vis spectroscopy were employed to elucidate the synthesized titanate nanostructure characteristics which were microstructure, phase transformation, specific surface area, and band gap energy, respectively. With an increase in the hydrothermal treating temperature from 90 to 120 °C, the specific surface area of titanate nanostructures was increased from 83 to 258 m²/g, while the band gap energy of titanate nanostructures was increased from 3.44 to 3.84 eV and then slightly decreased to 3.81 eV at 150 °C. The fabricated titanate nanostructures could exhibit higher UV adsorption capability but lower photocatalytic activity when compared with that of commercial TiO₂ powders.     

Comparison of the electrochemical properties of intermediate temperature solid oxide fuel cells based on protonic and anionic electrolytes

The physico-chemical properties of two protonic electrolytes BaCe_0.8Y_0.2O_3-δ and BaCe_0.9Y_0.1O_3-δ were investigated. The BaCe_0.8Y_0.2O_3-δ electrolyte showed better crystallographic purity and lower amount of carbonate phase on the surface. A comparison between the BaCe_0.8Y_0.2O_3-δ protonic electrolyte supported cell and an anionic (Ce_0.8Gd_0.2O_1.95) one was made. The maximum power densities (IR-free) of 183 mW cm⁻² and 400 mW cm⁻² were obtained in H₂ (R.H. 3%) at 700 °C, for the protonic and anionic electrolyte based cells, respectively.     

Microstructure and morphology in the PVDF films doped with BiCl<Subscript>3</Subscript>

Polyvinylidene fluoride (PVDF) thick films doped with BiCl₃ were fabricated by solvent casting method, and their physical properties were systematically investigated, respectively, by X-ray diffraction (XRD), Fourier transform Infrared (FTIR), and scanning electron microscopy (SEM) in this article. It revealed that the degree of crystallinity increased with the increase of the mass fraction of BiCl₃, and the maximum β-phase content was achieved if the mass fraction was 2%. When 2% BiCl₃ was added, the films became compact and the character morphology of β-phase of spherulitic crystal was proved by the typical organic material with snow-shaped structures. The experimental results suggested that a complex was formed due to the electric ions ionized by BiCl₃ and the free radicals with electric charge, destroyed the structure around the lattice, and returned some free radicals to their original positions, thus enhancing the degree of crystallization of β-phase PVDF. The relative dielectric constant and loss became greater as the mass fraction of BiCl₃ increased, but the loss decreased at 2% BiCl₃. The relationship between the microstructure and dielectric properties was discussed.     

Solubility of CO2 in solid-state PET measured by pressure-decay method

The solubility of CO₂ in solid-state PET was measured using a pressure-decay method. In order to calculate the solubility of CO₂ in the amorphous region of PET, the crystallinity of solid state PET dissolved in CO₂ at different pressures and temperatures was measured by differential scanning calorimetry (DSC). The solubility increases with increasing pressure and it follows a linear relationship and obeys Henry’s law when the pressure is below 8 MPa. The effect of temperature on solubility is weak and the solubilities at different temperatures are almost the same under low pressures. At higher pressure, the solubility decreases with an increase in temperature. The solubility of CO₂ in the amorphous region of PET at 373.15 K, 398.15 K and 423.15 K was correlated with the Sanchez-Lacombe equation of state with a maximal correlation error of 6.69%. __________ Translated from Journal of East China University of Technology (Natural Science Edition), 2007, 33(4): 445–449 [译自: 华东理工大学学报(自然科学版)]     

Polymorphism of POS. II. kinetics of melt crystallization

Melt crystallization of four polymorphs of POS, α,δ, pseudo-β′ andβ, was examined with pure samples (>99.9%). Induction time, τ, for newly occurring crystals was measured with a polarizing microscope equipped with a temperature-controlled growth cell. Rate of crystallization, 1/τ, was obtained for each polymorph, whose identification was done with x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Two modes of crystallization, melt cooling and melt mediation, were applied. From these experiments, the following conclusions were obtained: (i) The rate of melt-mediated crystallization was always higher than of simple melt cooling; (ii) the pseudo-β′ form was crystallized in a wider range of temperature than the less stable δ form; (iii) the occurrence behavior of the polymorphs differed between simple melt cooling and melt mediation; (iv) the δ form was crystallized only by simple melt cooling in a narrow range of temperature, 25.5°C∼28.3°C. This means that there is a possibility that δ may result from racemic compounds that are crystallized in a specific manner. The experimental results are discussed in comparison to 1,3-dipalmitoyl2-oleoylglycerol (POP), 1,3-distearoyl-2-oleoylglycerol (SOS) and cocoa butter.     

