Sol-gel Reaction Of Tetraethoxysilane Research Articles

Preparation of Nanoporous Silica Gel Using Oxidatively Degradable Polymer in Organic–Inorganic Hybrid

The sol-gel reaction of tetraethoxysilane was performed in the presence of a polyester bearing a diacylhydrazine moiety to prepare an organic-inorganic hybrid, which was oxidatively degraded at roo...

Fabrication of Hollow Silica Microspheres with Orderly Hemispherical Protrusions and Capability for Heat-Induced Controlled Cracking.

Hollow silica microspheres with orderly protrusions on their outer and inner surfaces were fabricated in three simple steps: (1) suspension polymerization of a polymerizable monomer containing silica nanoparticles to obtain polymeric microspheres with a layered shell of silica particles; (2) sol-gel reaction of tetraethoxysilane (TEOS) on the surface of the microspheres to connect the silica nanoparticles; (3) removal of polymer core by calcination. The shell composed of silica-connected silica nanoparticles remained spherical even after calcination, and the characteristic surface morphology with protrusions were obtained on both inner and outer surfaces. Measurements of the mechanical strength revealed that the compression modulus of the hollow microspheres increased with increasing thickness of the silica layer, which could be controlled by changing the concentration of TEOS in the sol-gel reaction. Rapid heating of the hollow silica microspheres with the thin silica-connected layer led to silica shell cracking, and the cracks were mostly observed in the connecting layer between the silica nanoparticles. The stress was probably concentrated in the connecting layer because of its lower thickness than the nanoparticles. Such characteristic of the hollow microspheres is useful for a capsule with capability for heat-induced controlled cracking caused by internal pressure changes.

Reinforced chloroprene rubber by in situ generated silica particles: Evidence of bound rubber on the silica surface

ABSTRACTNano silica is generated in situ inside the uncrosslinked chloroprene rubber (CR) by the sol‐gel reaction of tetraethoxysilane (TEOS). This results in appreciable improvement in mechanical properties of the CR composites at relatively low filler content. Furthermore, exploitation of reactive organosilanes, γ‐aminopropyltrimethoxysilane (γ‐APS) in particular, in the silica synthesis process facilitates growing of spherical silica particles with a size distribution in the range of 20‐50 nm. The silica particles are found to be uniformly dispersed and they do not suffer from filler‐filler interaction. Additionally, it is observed that the silica particles are coated by silane and rubber chains together which are popularly known as bound rubber. The existence of the bound rubber on silica surface has been supported by the detailed investigations with transmission electron microscopy (TEM), energy filtered transmission electron microscopy (EFTEM) and energy dispersive X‐ray spectroscopy (EDAX). The interaction between rubber and silica, via bi‐functionality of the γ‐APS, has been explored by detailed FTIR studies. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43717.

The Preparation of Magnetic Silica Nanospheres and Incorporation of CdSe/ZnS Quantum Dots-DNA Probe.

Silica nanospheres containing magnetic particles were prepared, and CdSe/ZnS QDs functionalized with carboxyl group were incorporated into the silica nanospheres by EDC/NHS coupling reaction. The silica nanospheres were prepared by a co-precipitation of ferrous and ferric solutions followed by the sol-gel reaction of TEOS (tetraethoxysilane) and APTES (3-aminopropyltriethoxysilane) using base catalyst. The size of magnetic silica nanospheres was confirmed by Transmission electron microscope (TEM). Thiol group modified single stranded oligonucleotides were immobilized on the surface of QDs and fluorescence quenching by intercalation dye (TOTO-3) after hybridization with target oligonucleotide was observed. The fluorescence from QDs could be quenched by intercalating dye (TOTO-3) after hybridization of target DNA to probe DNA. This shows that the magnetic silica-QD-DNA probe can be used to detect specific DNA.

Synthesis and shell structure design of hollow silica nanoparticles using polyelectrolyte as template

Hollow silica (SiO2) nanoparticles with tunable shell microstructures were synthesized in ethanol solvent by using a polyelectrolyte as template. The polyelectrolyte template was composed of poly (acrylic acid) (PAA) with small amount of ammonia solution (NH4OH) and prepared by dispersion of the PAA-NH4OH mixture in ethanol. Upon the addition of silica precursor, tetraethoxysilane (TEOS), into the PAA-NH4OH/ethanol suspension, a certain thickness of SiO2 shell could be gradually formed outside the template through+the sol-gel reaction of TEOS, which was supposed to be driven by the catalytic effect of NH4 ions suspended on the surface of the template. By varying the NH4OH amount in reaction solution, it was found that the hollow SiO2 nanoparticles could be obtained only in the case of NH4OH amount below a critical value. Furthermore, it was found that the water amount in reaction solution had a significant influence on the shell microstructure of hollow SiO2. The shells formed in water-free solution were thick, rough and rich of mesopores, which became relatively thinner, smoother and richer of micropores if the water amount was gradually increased within a limited range. Therefore, it was thought to be possible for the controllable synthesis and shell structure design of hollow SiO2 nanoparticles by optimizing the NH4OH and water amount in reaction solution.

