Preparation and characterization of TiO2 sols and their UV-cured hybrid thin films on plastic substrates

In this research, TiO₂ sols were synthesized via a sol?Cgel reaction at room temperature followed by heating under reflux. Hybrid thin films were prepared using the TiO₂ sols and dipentaerythritol hexacrylate on poly(methyl methacrylate) substrates via spin coating followed by UV-curing. The images of transmission electron microscopy (TEM) and results of dynamic light scattering (DSL) showed that some originally synthesized TiO₂ nanoparticles aggregated while many small-sized (~5?nm) TiO₂ nanoparticles still existed after reflux heating. The synthesized TiO₂ sols showed poor photocatalytic ability, which might avoid degradation of organic moieties in the hybrids. The refractive indices of the hybrid thin films were increased from 1.66 to 1.82 while the water contact angles on the thin films were increased from 70.2° to 87.7° with the increment of TiO₂ content. Increasing the heating time of the TiO₂ sol resulted in an increase in the refractive index and contact angle.     

Influence of nanoparticles on elastic and optical properties of a polymeric matrix: Hypersonic studies on ethylene-vinyl alcohol copolymer-titania nanocomposites

High resolution Brillouin spectroscopy (HRBS) backscattering elastic data in nanocomposites of ethylene-vinyl alcohol copolymer (EVOH) and TiO₂ nanoparticles present anomalous dependence with concentration, while Young’s modulus and microhardness data show the expected behaviour. When performing HRBS with the 90A scattering geometry to asses the effective elastic constant, the expected behaviour for low concentration of TiO₂ nanoparticles is again obtained. This unusual disagreement can be solved assuming that the inclusion of TiO₂ nanoparticles induces anomalous refractive index behaviour at the applied laser wavelength for the different EVOH-TiO₂ nanocomposites. Comparison with experimental elastic and optical data obtained in isotactic-polypropylene-TiO₂ nanocomposites proves that EVOH-TiO₂ nanocomposites show an unusual optical behaviour at the laser wavelength, possibly due to a singular bonding between the EVOH polymer and the TiO₂ nanoparticles.     

TiO2 nanoparticles synthesized in an aprotic solvent and applied to prepare high-refractive-index TiO2-polyimide hybrid thin films

In this study, very small (2–5 nm) TiO₂ nanoparticles were synthesized in an aprotic solvent, N,N-dimethylacetamide, via hydrolysis and condensation of titanium alkoxide at room temperature. The synthesized TiO₂ sol showed 30 days of storage stability and could be used to prepare high-refractive-index TiO₂-polyimide hybrid thin films by an ex-situ method that involved a spin coating and multistep baking process. The field emission scanning electron microscope image showed a flat and uniform morphology of the hybrid thin film. TiO₂ domains were in the nanometer range, thus avoiding light scattering. The refractive index at 633 nm of the hybrid thin film reached 2.05, which suggested potential applications of the film to anti-reflective coatings and optical waveguides.     

TiO2掺杂调控聚苯乙烯微球折射率及胶体光子晶体结构色

胶体光子晶体由于其可调变的结构色在绿色印刷、印染等领域备受关注,而其光子带隙的宽度和位置由光子晶体的晶格参数(晶面间距,通常受胶体微球尺寸影响)和介质的折射率决定。现有人工胶体光子晶体主要基于SiO_2和高分子(如聚苯乙烯(PS)等)微球的组装制备,由于胶体微球材质种类有限,折射率调控受限,因而目前调控胶体光子晶体结构色主要靠改变胶体微球的尺寸来实现。本文首先制备高折射率(2.6)的TiO_2纳米晶,在乳液聚合制备单分散的PS(折射率1.6)微球过程中,将所制备的TiO_2纳米晶掺杂于PS微球中,通过TiO_2的掺杂量有效调控胶体微球的折射率,进而实现胶体光子晶体的结构色调控。以多色胶体光子晶体微球的水溶液为墨水,采用彩色喷墨打印技术打印了电脑设计的光子晶体彩画。本文发展的光子晶体结构色调控新技术拓展了胶体光子晶体的应用。     

