An investigation on the dispersion of montmorillonite (MMT) primary particles in PP matrix

A novel path of preparing PP/o-MMT nanocomposites, which pay attention to the breaking up of MMT original agglomerates and dispersing of its primary particles, rather than the intercalation or exfoliation degree of o-MMT, was reported. The method of predispersing the o-MMT particles into a polar poly(vinyl alcohol) (PVA) matrix and then melt blending the pre-treated PVA/o-MMT hybrids with PP was studied. 3-Isopropenyl-α,α-dimethylbenzene-isocyanate (TMI) was used as a modifier of PVA to improve the compatibility between PVA and PP matrix. Pre-disperse o-MMT with TMI modified PVA was proved to be an effective way to get a composite with fine o-MMT particles dispersion. But the method, which is pre-dispersing o-MMT with non modified PVA and then using TMI to modify such PVA/o-MMT hybrid, would largely reduce the reaction degree between TMI and PVA because of the relatively lower reaction temperature. Although the latter method also can obtain finer dispersion composites than that with using PP-g-MAH as compatibilizer, the relatively higher degradation degree of PP matrix in this method will limit the use of this nanocomposite.     

In situ growth of metal particles on 3D urchin-like WO3 nanostructures

Metal/semiconductor hybrid materials of various sizes and morphologies have many applications in areas such as catalysis and sensing. Various organic agents are necessary to stabilize metal nanoparticles during synthesis, which leads to a layer of organic compounds present at the interfaces between the metal particles and the semiconductor supports. Generally, high-temperature oxidative treatment is used to remove the organics, which can extensively change the size and morphology of the particles, in turn altering their activity. Here we report a facile method for direct growth of noble-metal particles on WO(3) through an in situ redox reaction between weakly reductive WO(2.72) and oxidative metal salts in aqueous solution. This synthetic strategy has the advantages that it takes place in one step and requires no foreign reducing agents, stabilizing agents, or pretreatment of the precursors, making it a practical method for the controlled synthesis of metal/semiconductor hybrid nanomaterials. This synthetic method may open up a new way to develop metal-nanoparticle-loaded semiconductor composites.     

Biochemical investigation of the formation of three-dimensional networks from DNA-grafted large silica particles

DNA is used to rationally build up networks of silica nanoparticles (SiNPs) based on the molecular recognition properties of complementary sequences. Network self-assembly is controlled from DNA covalently grafted at the surface of chemically modified SiNPs. Two strategies are compared, where grafted DNA sequences are designed in a three-strand system using noncomplementary sequences and an extra DNA linker, or in a two-strand approach for direct hybridization. In this paper, both systems are compared in terms of DNA hybridization stability, network size, and three-dimensional organization using a combination of dynamic light scattering and electron microscopy. The observed differences are discussed in terms of hybridization interactions between DNA sequences in particle-free systems through fluorescence, circular dichroism, and UV spectroscopy techniques.     

Correlation between crystallite size and photocatalytic performance of micrometer-sized monoclinic WO3 particles

The correlation between crystallite size and the characteristics of micrometer-sized photocatalyst particles was investigated. As a model of photocatalyst, monoclinic tungsten trioxide particles with controllable crystallite sizes were used. The crystallite size was controlled independently in the constant particle outer diameters to comprehend the crystallite size parameters precisely. To minimize the misleading photocatalytic measurements due to the over-dominancy of other catalytic parameters (such as excessive surface area and quantum confinement effect), the present study utilized micrometer-sized particles. The results revealed that in the constant process condition, the photocatalytic properties were strongly dependent on the material crystallinity. Increases in the crystallite sizes had a strong influence to the enhancement of the photodecomposition rate of organic material. The tendency for the impact of crystallite size was also confirmed by varying the number of catalysts in the photocatalytic process. To confirm the analysis of photocatalysis, the study was completed with the theoretical consideration and the proposal of the particle formation as well as the phenomena that happen during the photocatalytic process.     