The Preparation of Core–Shell Magnetic Silica Nanospheres for Enhancing Magnetism and Fluorescence Intensity

Recently, magnetic and luminescent composite silica with structure of micro- and nanospheres containing both magnetic (Fe3O4) nanoparticles (MPs) and quantum dots (QDs) has attracted great interests. In this study, we have prepared core-shell structure of silica spheres in which magnets are incorporated into silica core and QDs into a mesoporous silica shell by using C18-TMS (octade-cyltrimethoxysilane). MPs were synthesized by a co-precipitation method from ferrous and ferric solutions with a molecular ratio of 2:3. Monodisperse magnetic silica cores have been prepared via sol-gel reaction of TEOS (tetraethoxysilane) and water using base catalyst. The size of magnetic silica nanospheres was confirmed by dynamic laser light scattering system (DLS) and scanning electoron microscope (SEM). The pore volume and surface area were calculated by using BET after calcination. The core-shell structure plays an important role in providing more domains for MPs in silica Core and QDs in silica shell. QDs were incorporated into the mesoporous shell by hydrophobic interactions. Magnetic characterization was performed using a superconducting quantum interference device (SQUID). The optical properties of the particles were characterized with UV/Vis spectrometer, PL spectrometer, and fluorescence microscope.

Peroxide Cross-linked Soft Composite<br>Prepared from Natural Rubber Latex and Silica Generated <i>in situ</i>

Peroxide cross-linked silica filled natural rubber composite was prepared from a commercial natural rubber (NR) latex containing ammonia and silica generated in situ by using a sol-gel reaction of tetraethoxysilane (TEOS). The silica content was ten parts per one hundreds rubber by weight. Morphology of the in situ silica in the soft composite, which was observed by transmission electron microscopy, showed that the in situ silica was formed into aggregates in a few hundreds nanometer level. Reinforcement effects of the in situ silica and strain-induced crystallization (SIC) were investigated by simultaneous time-resolved wide-angle X-ray diffraction and tensile measurements at SPring-8. The effect of silica filling in situ was larger than that of SIC in the soft composite. The sol-gel reaction of TEOS in the NR latex is supposed to have an advantage in generating an interaction between in situ silica and non-rubber components on the surface of rubber particles through quaternary ammonium ions. This interaction may bring about a unique mechanical properties to the in situ silica filled soft composite. The method using NR latex may be useful for preparation of high performance soft composites.

High proton conducting SPEEK/SiO2/PWA composite membranes for direct methanol fuel cells

Sulfonated polyether ether ketone (SPEEK) based composite membranes for direct methanol fuel cell (DMFC) application were prepared by sol-gel reaction of tetraethoxysilane (TEOS) in the SPEEK matrix and the incorporation of phosphotungstic acid (PWA). The conductivity of the developed membranes was determined by impedance spectroscopy and the methanol permeability through the membranes was obtained from diffuseness experiments. The SEM images show that the addition of SiO2 and the covalent cross-linking structure lead to fine PWA particles and more uniformly dispersion. The swelling of composite membranes remains in the range of 5%–8% at 30–90 °C and the effusion of PWA reduces significantly. The composite membranes show a good balance in higher proton conductivity and lower methanol permeation. The cell with composite membrane has higher open circuit voltage(0.728 V) and higher peak power density(45 mW/cm2) than that with Nafion117.

<i>In Situ</i> Silica Filled Styrene Grafted Natural Rubber by the Sol-Gel Process

In situ silica filling of styrene grafted natural rubber (ST-g-NR) was carried out by using sol-gel reaction of tetraethoxysilane (TEOS). The effects of concentration of catalyst and reaction temperature on the in situ silica content were investigated. ST-g-NR was synthesized via an emulsion polymerization using cumene hydroperoxide (CHPO) and tetraethylene pentamine (TEPA) as initiators. The synthesized ST-g-NR was characterized by a Fourier Transform Infrared Spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR). The content of in situ silica generated in ST-g-NR matrix was determined by Thermogravimetry Analysis (TGA). In situ silica up to 50 parts per hundred rubbers by weight (phr) was successfully filled in the ST-g-NR matrix. The silica content increased with the increase of n-hexylamine concentration. However, the effect of reaction temperature was insignificant to silica content.

