Effect of sol–gel derived in situ silica on the morphology and mechanical behavior of natural rubber and acrylonitrile butadiene rubber blends

Silica particles were generated and grown in situ by sol–gel method into rubber blends comprised of natural rubber (NR) and acrylonitrile butadiene rubber (NBR) at various blend ratios. Silica formed into rubber matrix was amorphous in nature. Amount of in situ silica increased with increase in natural rubber proportion in the blends during the sol–gel process. Morphology studies showed that the generated in situ silica were nanoparticles of different shapes and sizes mostly grown into the NR phase of the blends. In situ silica filled NR/NBR blend composites showed improvement in the mechanical and dynamic mechanical behaviors in comparison to those of the unfilled and externally filled NR/NBR blend composites. For the NR/NBR blend at 40/60 composition, in particular, the improvement was appreciable where size and dispersion of the silica particles into the rubber matrix were found to be more uniform. Dynamic mechanical analysis revealed a strong rubber–in situ silica interaction as indicated by a positive shift of the glass transition temperature of both the rubber phases in the blends.     

AFM substantiation of the fracture behavior and mechanical properties of sol–gel derived silica packed epoxy networks

Silica packed epoxy networks are prepared in two steps via in situ, solvent free sol–gel processing of tetraethoxysilane in liquid epoxy monomer and curing the mixture with a flexible diamine afterwards. The influence of filler content and processing conditions on the mechanical properties and the fracture behavior is studied by means of the static mechanical analysis and AFM characterization of the pristine and the fractured polymer surfaces, and a mechanism to enhance polymer strength and toughness is proposed. The in–situ evolution and packing of silica nanostructures into epoxy networks influences the overall morphology and performance of polymers under high stress. It is found that smaller silica domains distributed at the molecular level cause efficient crack distribution by absorbing energy and thus improve the strength and toughness of silica packed epoxy polymers.     

Silver containing sol–gel derived silica thin films: effect of aluminum incorporation on optical,microstructural and bactericidal properties

Silver containing silica (Ag–SiO₂) thin films with and without aluminum (Al) were prepared on soda-lime-silica glass by spin coating of aqueous sols. The coating sol was formed through mixing tetraethyl orthosilicate [Si(OC₂H₅)₄]/ethanol solution with aqueous silver nitrate (AgNO₃) and aluminum nitrate nonahydrate [(AlNO₃)₃·9H₂O] solutions. The deposited films were calcined in air at 100, 300 and 500 °C for 2 h and characterized using x-ray diffraction, UV-visible and x-ray photoelectron spectroscopy. The effect of Al incorporation and calcination treatment on microstructure and durability of the films, and chemical/physical state of silver in the silica thin film have been reported. The bactericidal activity of the films was also determined against Staphylococcus aureus via disk diffusion assay studies before and after chemical durability tests. The investigations revealed that the optical, bactericidal properties and chemical durability of Ag–SiO₂ films can be improved by Al addition. The Al-modified Ag–SiO₂ thin films do not exhibit any coloring after calcination in the range of 100–500 °C, illustrating that silver is incorporated within the silica gel network in ionic form (Ag⁺). Al incorporation also improved the overall durability and antibacterial endurance of Ag–SiO₂ thin films.     

Physical and optical properties of organo-modified silica nanoparticles prepared by sol–gel

A comparative study on the physical and optical properties of silica nanoparticles prepared by sol–gel has been carried out. Post-modification of as-synthesized silica nanoparticles produced organo-functionalized silica nanoparticles slightly increased in size (~20%) and relatively high aggregation. However, in situ method produced sixfold bigger functionalized particles with good dispersion and less aggregation. Higher organic content was observed for in situ modified nanosilica, leading to a higher surface hydrophobicity that improved compatibility and dispersion in preparation of silica-polymer nanocomposite. Furthermore, in situ and post-modified nanosilica demonstrated a distinct optical activity, photoluminescence and UV compared to the unmodified nanoparticles.     

One-pot synthesis of organo-silica hybrids with high thermal properties via a simple sol–gel process

Journal of Thermal Analysis and Calorimetry - Organic–inorganic hybrid composites have received much attention of scientists in the recent years due to the notable improvement of thermal...     

