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Silicic Acid (silicic + acid)
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] Oxazoline chemistry part III.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2003-anilinyl)-2-oxazolines], Synthesis, characterisation of [2-(, some related compounds The syntheses and characterisation of a series of chiral and achiral 2-(aminophenyl)-2-oxazolines and some related compounds is reported. All of the derivatives have been produced by a one-step procedure involving the treatment of isatoic anhydride (i.e. [2H]-3, 1-benzoxazine-[1H -2,4-dione: 1) or its 5-chloro analogue with a slight excess of appropriate amino-alcohols. In most cases, anhydrous ZnCl2 is shown to be an effective Lewis acid catalyst for this reaction at reflux temperature in high boiling aromatic solvents (PhCl or PhMe). Oxazolines have been readily formed using rac -2-amino-1-butanol, (S)-phenylglycinol, 2-methyl-2-amino-1-propanol and (1S,2R) or (IR,2S)-cis - 1 -amino-2-indanol; yields range from 85% to 22%. The use of aminoalcohols such as 2-ethanolamine, (±)-2-amino-1-phenyl-1-propanol or 3-amino-1-propanol (to give the corresponding 4,5-dihydro-1,3-oxazine) results in poor yields. The use of other Lewis acid catalysts (silicic acid, Cd(acac)2·2H2O, CuCl2·2H2O, InCl3) or higher temperatures did not improve the yields with these latter two substrates. Benzoxazoles and N-substituted benzoxazoles can also be obtained in reasonable yields from 1 using 2-aminophenol (36%) or 2-amino-3-hydroxypyridine (45%). [source] BIOCHEMISTRY OF SILICA BIOMINERALIZATION IN DIATOMSJOURNAL OF PHYCOLOGY, Issue 2000M. Sumper Diatoms are well known for the intricate patterns of their silica-based cell walls. The complex structures of diatom cell walls are species specific and become precisely reproduced during each cell division cycle, indicating a genetic control of silica biomineralization. Therefore, the formation of the diatom cell wall has been regarded as a paradigm for controlled production of nanostructured silica. However, the mechanisms allowing biosilicification to proceed at ambient temperature at high rates have remained enigmatic. Recently, we have shown that a set of highly cationic peptides (called silaffins) isolated from Cylindrotheca fusiformis shells are able to generate networks of silica nanospheres within seconds when added to a solution of silicic acid. Different silaffin species produce different morphologies of the precipitated silica. Silaffins contain covalently modified Lys-Lys elements. One of these lysine residues bears a novel type of protein modification, a polyamine consisting of 6,11 repeats of the N-methyl-propylamine unit. In addition to the silaffins, additional polyamine-containing substances have been isolated from a number of diatom species that may be involved in the control of biosilica morphology. Scanning electron microscopic analysis of diatom shells isolated in statu nascendi provide insights into the processes of pattern formation in biosilica. A model will be discussed that explains production of nanostructured biosilica in diatoms on the basis of these experimental results. [source] Interaction of silicic acid with poly(1-vinylimidazole)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2006V. V. Annenkov Abstract Poly(1-vinylimidazole) reacts with silicic acid and poly(silicic acid), giving rise to water-soluble complexes and insoluble composites because of hydrogen bonding. The composition, structure, and morphology of the obtained products have been studied with elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The main direction of the reaction depends not only on the initial ratio of the components, concentration, and pH but also on the sequence of the reagent mixing: the presence of poly(1-vinylimidazole) macromolecules during the formation of silicic acid stabilizes soluble complexes, which precipitate with an excess of H4SiO4 only. These soluble complexes may serve as a pattern of particles responsible for the transport of silicic acid in diatom algae and other organisms that assimilate silicon from the environment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 820,827, 2006 [source] Synthesis of polyethylene-octene elastomer/SiO2 -TiO2 nanocomposites via in situ polymerization: Properties and characterization of the hybridJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2005Chin-San Wu Abstract In this study, a silicic acid and tetra isopropyl ortho titanate ceramic precursor and a metallocene polyethylene-octene elastomer (POE) or acrylic acid grafted metallocene polyethylene-octene elastomer (POE-g-AA) were used in the preparation of hybrids (POE/SiO2TiO2 and POE-g-AA/SiO2TiO2) using an in situ sol-gel process, with a view to identifying a hybrid with improved thermal and mechanical properties. Hybrids were characterized using Fourier transform infrared spectroscopy, 29Si solid-state nuclear magnetic resonance (NMR), X-ray diffraction, differential scanning calorimetry, thermogravimetry analysis, dynamic mechanical thermal analysis, and Instron mechanical testing. Properties of the POE-g-AA/SiO2TiO2 hybrid were superior to those of the POE/SiO2TiO2 hybrid. This was because the carboxylic acid groups of acrylic acid acted as coordination sites for the silica-titania phase to allow the formation of stronger chemical bonds. 