Strip-Loaded High-Confinement Waveguides for Photonic Applications

Sol-gel is a promising deposition technique for the fabrication of silica-on-silicon photonic components. Silica-titania compositions provide large index differences, and thus strong mode confinement, and are suitable hosts for Er-doped optical amplifiers. We have developed channel waveguides based on phosphosilicate strip loads over high index titania-doped guiding layers. Here we demonstrate that low propagation loss (0.3 dB/cm) can be obtained in such guides at optical communication wavelengths. Alumina co-doped guiding layers are shown to inhibit OH retention without causing titania segregation, and reduced humidity during spinning is shown to be necessary to achieve low propagation losses.     

甲基丙烯酸3-三甲氧基硅丙酯在乳液体系中的分配

通过气相色谱(GC)研究了甲基丙烯酸3_三甲氧基硅丙酯(MPS)在乳液体系各相中的分配行为,并测得了MPS在各种情况下的分配系数.发现当MPS加入量达到聚合物种子的约10 wt%时,体系进入饱和状态,且大部分MPS分配在粒子相中.通过对单体相分配行为的理论分析,并结合实验数据,发现种子乳胶粒粒径、聚合物种子中的化学组成对MPS的分配行为影响很小,而温度则使MPS在各相中的饱和浓度增加.     

Synthesis of polymeric organic-inorganic hybrid materials. Partially deacetylated chitin-silica hybrid

This work reports the synthesis of a novel polymeric organic-inorganic hybrid. The inorganic component is a silica network obtained by controlled hydrolysis of tetraethyl orthosilicate via sol-gel process and the organic counterpart is partially deacetylated chitin (CHI). The resulting polymer hybrids were homogeneous transparent film forming glassy materials being compatible through a wide composition range. Simultaneous thermal analysis of a CHI/silica 1:1 mixture confirms the intermolecular complex formation between organic and inorganic polymers.     

Template Mediated Hybrid from Dendrimer

Novel dendrimer-titania hybrids were prepared in this work from hydroxy and amine terminated polyamidoamine dendrimer (PAMAM generation 4) and titanium alkoxide by an in-situ sol-gel process in presence of a ligand. Dendritic polymers are chosen because of their unique architectural features. Such dendrimer nanocomposite (DNC) can then be used for optical, catalytic, biomedical applications. The hybrid material formed in situ is found to be transparent, brittle and yellow in colour. The hybrids show higher thermal stability than their organic precursors. This is due to enhanced interaction of the inorganic material with the dendrimer through hydrogen bonding as evidenced by PA-FTIR. XPS studies show predominantly the existence of tetravalent titanium due to titania formation.     

Microstructure and Properties of Triethoxysilylpropylamine-Capped Polyurethane/Titania Hybrid Films

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.     

Effect of preparation of titania sol on the structure and properties of acrylic resin/titania hybrid materials

Acrylic resin/titania organic–inorganic hybrid materials were prepared by mixing titania sol produced by the sol–gel process with synthesized thermoplastic acrylic resins. The effects of the amounts of water and acid on hydrolysis and condensation of the sol–gel precursor (titanium n‐butoxide) were characterized by nuclear magnetic resonance, and their corresponding influences on the structure and properties of the hybrid films were investigated by small‐angle X‐ray scattering (SAXS), atomic force microscopy, dynamical mechanical analysis, an Instron testing machine, and ultraviolet–visible spectroscopy. SAXS indicated an open structure and nanoscale size for the titania phase of the hybrids. Higher titania content and a greater amount of water or acid in the sol–gel process resulted in titania domains that were larger size and had a more compact structure. The mechanical and UV‐shielding properties of the organic polymer obviously were improved with titania embedded. As the amount of water or acid in the sol–gel process increased, integrative mechanical properties decreased, with the amount of water having a greater impact than the amount of acid on the structure and optical properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3682–3694, 2004     

