Synthesis of neodymium hydroxide nanotubes and nanorods by soft chemical process

A facile soft chemical approach using cetyltrimethylammoniurn bromide (CTAB) as template is successfully designed for synthesis of neodymium hydroxide nanotubes. These nanotubes have an average outer diameter around 20 nm, inner diameter around 2 nm, and length ranging from 100 to 120 nm, high BET surface area of 495.71 m(2) g(-1). We also find that neodymium hydroxide nanorods would be obtained when CTAB absented in reaction system. The Nd(OH)(3) nanorods might act as precursors that are converted into Nd2O3 nanorods through dehydration at 550 degrees C. The nanorods could exhibit upconversion emission characteristic under excitation of 591 nm at room temperature.

Synthesis and photoluminescence of Y2O3 : RE3+ (RE = Eu, Tb, Dy) porous nanotubes templated by carbon nanotubes

Y2O3:RE3+ (RE = Eu, Tb, Dy) porous nanotubes were first synthesized using carbon nanotubes as template. The morphology of the coated precursors and porous Y2O3:Eu3+ nanotubes was determined by scanning electron Microscopy (SEM) and transmission electron microscopy (TEM). It was found that the coating of precursors on carbon nanotubes (CNTs) is continuous and the thickness is about 15 nm, after calcinated, the Y2O3:Eu3+ nanotubes are porous with the diameter size in the range of 50-80 nm and the length in micrometer scale. X-ray diffraction (XRD) patterns confirmed that the samples are cubic phase Y2O3 and the photoluminescence studies showed that the porous rare earth ions doped nanotubes possess characteristic emission of Eu3+, Tb3+, and Dy3+. This method may also provide a novel approach to produce other inorganic porous nanotubes used in catalyst and sensors.

The influence of arrangement of St in MBS on the properties of PVC/MBS blends

Three series of MBS core-shell impact modifiers were prepared by grafting styrene and methyl methacrylate onto PB or SBR seed latex in emulsion polymerization. All the MBS modifiers were designed to have the same total chemical composition, and MMA/Bd/St equals 30/42/28, which is a prerequisite for producing transparent blends with PVC. Under this composition, there were three different ways of arrangement for styrene in MBS, which led to the different structure of MBS modifier. The concentration of MBS in PVC/MBS blends was kept at a constant value of 20 wt.%. The effects of arrangement of St in MBS on the mechanical and optical properties of PVC/MBS blends were studied. The notched Izod impact test results showed that the MBS with a PB homopolymer core grafted with St had a lowest brittle-ductile transition (BDT) temperature and BDT temperature increased with the amount of St copolymerized with Bd in the core of MBS. The transparency of blends also increased with the amount of St copolymerized with Bd in the core. TEM results showed that the arrangement of St in MBS influenced the deformation behavior. Two deformation modes were observed in the blends: cavitation and shear yielding.

Independence of the brittle-ductile transition from the rubber particle size for impact-modified poly(vinyl chloride)

A series of acrylic impact modifiers (AIMS) with different particle sizes ranging from 55.2 to 927.0 nm were synthesized by seeded emulsion polymerization, and the effect of the particle size on the brittle-ductile transition of impact-modified poly(vinyl chloride) (PVC) was investigated. For each AIM, a series of PVC/AIM blends with compositions of 6, 8, 10, 12, and 15 phr AIM in 100 phr PVC were prepared, and the Izod impact strengths of these blends were tested at 23 degrees C. For AIMs with particle sizes of 55.2, 59.8, 125.2, 243.2, and 341.1 nm, the blends fractured in the brittle mode when the concentration of AIM was lower than 10 phr, whereas the blends showed ductile fracture when the AIM concentration reached 10 phr. It was concluded that the brittle-ductile transition of the PVC/AIM blends was independent of the particle size in the range of 55.2-341.1 nm. When the particle size was greater than 341.1 nm, however, the brittle-ductile transition shifted to a higher AIM concentration with an increase in the particle size. Furthermore, the critical interparticle distance was found not to be the criterion of the brittle-ductile transition for the PVC/AIM blends.

