Effects of light scattering TiO2 surface-modified by dual oxide coating in dye-sensitized solar cells

The surface of light scattering TiO₂ particles in the dye-sensitized solar cell (DSSC) was dual-coated with Al₂O₃ and SiO₂ nanoparticles. The surface modification of the light scattering TiO₂ particles was performed by a modified sol–gel method using the colloidal alumina and the colloidal silica as surface coating precursors. It was revealed that the dual-coated light scattering TiO₂ particles leads to an increase in short-circuit photocurrent of DSSC device, resulting in an increase in energy conversion efficiency. This seems to be due to the increase of the light scattering by a combination of the light scattering TiO₂ particles and the oxide nanoparticles such as Al₂O₃ and SiO₂.     

Strengthening of basalt fibers with nano-SiO2–epoxy composite coating

Coatings, which were made from pure epoxy and SiO₂ nanoparticle modified epoxy composite, respectively, were applied onto the basalt fiber rovings. The SiO₂ nanoparticles were synthesized using a sol–gel method and modified using coupling agent. Fourier transform infrared spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC) analyses indicated the formation of modified SiO₂ nanoparticles. The SiO₂ nanoparticle–epoxy composite coating gave rise to a significant increase in the tensile strength of the basalt fibers as compared with the pure epoxy coating, and also the coating endowed the basalt fiber with a promising interfacial property in the basalt fiber reinforced resin matrix composite. The coating modification was an effective way in improving the mechanical properties of basalt fibers and the properties of basalt fiber/epoxy resin composites.     

Synthesis of TiO2-doped SiO2 composite films and its applications

The TiO₂-doped SiO₂ composite films were prepared by two-step sol-gel method and then it was applied in the degradation of methylene red (MR) as photocatalysts. In XRD, FT-IR, and TEM investigations of these TiO₂-doped SiO₂ composite films, the titanium oxide species are highly dispersed in the SiO₂ matrixes and exist in a tetrahedral form. And special attention has been focused on the relationship between the local structure of the titanium oxide species in the TiO₂-doped SiO₂ composite films and the photocatalytic reactivity in order to provide vital information for the design and application of such highly efficient photocatalytic systems in the degradation of toxic compounds diluted in a liquid phase.     

碳纤维颗粒增强CeO2/PMMA/PVDF超疏水复合涂层及其耐磨性能

提高耐磨性能是推动仿生超疏水表面走向实际应用的关键挑战之一。设计了二氧化铈微米粒子增强PMMA/PVDF超疏水复合涂层配方,获得了水珠接触角达152°、水珠滚动角为5°的超疏水复合涂层。该涂层经过落砂磨损试验后接触角下降为103°、滚动角增大为20°。采用碳纤维颗粒对CeO2/PMMA/PVDF超疏水复合涂层进行增强,优化配方的接触角达153°、滚动角达到5°。经过相同落砂磨损试验后,增强后的复合涂层水珠接触角能在一定程度磨损后达到140°左右。可见,CeO2/PMMA/PVDF复合涂层具有良好的超疏水性能,碳纤维颗粒增强是提高该涂层耐磨性能的有效方法。     

The light scattering of dielectric films

The Rayleigh scattering of dielectric films was measured at 441.6 nm wavelength. The total scattering losses of TiO₂, SiO₂, ZnS and MgF₂ films show a close correlation with the evaporation parameters. The light scattering of the TiO₂SiO₂ and ZnSMgF₂ film systems can be explained by scattering at the interfaces. By comparing curves of the light scattering as a function of scattering angle with the results of a numerical computing method the statistical parameters of the interfaces were obtained and were found to be in good agreement with electron microscope results.     