Synthesis and Characterization of Mesoporous Core-Shell Silica with Incorporation of Dye

We have prepared nano size mesoporous silica using sol-gel reaction and incorporated fluorescent dye inside the silica network, and investigated fluorescent properties of the particles. Monodisperse core silica has been prepared via sol-gel reaction of TEOS (tetraethoxysilane) and water using base catalyst. The SEM images of silica cores showed that most particles were uniform and spherical with particle diameters of 187 nm. Mesoporous core-shell structure of silica with shell was prepared via further reaction with C18-TMS (octadecyltrimethoxysilane) and heat treatment. The SEM image of core-shell silica shows that the average diameter is 305 nm and the thickness of shell is 118 nm. The size of silica particles was measured by electrophoretic light scattering system (ELS-8000, Otsuka). The pore volume and surface area were increased after calcination. A typical value for the specific surface area, calculated according to the BET (Brunauer−Emmett−Teller) method from nitrogen isotherms is a s = 400 m2/g. Fluorescein isothiocyanate (FITC) could be incorporated into the silica network by coupling reaction with organic functionalized silane. The optical properties of the particles were characterized with UV/Vis spectrometer and PL spectrometer.

Preparation of “Green” Composites by the Sol-Gel Process: In Situ Silica Filled Natural Rubber

“Green” composites with different amounts of in situ silica nano-particles were prepared by a sol-gel reaction of tetraethoxysilane (TEOS) in natural rubber (NR). The control of swelling degree of TEOS in NR and concentration of n-butylamine in water was useful to change the amount of generated in situ silica in the uncured NR matrix. In situ silica up to 42 parts per hundred rubber by weight (phr) was successfully filled in the NR matrix. The particle size of in situ silica became larger with the increase of silica content from ca. 10 nm to ca. 40 nm for 10 phr--40 phr loadings in the NR matrix, respectively. Even when the amount of in situ silica content was high, the dispersion of in situ silica particles was more homogeneous than that of commercial silica (VN-3). The reinforcement effect of the in situ silica for NR vulcanizates increased with increasing the in situ silica content.

Effect of silane-coupling agent on natural rubber filled with silica generated in situ

The effect of silane coupling agent was investigated for the novel in situ silica loading to the natural rubber (NR) matrix. The silica was generated in situ by the sol-gel reaction of tetraethoxysilane in the NR matrix before its crosslinking. γ-mercaptopropyltrimethoxysilane (γ-MPS) significantly prevented the delay of sulfur curing and increased the wettability of NR onto in situ silica, which resulted in the increase of reinforcement effect for the NR vulcanizate. γ-MPS decreased the interaction between the in situ silica particles followed by dispersing the in situ silica particles homogeneously and decreasing the hardness, compression set, hysteresis loss and storage modulus at the rubbery state of in situ silica-filled NR vulcanizate. The NR/in situ silica composite with γ-MPS is a promising material for a high performance rubber product.

In situ formation of particulate silica in natural rubber matrix by the sol-gel reaction

The sol-gel reaction of tetraethoxysilane was conducted in natural rubber (NR) matrix to obtain NR/in situ silica mixtures. In other words, in situ filling of silica onto NR was conducted. The mixtures were compounded with curing regents, and their viscosities were evaluated. The in situ silica with a coupling agent afforded the lowest viscosity compared not only with a conventional silica (VN-3) but also with a carbon black (HAF). The curing behaviors were most favorable for in situ silica compound. Physical properties of the vulcanizates were also evaluated, and again in situ silica stock gave the best result.

Preparation of C60-silica hybrid monolith by sol-gel process

A C60–silica hybrid monolith was prepared by the hydrosilylation of C60 in the presence of platinum catalyst followed by sol-gel process with tetraethoxysilane. The hydrosilylation with trichlorosilane, triethoxysilane, chlorodiphenylsilane, and dichlorophenylsilane gave silylated C60s as a brown pasty liquid. The formula was estimated to be C60{Si(OEt)3}2.6H2.6 or C60(SiPh2Cl)3.2H3.2 based on the proton nuclear magnetic resonance spectrum. A C60–silica hybrid gel monolith was obtained by sol-gel process of the silylates and tetraethoxysilane in ethanol followed by aging for 3 weeks at room temperature. The monolith was brown and transparent with a diameter of 25 mm. On the other hand, the sol-gel reaction of tetraethoxysilane, trimethoxyphenylsilane, and C60 provided a heterogeneous gel with a phase separation of C60.