Extended Cauchy Model for Tunable Refractive Index of Titania Nanoparticles at Visible Region

The extended Cauchy model is derived based on the experimental data for describing the mass fraction-, crystallite size-, and calcination-dependent refractive index of anatase and rutile TiO₂ nanoparticles. This model fits the experimental data of TiO₂ nanoparticles well in the visible spectral region. There is a tunable correlation between the refractive index of TiO₂ nanoparticle and the anatase nanoparticle size at visible region. Moreover, there is a near correlation between experimental and calculated Abbe number at 588 nm.     

Low Temperature Preparation of High Refractive Index and Mechanically Resistant Sol-gel TiO2 Films for Multilayer Antireflective Coating Applications

TiO₂ sol-gel thin films have attracted a large attention for applications which require high refractive index transparent layers. In this work, sol-gel TiO₂ layers were prepared by Aerosol-gel deposition followed by a thermal treatment procedure in air. Depending on the experimental conditions, abrasion resistant and high refractive index layers could be obtained after post-treatment at only 110°C. In this paper, the experimental parameters which allow the preparation of functional TiO₂ sol-gel layers at such low temperature are discussed. It is concluded that the preparation of high refractive index and mechanically resistant TiO₂ layers can be interpreted in terms of competition between polycondensation and densification mechanisms. This result allows to envisage the sol-gel processing at low temperature of multilayer antireflective coatings.     

PMMA films refractive index modulation via TiO2 nanoparticle inclusions and corona poling

The present study is focused on the characterization of optical properties of poly (methyl methacrylate) (PMMA) films and the possibilities of modulation and fine tuning of their refractive index by the inclusion of different concentrations of nano-sized titanium dioxide (TiO₂) particles (less than 33 nm) and corona poling. The samples are prepared by the “spin coating” method and they are charged in a conventional point-to-plain corona system. The transparent PMMA/TiO₂ films exhibit good optical properties in the visible range. An investigation of the film’s surface refractive index by two wavelengths laser refractometry utilizing the disappearing diffraction pattern method is carried out. The refractive index increases with increasing the TiO₂ content in the nanocomposite films. The corona poling increases the refractive index values for all samples regardless of the polarity and concentration of TiO₂ nanoparticles. The results show that the prepared nanocomposite films have a potential application for optical devices.     

PREPARATION OF NANOMETER TiO2 ORGANIC SOLUTION —EFFECT OF ORGANIC SILOXANE ON SOL PROPERTIES*

A homogeneous longtime stabilized transparent nanometer TiO2 organic solution was obtained by means of the simultaneous hydrolysis and co-polycodensation of tetrabutyltitanate (TBT) and methacryloxypropyltrimethoxysilane (MAPTMS) by the sol-gel process. The particle size of nanometer titanium dioxide was controlled by use of bifunctional silanes, such as diphenyldimethoxysilane (DPDMS), diphenyldiethoxysilane (DPDES) and dimethyldiethoxysilane (DMDES). The effect of TiO2 content in the solution on the refractive index of system was discussed in detail. The result shows that the refractive index of solution increases linearly with TiO2 content. The refractive index of the three hybrid nanometer materials attained 1.6053, 1.5846 and 1.5346, respectively. The size of nanometer particles was characterized by TEM and the particle diameter thus obtained is in the range of 20-90 nm. FT-IR spectra of the materials show that the TiO-Si bond is formed.     