Sub-glassy relaxation modes in PMMA and PMMA + SiO<Subscript>2</Subscript> hosts of non-polar perylene derivatives

The dielectric response of poly(methyl methacrylate) (PMMA) in solid solutions of perylene derivative laser dyes in PMMA and PMMA + SiO₂ has been studied by means of the thermally stimulated depolarization currents (TSDC) technique, with the aim to isolate molecular and phase interactions in the dye blends. The changes in characteristics of the β-relaxation mode of PMMA are interpreted with respect to the dissimilar local environments of the polar carboxy-methyl pendant groups of PMMA. An important "chemical" effect on the β relaxation mechanism recorded in the organic-inorganic composites, is the formation of hydrogen bonds between the acidic pore surfaces of SiO₂ and the acetate side-groups. Several "physical" effects produced by the chromophores and the geometrical confinement, like the modification of the monomer-to-polymer conversion rates, the polymer's free volume and the extent of the PMMA-SiO₂ interaction, are discussed.     

Optical properties of core–shell structured Ag/SiO2 nanocomposites

Silver nanoclusters coated by SiO₂ were synthesized by a reverse micelle technique to obtain a core–shell microstructure with tunable particle size less than 50 nm. The refractive indices of the Ag/SiO₂ nanocomposites were calculated based on a theoretical model for binary composite materials which illustrated a strong correlation to the size of the metallic core and the dielectric shell. Dynamic light scattering analysis of the Ag/SiO₂ nanocomposites revealed that the refractive index of the nanocomposites was about 2.40, which was well in the range predicted by theoretical modeling. Optical absorption spectra and silver quantum dot size induced color change of the Ag/SiO₂ nanocomposites suspension were also investigated.     

Synthesis of ZnO/Zn2SiO4/SiO2 composite pigments with enhanced reflectance and radiation-stability under low-energy proton irradiation

ZnO/Zn₂SiO₄/SiO₂ composite pigments with nano-sized α-Zn₂SiO₄ interface phase were synthesized by a simple solid-state reaction method. It was found that the composite pigments exhibit significant improvement on the spectral reflectance and the proton radiation-stability compared with the pure ZnO pigment. The investigations have demonstrated that the enhancements on the spectral reflectance and the radiation-stability are attributed to the introduction of willemite Zn₂SiO₄ interface phase on the surface of ZnO matrix particles. In addition, the enhancement mechanisms of radiation-stability for ZnO/Zn₂SiO₄/SiO₂ composite pigments were discussed.     

Influence of SiO2 pore structure on phase change enthalpy of shape-stabilized polyethylene glycol/silica composites

Polyethylene glycol (PEG2000)/silica (SiO₂) composites with various weight percentages of PEG were prepared as solid–liquid shape-stabilized phase change materials using sol–gel method. In the composite, PEG and SiO₂ were chosen as the phase change substance and the supporting material, respectively. The composites were characterized by differential scanning calorimetry and scanning electron microscope. The pore structure of the SiO₂ matrix with removal of PEG was studied using N₂ adsorption analysis. The phase change enthalpy of PEG in the composite was determined. It was lower than the theoretical value, and decreased with the increase of PEG content. PEG in the composite was strongly confined during the phase transition, and the confinement effect was related with the pore structure of the silica matrix. By correlating the phase change enthalpy with the average pore diameter of the SiO₂ matrix by employing a confined phase change model with a constraint layer, the effect of the pore structure on phase transition of PEG was quantitatively evaluated. The phase change enthalpy of PEG in the composite depended on the average pore diameter of the SiO₂ matrix, the pore geometrical shape, and the thickness of the PEG constraint layer.     

Interferometric fidelity of self-pumped phase conjugation in BaTiO3 and a four-wave mixing set-up with Bi12SiO20 using nanosecond pulses

Abstract

The fidelity of a self-pumped phase conjugating mirror (SPPCM) in the so-called cat configuration is studied with an interferometric method for a cobalt-doped barium titanate crystal (BaTiO₃:Co) under pulse illumination (8 ns, 532 nm). With this SPPCM a phase conjugating four-wave mixing set-up using the sillenite-type crystal Bi₁₂SiO₂₀ (BSO) was realized. It is shown that the fidelity of both phase conjugating processes under pulse illumination nearly reaches the fidelity of continuous-wave experiments.     

