Poly(methylmethacrylate)/silica/titania films were prepared via a nonaqueous sol–gel route at ambient temperature, followed by spin-coating and multistep baking. The acrylic monomers used were methyl methacrylate (MMA) and 3-(trimethoxysilyl)propyl methacrylate (MSMA). Silicic acid and titanium(IV) chloride were used as the precursors of the inorganic component. FTIR results indicated the successful bonding between TiO2 and SiO2. TEM images suggested the silica/titania particles were well dispersed in the Poly(methyl methacrylate) (PMMA) matrix with the particles size smaller than 40 nm in our study. The refractive index and extinction coefficient were also studied. The refractive index of the hybrid increased with increasing the titania content, and the hybrid films showed high optical transparency in visible region. 相似文献
Manipulation of colloidal systems via optical trapping techniques requires a refractive index mismatch between particles and solvent which leads to strong interparticle van der Waals interactions. Investigation of the behavior of systems without such strong attractive interactions, however, requires the uncoupling of particle refractive index and particle-particle interactions. To accomplish this, the synthesis of core-shell titania/silica particles has been performed. By index matching a silica shell on a titania core using a mixture of toluene and propanol, the van der Waals interactions between particles can be minimized. Due to the mismatch of the refractive index between the solvent and titania core, however, a strong trapping force can be generated, making optical manipulation feasible. In order to confirm that the silica shell was indeed matched, pure silica particles were synthesized by the method of St?ber (1968) and added to the core-shell system. In these mixed systems of core-shell and pure silica particles in silica-index-matching solvents, only the core-shell particles were trappable. Copyright 2000 Academic Press. 相似文献
We have demonstrated a facile approach for the low‐temperature synthesis of crystalline inorganic/metallic nanocrystal‐halloysite composite nanotubes by employing the bulk controlled synthesis of inorganic/metallic nanocrystals on halloysite nanotubes. The halloysite clay nanotubes can adsorb the target precursor and induce inorganic/metallic nanocrystals to grow in situ. The crystalline phase and morphology of the composite clay nanotubes is tunable. By simply tuning the acidity of the titania sol, the crystalline titania‐clay nanotubes with tunable crystalline phases of anatase, a mixture of anatase and rutile or rutile are achieved. The approach is general and has been extended to synthesize the representative perovskite oxide (barium and strontium titanate)‐halloysite composite nanotubes. Metallic nickel nanocrystal can also be grown on the surface of halloysite nanotubes at low temperature. The traditional thermal treatment for crystallite transformation is not required, thus intact contour of halloysite nanotubes and the crystallinity structure of halloysite nanotubes can be guaranteed. The combined properties from inorganic/metallic nanocrystal (high refractive index, high dielectric constant and catalytic ability) and the halloysite clay nanotubes are promising for applications such as photonic crystals, high‐k‐gate dielectrics, photocatalysis and purification. 相似文献
Nearly monodisperse SiO2/TiO2/SiO2 multiply coated submicrospheres with nearly monodisperse silica submicrospheres as cores, thick titania layers, and thin silica skin were prepared to increase the refractive index of complex submicrospheres while keeping their near monodispersity and perfect surface properties. Nearly monodisperse colloidal silica submicrospheres as cores with a diameter of 200 nm were synthesized by a seeding technique on the basis of the hydrolysis of tetraethyl orthosilicate (TEOS) in an aqueous ethanol solution with ammonia as catalyst. On the basis of the hydrolysis of tetrabutyl orthotitanate, a procedure combining continuous feeding with multistep coating was determined to prepare titania coatings about 40 nm thick and increase the refractive index of the complex submicrospheres. The hydrolysis of TEOS was still used to get the outmost silica coating about 10 nm thick on titania coated silica submicrospheres to eliminate random aggregation caused by the TiO2 surface properties of the TiO2/SiO2 complex submicrospheres during the final fabrication of photonic crystals. 相似文献
A previously proposed method for preparing monodispersed titania particles was extended to preparation of titania-coated silica spherical particles. The core silica particles with an average size of 264 nm were prepared with Stöber method. The titania-coating was performed in ethanol/acetonitrile solvent in the presence of silica particles by a sol-gel method with the use of titanium tetraisopropoxide (TTIP) and methylamine (MA) catalyst. Average size of the silica-titania particles decreased from 457 to 292 nm with an increase in concentration of silica particles. Coefficient of variation for the particle size was less than 5%. Colloidal crystals could be fabricated with a dip-coating technique and a sedimentation process, respectively. Measurements of reflectance revealed peaks based on the Bragg diffraction. Those peaks red-shifted with an increase in titania shell thickness because of a high refractive index of titania. Annealing at high temperature transformed crystal structure of titania shell from amorphous to anatase (500°C) and rutile (1000°C), which led to red-shift of reflection peak because of an increase in refractive index of titania due to the crystallization. 相似文献
