Multiform oxide optical materials via the versatile Pechini-type sol-gel process: Synthesis and characteristics

This feature article highlights work from the authors' laboratories on the various kinds of oxide optical materials, mainly luminescence and pigment materials with different forms (powder, core-shell structures, thin film and patterning) prepared by the Pechini-type sol-gel (PSG) process. The PSG process, which uses the common metal salts (nitrates, acetates, chlorides, etc.) as precursors and citric acid (CA) as chelating ligands of metal ions and polyhydroxy alcohol (such as ethylene glycol or poly ethylene glycol) as a cross-linking agent to form a polymeric resin on molecular level, reduces segregation of particular metal ions and ensures compositional homogeneity. This process can overcome most of the difficulties and disadvantages that frequently occur in the alkoxides based sol-gel process.

Facile Synthesis and Luminescence Properties of Highly Uniform MF/YVO4:Ln(3+) (Ln = Eu, Dy, and Sm) Composite Microspheres

Uniform MF/YVO4:Ln(3+) (Ln = Eu, Dy, and Sm) composite microspheres have been prepared via a simple and economical wet-chemical route at ambient pressure and low temperature. Monodisperse micrometer-sized melamine formaldehyde (MF) colloidal particles were first fabricated by a condensation process of melamine with formaldehyde. Subsequently, well-dispersed YVO4 nanoparticles were successfully grown onto the MF microspheres to form core-shell structured composite particles in aqueous Solution. The as-obtained composite microspheres with perfect spherical shape are uniform in size and distribution, and the thickness and roughness of the YVO4 shells on MF cores could be tuned by varying the reaction temperature. The MF/YVO4:Ln(3+) composite phosphors show strong light emissions with different colors coming from different activator ions under ultraviolet excitation, which might find potential applications in fields such as light phosphor powders and advanced flat panel displays.

General and Facile Method To Prepare Uniform Y2O3:Eu Hollow Microspheres

Well-shaped Y2O3:Eu hollow microspheres have been successfully prepared on a large scale via a urea-based homogeneous precipitation technique in the presence of colloidal carbon spheres as hard templates followed by a subsequent heat treatment process. XRD results demonstrate that all the diffraction peaks of the samples can be well indexed to the pure cubic phase Of Y2O3. TEM and SEM images indicate that the shell of the uniform hollow spheres, whose diameters are about 250 nm, is composed of many uniform nanoparticles with diameters of about 20 nm, basically consistent with the estimation of XRD results. Furthermore, the main process in this method was carried out in aqueous condition, without the use of organic solvents or etching agents. The as-prepared hollow Y2O3:Eu microspheres show a strong red emission corresponding to the D-5(0)-F-7(2) transition of the Eu3+ ions under ultraviolet or low voltage excitation, which might find potential applications in fields such as light phosphor powders, advanced flat panel displays, field emission display devices, and biological labeling.

A study of the effect of shell content on the mechanical properties of polycarbonate/poly(butyl acrylate)-cs-poly(methyl methacrylate) blends

The toughening effect of the shell content of a core-shell latex polymer poly(butyl acrylate) (PBA)-cs-poly(methyl methacrylate) (PMMA) on its blends with polycarbonate (PC) was studied. The changes of mechanical properties, morphology, and compatibility of the blends of PC/PBA-cs-PMMA with the change of the shell thickness of PBA-cs-PMMA were investigated. It is interesting to notice that mechanical properties of the blends are very sensitive to the shell thickness (i.e., shell content), and that there is a possibility to adjust the impact and tensile properties of the blend by selecting a PBA-cs-PMMA with a proper core/shell ratio. Hence, a modified PC material with balanced mechanical properties may be prepared.

Spatially separated excitons in quantum-dot quantum well structures

In the framework of the effective-mass envelope-function theory, the electronic and optical properties of a spherical core-shell quantum-dot quantum well (QDQW) structure with one and two wells have been investigated. The results show that the energies of electron and hole states depend sensitively on the well thickness and core radius of quantum-dot quantum well structure. An interesting spatially separated characteristic of electron and hole in QDQW is found and enhanced significantly in the two-wells case. The normalized oscillator strength for the optical transition between the electron and hole states in QDQW exhibits a deep valley at some special well thickness. The Coulomb interaction between the electron and hole is also taken into account. [S0163-1829(98)02412-6].