Sol–gel titania coating on unmodified and surface-modified polyimide films

Sol–gel coating of metal oxides on polymer substrates is a useful process to fabricate various organic–inorganic hybrid materials under mild conditions. However, this process is hardly applicable to pristine polyimide (PI) films because their surfaces do not display effective functional groups for metal oxide coatings. In this study, we firstly examined direct sol–gel coating of titania thin layers on unmodified PI film surfaces. The results confirmed homogeneous, ultrathin titania layer coating and showed that the thickness and microscopic morphology of the titania layers were affected by titanium alkoxide concentrations in the spin coating solutions. We next investigated titania layer coating on surface-modified PI films that prepared using alkaline hydrolysis, which generated carboxylic acid groups on the film surfaces. Optimal hydrolysis time was determined using FT-IR spectroscopy and contact angle measurements. After sol–gel titania coating on the hydrolyzed PI film surfaces, the Scotch tape test was conducted to evaluate adhesion strength between the titania layers and PI film surfaces. Morphological observations of the sample surfaces after the tests clearly showed that surface modification of PI films increased titania layer adhesions. Effect of hydrothermal treatments on film formability and adhesion strength between titania-PI film interfaces was also evaluated.     

Polymer Sol-Gel Synthesis of Hybrid Nanocomposites

The current state and main problems of polymer sol-gel synthesis as a method of the preparation of hybrid polymer-inorganic nanocomposites are analyzed. The general characterization of sol-gel reactions is given and the routes of the combination of sol-gel synthesis with the polymerization of traditional monomers are considered. Particular attention is given to the formation of sol-gel precursors in the presence of organic polymers, including the formation of interpenetrating hybrid networks. The specificity of hybrid nanocomposites based on multicomponent ceramics is discussed. The sol-gel process is analyzed as a promising route for the preparation of bioceramics in the presence of templates.     

Scratch Resistant and Transparent UV-Protective Coating on Polycarbonate

UV-protective coating material has been developed to improve the scratch resistance and transparency of polycarbonate substrates. Acetyl acetone (AcAc) chelated silanes and 3-glycidoxypropyl-trimethoxysilane (GPTMS) modified nano-titania sols were used for the UV-protective hard coating materials by the sol-gel technique. The hybrid network is formed as a result of the controlled hydrolysis and condensation of the MTMS (Methyl Tri Methoxy Silane) and DMDMS (Di Methyl Di Methoxy Silane). Surface modified TiO₂ nano particles were dispersed in sterically stabilized in the hybrid network by the chelating agent. The coatings dried at 130°C after spray coating were shown to have excellent scratch resistance and adhesion and in addition, it roles as efficient UV-protector under UV irradiation. The long time UV test resulted in no crack formation, without loss of adhesion within the test period of 20 weeks.     

Resonant opto-optical switching in organic polymer waveguides

Photochromic polymer films are prepared by doping a polymer matrix like PMMA up to a few wt% with the fulgides “Aberchrome”. Opto optical switching is achieved in planar waveguides. Optical switching with gratings in waveguides and in transparent films is reported for latent gratings activated by uniform exposure.     

溶胶-凝胶法制备二氧化钛纳米粒子及在光固化体系中的稳定分散

选用3种不同的稳定剂,乙酰丙酮(acac),异丙氧基三(焦磷酸二辛酯)钛(TTPO)和可聚合有机磷酸酯(MAP),采用钛酸四正丁酯(TBT)通过溶胶-凝胶法合成了一系列二氧化钛溶胶,并与树脂/单体相混合,制备成有机-无机杂化光固化涂料.利用FT-IR监测了TBT水解缩合形成溶胶的过程及杂化体系的光聚合过程.杂化固化膜SEM结果显示,在合成溶胶过程中添加不同的稳定剂对杂化固化膜中无机粒子粒径尺寸等形态有显著影响,其中使用TTPO作为稳定剂得到的无机粒子分散最均匀,粒径最小,约20 nm.物理性能测试表明光固化杂化膜在硬度和柔韧性方面都有明显的改善.     

Hybrid Pigments via Sol-Gel Processing

The incorporation of organic dyes into inorganic and hybrid sol-gel derived materials is a valuable method for the fabrication of colored layers for optical applications like filters, solar energy conversion, non-linear optical devices, and active laser media. There have been clear hints for photochemical stabilization of the organic dyes, therefore, our aim was to investigate the light stability of organic dyes within hybrid solids. Besides the traditional way of doping sol-gel coatings with dyestuffs, they were also covalently attached to the hybrid matrix and pigments were produced by spray-drying processes.The resulting spherical powders were investigated with respect to their morphological, structural and photochemical properties. The results show that uniformly shaped and colored hybrid pigments can be synthesized. The spectroscopic studies demonstrate the fixation of the dye to the matrix and the high degree of crosslinking achieved in the composite. Additionally, the hybrid pigments drastically improve the resistance of the dye against bleeding from thermoplastic polymers. Furthermore, a higher photochemical stability of the dye is observed within the hybrid matrix compared to a solution, and purely organic or inorganic solid hosts.     