Mesoporous titania-silica composite films with highly aligned cylindrical pores are prepared by the sol-gel method using a substrate with structural anisotropy. The strong alignment effect of a rubbing-treated polyimide film on a substrate provides a narrow alignment distribution in the plane of the film regardless of the fast condensation rate of titania precursors. The collapse of the mesostructure upon the surfactant removal is effectively suppressed by the reinforcement of the pore walls with silica by exposing the as-deposited film to a vapor of a silicon alkoxide. The existence of a silica layer on the titania pore wall is proved from the distributions of Ti and Si estimated by the elemental analysis in high resolution electron microscopy. The obtained mesoporous titania-silica composite film exhibits a remarkable birefringence reflecting the highly anisotropic mesoporous structure and the high refractive index of titania that forms the pore wall. The Δn value estimated from the optical retardation and the film thickness is larger than 0.06, which cannot be achieved with the conventional mesoporous silica films with uniaxially aligned mesoporous structure even though the alignment of the pores in the films is perfect. These inorganic films with mesoscopic structural anisotropy will find many applications in the field of optics as phase plates with high thermal/chemical/mechanical stabilities. 相似文献
The optical properties of spin-coated titanium dioxide films have been tuned by introducing mesoscale pores into the inorganic matrix. Differently sized pores were templated using Pluronic triblock copolymers as surfactants in the sol-gel precursor solutions and adjusted by varying the process parameters, such as the polymer concentration, annealing temperature, and time. The change in refractive index observed for different mesoporous anatase films annealed at 350, 400, or 450 °C directly correlates with changes in the pore size. Additionally, the index of refraction is influenced by the film thickness and the density of pores within the films. The band gap of these films is blue-shifted, presumably due to stress the introduction of pores exerts on the inorganic matrix. This study focused on elucidating the effect different templating materials (Pluronic F127 and P123) have on the pore size of the final mesoporous titania film and on understanding the relation of varying the polymer concentration (taking P123 as an example) in the sol-gel solution to the pore density and size in the resultant titania film. Titania thin film samples or corresponding titanium dioxide powders were characterized by X-ray diffraction, cross-section transmission electron microscopy, nitrogen adsorption, ellipsometery, UV/vis spectrometry, and other techniques to understand the interplay between mesoporosity and optical properties. 相似文献
Titania is an important material in modern materials science, chemistry, and physics because of its special catalytic, electric, and optical properties. Here, we describe a novel method to synthesize colloidal particles with a crystalline titania, anatase core and an amorphous titania-shell structure. We demonstrate seeded growth of titania onto titania particles with accurate particle size tunability. The monodispersity is improved to such an extent so that colloidal crystallization of the grown microspheres becomes feasible. Furthermore, seeded growth provides separate manipulation of the core and shell. We tuned the refractive index of the amorphous shell between 1.55 and 2.3. In addition, the particles show luminescence when trace amounts of aminopropyl-triethoxysilane are incorporated into the titania matrix and are calcined at 450 °C. Our novel colloids may be useful for optical materials and technologies such as photonic crystals and optical trapping. 相似文献
The fabrication of small structured spherical particles that are essentially small photonic crystals is described. The particles are 1-50 microm in diameter and are porous with nearly close-packed monodisperse pores whose size is comparable to the wavelength of light. The solid matrix of the particles is titania, which provides a large refractive index contrast between the particle matrix and pores. The particles are made by encapsulating polymer colloidal particles in emulsion droplets of hexanes in which a titanium alkoxide precursor is dissolved. Subsequent osmotic removal of the hexanes from the droplets and condensation of the alkoxide precursor leads to spherical aggregates of polymer spheres with titania filling the spaces between the polymer spheres. The polymer particles are then burned out leaving behind the desired porous titania particles. The size and structure of the pores and high refractive index of the titania matrix are expected to produce particles that are very efficient scatterers of light, making them useful as pigments. 相似文献
Monodisperse titania/polymer core-shell microspheres were prepared by a two-stage reaction with titania as core and poly(ethyleneglycol
dimethacrylate) (PEGDMA) as shell, in which the titania cores were synthesized by a sol-gel method and subsequently grafted
with 3-trimethoxysilyl methacrylate as the first-stage reaction to incorporate the vinyl groups on the surface of inorganic
core. The PEGDMA shell was then encapsulated over the MPS-modified titania core by distillation precipitation polymerization
of ethyleneglycol dimethacrylate in neat acetonitrile during the second-stage polymerization via capture of the radicals of
EGDMA with the aid of the reactive vinyl groups on the surface of inorganic core without any stabilizer or surfactant. The
shell thickness of the core-shell hybrid microspheres was controlled by the feed of EGDMA monomer during the polymerization.