Chemical assembling of silica surface using a reaction of catalytic hydrosilylation

Chemical assembling of the silica surface modified by dimethylchlorosilane was performed by the catalytic hydrosilylation of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, α-methyl styrene, acetophenone, allyl butyl and allyl glycidyl ethers with dimethylchlorosilane. The effect of the nature of complexes of platinum, palladium, rhodium and ruthenium on the parameters of hydrosilylation was studied. It was shown that the maximum rate of hydrosilylation was observed in the reaction with allyl glycidyl ether, and minimum, with α-methylstyrene; the most effective catalyst of hydrosilylation was [Rh(CO)₂(acac)].     

Gas chromatography on 10 um silica particles

Summary Porous silica microparticles designed for modern liquid chromatography have proven effective in gas chromatography. Columns of 35–50 cm gave plate heights as low as 3.3 particle diameters and speeds of 2400 theoretical plates per second or 500 effective theoretical plates per second. Inlet pressures up to 70 atmospheres were required using hydrogen as carrier gas. The particles as received were too retentive for fast chromatography and gave asymmetric peaks. A coating of fluorosilicone oil overcame both problems. Other coatings were less effective. Bonded phases proved less satisfactory on both counts and also gave substantially less efficient columns and greater flow resistance. Column efficiency and flow resistance were sharply dependent on physical properties of the particles. The most efficient packing was clearly spherical particles of 5–10 μm diameter with narrow size distribution, pore diamters about 50 nm, BET surface areas of 25–50 m²/g and surfaces modified with trifluoropropyl silicone. A six-component hydrocarbon sample was separated in 33 s with a resolution of 4 for the most difficult pair and in 2.6 s with a minimal resolution. Performance was limited by end effects and by available pressure so that much better performance can be expected from longer columns and higher pressures.     

An investigation of the properties of poly(dimethylsiloxane)-bioinspired silica hybrids

Elastomers typically require the incorporation of reinforcing fillers in order to improve their mechanical properties. For commercial silicone systems silica and titania are typically used as fillers. Fumed and precipitated silica are made on an industrial scale for many applications; however, we have shown recently that biological and synthetic macromolecules can generate new silica structures using a bioinspired route. Herein we have incorporated bioinspired silica fillers into poly(dimethylsiloxane) (PDMS) elastomers and investigated their mechanical, morphological and thermal properties as a function of filler loading. The equilibrium stress-strain characteristics of the PDMS-bioinspired silica hybrids were determined as a function of bioinspired filler loading and the Mooney-Rivlin constants (2C₁ and 2C₂) were calculated. The thermal characteristics, in particular glass transition temperatures (T_g) and melting points (T_m), of the PDMS-bioinspired silica hybrids were characterized using differential scanning calorimetry (DSC). The thermal stability of these hybrid materials were investigated using thermogravimetric analysis (TGA). The morphology of the samples was characterized using scanning electron microscopy (SEM), and the filler dispersion was characterized using ultra small angle X-ray scattering (USAXS) and scanning electron microscopy (SEM). Although spherical silica particles were used here, we have demonstrated elsewhere that this bioinspired synthetic route also enables highly asymmetric silica structures to be prepared such as fibres and sheets. This methodology therefore offers the interesting possibility of preparing new hybrid systems where the properties are highly anisotropic.     

Modification of the silica particles surface with perfluoroalkylmethyloxiranes

Silica particles have been prepared via the sol-gel process in the presence of perfluoropropyl- and perfluorobutylmethyloxiranes. Nanoparticles are formed in the presence of acidic catalyst. Under conditions of basic catalysis the attack of silanol group (formed in situ via hydrolysis of tetraethoxysilane) on the oxirane ring leads likely to the Si-O-C bond formation.     

Composite particles of polyethylene @ silica

Polyethylene (PE) and silica are perhaps the simplest and most common organic and inorganic polymers, respectively. We describe, for the first time, a physically interpenetrating nanocomposite between these two elementary polymers. While polymer-silica composites are well known, the nanometric physical blending of PE and silica has remained a challenge. A method for the preparation of such materials, which is based on the entrapment of dissolved PE in a polymerizing tetraethoxysilane (TEOS) system, has been developed. Specifically, the preparation of submicron particles of low-density PE@silica and high-density PE@silica is detailed, which is based on carrying out a silica sol-gel polycondensation process within emulsion droplets of TEOS dissolved PE, at elevated temperatures. The key to the successful preparation of this new composite has been the identification of a surfactant, PE-b-PEG, that is capable of stabilizing the emulsion and promoting the dissolution of the PE. A mechanism for the formation of the particles as well as their inner structure are proposed, based on a large battery of analyses, including transmission electron microscopy (TEM) and scanning electron microscopies (SEM), surface area and porosity analyses, various thermal analyses including thermal gravimetric analysis (TGA/DTA) and differential scanning calorimetry (DSC) measurements, small-angle X-ray scattering (SAXS) measurements and solid-state NMR spectroscopy.     