Synthesis of tin oxide nanoparticles by sol–gel process: effect of solvents on the optical properties

Tin oxide (SnO₂) nanoparticles were synthesized by the reaction of SnCl₄·5H₂O in methanol, ethanol and water via sol–gel method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared, Scanning electron microscopy and Transmission electron microscopy. The optical properties of the as-prepared samples were investigated. The XRD analysis showed well crystallized tetragonal SnO₂ can be obtained and the crystal sizes were 3.9, 4.5 and 5 nm for the sample calcined at 400 °C for 2 h. It was found that solvents played important roles in the particle size effect of nanocrystalline SnO₂.     

Synthesis and luminescence properties of Eu(III)-doped silica nanorods based on the sol–gel process

Uniform Eu³⁺-doped SiO₂ nanorods were synthesized through a simple sol–gel method using cetyltrimethylammonium bromide (CTAB) as surfactant template and tetraethylorthosilicate as silicon source. X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrum, scanning electron microscope (SEM), transmission electron microscopy, and photoluminescence spectra were employed to characterize the products in detail. The nanorods have good uniformity and their diameters and lengths are in the range of 200–300 and 500–700 nm through the SEM images, respectively. The formation of the nanorods was studied by taking SEM images after different aging time. The experimental results indicate that CTAB plays a crucial role in the formation of the silica nanorods. The luminescence of Eu³⁺-doped SiO₂ nanorods is dominated by red-emission around 612 nm due to intra-atomic 4f → 4f (⁵D₀ → ⁷F₂₎ transition of Eu³⁺ ions. Furthermore, the effect of doping concentrations of Eu³⁺ ions on the luminescence was investigated.     

Effect of synthesis conditions on the microstructure of TEOS derived silica hydrogels synthesized by the alcohol-free sol–gel route

Silica matrices synthesized from a pre-hydrolysis step in ethanol followed by alcohol removal at low pressure distillation, and condensation in water, are suitable for encapsulation of biomolecules and microorganisms and building bioactive materials with optimized optical properties. Here we analyze the microstructure of these hydrogels from the dependence of I(q) data acquired from SAXS experiments over a wide range of silica concentration and pH employed in the condensation step. From the resulting data it is shown that there is a clear correlation between the microscopic parameters—cluster fractal dimension (D), elementary particle radius (a) and cluster gyration radius (R)—with the attenuation of visible light when the condensation step proceeds at pH < 6. At higher pHs, there is a steep dependence of the cluster density (~R ^D−3) with the condensation pH, and non-monotonous changes of attenuance are less than 20%, revealing the complexity of the system. These results, which were obtained for a wide pH and silica concentration range, reinforce the idea that the behavior of gels determined in a restricted interval of synthesis variables cannot be extrapolated, and comparison of gelation times is not enough for predicting their properties.     

Effect of glycerol on the optical and physical properties of sol–gel glass matrices

Glass samples are prepared with different amount of glycerol as drying control chemical additive (DCCA) via acid catalysed sol–gel method. These samples are given solvent treatment namely rinse and dip with methanol while drying of the sample. In rinse treatment solid sample is rinsed with small amount of methanol while in dip treatment sample is dipped for 5 h in methanol. Comparative studies of these treated samples containing varied DCCA concentration are carried out by measuring optical transmission, mechanical strength and bulk density. Various instrumental techniques used for analysis are FTIR, DTA-TGA, XRD, SEM and TEM. The untreated samples take long time to dry up and to come out of the cuvette and show very less transmission in UV region which is much enhanced by solvent treatment. On the basis of this study, the solvent treated glass samples with DCCA amount 8 ml in the composition used are found to have the maximum UV transmission, good mechanical strength and may be useful as silica gel host matrices for solid state dye lasers and other applications. The UV transmission reported in the present studies is 90% in 337 nm region, which is the wavelength of N₂ laser pumping.     

Influence of cerium concentration on the structure and properties of silica-methacrylate sol–gel coatings

The aim of this work was to study the effect of the incorporation of cerium nitrate in a silica-methacrylate sol–gel hybrid matrix reinforced with silica nanoparticles. Sols, coatings and powders have been studied, focusing specially in the determination of the redox ratio Ce³⁺/Ce⁴⁺ and films structure. Sols have been characterised using viscosity measurements and FT-IR spectroscopy, and powders and coatings obtained with different Ce contents through UV–Vis and FT-IR spectroscopy, TGA, TEM, AFM and FE-SEM. The goal was to reach the best compromise between maximum cerium concentration and coating stability to better understand the mechanisms acting in active anti-corrosive processes.     