29Si solid-state NMR showed that Si atoms coordinated around SiO4 units were predominantly Q3 and Q4. The 10 wt % SiO2TiO2 hybrids gave the maximum values of tensile strength and glass transition temperature in both POE/SiO2TiO2 and POE-g-AA/SiO2TiO2. It is proposed that above this wt %, excess SiO2TiO2 particles caused separation between the organic and inorganic phases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1690,1701, 2005 [source] High Rate Silicification of Peptide-Polymer Assemblies Toward Composite NanotapesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2008Stefanie Kessel Abstract Well-defined silica composite nanofibers are generated in a silicification process of self-assembled poly(ethylene oxide)-peptide nanotapes. Inspired by biological silica morphogenesis processes the nanotapes exhibit strong binding capabilities for silicic acid. Thus, pre-hydrolyzed tetramethoxysilane could be used as silica precursor. Very low concentrations (270 µM) and short contact times (10 s) are sufficient to form effectively integrated nano-composite tapes. [source] Effect of 2,6-dichloroisonicotinic acid, its formulation materials and benzothiadiazole on systemic resistance to alternaria leaf spot in cottonPLANT PATHOLOGY, Issue 2 2000E.S. Colson-Hanks A wettable powder (WP) formulation providing 5,25 ,g mL,1 of 2,6-dichloroisonicotinic acid (INA) and 15,75 ,g mL,1 of WP applied to cotton cotyledons significantly increased the resistance of the next two leaves to challenge inoculation by Alternaria macrospora. The wettable powder alone at 15,75 ,g mL,1 had a lesser effect. A wettable granule (WG) formulation supplying 35 ,g mL,1 of benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) and 35 ,g mL,1 of WG, applied as a cotyledonary treatment, significantly reduced the formation of lesions on the subsequent two leaves when challenged with A. macrospora. The WG control had no effect. Each treatment except for the WG control also raised the activities of ,-1,3-glucanase in unchallenged leaf and stem tissue. Each of the components of the wettable powder without INA applied to cotyledons raised enzyme activities in the next leaves. Individual components, as suspensions of silicic acid and kaolin and solutions of the detergent Attisol II, the wetting agent Ultravon W300 and pure INA, applied to cotyledons increased the resistance of the next leaves to A. macrospora. The responsiveness of cotton to BTH and to each of the components of formulated INA is discussed in relation to knowledge of the effects of BTH and INA on other plants and to possible ways in which the other components of the wettable powder may affect the process of signalling for systemic resistance to disease. [source] Effects of interactions among polyaniline, camphorsulfonic acid and silica on the structure and properties of their conductive hybridsPOLYMER ENGINEERING & SCIENCE, Issue 3 2008Hsun-Tsing Lee In this work, the effects of interactions among polyaniline (PAn), camphorsulfonic acid (CSA), and silica on the structure and properties of their sol-gel hybrids are investigated. These interactions were revealed by FTIR, UV,vis spectra, and XRD patterns. The interaction between PAn and CSA raises conductivities of the CSA-doped PAn/SiO2 (c-PAn/SiO2) hybrids. Moreover, the hydrogen bonding interaction between c-PAn and silicic acid (precursor of SiO2) leads to a less degree of three-dimensional network structure of the SiO2 component in a hybrid with higher PAn content. In addition, because of the interactions among CSA, Pan, and SiO2, the conductive c-PAn-rich phase distributes uniformly in the hybrid and thermal resistance of the hybrid is enhanced consequently. Besides, the c-PAn/SiO2 hybrid with higher SiO2 content exhibits more significant blue-shift of its polaron band, lower conductivity, and higher thermal resistance. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Preparation 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] A Molecular Dynamic Study of Cementitious Calcium Silicate Hydrate (C,S,H) GelsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Jorge S. Dolado In this article, we study the polymerization of silicic acids (Si(OH)4) in the presence of calcium ions by molecular dynamics simulations. We focus on the formation and structure of cementitious calcium silicate hydrate (C,S,H) gels. Our simulations confirm that, in accordance with experiments, a larger content of calcium ions slows down the polymerization of the cementitious silicate chains and prevents them from forming rings and three-dimensional structures. Furthermore, by an analysis of the connectivity of our simulated silicate chains and by a count of the number of Ca,OH and Si,OH bonds formed, the relationship with commonly used structural models of C,S,H gels, such as 1.4 nm tobermorite and jennite, is discussed. [source] | |||||||||||||