Preparation and colloidal dispersion behaviors of silica sol doped with organic pigment

Silica sol doped with organic pigment was prepared by hydrolyzing tetraethoxysilane with a basic catalyst via dispersing pigment in silica sol. The colloidal properties of SiO₂/pigment hybrid sol and its deposited film were investigated. The presence of pigment in SiO₂/pigment hybrid sol affects the Zeta potential, particle size and surface tension compared to the silica sol without pigment. The SiO₂/pigment hybrid sol exhibited good dispersion stability in the centrifuge process. The maximum absorption wavelength was consistent with that of the pigment disperse solution, indicating that the pigment in SiO₂/pigment hybrid sol remained unchanged. Thermogravimetric analysis of the contents of organic component in silica sol and SiO₂/pigment hybrid sol were conducted, and the differential value was ascribed to the weight of the pigment and the condensate of polyoxyethylene octylphenol ether (OP-10) and γ-Glycidoxypropyltrimethoxysilane (KH-560). The surface topography of SiO₂/pigment hybrid silica film was characterized by AFM. The analysis of silica sol doped with organic pigment provides useful information for an effective pathway to disperse pigment on fiber and other substrates.     

Preparation and characterization of CuO/SiO2 and NiO/SiO2 with bimodal pore structure by sol-gel method

CuO/SiO₂ and NiO/SiO₂ with bimodal pore structure were prepared by sol-gel reactions of Tetra-methoxysilane (TMOS) and the respective metal nitrate in the presence of poly (ethylene oxide) (PEO) with an average molecular weight of 10 000 and the catalyst of acetic acid. In this process, the interconnected macroporous morphology was formed when transitional structures of spinodal decomposition were frozen by the sol-gel transition of silica. The addition of copper and nickel into the silica-PEO system had a negligible effect on the morphology formation. In gel formation, it was found that NiO crystalline sizes in the samples increased with decreasing Si/Ni molar ratio. It was considered that PEO interacted with both silica and nickel cations. In the CuO/SiO₂ with the presence of PEO_, CuO crystalline sizes were larger than those of NiO/SiO_2. It was considered that there was no obvious interaction between the Cu cation and PEO, most of the copper ions in wet silica gel were present in the outer solution. They easily aggregated as copper salts in the drying process of wet gel and decomposed into CuO particles in heating. While in the CuO/SiO₂ with the absence of PEO, the Cu was selectively entrapped as small particles in the gel skeleton due to the interaction between Cu aqua complex and silica gel network.     

Photophysical Properties of a Novel Organic–Inorganic Hybrid Material: Eu(III)-β-Diketone Complex Covalently Bonded to SiO2/ZnO Composite Matrix

In this article, dibenzoylmethane (DBM) was first grafted with the coupling reagent 3-(triethoxysilyl)-propyl isocyanate (TESPIC) to form precursor DBM–Si, and ZnO quantum dot was modified with 3-mercaptopropyltrimethoxysilane (MPS) to form SiO₂/ZnO nanocomposite particle. Then the precursor DBM–Si and the terminal ligand 1,10-phenthroline (phen) were coordinated to Eu³⁺ion to obtain ternary hybrid material phen–Eu–DBM–SiO₂/ZnO after hydrolysis and copolycondensation between the tetraethoxysilane (TEOS), water molecules and the SiO₂/ZnO network via the sol–gel process. In addition, for comparison, the binary hybrid material with SiO₂/ZnO network and ternary hybrid material with pure Si–O network were also synthesized, denoted as Eu–DBM–SiO₂/ZnO and phen–Eu–DBM–Si, respectively. The results reveal that hybrid material with SiO₂/ZnO network phen–Eu–DBM–SiO₂/ZnO exhibits the stronger red light, the longer lifetimes and higher quantum efficiency than hybrid material with pure Si–O network phen–Eu–DBM–Si, suggesting that SiO₂/ZnO is a favorable host matrix for the luminescence of rare earth complexes.     

Preparation of poly(methyl methacrylate)/CaCO3/SiO2 composite particles via emulsion polymerization

A novel method to prepare organic/inorganic composite particles, i.e. poly(methyl methacrylate)/CaCO₃/SiO₂ three-component composite particles, using emulsion polymerization of methyl methacrylate with sodium lauryl sulfate as a surfactant in an aqueous medium was reported. CaCO₃/SiO₂ two-component inorganic composite particles were obtained firstly by the reaction between Na₂CO₃ and CaCl₂ in porous silica (submicrometer size) aqueous sol and the specific surface area of the particles was measured by the Brunauer–Emmett–Teller (BET) method. The results show that the BET specific surface area of the CaCO₃/SiO₂ composite particle is much smaller than that of the silica particle, indicating that CaCO₃ particles were adsorbed by porous silica and that two-component inorganic composite particles were formed. Before copolymerization with methyl methacrylate, the inorganic composite particles were coated with a modifying agent through covalent attachment. The chemical structures of the poly(methyl methacrylate)/CaCO₃/SiO₂ composite particles obtained were characterized by Fourier transform IR spectroscopy and thermogravimetric analysis. The results show that the surface of the modified inorganic particles is grafted by the methyl methacrylate molecules and that the grafting percentage is about 15.2%.     

