Home About us Contact
|
Home About us Contact | ||
|
|
||
Silica Composite (silica + composite)
Selected AbstractsPreparation and properties investigation of PMMA/silica composites derived from silicic acidPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2009H. P. Fu Abstract Hybrid materials based on silicic acid and polymethyl methacrylate (PMMA) were prepared by in situ bulk polymerization of a silicic acid sol and MMA mixture. Silicic acid sol was obtained by tetrahydrofuran (THF) extraction of silicic acid from water. Silicic acid was prepared by hydrolysis and condensation of sodium silicate in the presence of 3.6,M HCl. As a comparative study, PMMA composites filled by silica particles, which were derived from calcining the silicic acid gel, were prepared by a comparable in situ polymerization. Each set of PMMA/silica composites was subjected to thermal and mechanical studies. Residual THF in PMMA/silicic acid composites impacted the properties of the polymer composites. With increase in silica content, the PMMA composites filled with silica particles showed improved thermal and mechanical properties, whereas a decrease in thermal stability and mechanical strength was found for PMMA composites filled with silicic acid dissolved in THF. With a better compatibility with polymer matrix, silicic acid sol shows better reinforcement than silica particles in PMMA films prepared via blending of the corresponding THF solutions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Cationic Polymerization of 2-Vinylthiophene by Chloroarylmethanes as Surface Initiators on Silica and Consecutive Hydride Abstraction by AcceptorsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 12 2004Susanne Höhne Abstract Summary: 2-Vinylthiophene (2-VT) has been cationically polymerized using chloroarylmethane derivatives as the surface polymerization initiator on silica. By applying this procedure a soluble fraction of poly(vinylthiophene) (PVT) and PVT/silica composites can be simultaneously synthesized. The mass balance of the products (soluble fraction and hybrid particle fraction) depends significantly on temperature and 2-VT/silica ratio. The hydride abstraction reaction of PVT both in solution and immobilized on silica particle surface has been studied using 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ), tetrachloro-1,4-quinone (chloranile,=,ClA) and triphenylmethylium as reagents. The transformation process of PVT towards conjugated polymers has been studied with UV-vis spectroscopy and ESR spectroscopy. Cyclic voltammetry shows that chloranil is complexated with the formed polymer. Radical formation increases with increasing degree of conversion. The soluble fraction of the conjugated PVT sections formed is capable of reacting with each other as evidenced by GPC data. Structure of PVT/silica and resulting hybrid materials have been investigated by solid state 13C {1H} CP MAS NMR-spectroscopy showing a reaction of methine and methylene hydrogen atoms after treatment with DDQ or chloranil as hydride acceptors. For all poly-(2-vinylthiophene)/hydride acceptor systems studied, chloranil has been found to be the best reagent for the transformation of PVT towards conjugated polymers. Transformation of PVT in poly(2-ethinylthiophene) (PET) and PVT-PET copolymers. [source] Preparation of a variety of fluoroalkyl end-capped N -(1,1-dimethyl-3-oxobutyl)acrylamide oligomer/silica nanocomposites possessing no weight loss characteristic at 800°CPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2008Hideo Sawada Abstract A variety of fluoroalkyl end-capped N -(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF -(DOBAA)n - RF]/silica nanocomposites, in which the oligomer contents are 18,96%, were prepared by reactions of the corresponding fluorinated oligomer with tetraethoxysilane and silica nanoparticles under alkaline conditions. Each fluorinated oligomer/silica composite thus obtained is nanometer size-controlled very fine particles (22,68,nm) possessing a good dispersibility and stability in a variety of solvents including water. Interestingly, the weight loss of RF -(DOBAA)n -RF/silica nanocomposites, in which the oligomer contents are 18,72%, were not observed at all even at 800°C, as well as the original silica nanoparticles, although the corresponding sub-micrometer size-controlled RF - (DOBAA)n -RF/silica composites (particle size: 359,nm) decomposed completely at 800°C to afford the weight loss in proportion to the content of RF -(DOBAA)n -RF oligomer in composites. On the other hand, a slight weight loss of RF -(DOBAA)n -RF/silica nanocomposites, in which the oligomer contents are 75,94%, was observed at 800°C compared to