Antireflective sol–gel TiO2 thin films for single crystal silicon and textured polycrystal silicon

In this paper, antireflective TiO₂ thin films have been prepared on single crystal silicon, and textured polycrystal silicon by sol–gel route using the dip-coating technique. The thickness and the refractive index of the films have been optimised to obtain low reflexion in the visible region, by controlling both the concentration of the titanium isopropoxide (Ti(ⁱOPr)₄), and the annealing temperature. We showed that the use of a TiO₂ single layer with a thickness of 64.5 nm, heat-treated at 450 or 300 °C, reduces the reflection on single crystal silicon at a level lower than 3% over the broadband spectral ranges 670–830 nm and 790–1010 nm, respectively. In order to broaden the spectral minimum reflectance as much as possible, we have proposed to texture polycrystal silicon wafers, and to coat these wafers by a TiO₂ single layer with a thickness of 73.4 nm. In this case, the reflectance has been reduced from 27 to 13% in the spectral range 460–1000 nm.     

Preparation and characterization of TiO<Subscript>2</Subscript> hybrid sol for UV-curable high-refractive-index organic–inorganic hybrid thin films

In this study, UV-curable hybrid thin films were successfully prepared from TiO₂ and TiO₂ hybrid sols containing the acrylic monomer DPHA on PMMA substrates. The prepared TiO₂ and TiO₂ hybrid sols showed long-term storage stability and can provide operating control for the preparation of high-refractive-index hybrid thin films. The existence of interaction between the TiO₂ particle and the coupling agent was evidenced by FT-IR and UV–visible spectra. All hybrid thin films showed good adhesion to the PMMA substrate with refractive index falling over the range 1.64–1.77. These results suggested the potential application of present TiO₂ hybrid films in optical devices, such as anti-reflective coatings.     

二氧化钛反蛋白石薄膜的制备及其在化学传感器中的应用

用提拉成膜法将单分散295 nm聚甲基丙烯酸甲酯(PMMA)胶体微球自组装成蛋白石光子晶体膜. 在PMMA蛋白石光子晶体膜的空隙里填充15 nm二氧化钛纳米颗粒, 经500 ℃的处理除去PMMA膜板, 制备出大面积, 结构均一的二氧化钛反蛋白石光子晶体膜. 扫描电子显微镜(SEM)观察和X射线光电能谱(XPS)分析表明, 这种二氧化钛反蛋白石光子晶体薄膜是六方紧密堆积. 用这种二氧化钛反蛋白石光子晶体膜对溶液折射率的检测实验表明该传感膜分辨率可达0.01.     

Transparent poly(bisphenol A carbonate)-based nanocomposites with high refractive index nanoparticles

Transparent organic-inorganic nanocomposites were successfully synthesized from sulfonic acid-modified poly(bisphenol A carbonate) (SPC) and TiO₂ or ZrO₂ nanoparticles. The dispersibility of nanoparticles was significantly improved by both the surface treatment of nanoparticles with phosphoric acid 2-ethylhexyl esters (PAEH) and the introduction of a sulfonic acid moiety into the PC chain. It was found that in some cases, crystallization of the matrix caused a reduction in transparency. Efficient dispersion of nanoparticles and the absence of crystallization resulted in highly transparent nanocomposites with up to 42 wt% TiO₂ and 50 wt% ZrO₂ nanoparticles. The refractive indices of the nanocomposites based on SPC increased with the increasing amount of nanoparticles. Theoretical equation based on Maxwell-Garnett effective medium theory provided reasonably close estimation of the refractive indices to the experimentally observed values. The prepared nanocomposites had lower thermal stability than the host matrix polymers.     

不同基底对TiO2和SiO2薄膜的光学性能的影响

采用溶胶-凝胶法分别在K9玻璃、单晶硅和石英玻璃基底上制备了纳米TiO₂和SiO₂薄膜。利用SEM、UV-Vis及反射式椭圆偏振光谱仪对薄膜的微观结构及光学特性进行了表征和分析。结果表明:3种基底中, 单晶硅基底上TiO₂和SiO₂薄膜折射率最大;在非晶态K9玻璃和石英玻璃基底上TiO₂薄膜折射率和透光率差异较大;SiO₂薄膜在非晶态基底上折射率、透光率相近;3种基底上薄膜的折射率和消光系数都有随波长增大而减小的趋势, 同时Cauchy模型能较好的描述单晶硅基底上两种薄膜在400~800 nm波段的光学性能。     