Flower-like silicon dioxide/polymer composite particles synthesized by dispersion polymerization route

A vital issue for the manufacture of multifunctional thin films is to synthesize polymer/ceramic hybrid particles. Silicon dioxide (SiO₂)/polymer composite particles were synthesized through dispersion copolymerization of methyl methacrylate (MMA) in the presence of SiO₂ bullet-like particles, using a “grafting-through” approach. The SiO₂ particles were previously modified with the silane-coupling agent 3-(trimethoxysilyl)propyl methacrylate (MPTS). Scanning electron microscopy and transmission electron microscopy analyses confirmed the formation of particles with a rough surface and flower-like morphology. Fourier transform infrared spectroscopy, thermogravimetric analysis, and energy-dispersive X-ray investigations indicated that a nucleation and aggregation process of the growing copolymer MPTS/poly(methyl methacrylate) (PMMA) occurred on the surface of the modified SiO₂ particles. As a result, the SiO₂ core became embedded in a PMMA shell. The influence of MPTS and the concentration of polyvinylpyrrolidone as a steric stabilizer on the flower-like morphology was demonstrated. Dispersion polymerizations have been proven to be simple and effective ways to synthesize composite particles with a high surface area. By using homogeneous systems (i.e., the monomer was soluble in the reaction solvent), no emulsification process was required, and copious amounts of well-dispersed particles were produced. These characteristics open many application possibilities for the use of the synthesized particles in functional coatings and optical devices, for mechanical reinforcement in polymeric materials, and as biomaterials.     

Excellent electrical performance and thermal properties insulation paper based on polyimide porous fiber membrane modified by nano-SiO2

Oil-paper insulation system is an important insulation structure of converter transformer. At present study, polyamic acid introduced was synthesized firstly, then perform electrospinning and thermal imidization to prepare polyimide (PI) porous fiber membrane, and the nano-SiO₂ was introduced into the fiber membrane by in-situ polymerization. FT-IR was used to characterize PI porous fiber membrane chemical structure. Consequently, when the SiO₂ addition amount is 4 wt.%, the breakdown voltage of the SiO₂/PI composite fiber reaches the maximum, which is 74 kV/mm. The dielectric constant and dielectric loss of the composite fiber film are 1.98–0.0013 (10⁷ Hz). It is worth noticing that nano-SiO₂ available in PI significantly improved its electrical performance.

     

New intelligent multifunctional SiO2/VO2 composite films with enhanced infrared light regulation performance,solar modulation capability,and superhydrophobicity

Abstract

Highly transparent, energy-saving, and superhydrophobic nanostructured SiO₂/VO₂ composite films have been fabricated using a sol–gel method. These composite films are composed of an underlying infrared (IR)-regulating VO₂ layer and a top protective layer that consists of SiO₂ nanoparticles. Experimental results showed that the composite structure could enhance the IR light regulation performance, solar modulation capability, and hydrophobicity of the pristine VO₂ layer. The transmittance of the composite films in visible region (T_lum) was higher than 60%, which was sufficient to meet the requirements of glass lighting. Compared with pristine VO₂ films and tungsten-doped VO₂ film, the near IR control capability of the composite films was enhanced by 13.9% and 22.1%, respectively, whereas their solar modulation capability was enhanced by 10.9% and 22.9%, respectively. The water contact angles of the SiO₂/VO₂ composite films were over 150°, indicating superhydrophobicity. The transparent superhydrophobic surface exhibited a high stability toward illumination as all the films retained their initial superhydrophobicity even after exposure to 365 nm light with an intensity of 160 mW^.cm^?2 for 10 h. In addition, the films possessed anti-oxidation and anti-acid properties. These characteristics are highly advantageous for intelligent windows or solar cell applications, given that they can provide surfaces with anti-fogging, rainproofing, and self-cleaning effects. Our technique offers a simple and low-cost solution to the development of stable and visible light transparent superhydrophobic surfaces for industrial applications.     

