Hydrolysis of tetraethoxysilane

Examples of known phosphazene polymer blends are those in which phosphazenes with methylamino, trifluoroethoxy, phenoxy, or oligo-ethyleneoxy side groups form blends with poly(vinyl chloride), polystyrene, poly(methyl methacrylate), or polyethylene oxide).97 100 IPNs have been produced from [NP(OCH2CH2OCH2CH2OCH3)2] (MEEP) and poly(methyl methacrylate).101-103 In addition, a special type of IPN has been reported in which a water-soluble polyphosphazene such as MEEP forms an IPN with a silicate or titanate network generated by hydrolysis of tetraethoxysilane or tetraalkoxytitanane.104 These materials are polyphosphazene/ceramic composites, which have been described as suitable materials for the preparation of antistatic layers in the manufacture of photographic film. 

Throughout the reaction, only tetraethoxysilane is detected from the top phase. The gas chromatograms of the trimethylsilylated derivatives obtained from the bottom phase at various time intervals are shown in Fig. 2. After 1 h of stirring, only the monomer (SiO -) is detected, which would have been formed by the hydrolysis of tetraethoxysilane. After 2 h of stirring, the small peak corresponding to the dimer (SioOy-) appears. It is assumed that the amount of hydrolyzed product of tetraethoxysilane increases with time, and the polymerization proceeds in the bottom aqueous phase. 

As the exothermal reaction occurs after 200 min of stirring, the cubic octamer and the species with molecular weights higher than the cubic octamer are recovered from the bottom phase. As indicated with the mixture containing sodium ions, it appears that the polymerization of silicate species following the hydrolysis of tetraethoxysilane proceeds abruptly when the exothermal reaction occurs. Actually, the amount of tetraethoxysilane in the top phase decreases pronouncedly as the temperature rises, and the mixture becomes a single phase within a few minutes of the exothermal reaction. 

A colloidal silica with 10-500 run particles can be prepared by the hydrolysis of tetraethoxysilane with aqueous ammonia. The particle morphology appears to be independent of the chemical properties of the silane but depends on the nature of the reaction medium. Large, irregularly shaped particles are produced at lower temperatures using solutions having a high ammonia concentration. Smaller, spherical particles result when the tetraethoxysilane concentration is low. ... 

The characterization of polysiloxane-modified mesoporous silica gels derived from the acid catalyzed hydrolysis of tetraethoxysilane and oligomeric silanol terminated polydimethylsiloxane using Si CPMAS NMR has been report. ... 

Particle aggregates with high and low packing densities such as silica hydro- and xe-rogels are obtained in industry by the decomposition of sodium silicate by sulfuric acid of medium concentration and in controlled pH and temperature. They have a wide variety of surface area and porosity and are used as hydrophilic and acid- resistant adsorbents, catalyst carriers, composite materials and etc. Since this material contains various impurities, the material obtained by the hydrolysis of tetraethoxysilane is sometimes used for research purposes because of its purity. 

TTHE SYNTHESIS OF UNCOATED AND SURFACE-MODIFIED silica particles via the hydrolysis of tetraethoxysilane (TEOS) in a homogeneous alcoholic solution of water and ammonia is well documented in the literature (1-7). TEOS and other metal alkoxides (including those of titanium and iron) can... 

Aelion et al. (3, 4) showed that hydrolysis of tetraethoxysilane (TEOS) is acid or base catalyzed with a minimum rate at pH 7. Studies of alkyltrialkoxysilane hydrolysis in buffered aqueous solutions indicate that hydrolysis is both specific acid and specific base catalyzed (5, 6). 

Ryabenko et al. (66) developed a method for synthesizing highly pure silica by heterogeneous hydrolysis of tetraethoxysilane followed by the concentration of the sol of polysilicic acid and thermal treatment. 

Write suitable mechanisms for (a) acid-catalyzed and (b) base-catalyzed hydrolysis of tetraethoxysilane (TEOS). How do these catalysts affect the morphology of the resultant aerogels ... 

The chemical process at the basis of the silica formation is the controlled hydrolysis of tetraethoxysilane (TEOS) molecules and their ammonia catalysed condensation in ethanol/water/ammonia solution. This method allows the continuous and easy control of the nanoparticle dimensions by a suitable choice of the concentrations and ratios of the components of the reaction mixture (TEOS, water and ammonia). Several optimized synthetic protocols with well defined experimental conditions allow one to obtain nanoparticle samples in a dimensional range of about... 

The silica sol was prepared from hydrolysis of tetraethoxysilane (TEOS) with a procedure described as following To 10 g of TEOS, 2.1 g of water, 1.5 g of methanol and 100 mg of hydrochloric add(35%) were added. The mixture was stirred at room temperature. After a few minutes the mixture became homogenous, the solution was stirred for further 1 hr to give the silica sol solution. 