不同基底对TiO2和SiO2薄膜的光学性能的影响

采用溶胶-凝胶法分别在K9玻璃、单晶硅和石英玻璃基底上制备了纳米TiO₂和SiO₂薄膜。利用SEM、UV-Vis及反射式椭圆偏振光谱仪对薄膜的微观结构及光学特性进行了表征和分析。结果表明：3种基底中, 单晶硅基底上TiO₂和SiO₂薄膜折射率最大;在非晶态K9玻璃和石英玻璃基底上TiO₂薄膜折射率和透光率差异较大;SiO₂薄膜在非晶态基底上折射率、透光率相近;3种基底上薄膜的折射率和消光系数都有随波长增大而减小的趋势, 同时Cauchy模型能较好的描述单晶硅基底上两种薄膜在400~800 nm波段的光学性能。     

Improved efficiency of dye-sensitized solar cells by design of a proper double layer photoanode electrodes composed of Cr-doped TiO2 transparent and light scattering layers

A new strategy for enhancing the efficiency of TiO₂ dye-sensitized solar cells (DSSCs) by design of a new double layer film doped with Cr ions, with various morphologies, is reported. X-ray diffraction and field emission scanning electron microscope (FE-SEM) analyses revealed that the synthesized nanoparticles had uniform and nanometer grains with different phase compositions and average crystallite size in the range of 10–12 nm depending upon Cr atomic percentage. UV–vis absorption showed that Cr introduction enhanced the visible light absorption of TiO₂ nanoparticles by shifting the absorption onset to visible light region. Furthermore, the band gap energy of nanoparticles decreased with an increase in dopant concentration due to reduction of particle size. It was found that, 3 at.% Cr-doped TiO₂ DSSC in the form of a double-layer film composed of TiO₂ nanoparticles, as the under-layer, and mixtures of nano- and micro-particles with weight ratio of 80:20, as the over-layer, (i.e., CT3/NM3 solar cell) had the highest power conversion efficiency of 7.02 %, short current density of 17.32 mA/cm² and open circuit voltage of 674 mV. This can be related to achievement of a balance among the electron injection, light scattering effect and dye sensitization parameters. Optimization of light scattering effect of photoanode electrode led to improve the photovoltaic performance of CT3/NM3 double-layer solar cell and was demonstrated by diffuse reflectance spectroscopy. The presented strategy would open up new insight into fabrication of low-cost TiO₂ DSSCs with high power conversion efficiency.     

Preparation and nonlinear optical properties of Au nanoparticles doped TiO2 thin films

Nano-sized noble metal nanoparticles doped dielectric composite films with large third-order nonlinear susceptibility due to the confinement and the enhancement of local field were considered to be applied for optical information processing devices, such as optical switch or all optical logical gates. In this paper, sol–gel titania thin films doped with gold nanoparticles (AuNPs, ~10 nm in average size) were prepared. AuNPs were firstly synthesized from HAuCl₄ in aqueous solution at ~60 °C, using trisodium citrate as the reducing agent, polyvinylpyrrolidone as the stable agent; then the particle size and optical absorption spectra of the AuNPs in aqueous solutions were characterized by transmitting electron microscopy and UV–Vis–NIR spectrometry. Sol–gel 2AuNPs–100TiO₂ (in %mol) thin films (5 layers, ~1 μm in thickness) were deposited on silica glass slides by multilayer dip-coating. After heat-treated at 300–1,000 °C in air, the AuNPs–TiO₂ thin films were investigated by X-ray diffraction, scanning electron microscopy and atomic force microscopy. The nonlinear optical properties of the AuNPs–TiO₂ thin films were measured with the Z-scan technique, using a femtosecond laser (200 fs) at the wavelength of 800 nm. The third-order nonlinear refractive index and nonlinear absorption coefficient of 2AuNPs–100TiO₂ films were at the order of 10^?12 cm²/W, and the order of 10^?6 cm/W, respectively, and the third-order optical nonlinear susceptibility χ⁽³⁾ was ~6.88 × 10^?10 esu.     