that of the original silica nanoparticles. Copyright © 2008 John Wiley & Sons, Ltd. [source] Synthesis of Rhodium Colloidal Nano-Coating Grafted Mesoporous Silica Composite and its Application as Efficient Environmentally Benign Catalyst for Heck-Type Reaction of Arylboronic AcidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2008Liang Li Abstract The synthesis and characterization of rhodium colloidal layer grafted mesoporous SBA-15 material, designated as SBA-Rh, are presented. In the preparation of this new catalyst, SBA-15 mesoporous material was used as support without any pretreatment. The SiH functional groups were introduced onto the surface which resulted in highly dispersed metal colloid layer both on the outer and inner surface of the supporting material. The material was investigated for Heck-type coupling reactions of alkenes with ayboronic in organic/water solvent. The ultrahigh specific area, large pore opening, and highly dispersed catalyst species in SBA-Rh material created one of the most active heterogeneous catalysts for such reactions. Rhodium element was not detected in the final mixture by ICP after reaction. The catalyst species showed very high stability against leaching from the matrix and can be recycled for repeated use. [source] Preparation of a variety of fluoroalkyl end-capped N -(1,1-dimethyl-3-oxobutyl)acrylamide oligomer/silica nanocomposites possessing no weight loss characteristic at 800°CPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2008Hideo Sawada Abstract A variety of fluoroalkyl end-capped N -(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF -(DOBAA)n - RF]/silica nanocomposites, in which the oligomer contents are 18,96%, were prepared by reactions of the corresponding fluorinated oligomer with tetraethoxysilane and silica nanoparticles under alkaline conditions. Each fluorinated oligomer/silica composite thus obtained is nanometer size-controlled very fine particles (22,68,nm) possessing a good dispersibility and stability in a variety of solvents including water. Interestingly, the weight loss of RF -(DOBAA)n -RF/silica nanocomposites, in which the oligomer contents are 18,72%, were not observed at all even at 800°C, as well as the original silica nanoparticles, although the corresponding sub-micrometer size-controlled RF - (DOBAA)n -RF/silica composites (particle size: 359,nm) decomposed completely at 800°C to afford the weight loss in proportion to the content of RF -(DOBAA)n -RF oligomer in composites. On the other hand, a slight weight loss of RF -(DOBAA)n -RF/silica nanocomposites, in which the oligomer contents are 75,94%, was observed at 800°C compared to that of the original silica nanoparticles. Copyright © 2008 John Wiley & Sons, Ltd. [source] Release of gentamicin from bone regenerative materials: An in vitro studyJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007M. Teller Abstract Antibiotic loading of bone regenerative materials is a promising way to protect augmentation procedures from infection during the resorption phase of bone substitutes. Especially in the early stage of implantation, it should protect the grafted site against microbiological pathogens. The present study reports the release kinetics of gentamicin after loading from two synthetic bone filling materials. The first, BONITmatrix®, is a biphasic calcium phosphate silica composite obtained by the sol,gel route consisting of 13% silicon dioxide (w/w) and calcium phosphates (hydroxyapatite/,-tricalcium phosphate 60/40 w/w). The second, Synthacer®, is a sintered hydroxyapatite ceramic. Gentamicin was loaded by dipping and by vacuum coating. Release kinetics of the loaded Gentamicin was investigated by fluorescence polarization immunoassay and by staphylococcus aureus assay. By dipping, loading failed for Synthacer, and it was 12.7 mg gentamicin per gram bone substitute for BONITmatrix. By vacuum coating, loading was 11.3 mg gentamicin per gram bone substitute for Synthacer and 7.4 mg gentamicin per gram bone substitute for BONITmatrix. Distinct release kinetics were measured. For Synthacer, a high initial release was followed by a lower protracted release level up to 28 days. For BONITmatrix release was continuous over the investigated 70-day period. The present data suggest that the porosity properties at the nano- and microscopic levels, or the composition are responsible for antibiotic loading and subsequent release. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Effect of nanoscale confinement on fluorescence of MEH-PPV/MCM-41 compositePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2010German M. Telbiz Abstract Fluorescence spectra and kinetics of poly(2-methoxy-5-(2,-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV)/MCM41 silica composite have been analyzed at different temperatures and compared with fluorescence properties of MEH-PPV solutions and spin coated films. As follows from this comparison, the composite possesses significantly wider fluorescence spectra, longer fluorescence relaxation and weaker temperature dependence of its intensity. These peculiarities are explained in terms of the reduced exciton diffusion and an increased torsional disorder of polymer chains embedded in pores. [source] Synthesis, characterization and single crystal structure determination of aluminum alkoxydisilanolates: precursors for silica,alumina compositeAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2010Mostafa M. Amini Abstract Several novel aluminum alkoxydisilanolate complexes were prepared by reaction of triphenylsilanol with aluminum 2-methoxyethoxide, aluminum 2-ethoxyethoxide, aluminum sec -butoxide and aluminum iso -propoxide. All new complexes, [(Ph3SiO)2Al(OR)]2 [where R = CH2CH2OCH3 (1), CH2CH2OC2H5 (2), CH(CH3)CH2CH3 (3) and CH(CH3)2 (4)] were characterized by elemental analysis, mass spectrometry and infrared spectroscopy (IR), as well as 1H, 13C, 29Si and 27Al NMR spectroscopies. The solid-state structures of the representative compound 2 and 4 were also verified by single-crystal X-ray analyses. Complexes 2 and 4 are dimers having distorted trigonal bipyramidal and tetrahedral coordination at the aluminum center, respectively. The 27Al NMR spectrum of compound 2 showed that the solid-state structure of the complex was not retained in solution, and tetracoordinated aluminum was found in solution in contrast to the pentacoordinated geometry in the solid state. The hydrothermal treatment of 1 and 4 at 200 °C and the subsequent calcination at 1000 °C resulted in the formation of alumina,silica composite (4SiO2·Al2O3) with ,-alumina in the silica matrix. Copyright © 2010 John Wiley & Sons, Ltd. [source] Hydrogen separation of methyltriethoxysilane templating silica membraneAICHE JOURNAL, Issue 12 2007Jong-Ho Moon Abstract Hydrogen separation on microporous methyltriethoxysilane-templating silica composite/,-alumina membranes (below MTES membrane) was studied using three binary gas mixtures: H2/N2, H2/CO2, and H2/CH4. The characteristics of unsteady and steady-state permeation/separation on the MTES membrane were compared to each other. Although permeation flux in the H2/N2 mixture was comparatively low, H2 selectivity was high (H2/N2 SF , 30,60). On the contrary, the H2/CO2 mixture showed high permeation flux but low H2 selectivity (H2/CO2 SF , 1.5,6.5). The H2/CH4 mixture showed a large difference between permselectivity (28,48) and separation factor (10,22). Results from this study revealed that it was difficult to predict the separation factor using the one-component permeation ratio (permselectivity) over the experimental range tested. These separation characteristics could be primarily ascribed to the molecular size and structure of each gas, which likely contributed to steric hindrance or molecular sieving within the membrane pore. In addition, the adsorption affinity of each molecule on the membrane surface acted as a key factor in separation performance because it significantly influenced surface diffusion. The generalized Maxwell-Stefan model incorporating the dust gas model, and the Langmuir model could successfully predict the transient and steady-state permeation/separation. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Templated Synthesis of Mesoporous Superparamagnetic Polymers,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007B. Fuertes Abstract We present a novel synthetic strategy for fabricating superparamagnetic nanoparticles randomly dispersed in a mesoporous polymeric matrix. This method is based on the use of mesoporous silica materials as templates. The procedure used to obtain these mesoporous magnetic polymers consisted in: a),generating iron oxide ferrite magnetic nanoparticles (FMNP) of size ,,7,8,nm within the pores of the silica, b),loading the porosity of the silica/FMNP composite with a polymer (Polydivinylbenzene), c),selectively removing the silica framework from the resulting silica/FMNP/polymer composite. Such magnetic porous polymeric materials exhibit large surface areas (up to 630,m2,g,1), high pore volumes (up to 0.73,cm3,g,1) and a porosity made up of mesopores. In this way, it is possible to obtain superparamagnetic mesoporous hybrid nanocomposites that are easily manipulated by an external magnetic field and display different magnetic behaviours depending on the textural properties of the template employed. [source] | |||||||||||||