Crystallization kinetics of palm stearin in blends with sesame seed oil

This study investigates the crystallization kinetics of palm stearin (PS), a palm oil fraction, in blends with sesame seed oil. The results indicate that the crystallization behavior of PS in sesame oil is mainly associated with the crystallization of tripalmitin. Therefore, crystallization of blends of 26, 42, 60, and 80% (wt/vol) PS in sesame oil was described by equations developed for simpler systems (e.g., Fisher and Turnbull equation). The isothermal crystallization, melting profile, and fitting of the kinetics of nucleation to the Fisher and Turnbull equation showed that the 26, 42, and 60% PS/sesame oil blends crystallized mainly in the β₁′ polymorph state. In contrast, the 80% blend crystallized in two different polymorph states (i.e., β₁′ at T⪯307.6 K and β₁ at T≽308.2 K). The data indicated that, in spite of the higher concentration of PS in the 80% PS/sesame oil system, crystallization in the β₁ state required more free energy for nucleation (δG _c ) than β₁′ crystallization in the 26, 42, and 60% PS/sesame oil. At the low cooling rate used (1 K/min) it was observed that, for a particular PS blend, the higher the effective supercooling the higher the viscosity of the oil phase and the smaller the induction time of crystallization (T_i). Additionally, the β₁′ crystals from PS, developed at the highest effective supercooling investigated, were smaller than the β₁ crystals obtained at lower effective supercooling.     

Investigation on multiple-melting behavior of nano-CaCO3/polypropylene composites

The multiple melting-peak behavior of polypropylene (PP) in nano-CaCO₃/PP composites and modified nano-CaCO₃/PP composites were investigated under the condition of isothermal crystallization and nonisothermal crystallization. The result indicated that the addition of nano-CaCO₃ markedly increased the crystallization temperatures of PP and induced the formation of the β-crystal of PP. The crystallization temperatures of nano-CaCO₃/PP composites modified by reactive monomers were further increased, but the melting-peak intensity of the β-crystal of PP was not greatly influenced. While in the presence of dicumyl peroxide, nano-CaCO₃/PP composites modified by reactive monomers led to the significant increase in the melting-peak intensity of the β-crystal of PP. The double melting-peak of PP was observed, which was attributed to the formation of two kinds of different crystallization forms of α-crystal or β-crystal during the crystallization of PP. With the increase of crystallization temperatures, the double melting-peak moved toward the high-temperature side. The intensity of high-temperature melting peak was higher than that of low-temperature melting peak in nano-CaCO₃/PP composites. While in modified nano-CaCO₃/PP composites crystallized at higher temperature, the intensity of high-temperature melting peak was lower than that of low-temperature melting peak. The isothermal crystallization time had little effect on the melting temperatures. Translated from Acta Scientiarum Naturalium Universitatis Sunyatseni, 2006, 45(2): 41–45 [译自: 中山大学学报 (自然科学版)]     

Effect of fast neutrons on dielectric properties of pure and gelatin doped-poly (vinyl alcohol) films

Cast thin films of pure and gelatin doped poly(vinyl alcohol) (PVA) with concentrations of 2, 5, 7, 10, and 15 wt% were prepared and subjected to fast neutron fluences in the range of 10⁵–10⁸ n/cm². The dielectric constant (ε′), dielectric loss tangent (tanδ) and a.c. electrical conductivity (σ_a,c) were investigated as a function of field frequency and temperature for all samples before and after irradiation. A clear glass transition peak was observed in ε′(T) and tanδ(T) curves. The irregular shift in the position of the glass transition temperature (T_g) in tanδ spectra with increasing neutron fluence can be attributed to either degradation or the predominance of the crosslinking process. The electric dipole moment and activation energy were calculated for pure and gelatin doped PVA samples before and after neutron irradiation.