Network structure of fine silica particles

The network structure of silica aerogels heated at 300, 400 and 500°C in dried air have been determined by neutron total scattering measurements using a pulsed spallation neutron source. SANS experiments were also performed to obtain the particle size of the silica constituting aerogel. The elementary particle size obtained is about 13Å in diameter. The distances of the Si-O and O-O interactions in such fine silica particles are 1.61 and 2.64 Å, respectively, which are the same as those of fused silica. The coordination numbers of these pairs are found to be less evident than those of fused silica. In addition, the distances of the Si-Si pairs in the aerogels are slightly longer than that of fused silica. According to the heat treatment temperature, the coordination numbers of the Si-O and O-O interactions increase and the distance of the Si-Si pair decreases. These results indicate that although the network structure of fine silica particles treated at lower temperature is loose and imperfect, such structure can be changed by heating at relatively low temperature. The Raman spectra and the skeletal density measurements of the aerogels support also these results.     

Surface modification of colloidal silica particles

Colloidal silica particles in organic solvents were grafted, using several reagents, in order to make them hydrophobic. The hydrophobicity of the beads could be easily varied. Quasielastic light scattering and transmission electron microscopy experiments showed that no aggregation occurs during the reaction when monofunctional agents are used. Elemental analysis and solid-state NMR measurements gave us the rate of surface modification of the silanol groups. We also studied the rheological behaviour of the grafted particles as a function of the volume fraction in solvents of various hydrophobicity. Hexamethyldisilazane-grafted particles display hard-sphere behaviour in polar solvents such as 2-propanol, but not in alkanes, whereas dimethyldodecylchlorosilane-grafted particles flocculated in polar solvents but could easily be dispersed in apolar solvents. Received: 15 March 2000 Accepted: 11 July 2000     

纳米二氧化硅的表面改性研究

以γ-缩水甘油醚丙基三甲氧基硅烷(GPTMS)对酸催化水解正硅酸乙酯(TEOS)聚合得到的纳米二氧化硅胶粒表面进行接枝改性,用激光粒径仪测定二氧化硅颗粒的粒径,并用透射电子显微镜(TEM)观察了改性前后二氧化硅胶粒的分散状况,采用傅立叶红外(FTIR)光谱法对改性前后的二氧化硅粉体进行了分析,通过热失重分析(TGA)法对GPTMS接枝改性二氧化硅胶粒表面的接枝度进行分析计算,同时对颗粒溶胶的ζ电位进行了测试,结果表明:改性后二氧化硅胶粒分散性大大提高,硅烷偶联剂浓度对接枝度有显著影响,当GPTMS的浓度为1mL/S iO2(g)时,接枝度达到最大,且颗粒表面的物理化学性能发生显著变化。     

Adsolubilization of dihydroxybenzenes into CTAB layers on silica particles

The adsolubilization of dihydroxybenzenes (catechol and hydroquinone) into cetyltrimethylammonium bromide (CTAB) layers on silica particles have been investigated by dye method and UV spectrum. It is found that the adsolubilization amount of catechol increases with increasing the concentration of CTAB, reaches a maximum value at the critical micelle concentration (CMC), and then decreases with further increment of CTAB concentration. For hydroquinone, different phenomenon is observed. The maximum adsolubilization amount reaches at critical surface aggregation concentration (CSAC) instead of CMC of the CTAB and then decreases to constant values. In order to analyze the adsolubilization difference between catechol and hydroquinone, we determined the interaction between them and CTAB in the bulk solution by measuring the diffusion coefficient of dihydroxybenzenes with ultramicroelectrode (UME). The individual contributions to the overall apparent diffusion coefficient of dihydroxybenzenes in CTAB solutions were also calculated. The results indicate that more hydroquinone than catechol could interact with CTAB molecules. However, rarely hydroquinone could interact with CTAB micelles compared with catechol. It is suggested that the substitution positions of hydroxyl lead to the difference of the interaction between dihydroxybenzenes and CTAB, which is responsible for the difference of the adsolubilization.     