Complex aggregates of spherical colloids via modified micromolding in capillaries

This paper describes a simple approach to fabricate aggregates composed of monodispersed silica microspheres by modified micromolding in capillaries (MIMIC). Two different kinds of contact modes, namely, conformal contact and non-conformal contact, between the poly(dimethylsiloxane) (PDMS) mold and the underlying prepatterned substrate, can be controlled during the micromolding, which result in the formation of different aggregates under the influence of template confinement and capillary forces. These aggregates, including woodpile structure, discoid, conoid and rectangular clusters, possess well-controlled sizes and orientation. The possible mechanisms for the formation of different aggregates are discussed in detail.

Hydrazide-functionalized hollow porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) spheres for immobilization of enzyme

Hollow porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate)(HEMA-co-EDMA) spheres were prepared by emulsifier-free emulsion polymerization, swelling, seed emulsion polymerization and extraction. Then the spheres activated with 2,4,6-trichloro-1,3,5-triazine were functioned with adipohydrazide (AH). After periodate oxidation of its carbohydrate moieties, horseradish peroxidase was immobilized on the hydrazide-functionalized hollow porous poly(HEMA-co-EDMA) spheres. The amount of immobilized enzyme was up to 43.4 mu g of enzyme/g of support. Moreover, the immobilized horseradish peroxidase exhibited high activity and good stability.

A novel way to synthesize high regular and periodic organic mesoporous silicas

Organic mesoporous silicas (OMSs) were synthesized in the presence of urea via one-pot synthesis method, in which tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethoxysilica (APTES) were used as the silica resources, non-ionic surfactant was used as the template. XRD results showed that the average periodic mesopore sizes of OMSs in the presence of urea were larger than those in the absence of urea. It was also found that the pore sizes of the products in the presence of urea distributed more narrowly than those in the absence of urea, and the contents of organosiloxane incorporated into OMSs, the pore wall thicknesses, the pore volumes and the surface areas of the products all increased with the use of urea. This shows a novel way to synthesize high regular and periodic organic mesoporous silicas.

Melt rheological properties of polypropylene-polyarnide6 blends compatibilized with maleic anhydride-grafted polypropylene

The melt rheological properties of binary uncompatibilized polypropylene -polyamide6 (PP-PA6) blends and ternary blends compatibilized with maleic anhydride-grafted PP (PP-PP-g-MAH-PA6) were studied using a capillary rheometer. The experimental shear viscosities of blends were compared with those calculated from Utracki's relation. The deviation value delta between these two series of data was obtained. In binary PP-PA6 blends, when the compatibility between PP and PA6 was poor, the deformation recovery of dispersed PA6 particles played the dominant role during the capillary flow, the experimental values were smaller than those calculated, and delta was negative. The higher the dispersed phase content, the more deformed the droplets were and the lower the apparent shear viscosity. Also, the absolute value of delta increased with the dispersed phase composition. In ternary PP-PP-g-MAH-PA6 systems, when the compatibility between PP and PA6 was enhanced by PP-g-MAH, the elongation and break-up of the dispersed particles played the dominant role, and the experimental values were higher than calculated. It was observed that the higher the dispersion of the PA6 phase, the higher the delta values of the ternary blends and the larger the positive deviation.

Deformation mechanism of polystyrene toughened with sub-micrometer monodisperse rubber particles

Core-shell polybutadiene-graft-polystyrene (PB-g-PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core-shell rubber particles were then blended with polystyrene to prepare PS/PB-g-PS blends with a constant rubber content of 20 wt%. PB-g-PS particles with a lower PB/PS ratio (<= 570/30) form a homogeneous dispersion in the polystyrene matrix, and the Izod notched impact strength of these blends is higher than that of commercial high-impact polystyrene (HIPS). It is generally accepted that polystyrene can only be toughened effectively by 1-3 mu m rubber particles through a toughening mechanism of multiple crazings. However, the experimental results show that polystyrene can actually be toughened by monodisperse sub-micrometer rubber particles. Scanning electron micrographs of the fracture surface and stress-whitening zone of blends with a PB/PS ratio of 70/30 in PB-g-PS copolymer reveal a novel toughening mechanism of modified polystyrene, which may be shear yielding of the matrix, promoted by cavitation.

