Stimulated light scattering in synthetic opal filled with dielectrics

We have studied characteristics of stimulated light scattering in synthetic opal crystals made up of silica spheres. This type of light scattering results from interaction between pulsed laser radiation and dielectric nanoparticles, such as silica (SiO₂) spheres in the structure of synthetic opal. The Stokes shift in the scattered radiation spectrum was 0.4–1.0 cm^?1. The Stokes shift was determined as a function of scattering geometry, sphere diameter, sample temperature, and the type of dielectric in the opal pores. The results are of interest for assessing the size of nanoparticles in spatially ordered inorganic structures.     

Colloidal and transparent opal-matrix nanocomposites filled with europium-doped silica sols

Three-dimensional ordered opal-matrix composites filled with europium-doped silica sols have been produced using methods of colloid chemistry. According to elemental analysis data, the Eu concentration in the nanocomposites was ～30 ppm. A uniform europium distribution over the tetrahedral and octahedral pores of the 3D opal matrix was ensured by repeatedly filling the opal pores with silica sols doped with europium salts or europium oxide. Varying high-temperature annealing conditions, one can control the microstructure of 3D ordered nanocomposites, producing opaline and transparent photonic crystals. The microstructure of opal photonic crystals has the form of an ordered fcc lattice of amorphous silica spheres, whose tetrahedral and octahedral pores are filled with mesoporous europium-doped glass. Partial sintering of the silica spheres and mesoporous glass in transparent photonic crystals results in a periodic arrangement of quantum dots enriched in Eu-doped silica.     

Growth and optical properties of synthetic opal filled with Bi12SiO20 and Bi12GeO20 nanocrystals

We report a technique for producing Bi₁₂SiO₂₀ and Bi₁₂GeO₂₀ nanocrystals in pores of synthetic opal. Bragg reflection and Raman spectroscopies are used to assess the degree of filling of opal pores and diagnose the state of the substance in the pores. The substance in the pores is shown to be in a crystalline state. The measured Raman spectra of the nanocrystals are compared to those of powders and single crystals. The spectra of the photonic crystals obtained contain new lines. We observe intensity redistribution at low frequencies and changes in the frequency of several Raman lines compared to the spectra of powders and single crystals.     

Reduction of various metal salts in opal matrices with supercritical isopropanol

We have studied the reactions between supercritical isopropanol and salts of various elements (silver, copper, gold, zinc, iron, nickel, cobalt, manganese, europium, ruthenium, antimony, bismuth, and tellurium) infiltrated into opal photonic crystals. According to transmission electron microscopy data, the diameter of the SiO₂ spheres in the opal crystals is 260 nm, and the nanoparticles of the metals and incomplete reduction products range in size from 2 to 80 nm, i.e., are no greater in size than the opal pores.     

Ni,Co, Cu,Ni-Co,and Ni-Cu nanoparticles in opal matrices and mesoporous silica gels

NiCo solid solutions and Ni-Cu bimetallic particles have been prepared in opal-matrix nanocomposites by reacting Ni, Co, and Cu double salts and oxides with supercritical (SC) isopropanol. According to X-ray diffraction and transmission electron microscopy data, the nanocomposites have an X-ray amorphous opal matrix and contain crystalline nanoparticles of individual metals, solid solutions, or bimetallic materials of various morphologies in the opal pores. Mesoporous silica gel matrix composites remain X-ray amorphous after treatment in SC alcohols because of the small particle size of the metallic phase, or form solid solutions between Ni and Co silicates. The phase composition of the composites can be controlled by varying experimental conditions.     

Visible reflection spectra of synthetic opal infiltrated with gold nanoparticles

A technique has been developed for infiltrating gold nanoparticles into the pores of synthetic opal using laser ablation and high-temperature annealing, and the reflection spectra of gold-infiltrated opal photonic crystals have been measured. When a halogen lamp was used as a broadband light source, the peak-reflection wavelength of the gold-infiltrated opal was longer than that of the uninfiltrated opal. We calculated the dispersion laws for the two lower photon bands of the synthesized photonic crystals and obtained the corresponding frequency dependences of the refractive index.     

Bi,Te, and Bi-Te nanoparticles in opal matrices

Bi, Te, and Bi₂Te₃ nanoparticles have been prepared by reducing bismuth salts, telluric acid, and their decomposition products with supercritical isopropanol in opal pores.     

Role of dopant cations in the gelation behaviour of silica sols

Gelation times of tetraethyl orthosilicate-derived sols containing selected di- to tetravalent cations as dopants were noted at different temperatures (15°–50°C). An analysis of these data, in conjunction with relevant published information, led to the tentative conclusions that (i) unhydrolyzed cations in bare form linked negatively charged silicate polymers in sols, thereby accelerating gelation and (ii) hydrolyzed cations retarded the process by offering molecular size-related hindrance and competition for the available water for hydrolysis.     

Preparation of bismuth nanoparticles in opal matrices through reduction of bismuth compounds with supercritical isopropanol

Bismuth nanoparticles have been produced in pores of opal matrices by reducing bismuth salts and oxide compounds with supercritical isopropanol. According to transmission electron microscopy data, the diameter of the SiO₂ spheres in the opal matrices is about 260 nm, and that of the bismuth nanoparticles does not exceed 80 nm.     

Experimental observation of photonic and polaritonic gaps in a silica opal

Experimental observations of the simultaneous presence of a polaritonic and a photonic gap in a three-dimensional photonic crystal is reported, to the best of our knowledge, for the first time. The photonic crystal was made of monodispersed silica microspheres sedimented into a face-centered-cubic structure. Silica has a polaritonic gap for wavelengths between 8 and 9.35 microm. Four different sphere sizes were used, with diameters of d=0.49, 0.73, 0.99, and 1.57 microm. The photonic crystals were studied by normal incidence infrared reflectance measurements in the wavelength interval 0.8-12 microm. Four peaks with the a magnitude of approximately 0.6, originating from the periodicity of the crystal, were recorded in the interval between 1 and 4 microm. Another peak, the polaritonic reflectance peak (approximately 0.4), is observed for wavelengths around 9 microm for all four crystals.     