There has been a report of enzyme-like activity in a block copolypeptide, which enhances the rate of hydrolysis of tetraethoxysilane (TEOS, a standard reagent in sol-gel chemistry) as a suspension in water. If this block structure is a sequence of units of a hydrophilic amino followed by units of a hydrophobic amino acid, it would be expected to be active at a water-solvent interface. The morphology of the silica that forms is dependent on the structure of the copolymer. This system is biomimetic both in the sense of employing a polypeptide catalyst and in the sense of it functioning in a multiphase system, since biological processes rarely occur in homogeneous solutions. 

Work at the Mobil Corporation showed that mesoporous silica could be formed by hydrolysis of tetraethoxysilane entrained in a highly concentrated water/silane/surfactant system. In this regime, the three-component mixture forms ordered structures with a range of symmetries. In one hexagonal phase, rods of water are surrounded by surfactant and embedded in a hydrophobic silane matrix. Hydrolysis of the silane under suitable conditions, followed by drying and sintering, results in a porous silica with aligned pores of a few nanometers diameter. 

Silica thick films have been prepared on a stainless steel sheet by the electrophoretic sol-gel deposition in the presence of sodium dodecyl sulfate (SDS) as dispersant in a sol containing sihca particles (Nishimori, 1995, 1997). Silica particles were prepared by hydrolysis of tetraethoxysilane (TEOS) under basic conditions. SDS was dissolved in 0.5 moldm NH3 aqueous solution, and TEOS was diluted separately with the same amount of ethanol (EtOH). These two solutions were mixed and stirred at 25°C. The molar ratio ofTEOS/HjO/EtOH was fixed to be 0.2/10/10. The content of SDS was changed from 0 to 0.3 mass% against the total weight ofthe sols. 

Aksay and coworkers [20] produced mesoscopic patterning of oriented nan-ostructured silica thin films polymerized by a surfactant-templated sol-gel technique [21] in combination with a micromolding technique, which is another microfabrication technique without photolithography proposed by Xia and Whitesides [19]. A network pattern of microcapillaries (submicrometer scale) was transferred to an elastomeric PDMS stamp as a microreplica molding. An aqueous mixture of tetraethoxysilane and a cationic surfactant (CTAC cetyltri-methylammonium chloride) was introduced into the microcapillaries. After hydrolysis of tetraethoxysilane at the cationic interface of the tubular surfactant assemblies, a mesoscopic supramolecular structure hierarchically constituted from hexagonally packed nanoscopic tubules of silica was formed in the microscopic capillary. 

Controlled hydrolysis of tetraethoxysilane in a nonionic water-in-oil microemulsion a statistical model of silica nucleation. Colloids and Surfaces, 154, 311-26. 

We have already fabricated hollow silica-alumina composite spheres prepared by sol-gel based method using aqueous ammonia solution as a promoter of sol-gel reaction [4], and have revealed the influence of their nanostructure of the hollow spheres on their catalytic activity for hydrolysis of NH3BH3 [4], In the present study, we fabricated hollow silica-alumina composite spheres using PS template method and investigated their activity for hydrolytic dehydrogenation of ammonia borane. In addition, we firstly fabricated the hollow spheres using L(+)-arginine as the promoter for hydrolysis of tetraethoxysilane (TEOS) [16],... 

Silica-coated Pt-Ni alloys (denoted as coated Pt-Ni) were prepared in a water-in-oil-type microemulsion [3-6]. Mixed aqueous solutions of H2PtCle and Ni(N03)2 were used for the preparation of coated Pt-Ni. The microemulsion system was prepared by adding aqueous solutions containing the metal cations described above into a surfactant solution in cyclohexane. Polyoxyethylene (n = 15) cetyl ether was used as a surfactant. Nanoparticles containing the metal species were formed by the addition of aqueous NH3 into the microemulsion. Hydrolysis of tetraethoxysilane (TEOS) was carried out in the microemulsion by the addition of TEOS and aqueous NH3. After filtration, the samples were calcined at 773 K for 2 h in air. The calcined samples were washed with aqua regia at room temperature to remove the metal species not covered with silica layers. The metal loading was evaluated using XRF spectra and found to be 2.0 wt% Pt and 0.2 wt% Ni in the coated Pt-Ni. 

The general structure of the used silane components is R— Si(OM)3, where R is an organic functional group such as vinyl, amine, etc., and M is a group of alkoxy or halide in order to gain property of hydrolysis. Hydrolysis of silane components starts in presence of acidic or hydroxide catalyst easily. Because water and silane components are insoluble, a mutual solvent for the homogenous reaction is used. Hydrolysis of tetraethoxysilane and dehydration of the reaction products can be shown as follows ... 

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