Engineered silica nanoparticles as additives in lubricant oils

Silica nanoparticles (SiO₂ NPs) synthesized by the sol–gel approach were engineered for size and surface properties by grafting hydrophobic chains to prevent their aggregation and facilitate their contact with the phase boundary, thus improving their dispersibility in lubricant base oils. The surface modification was performed by covalent binding of long chain alkyl functionalities using lauric acid and decanoyl chloride to the SiO₂ NP surface. The hybrid SiO₂ NPs were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, simultaneous differential thermal analysis, nuclear magnetic resonance and dynamic light scattering, while their dispersion in two base oils was studied by static multiple light scattering at low (0.01% w/v) and high (0.50%w/v) concentrations. The nature of the functional layer and the functionalization degree seemed to be directly involved in the stability of the suspensions. The potential use of the functional SiO₂ NPs as lubricant additives in base oils, specially designed for being used in hydraulic circuits, has been outlined by analyzing the tribological properties of the dispersions. The dendritic structure of the external layer played a key role in the tribological characteristics of the material by reducing the friction coefficient and wear. These nanoparticles reduce drastically the waste of energy in friction processes and are more environmentally friendly than other additives.     

N-channel thin-film transistors based on 1,4,5,8-naphthalene tetracarboxylic dianhydride with ultrathin polymer gate buffer layer

N-channel operation of thin-film transistors based on 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) with a 9-nm-thick poly(methyl methacrylate) (PMMA) gate buffer layer was examined. The uniform coverage of the ultrathin PMMA layer on an SiO₂ gate insulator, verified by X-ray reflectivity measurement, caused the increase of electron field-effect mobility because of the suppression of electron traps existing on the SiO₂ surface. In addition, air stability for n-channel operation of the NTCDA transistor was also improved by the PMMA layer which possibly prevented the adsorption of ambient water molecules onto the SiO₂ surface.     

Engineered silica nanoparticles as additives in lubricant oils

Abstract

Silica nanoparticles (SiO₂ NPs) synthesized by the sol–gel approach were engineered for size and surface properties by grafting hydrophobic chains to prevent their aggregation and facilitate their contact with the phase boundary, thus improving their dispersibility in lubricant base oils. The surface modification was performed by covalent binding of long chain alkyl functionalities using lauric acid and decanoyl chloride to the SiO₂ NP surface. The hybrid SiO₂ NPs were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, simultaneous differential thermal analysis, nuclear magnetic resonance and dynamic light scattering, while their dispersion in two base oils was studied by static multiple light scattering at low (0.01% w/v) and high (0.50%w/v) concentrations. The nature of the functional layer and the functionalization degree seemed to be directly involved in the stability of the suspensions. The potential use of the functional SiO₂ NPs as lubricant additives in base oils, specially designed for being used in hydraulic circuits, has been outlined by analyzing the tribological properties of the dispersions. The dendritic structure of the external layer played a key role in the tribological characteristics of the material by reducing the friction coefficient and wear. These nanoparticles reduce drastically the waste of energy in friction processes and are more environmentally friendly than other additives.     

Photocatalytic degradation of formaldehyde by nanostructured TiO2 composite films

Interest in the photocatalytic oxidation of formaldehyde from contaminated wastewater is growing rapidly. The photocatalytic activity of the nanocrystalline Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film for the degradation of formaldehyde solution under visible light was discussed in this study. The films were characterised by field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy, X-ray diffraction (XRD), BET surface area, UV–Vis absorption spectroscopy, and photoluminescence spectroscopy. The FE-SEM results revealed that the Fe³⁺/F^? co-doped TiO₂–SiO₂ film was composed of uniform round-like nanoparticles or aggregates with the size range of 5–10 nm. The XRD results indicated that only the anatase phase was observed in the film. Compared with a pure TiO₂ film and a singly modified TiO₂ film, the Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film showed the best photocatalytic properties due to its strong visible light adsorption and diminished electrons-holes recombination.     