Dye-sensitized solar cells based on WO3

In research on alternative photoanode materials for dye-sensitized solar cells (DSCs), there is rarely any report on WO(3), probably due to its acidic surface and more positive (vs NHE) conduction band edge position compared to TiO(2) and ZnO. For the first time, dye-sensitized solar cells based on porous WO(3) nanoparticle films were successfully fabricated with efficiency of up to 0.75%. The multicrystalline structure of WO(3) was examined by Raman spectroscopy and X-ray diffraction analysis. It was found that significant performance enhancement can be obtained from treating the WO(3) nanoparticle film with TiCl(4); the TiCl(4)-treated WO(3) DSCs were recorded with efficiency reaching 1.46%.     

Synthesis of silica in elastomer's matrix

We tried to synthesise silica's fillers in polar and nonpolar elastomers. Di-, tri- and tetraalkoxysilanes were used as a precursor of silica. Such functionality allowed us to obtain a filler with different ratio of crosslinking. We could expect some interactions between elastomer and silanes, which contained additional functional groups. We investigated vulcanizates by using the following methods: crosslink density in toluene and 10% solution of ethylenediamine in toluene, mechanical properties, IR microscopy, DMA. It appeared that alkoxysilanes influenced advantageously on elastomers and properties.     

An expedient multicomponent assembling of 1-azaxanthones

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WO3 homojunction photoanode: Integrating the advantages of WO3 different facets for efficient water oxidation

The manipulation of the surface property of WO₃ photoanode is the main breakthrough direction to improve its solar water oxidation performance both in thermodynamics and kinetics.Here,we report a WO₃(002)/m-WO₃ homojunction film that is composed of an upper WO₃ layer with predominant(002)facet(WO₃(002))and a lower WO₃ layer with multi-crystal facets(m-WO₃)as a photoanode for solar water oxidation.Due to the synergistic effect of WO₃(002)layer and m-WO₃ layer,better water oxidation activity and stability are achieved on the WO₃(002)/m-WO₃ homojunction film relative to the m-WO₃ and WO₃(002)film.Specifically,the improved water oxidation performance on the WO₃(002)/m-WO₃ homojunction film is attributed to the followings.In thermodynamics,the band position differences between WO₃(002)layer and m-WO₃ layer lead to the formation of WO₃(002)/m-WO₃ homojunction,which has positive function of improving their charge separation and transfer.In kinetics,the upper WO₃(002)layer of the WO₃(002)/m-WO₃ film has superior activity in the adsorption and activation of water molecules,water oxidation on this homojunction film photoanode is inclined to follow the four-holes pathway,and the corrosion of photoanode from the H₂O₂ intermediate is restrained.The present work provides a new strategy to modify the WO₃ photoanodes for thermodynamically and kinetically efficient water oxidation.     

Characterization of polymer-coated silica particles by microelectrophoresis

Electrophoretic mobility measurements have been used to characterize monodispersed colloidal particles of silica, silica coated with alumina (cores), of these cores incorporating a dye (pigments), and finally of pigments coated with polymers. The latter consisted of poly(divinylbenzene), of poly(vinylbenzyl chloride), and of their copolymers, synthesized directly on the core or pigment particles, with and without subsequent sulfonation.     

Influence of the initial chemical conditions on the rational design of silica particles

The influence of the water content in the initial composition on the size of silica particles produced using the Stöber process is well known. We have shown that there are three morphological regimes defined by compositional boundaries. At low water levels (below stoichiometric ratio of water:tetraethoxysilane), very high surface area and aggregated structures are formed; at high water content (>40?wt%) similar structures are also seen. Between these two boundary conditions, discrete particles are formed whose size are dictated by the water content. Within the compositional regime that enables the classical Stöber silica, the structural evolution shows a more rapid attainment of final particle size than the rate of formation of silica supporting the monomer addition hypothesis. The clearer understanding of the role of the initial composition on the output of this synthesis method will be of considerable use for the establishment of reliable reproducible silica production for future industrial adoption.

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