The resultant titania particles and core-shell microspheres were studied by transmission electron microscopy, Fourier-transform
infrared spectra, X-ray photoelectron spectroscopy, and thermogravimetric analysis. 相似文献
Triethoxysilylpropylamine-capped waterborne polyurethane/titania hybrid films were prepared by in situ method via sol-gel process of titanium n-butoxide under acidic condition. In the paper, we studied the effect of the contents of titania sol on the microstructure, mechanical property, water resistance, and optical property of the hybrid films. It was found, with introducing the content of titania, some physical properties such as tensile strength, modulus, water resistance, refractive index, heat resistance, and ultraviolet absorbance will increase. SEM and SAXS study suggested that the hybrid films had good planarization. 相似文献
A synthetic method for preparing submicrometer-sized titania particles is proposed, which is based on hydrolysis of titanium alkoxide with the use of a cosolvent and an amine catalyst for alkoxide hydrolysis. The preparation was performed with different amines of ammonia, methylamine (MA), and dimethylamine (DMA) in different solvents of ethanol/acetonitrile, ethanol/methanol, ethanol/acetone, ethanol/acetonitrile, and ethanol/formamide for 0.1-0.3 M water and 0.03 M titanium tetraisopropoxide (TTIP) at temperatures of 10-50 degrees C. The use of the ethanol/acetonitrile solvent with MA was required for preparing monodispersed, spherical particles. The number average of the titania particle sizes and their coefficient of variation were varied from 143 to 551 nm and from 5.7 to 20.6%, respectively, with reaction temperature and concentrations of water and MA. Colloidal crystals of titania particles fabricated with a sedimentation method revealed reflection peaks attributed to Bragg's diffraction. Annealing at 100-1000 degrees C led to shrinkage and crystallization of titania particles followed by an increase in the refractive index of titania particles. 相似文献
Summary: Core/shell opal gels of sulfonated polystyrene were used as templates to synthesize structured crystalline titania materials. Under acidic conditions, opal materials with hollow spheres of controllable shell thickness and cavity size were prepared. Under neutral conditions, inverse opal inorganic materials with a tunable pore size were prepared. It is crucial that proton ions induce a preferential sol/gel process, forming titania in the gel.
Scanning electron micrograph of the interior region of a structured titania material derived from the G1 template used here. The inset shows broken spheres in which the internal cavity can be observed. 相似文献
Poly(methyl methacrylate) (PMMA)/silica/titania ternary nanocomposites with covalent bonding interaction between polymer and inorganic phases have been prepared using a novel non-hydrolytic sol-gel method. Transmission electron microscope (TEM) image of silica/titania binary inorganic component indicates a core-shell-like structure. Scanning electron microscope (SEM) images suggest that the well dispersed silica/titania particles in the hybrid are on the nanometer-scale. The transparencies of nanocomposites are maintained in visible region while the absorption band in ultraviolet (UV) region is red shifted with increasing inorganic content. The thermogravimetric analysis (TGA) results show that the thermal stability of PMMA copolymer increases dramatically with the addition of silica/titania moieties both in nitrogen and in air. 相似文献