Synthesis and characterization of TiO2/Rh3+ nanoparticulate sols, xerogels and cryogels for photocatalytic applications

Nanoparticulate TiO₂/Rh³⁺ sols have been synthesized by the colloidal sol?Cgel route. The combination of the data measured with optical techniques such as laser diffraction, dynamic light scattering and multiple light scattering with a near-infrared light allows us to follow up the evolution of the peptization process and to establish the effect of the presence of Rh³⁺ on it. It is observed that the presence of rhodium ions retards the peptization step (t₂) and decreases both the average particle size of the nanoparticles and the viscosity of the nanoparticulate sols. In addition, when Rh³⁺ is present the isoelectric point shifts up to higher pH, which suggests that chemical adsorption of the rhodium (III) cations onto the surface of the TiO₂ nanoparticles is produced. The xerogels and cryogels obtained from the sols are constituted by anatase as major phase and traces of brookite. The phase transition is observed at lower temperatures for the xerogels containing rhodium (III) and at higher temperatures in the case of the cryogels. Finally, photocatalytic activity is higher in the case of the TiO₂/Rh³⁺ sols due to the rhodium (III) effect on the electronic transitions from the valence band to the conduction band.     

Impact and mechanism of TiO2 nanoparticles on DNA synthesis in vitro

The impact of TiO₂ nanoparticles on DNA synthesis in vitro in the dark and the molecular mechanism of such impact were studied. The impact of TiO₂ nanoparticles on DNA synthesis was investigated by adding TiO₂ nanoparticles in different sizes and at various concentrations into the polymerase chain reaction (PCR) system. TiO₂ nanoparticles were premixed with the DNA polymerase, the primer or the template, respectively and then the supernatant and the precipitation of each mixture were added into the PCR system separately to observe the impact on DNA synthesis. Sequentially the interaction between TiO₂ nanoparticles and the DNA polymerase, the primer or the template was further analyzed by using UV-visible spectroscopy and polyacrylamide gel electrophoresis (PAGE). The results suggest that TiO₂ nanoparticles inhibit DNA synthesis in the PCR system in the dark more severely than microscale TiO₂ particles at the equivalent concentration and the inhibition effect of TiO₂ nanoparticles is concentration dependent. The molecular mechanism of such inhibition is that in the dark, TiO₂ nanoparticles interact with the DNA polymerase through physical adsorption while TiO₂ nanoparticles do with the primer or the template in a chemical adsorption manner. The disfunction levels of the bio-molecules under the impact of TiO₂ nanoparticles are in the following order: the primer > the template > the DNA polymerase.     

Sol–gel-derived titania-hydroxypropylcellulose hybrid thin films of high refractive indices: solution components affecting the refractive index and uncracking critical thickness

Optically transparent, ca. 200–800 nm thick TiO₂-hydroxypropylcellulose (HPC) hybrid thin films were prepared from Ti(OC₃H₇ⁱ)₄–HPC–HCl–H₂O–C₃H₇ⁱOH solutions by the sol–gel method, where the as-deposited films were dried at 120 °C. The effects of the amount of HPC, H₂O and HCl in the starting solutions on the refractive index and uncracking critical thickness of the films were studied, where the effects on the critical thickness was discussed on the basis of in situ stress measurements during heating. The increase in HPC content increased the critical thickness and lowered the refractive index. The increase in HCl content resulted in a decrease in critical thickness and an increase in refractive index. Larger H₂O contents gave rise to a maximum in critical thickness while the refractive index was unaffected. Such variation in critical thickness with varying solution compositions was demonstrated to result from the differences in in-plane stress generated during heating. By optimizing the processing parameters an 810 nm thick TiO₂–HPC hybrid film of a refractive index of 1.84 was obtained.