Foliar application of two silica sols reduced cadmium accumulation in rice grains

In the present study, pot experiments were conducted to investigate the effects of foliar application of two silica (Si) sols on the alleviation of cadmium (Cd) toxicity in contaminated soil to rice. Results showed that the foliar application of Si sols significantly increased the dry weight of grains (without husk) and shoots in rice grown in Cd contaminated soil, whereas the Cd concentration in the grains and shoots decreased obviously. The total accumulation of Cd in rice grains also decreased with the application of both of the Si sols, but no significant effect was found on the Cd accumulation in the shoots. For the optimal effect, Si-sol-B should be foliar applied at the tillering-stage during rice growth. The mechanism of Si foliar application to alleviate the toxicity and accumulation of Cd in grains of rice may be related to the probable Cd sequestration in the shoot cell walls.     

Optical solitons in nonlinear directional couplers with spatio-temporal dispersion

This paper addresses solitons in nonlinear directional couplers in non-Kerr law media, with spatio-temporal dispersion. Both twin-core couplers as well as multiple-core couplers are studied. The nonlinearities studied are Kerr law, power law, parabolic law, dual-power law and log law. Bright, dark and singular soliton solutions of the governing equation are studied.     

纳米填料填充辐射硫化三元乙丙橡胶的力学性能及分散形态

采用60Co γ射线作为辐射硫化的辐照源,制备了以纳米二氧化硅(SiO2)、纳米碳酸钙(CaCO3)等为填料的三元乙丙橡胶(EPDM).研究了多官能团单体(PFM)、纳米填料的种类、用量等因素对橡胶力学性能的影响,并考察了纳米粒子在辐射硫化胶中的分散形态.力学性能和扫描电镜结果表明,辐射硫化胶的力学性能与纳米粒子在胶中的分散尺寸和均匀性有关.纳米SiO2粒子以较小尺寸均匀分布在硫化胶中,它对辐射硫化三元乙丙橡胶有较好的补强效果;而采用CaCO3或者二者的混合物为填料,粒子在硫化胶中的分散尺寸相对较大,因而所得辐射硫化胶力学性能不理想.     

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. -mercaptopropyltrimethoxysilane (-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. -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 -MPS is a promising material for a high performance rubber product.     

Dispersion of electromagnetic waves in a resonant opal photonic crystal filled with Al2O3:Cr3+

We have studied the band structure and group velocity of electromagnetic waves in an opal photonic crystal filled with Al₂O₃:Cr³⁺. The results demonstrate that, when a resonance state of the chromium ion falls within the band gap of an unfilled photonic crystal, the group velocity of electromagnetic waves decreases anomalously. We have calculated the dispersion curves and frequency dependences of the group velocity of electromagnetic waves in an opal photonic crystal filled with Al₂O₃:Cr³⁺.     

Optical power flow in plastic-clad silica fibers

Using the time-independent power-flow equation, we have examined the mode coupling caused by intrinsic perturbation effects of step-index plastic clad silica fiber carrying more than 10(5) modes. Result show that the equilibrium mode distribution for this fiber is achieved at a length of approximate 550 m, which is longer than reported previously. While this coupling length is much longer than that of plastic optical fibers, it is sorter than that of all-glass fibers.     

Problem of hydroxyapatite dispersion in polymer matrices: a review

This review summarizes recent work on manufacturing biocomposites suitable for bone tissue engineering. There is a great need to engineer multi-phase (i.e. composite) materials that combine the advantages exhibited by each component of the material, with a structure and composition similar to that of natural bone. The discussion concentrates on the preparation of nanocomposites containing hydroxyapatite particles (one of the most widely used bioceramics materials) with polymer matrices. Special attention is paid to the preparation of nanocomposites with individual (non-aggregated) nanoparticles because this is a key problem in nanotechnology industrialization. Controlling the mixing between so two dissimilar phases is a critical challenge in the design of these inorganic-organic systems. Several approaches that may be applied to overcome this problem will be described in this review.     

Densified silica fume: particle sizes and dispersion in concrete

Dry densified silica fume is by far the most common form of silica fume used in current concrete practice; the alternative, slurried silica fume has become unavailable in many places. Densified silica fume as commonly supplied consists of particles of sizes up to several millimeters, which are generally not dispersable into individual silica fume spheres. Densified silica fumes from some sources can be dispersed by moderate ultrasonic treatment into small clusters or chains of spheres; others resist such treatment and mostly remain as large agglomerates. Under conventional concrete mixing, substantial contents of agglomerates almost always remain in the concrete. Thus the assumption that the densification process is somehow ‘reversible’ is not generally warranted. The sizes of undispersed agglomerates remaining in concrete after mixing often exceed the sizes of Portland cement particles, thus limiting any potential benefits attributed to the fine particle filler effect. Large undispersed grains appear to always undergo chemical reaction in concrete, but such reactions may induce ASR damage only under especially unfavorable circumstances.     

Radiation of a charge moving in a waveguide filled with a dielectric medium possessing resonance dispersion

The radiation of a point charged particle moving along the axis of a round waveguide filled with a dielectric medium possessing resonance dispersion is theoretically studied. It is shown that the dispersion significantly influences the frequencies of excited harmonic modes and the energy of radiation. Allowance for dispersion leads to suppression of all excited harmonics to an extent increasing with the order of harmonics.