Synthesis of silica nanoparticles by modified sol–gel process: the effect of mixing modes of the reactants and drying techniques

A modified preparation of silica nanoparticles via sol–gel process was described. The ability to control the particle size and distribution was found highly dependent on mixing modes of the reactants and drying techniques. The mixture of tetraethoxysilane and ethanol followed by addition of water (Mode-A) produced monodispersed powder with an average particle size of 10.6 ± 1.40 nm with a narrow size distribution. The freeze drying technique (FD) further improved the quality of powder. In addition, the freeze dried samples have shown unique TGA decomposition steps which might be related to the well-defined structure of silica nanoparticles as compared to the heat dried samples. DSC analysis showed that FD preserved the silica surface with low shrinkage and generated remarkably well-order, narrow and bigger pore size and pore volume and also large endothermic enthalpies (ΔH _FD = −688 J g⁻¹ vs. ΔH _HD = −617 J g⁻¹) that lead to easy escape of physically adsorbed water from the pore at lower temperature.     

Microencapsulation of an acrylate monomer in silica particles by sol–gel process

The sol–gel synthesis strategies combined with the templated growth of organic–inorganic hybrid networks provide access to an immense new area of innovative multi-functional advanced materials. One possible way to prepare such new advanced materials is to encapsulate liquid active agents (such as monomers, dyes, catalysts and hardeners) in microcapsules. Silica microcapsules of tetraethylortosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate (MPTS) were prepared in a precursor-monomer/NH₄OH water microemulsion system. Trimethylolpropane triacrylate (TMPTA)—a trifunctional monomer useful in manufacturing of coatings, inks and adhesives—and a corresponding photoinitiator (DAROCUR 1173) were entrapped inside the obtained microcapsules. MPTS was used to increase compatibility between TMPTA and the sol–gel precursors. As stability agent we added a “home made” product resulted from functionalization of poly (ethylene glycol) methyl ether (MPEG) with (3-isocyanatopropyl) triethoxysilane (NCOTEOS). Were obtained microcapsules containing incorporated monomer and having average particle size in range of 0.5–50 μm. Thermal analysis, morphology study and the increase of the silica microcapsules average diameter, measured by DLS technique confirm the monomer encapsulation.     

Crystallization of inorganic silica based on interaction between polyimide and silica by sol–gel method

Crystalline silica in cristobalite phase was successfully prepared at a relatively low temperature of 800 °C by calcinating polyimide/silica hybrid films under ambient air. X-ray photoelectron spectroscopy measurements show that the product is silica after calcination. It is found that the crystallinity is dependent on the removing rate and the strength of the interaction between polyimide and silica. The presence of polyimide plays an important role in the growth of silica. Calcination to remove polyimide with rapid heating results in lower crystallinity compared with calcination with slow heating. For samples with the same content of silica, the crystallinity changes with the strength of the interaction between polyimide and silica molecules.     

Preparation of hollow titania and strontium titanate spheres using sol–gel derived silica gel particles as templates

A facile approach, based on polyelectrolyte-mediated electrostatic adsorption of a water-soluble titanium complex on colloidal templates and hydrothermal treatment, is presented for the formation of hollow titania (TiO₂) and strontium titanate (SrTiO₃) spheres. Monodispersed silica gel particles were prepared by the sol?Cgel method and adopted as core templates. Deposition of a water-soluble titanium complex, titanium (IV) bis(ammoniumlactato)dihydroxide (TALH), on the silica gel particles was carried out via the layer-by-layer assembly technique. Hollow spheres were successfully formed from the core?Cshell particles. The silica gel particles used as core templates dissolved during hydrothermal treatment because of the particles?? undeveloped siloxane network. In addition, the hydrothermal treatment induced crystallization of the hollow shells. Therefore, the hydrothermal treatment played two roles; removal of the silica templates and crystallization of the hollow shells. When deionized water was used, hollow TiO₂ spheres were obtained. Hollow SrTiO₃ spheres could also be formed when an aqueous solution of Sr(OH)₂ was used. The approach presented here could be exploited as a novel and sustainable approach for the fabrication of a range of different inorganic hollow spheres.