Effects of SBS addition and temperature on 3D siliceous mesostructured cellular foam

Siliceous mesostructured cellular foam with three-dimensional (3D) wormhole structure (MSU-type) is prepared by using triblock copolymer (poly(styrene-b-butadiene-b- styrene), SBS) with both hydrophobic head and tail group as template in strong acid condition via microemulsion method. The effects of SBS addition and temperature on the morphology and physicochemical properties, such as pore diameters, surface areas and pore volumes of the materials have been investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM) and nitrogen adsorption-desorption analysis. The results show that the pore volumes, pore sizes and specific surface areas depend strongly on the SBS amount and forming micelles temperature. Moreover, the materials obtained with high wall thickness exhibit a relatively good thermal stability.

Controlling dispersed state and exfoliation process of clay in polymer matrix

In the present review, the authors do not try to provide a comprehensive review of researches on polymer/clay nanocomposites (PCNs), but some examples to demonstrate different exfoliation processes of the clay in various polymer matrixes and the dispersed state of clay. Interaction between polymers and layered silicates plays an important role in adjusting the exfoliation process of layered silicates and the microstructure of polymer nanocomposites. Properties of polymer/layered silicate nanocomposites mainly depend on the dispersed state of layered silicates. The authors will also address the outline of the present research in the direction of PCNs including the discussion of technical problems and their possible solutions.

Novel polyoxometalate-templated, 3-D supramolecular networks based on lanthanide dimers: Synthesis, structure, and fluorescent properties of [Ln(2)(DNBA)(4)(DMF)(8)][Mo6O19] (DNBA=3,5-dinitrobenzoate)

The spherical Lindquist type polyoxometalate, Mo6O192-, has been used as a noncoordinating anionic template for the construction of novel three-dimensional lanthanide-aromatic monocarboxylate dimer supramolecular networks [Ln(2)(DNBA)(4)(DMF)(8)][Mo6O19] (Ln = La 1, Ce 2, and Eu 3, DNBA = 3,5-dinitrobenzoate, DMF = dimethylformamide). The title compounds are characterized by elemental analyses, IR, and single-crystal X-ray diffractions. X-ray diffraction experiments reveal that two Ln(III) ions are bridged by four 3,5-dinitrobenzoate anions as asymmetrically bridging ligands, leading to dimeric cores, [Ln(2)(DNBA)(4)(DMF)(8)](2+); [Ln(2)(DNBA)(4)(DMF)(8)](2+) groups are joined together by pi-pi stacking interactions between the aromatic groups to form a two-dimensional grid-like network; the 2-D supramolecular layers are further extended into 3-D supramolecular networks with 1-D box-like channels by hydrogen-bonding interactions, in which hexamolybdate polyanions reside. The compounds represent the first examples of 3-D carboxylate-bridged lanthanide dimer supramolecular "host" networks formed by pi-pi stacking and hydrogen-bonding interactions encapsulating noncoordinating "guest" polyoxoanion species. The fluorescent activity of compound 3 is reported.

Molecular construction of oriented crystalline NaMnF3 and KMnF3 with perovskite structures at room temperature

In this work. we report the fabrication of high-quality (101)-oriented orthorhombic NaMnF3 and (100)-oriented cubic KMnF3 perovskites via an organic monolayer template at room temperature. The controlled crystallization under the organic monolayer template is explained in terms of the electrostatic interactions and beneficial lattice matching between the organic template and the ions undergoing nucleation. The present study is of great importance in the preparation of oriented perovskite materials as well as in the understanding of the mechanism for organic-template-directed crystallization.

Polyol-mediated synthesis of polyhedral silver clusters

Besides the spheres, polyhedral silver nanoclusters were prepared by the polyol process with 3-aminopropyl triethoxysilane (APTES). In the process, APTES acts as not only the stabilizer but also the template.

Biodegradable electrospun fibers for drug delivery

The influences of surfactants and medical drugs on the diameter size and uniformity of electrospun poly(L-lactic acid) (PLLA) fibers were examined by adding various surfactants (cationic, anionic, and nonionic) and typical drugs into the PLLA solution. Significant diameter reduction and uniformity improvement were observed. It was shown that the drugs were capsulated inside of the fibers and the drug release in the presence of proteinase K followed nearly zero-order kinetics due to the degradation of the PLLA fibers. Such ultrafine fiber mats containing drugs may find clinical applications in the future.