Dissolution kinetics of CsHSO4 and CsHSO4/SiO2 composites in aqueous solutions

Using a differential dissolution method, we have studied the dissolution kinetics of CsHSO₄ and CsHSO₄/SiO₂ composites (40, 60, and 70 mol % SiO₂) in aqueous solutions. The results demonstrate that the composites and bulk CsHSO₄ differ markedly in dissolution rate. In addition, the dissolution rate depends on the composition of the composite and decreases significantly as the SiO₂ content is raised from 0 to 70 mol %, even though the particle size of the salt is notably smaller in the composites. The composites of the same composition may contain cesium hydrogen sulfate in several states, differing in dissolution rate.     

Nanosilica/PMMA composites obtained by the modification of silica nanoparticles in a supercritical carbon dioxide–ethanol mixture

Nanosilica/poly(methyl methacrylate) (PMMA) composites are used to improve the mechanical properties of neat PMMA polymer. In order to obtain superior mechanical properties, it is essential to achieve good bonding between the SiO₂ nanoparticles and the PMMA matrix, which is typically achieved by coating silica nanoparticles with silane coupling agents. In this study, conventional and supercritical coating methods were investigated together with their influence on the mechanical properties of the obtained nanosilica/PMMA composites. The results indicate advantageous properties of nanosilica modified in the supercritical phase of carbon dioxide and ethanol in terms of particle size distribution, amount of coated silane, and dispersion in the PMMA matrix. Careful dispersion of the starting silica nanoparticles in ethanol at low temperatures in order to obtain a nanosilica sol plays an important role in deagglomeration, dispersion, and the coating process. The resulting nanosilica/PMMA composite containing nanoparticles obtained by supercritical processing of the nanosilica sol showed an increase in hardness by 44.6% and elastic modulus by 25.7% relative to neat PMMA, as determined using the nanoindentation technique. The dynamic mechanical analysis reveals that addition of nanoparticles as nanosilica sol and nanosilica gel enhances composite storage modulus by about 54.3 and 46.5% at 40 °C. At the same temperature, incorporation of modified silica nanoparticles with conventional method leads to an increase of 15.9% for the storage modulus, probably due to a large silica particle size and lower silane content in this sample.     

Crystallization behavior of PA6/SiO2 organic–inorganic hybrid material

Poly 2-hydroxy propylmethacrylate-methyl methacrylate/SiO₂ (PHPMA-MMA/SiO₂), an active composite was used to synthesize polyamide-6/SiO₂ (PA6/SiO₂) organic–inorganic hybrid materials via blending method. X-ray diffraction analysis (XRD) results showed that the addition of PHPMA-MMA/SiO₂ composite induced PA6 to transit from α to γ crystal form. The nonisothermal crystallization kinetics of PA6 and PA6/SiO₂ hybrid materials was investigated by differential scanning calorimetry (DSC). Jeziorny method derived from Avrami analysis and a method developed by Liu were employed to describe the nonisothermal crystallization process of PA6 and PA6/SiO₂ hybrid materials. Based on our experimental data, if the relative degree of crystallinity was approximately 60% or more, the Jeziorny method was not valid to describe the nonisothermal crystallization process, while Liu method was successful to describe the whole nonisothermal crystallization process. When X(t) was below about 60%, the crystallization rates of PA6 and PA6/SiO₂ hybrid materials were very approximate, but when X(t) was approximately 60% or more, the crystallization rate of PA6 was quicker than that of PA6/SiO₂ hybrid materials. Moreover, the addition of PHPMA-MMA/SiO₂ composite decreased the crystallization activation energy ΔE calculated by Kissinger equation because of the γ transition.