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SiO Bonds (sio + bond)

Distribution by Scientific Domains
Chemistry80%

Selected Abstracts

New straightforward route for the synthesis of some 1-oxa-2-silacyclopentane derivatives

JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2008
Kazem D. Safa
Tris(dimethylsilyl)methyl lithium, (HSiMe2)3CLi, reacts with allyl, phenyl, benzyl, n -propyl and n -butyl glycidyl ethers in THF at -5 °C to give 1-oxa-2-silacyclopentane derivatives. It seems that ring closure is facilitated by conversion of the SiH bond into an SiO bond. Glycidyl methacrylate (GM) random copolymers with 4-methyl- and 4-methoxy styrene, synthesized by solution free radical polymerization at 70 (±1) °C with ,,,-azobis(isobutyronitrile) (AIBN) as initiator, contained pendant epoxide functions. Treatment of these with (HSiMe2)3CLi did not lead to intramolecular nucleophilic attack as found for simple epoxides. [source]

Transport Processes at ,-Quartz,Water Interfaces: Insights from First-Principles Molecular Dynamics Simulations

CHEMPHYSCHEM, Issue 7 2008
Waheed A. Adeagbo Dr.
Abstract Car,Parrinello molecular dynamics (CP,MD) simulations are performed at high temperature and pressure to investigate chemical interactions and transport processes at the ,-quartz,water interface. The model system initially consists of a periodically repeated quartz slab with O-terminated and Si-terminated (1000) surfaces sandwiching a film of liquid water. At a temperature of 1000 K and a pressure of 0.3 GPa, dissociation of H2O molecules into H+ and OH, is observed at the Si-terminated surface. The OH, fragments immediately bind chemically to the Si-terminated surface while Grotthus-type proton diffusion through the water film leads to protonation of the O-terminated surface. Eventually, both surfaces are fully hydroxylated and no further chemical reactions are observed. Due to the confinement between the two hydroxylated quartz surfaces, water diffusion is reduced by about one third in comparison to bulk water. Diffusion properties of dissolved SiO2 present as Si(OH)4 in the water film are also studied. We do not observe strong interactions between the hydroxylated quartz surfaces and the Si(OH)4 molecule as would have been indicated by a substantial lowering of the Si(OH)4 diffusion coefficient along the surface. No spontaneous dissolution of quartz is observed. To study the mechanism of dissolution, constrained CP,MD simulations are done. The associated free energy profile is calculated by thermodynamic integration along the reaction coordinate. Dissolution is a stepwise process in which two SiO bonds are successively broken. Each bond breaking between a silicon atom at the surface and an oxygen atom belonging to the quartz lattice is accompanied by the formation of a new SiO bond between the silicon atom and a water molecule. The latter loses a proton in the process which eventually leads to protonation of the oxygen atom in the cleaved quartz SiO bond. The final solute species is Si(OH)4. [source]

Polyacrylate/(carboxymethylcellulose modified montmorillonite) superabsorbent nanocomposite: Preparation and water absorbency

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008
Haixia Qiu
Abstract Montmorillonite (MMT) was modified with carboxymethylcellulose (CMC). The X-ray diffraction (XRD) and FTIR analyses showed that the CMC chains had intercalated into the MMT sheets, and the strong chemical interaction between the ether bonds from CMC and SiO bonds from MMT was the driving force for intercalation. Polyacrylate (PAA)/modified MMT superabsorbent nanocomposites were fabricated by effectively dispersing the modified MMT in acrylic acid solution and polymerizing the acid. The superabsorbent composites were characterized by XRD, TEM, and FTIR. The influence of modified MMT, weight ratio of CMC to MMT, and modified MMT content in the nanocomposites on the water absorbency was investigated. Results showed that the introduction of pure MMT could decrease the water absorbency of the gel, but adding modified MMT could not only effectively increase the water absorbency of the gel, but also improve its water retention ability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Silicon nanoparticles with chemically tailored surfaces

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2010
Andrew S. Heintz
Abstract Silicon nanoparticles are useful materials for optoelectronic devices, solar cells and biological markers. The synthesis of air-stable nanoparticles with tunable optoelectronic properties is highly desirable. The mechanochemical synthesis of silicon nanoparticles via high-energy ball milling produces a variety of covalently bonded surfaces depending on the nature of the organic liquid used in the milling process. The use of the C8 reactants including octanoic acid, 1-octanol, 1-octaldehyde and 1-octene results in passivated surfaces characterized by strong SiC bonds or strong SiO bonds. The surfaces of the nanoparticles were characterized by infrared spectroscopy and nuclear magnetic resonance spectroscopy. The nanoparticles were soluble in common organic solvents and remarkably stable against agglomeration and air oxidation. The luminescence and optical properties of the nanoparticles were very sensitive to the nature of their passivating surface. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Transport Processes at ,-Quartz,Water Interfaces: Insights from First-Principles Molecular Dynamics Simulations

CHEMPHYSCHEM, Issue 7 2008
Waheed A. Adeagbo Dr.
Abstract Car,Parrinello molecular dynamics (CP,MD) simulations are performed at high temperature and pressure to investigate chemical interactions and transport processes at the ,-quartz,water interface. The model system initially consists of a periodically repeated quartz slab with O-terminated and Si-terminated (1000) surfaces sandwiching a film of liquid water. At a temperature of 1000 K and a pressure of 0.3 GPa, dissociation of H2O molecules into H+ and OH, is observed at the Si-terminated surface. The OH, fragments immediately bind chemically to the Si-terminated surface while Grotthus-type proton diffusion through the water film leads to protonation of the O-terminated surface. Eventually, both surfaces are fully hydroxylated and no further chemical reactions are observed. Due to the confinement between the two hydroxylated quartz surfaces, water diffusion is reduced by about one third in comparison to bulk water. Diffusion properties of dissolved SiO2 present as Si(OH)4 in the water film are also studied. We do not observe strong interactions between the hydroxylated quartz surfaces and the Si(OH)4 molecule as would have been indicated by a substantial lowering of the Si(OH)4 diffusion coefficient along the surface. No spontaneous dissolution of quartz is observed. To study the mechanism of dissolution, constrained CP,MD simulations are done. The associated free energy profile is calculated by thermodynamic integration along the reaction coordinate. Dissolution is a stepwise process in which two SiO bonds are successively broken. Each bond breaking between a silicon atom at the surface and an oxygen atom belonging to the quartz lattice is accompanied by the formation of a new SiO bond between the silicon atom and a water molecule. The latter loses a proton in the process which eventually leads to protonation of the oxygen atom in the cleaved quartz SiO bond. The final solute species is Si(OH)4. [source]