Fabrication of hydroxyl group modified monodispersed hybrid silica particles and the h-SiO(2)/TiO(2) core/shell microspheres as high performance photocatalyst for dye degradation

The monodisperse hybrid silica particles (h-SiO(2)) were firstly prepared by a modified sol-gel process and the surface was modified in situ with double bonds, then abundant carboxyl moieties were introduced onto the surface of the silica core via thiol-ene click reaction. Afterward, the h-SiO(2)/TiO(2) core/shell microspheres were prepared by hydrolysis of titanium tetrabutoxide (TBOT) via sol-gel process in mixed ethanol/acetonitrile solvent, in which the activity of TBOT could be easily controlled. The carboxyl groups on the surface of silica particles promote the formation of a dense and smooth titania layer under well control, and the layer thickness of titania could be tuned from 12 to 100nm. The well-defined h-SiO(2)/TiO(2) core/shell structures have been confirmed by electron microscopy and X-ray photoelectron spectroscopy studies. After calcination at 500°C for 2h, the amorphous TiO(2) layer turned into anatase titania. These anatase titania-coated silica particles showed good photocatalytic performance in degradation of methyl orange aqueous solution under UV light.     

高折射率有机/无机纳米杂化透明膜层材料的制备与性质研究

采用溶胶-凝胶法,将钛酸酯和硅烷偶联剂(KH-560)进行共水解,经涂膜、固化,制备了一系列含有无机二氧化钛纳米相的无机/有机杂化膜层材料,通过不同方法对杂化膜层的微结构、光学、机械和热性质进行了表征.结果表明,所得到的有机/无机纳米复合膜层,在可见光范围内的透过率均在90%以上,同时具有较好的耐热性和较高的折射率(nd=1.47~1.73),并且膜层与基材的附着性好,铅笔硬度达到4~5H.     

Synthesis and photoluminescence of titania nanoparticle arrays templated by block-copolymer thin films.

High-density arrays of titania nanoparticles were prepared using a polystyrene-b-poly(ethylene oxide) block copolymer (PS-b-PEO) as a template and a titanium tetraisopropoxide based sol-gel precursor as titania source via a spin-coating method. The hydrophilic titania sol-gel precursor was selectively incorporated into hydrophilic PEO domains of PS-b-PEO and form titania nanoparticle arrays, due to a microphase separation between the PS block and the sol-gel/PEO phase. Field emission scanning electron microscopy (FESEM) and scanning probe microscopy (SPM) images showed that the uniformity and long-range order of the titania/PEO domains improved with increasing sol-gel precursor amount. Grazing incidence small-angle X-ray scattering (GISAXS) results indicate that the ordered structures exist over large length scales. Titania nanocrystal arrays of anatase modification were obtained by calcination at 600 degrees C for 4 h. After calcination, separated particles were observed for low and medium amounts of sol-gel precursors. Films with higher precursor amounts showed wormlike structures due to the aggregation between neighboring particles. Removal of the polymer matrix via UV treatment leads to highly ordered arrays of amorphous titania while retaining the domain size and interparticle distance initially present in the hybrid films. Photoluminescence (PL) properties were investigated for samples before and after calcination. The PL intensity increases with the increasing amount of sol-gel precursor. Bands at 412 nm were ascribed to self-trapped exitons and bands at 461 and 502 nm to oxygen vacancies, respectively. Uncalcined or UV-treated samples also showed PL properties similar to calcined samples, indicating that the local environment of the titanium atoms is similar to the environment of the crystalline anatase modification.     