核壳结构改性剂增韧聚氯乙烯的机理及性能优化

我国是世界上聚氯乙烯产量最大的国家。由于在氯乙烯分子中氯的含量大于50%，而氯又是制碱工业的必然副产物，因此聚氯乙烯工业成为氯碱平衡中的主要杠杆。随着近年来世界石油资源的日益短缺和价格的上涨及国内聚氯乙烯产能过剩，开发聚氯乙烯的新用途，发展聚氯乙烯树脂的改性具有深远的意义。本工作的目的是以开发PVC核壳结构改性剂MBS和注塑级PVC/ABS合金为背景，对核壳粒子改性的聚氯乙烯的屈服机理和改性剂性能优化进行了研究。 对于增韧剂的研究，人们总是希望用最少的增韧剂用量来达到最好的增韧效果，即提高增韧剂的增韧效率，而且MBS改性的PVC在应用时还需要保持较高的透光率和具有一定的抗应力发白的能力。为此我们成功开发了具有高增韧效率、高透明及抗应力发白的MBS增韧剂，并研究了MBS结构特性对PVC/MBS共混物力学性能及屈服机理的影响。结果表明：粒径范围在80nm~280nm的橡胶粒子均能有效地对PVC进行增韧。大粒径的MBS通过空洞化释放三维静张应力引发基体的屈服来吸收能量，而小粒径的MBS不能产生空洞，但同样能引起基体的屈服起到增韧的作用。为了兼顾PVC/MBS共混物的韧性和透明性，我们在制备MBS时将一部分苯乙烯单体与丁二烯共聚结合来提高丁苯胶乳的折光指数与PVC基体相匹配，而另一部分苯乙烯单体以接枝的方式结合，这样可以保持MBS的弹性，并且制备的PVC/MBS共混物具有高韧性和高透明；同时我们发现MBS的内包容物及多层结构都会削弱PVC/MBS共混物的透光率。研究表明橡胶粒子的空洞化是引发共混物应力发白的主要原因。为此通过制备小粒径及具有一定交联程度的MBS来抑制空洞的产生，制备了兼有抗应力发白和韧性的MBS。成功开发了多个牌号的MBS产品，并在吉化集团公司建成了年产5000吨的生产车间，实现了MBS的工业化生产。 由于PVC的熔体流动性较差，通过与熔体流动性好的ABS树脂共混，成功开发了注塑级PVC/ABS合金。ABS树脂是SAN树脂和PB-g-SAN的共混物，在PVC中加入ABS使增韧对象由PVC基体转化为PVC/SAN共混基体，并研究了基体性质的改变对增韧效果的影响。结果表明随着PVC/ABS共混体系基体中PVC含量的增加共混物的冲击强度显著增加，形变机理发生了由银纹向剪切屈服的转变。

Synthesis and micellization of star-like hyperbranched polymer with poly(ethylene oxide) and Poly(epsilon-caprolactone) arms

Novel star-like hyperbranched polymers with amphiphilic arms were synthesized via three steps. Hyperbranched poly(amido amine)s containing secondary amine and hydroxyl groups were successfully synthesized via Michael addition polymerization of triacrylamide (TT) and 3-amino-1,2-propanediol (APD) with feed molar ratio of 1:2. H-1, C-13, and HSQC NMR techniques were used to clarify polymerization mechanism and the structures of the resultant hyperbranched polymers

Metal nanomaterials and carbon nanotubes - synthesis, functionalization and potential applications towards electrochemistry

This review focuses on the synthesis, assembly, surface functionalization, as well as application of inorganic nanostructures. Electrochemical and wet- chemical methods are demonstrated to be effective approaches to make metal nanostructures under control without addition of a reducing agent or protecting agent. Owing to the unique physical and chemical properties of the nano-sized materials, novel applications are introduced using inorganic nanomaterials, such as electrocatalysis, photoelectricity, spectrochemistry, and analytical chemistry.

Research progress on noble metal composite nanoparticles

Noble metal composite nanoparticles, as attractive building blocks of advanced functional materials, have received enormous attentions due to their specific optical, electronic and catalytic properties that are distant from those of the corresponding monometal nanoparticles. Such materials have important applications in such areas as sensors, optical materials, catalysis and biology, and developed into an increasingly important research area in nanomaterials science. This article reviews the recent progress in the synthesis, properties, and applications of noble metal composite nanoparticles with core-shell, heterostructure, and alloy structure.

A simple selenium source to synthesize CdSe via the two-phase thermal approach

A novel selenium source was developed to synthesize the size-controlled CdSe nanocrystals with relatively narrow size distribution successfully in a two-phase thermal approach. A highly reactive and aqueous soluble selenium source was provided by the reduction of selenite, and in this route the size of the nanocrystals can be adjusted by the reaction temperature and time. The size, crystalline structure and optical characteristics of these nanocrystals were investigated by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and photoluminescence spectroscopy. The influence factors for this approach were also discussed.