SIMULTANEOUS POLV(V1NVL ACETATE)/SILICA NETWORKS. INFLUENCE OF CROSSLINKING AGENTS

ABSTRACT The modification of the rate or formation of interpenetrant simultaneous inorsjanic-organic (SIPIN) networks of poly(vinyl acetate) (PVAc)-SiO; was studied. The P(VAc) network was formod by radical polymerization with benzoyl peroxide in the presence of a crosslinked monomer, diethylen glycol bis maleate. SiO: network was obtained by sol-gel reaction of tetraethoxysilane (TEOS) catalyzed by radical polymeriznble acids: maleic acid (MA) and acrylic acid (AA) The reaction medium was the ethylic alcohol-water mixture. The formation rate of SIPIN depends on the ratio of initial organic over aqueous phases in case of caialysis by MA. The yelling limes for MA are higher than those for AA. This behavior inversely proponional to the acid strength is assigned to the selective interaction of the acids wiih the hydrocarbonated or aqueous zone of initial systems. Crotonic acid (CrA) is partitioned in the hydrocarbonate zone where TEOS also lies The glass transition temperature of organic network, P(VAc) increases with the increase of crosslinking agent concentration. It is higher in the network prepared in presence of MA owing to the higher number of hydrogen bonds induced by COOH.

Reinforcement of natural rubber by silica generated <i>in situ</i>

New method to produce in situ silica in natural rubber (NR) matrix was developed for a NR/silica composite material, and the good reinforcement effect of the silica was observed on the NR vulcanizate. The silica was generated by the sol-gel reaction of tetraethoxysilane before crosslinking, which gave a homogeneous dispersion of in situ-generated silica particles in the NR matrix. This method is expected to be an industrially practical technique. It is estimated that the concentration of silanol groups on the silica surface were smaller than those on the conventional silica surface. Therefore, the silica-silica interaction of in situ silica seems to be weaker than that of silica-rubber to result in better dispersion compared with the conventional silica. The results suggest that NR which is a renewable resource and in situ silica omposite has much potential as a“green”material and a useful system for studying the reinforcement mechanism of inorganic filler onto NR.

Pore Size Control of High Surface-Area Silica by Use of Citric Acid

Abstract Pore size and pore volume of an amorphous silica with high specific surface area, ca. 1000 m2g−1, can be controlled in meso scale by using citric acid as a template in sol-gel reaction of tetraethoxysilane.

Silica and Silane Coupling Agent for in Situ Reinforcement of Acrylonitrile-Butadiene Rubber

Abstract In situ silica reinforcement for the acrylonitrile-butadiene rubber (NBR) vulcanizates, which were premixed with a conventional silica (VN-3) and γ-mercaptopropyltrimethoxysilane (γ-MPS), was achieved by the sol-gel reaction of tetraethoxysilane (TEOS) using ethylenediamine. It was observed that the reinforcement efficiency tended to increase with the increase of mechanically premixed conventional silica. From the observations of transmission electron microscopy and scanning electron microscopy, the simultaneous use of VN-3 and γ-MPS was found to promote the formation of large silica particles and clusters with a relatively good dispersion by the sol-gel reaction of TEOS in the NBR vulcanizate. The results of hysteresis measurements supported this promotion. It was considered to be due to the surface modification of VN-3 by the sol-gel reaction of TEOS and the presence of γ-MPS which worked as a dispersion agent for silica particles. The relationship between the mechanical properties and the morphology of the in situ silica filled vulcanizates is discussed.

Effect of catalyst onin situ silica reinforcement of styrene–butadiene rubber vulcanizate by the sol–gel reaction of tetraethoxysilane

In situ silica reinforcement of styrene–butadiene rubber (SBR) vulcanizate has been achieved by the sol–gel reaction of tetraethoxysilane (TEOS) using n-butylamine as a catalyst. SBR was vulcanized with sulfur and soaked in TEOS and in an aqueous solution of the catalyst. When hydrochloric acid was used as a catalyst for the sol–gel reaction, silica particles were not introduced into the SBR matrix in this study. The increase of the dynamic modulus and tensile strength at break was considered to be due to the interaction between the rubber and the in situ silica filler in the SBR vulcanizate.

New PI-Silica Hybrids Via Sol-Gel Process for Thin Film Dielectric Materials

Abstract A new class of polyimide-silica hybrid materials for thin film microelectronics were successfully prepared by the sol-gel reaction of tetraethoxysilane (TEOS) in the solution of polyimide precursor in N.N′-dimethylformamide. The composite films were obtained by the hydrolysis and polycondensation of TEOS in the polyimide precursor solution, followed by heating at 270 °C. The chemical structures of polyimide-silica hybrid films were characterized by analytical techiques. X-ray diffraction showed that the polyimide-silica hybrid material has an amorphous structure. The hybrid material was quite stable at elevated temperatures (> 400 °C), with the associated weight loss of 10 wt % only around 600 °C. The dielectric constant of the polyimide-silica (50 wt%) composite measured by ellipsometry was 3.935 to 3.885 as a function of frequency in the range of 1kHz to 20kHz.