Preparation and characterization of chemically bonded aramid-titania hybrids using isocyanatopropyltrimethoxysilane

Transparent aramid based titania hybrid films have been prepared by the sol–gel process. A mixture of m- and p-phenylenediamines was reacted with terephthaloyl chloride forming aromatic polyamide chains in dimethylacetamide solvent. The titania network was generated insitu in this matrix by the hydrolysis and condensation of the various amounts of tetraethylorthotitanate. Hybrid films with concentrations of titania varying from 2.5 to 12.5 wt% were prepared; the higher percentages of titania in the organic matrix showed a tendency towards phase separation. These films were tested for their thermo-mechanical properties. To achieve a further improvement in properties of the matrix, the aramid chain was functionalized and the inorganic network was chemically bonded using isocyanatopropyltrimethoxysilane. The bonded hybrids showed a narrower distribution of titania particles and these were distributed as a co-continuous phase. The glass transition temperature (Tg) of the hybrid films measured through dynamic mechanical analysis showed a relatively higher increase with inclusion of titania in the covalently bonded hybrids. The maximum value of Tg noted in the chemically bonded composites with 12.5 wt% titania was 361 °C and the storage modulus value was 5.214 GPa at 100 °C, showing an increase of 62 % over the pure polymer. The hybrid films with titania showed an improved UV-stability as compared to the pure polymer.     

The influence of methacryloxypropyltrimethoxysilane on the sol-gel process of TEOS

The influence of MPS on the hydrolysis and condensation process of TEOS is studied by means of hydrolysis time (t _H) and gelation time (t _G) curves. The addition of MPS to a mixture of TEOS, ethanol and water results in a substantial increase in t _G. The increase is most pronounced when adding takes place in the acid step of the sol-gel process of TEOS.In acid environment hydrolysis of MPS will be dominant compared to hydrolysis of TEOS. This results in an effective decrease of the amount of water available for the hydrolysis of TEOS. However, this decrease in water concentration cannot explain the complete effect of the addition of MPS. The hydrolysed MPS will also be incorporated in the gel network and will strongly influence the cross-linking ability. The lesser functionality of MPS compared to TEOS and the steric hindrance of the acrylate group results in a large increase in t _G.     

Oxygenation of conducting polymers facilitated by structure-breaking anions

Conducting polymers are an interesting class of materials that can be tuned to have a range of properties through counterion doping. For most conducting polymers, the insertion of anions (the doping process) leads to the formation of carbocations (positive charge carriers) along the conjugated polymer backbone. In this research, we report on a scenario that arises where certain (commonly used) anions in water induce oxygenation of the conducting polymers heteroatom. This is in contrast to the widely reported doping process, and the recently reported hydrolysis of conducting polymers. We observe that the transition between these different conducting polymer-interactions/reactions is well described by the concept of structure-making and structure-breaking anions. Poly(3,4-propylenedioxy thiophene dimethyl) (PProDOT-Me₂), polypyrrole (PPy), and poly(3,4-ethylenedioxy thiophene) (PEDOT) thin films are exposed to a range of anions in water. Both PProDOT-Me₂ and PPy are susceptible to oxygenation, while in contrast PEDOT is doped, when exposed to structure-breaking anions. All the polymers show hydrolysis for structure-making anions. The knowledge of the interaction and/or reaction of conducting polymers with anions in water is not only critical to their application in devices for aqueous environments (i.e., sensing), but also for their processing and fabrication using water.     

Tuning the optical properties of mesoporous TiO2 films by nanoscale engineering

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.     

FT-Raman-Spectroscopic Investigations of the System Glycidoxypropyltrimethoxysilane/Aminopropyltriethoxysilane

The base catalyzed sol-gel process in the system 3-glycidoxypropyltrimethoxysilane (GPTS)/3-aminopropyltriethoxysilane (APTS) is highly interesting for the synthesis of hybrid (inorganic-organic) polymers. FT-Raman spectroscopy with excitation in the near infrared as a versatile tool for in situ measurements was used to monitor the kinetic behavior of the hydrolysis reaction.An unexpected slow-down of the hydrolysis of GPTS recorded at higher temperatures can be attributed to a decrease of the pH-value during hydrolysis caused by silanol groups. After condensation has started, the pH-value reincreases and forces hydrolysis to reaccelerate. The results strongly suggest the existence of a pentacoordinated transition state with a negative charge at the silicon atom during base catalyzed hydrolysis.