Preparation and Characterization of Porous Silica Films by a Modified Base-Catalyzed Sol-Gel Process Containing PVA: I. The Precursor Solution Synthesis

A novel modified base-catalyzed Sol-Gel process containing polyvinyl alcohol (PVA) has been proposed to prepare the porous SiO₂ film. In this process, the growth of the sol particles was artificially broken off and controlled by acid-stabilising agent and PVA. As a result, a uniform and stable precursor solution was obtained in which the size of sol particles was stable. This new process efficiently overcomes the shortcomings of the traditional base-catalysed Sol-Gel process and can be employed to prepare porous SiO₂ films with desired porosity and thickness. The influence of the catalyst, the reaction temperature, the pH value, the stabilizing agent and the PVA additive on the size of the SiO₂ sol particles is systematically studied in part I.     

Synthesis and characterizations of new negatively charged organic–inorganic hybrid materials: effect of molecular weight of sol–gel precursor

A series of negatively charged hybrid (organic–inorganic) materials were prepared through sol–gel process. The alkoxysilane-containing sol–gel precursors PEO-[Si(OEt)₃]₂SO₃H were obtained by endcapping polyethylene oxide (PEO) of different molecular weights with 2,4-diisocyanate toluene (TDI), followed by a coupling reaction with phenylaminomethyl triethoxysilane (ND-42) and sulfonation afterwards. The negatively charged precursors were then hydrolyzed and condensed to generate hybrid sol–gel materials, which were characterized by IR, TGA, XRD as well as the conventional ion exchange measurements. The results showed that in the hybrid sol–gel precursors PEO-[Si(OEt)₃]₂SO₃H organic PEO component was incorporated with alkoxysilane-containing ND-42 covalently. As the molecular weight of the precursors increased, thermal stability and cation-exchange capacity of the hybrid material decreased. All the hybrid materials were amorphous and those prepared from higher molecular weight precursors were flexible.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Effect of hydrophobicity on the stability of sol–gel silica coatings in vacuum and their laser damage threshold

Silica antireflective coatings modified by hexamethyldisilazane (HMDS) were deposited on clean substrates (silicon wafer or K9 glass blanks) by sol–gel processing. The effects of HMDS on the contamination resistant capability and laser-induced damage threshold (LIDT) of coatings were investigated. Transmission electron microscopy revealed that a stable sol with uniformly distributed silica particles with an average particle size of about 15 nm was acquired by adding appropriate amount of HMDS into the standard SiO₂ sol. With the modified sol the resultant coatings were hydrophobic and the contact angle for water increased with increasing amount of HMDS in the reaction mixture. Such increase in hydrophobicity was not the result of surface roughness. The antireflective properties were retained after HMDS-treatment and the maximum transmission values were above 99 %. The introduction of HMDS into silica sols had also increased the LIDT of coatings from 24.3 to 37.0 J cm^?2 when the molar ratio of HMDS to tetraethoxysilane was 0.05:1. The increase in LIDT was attributed to the decrease of nodular defect and uniform microstructures of coatings as an effect of the HMDS modification. After some of the hydroxyl groups on the surface of the SiO₂ particle were replaced by methyl groups, from which the SiO₂ particle gained a water-repellent surface, the stability of coatings in vacuum was increased. The maximum transmission values of modified coatings decreased by only 0.25 % after storage under vacuum for 168 h. In contrast, the standard sol–gel silica coatings decreased about 2 % under similar conditions. The LIDT of modified coatings remained as high as 30.8 J cm^?2, more than that of standard coatings stored for the same duration in air.     

具有双亲特性的水相哑铃型SiO2纳米粒子的制备

以纳米SiO2水溶胶为原料,3?氨丙基三乙氧基硅烷(APTES)和3?氯丙基三乙氧基硅烷(CPTES)为改性剂,在水基环境下分别对SiO2纳米粒子进行改性,得到了具有亲水特性的APTES改性SiO2粒子和具有亲油特性的CPTES改性SiO2粒子水溶胶。2种粒子按不同比例混合,利用接枝在SiO2粒子表面氨基和氯丙基的取代反应,使得2种具有亲水/亲油特性的改性SiO2纳米粒子偶联,制备了粒径为40~50 nm的哑铃型SiO2纳米粒子。并通过透射电镜(TEM)、傅里叶变换红外光谱(FT?IR)、X射线光电子能谱(XPS)以及动态光散射(DLS)等方法对其进行了系统表征。结果表明,2种粒子成功偶联形成了具有哑铃型结构的水相SiO2纳米粒子,该粒子两面具有不同的亲水性,粒径近似等于APTES改性SiO2粒子和CPTES改性SiO2粒子的粒径之和。     

Chemical Modification of Silica Gels

Highly porous pure and polyethyleneglycol (PEG)-doped silica gels have been prepared from tetraethyl orthosilicate (TEOS) in ethanol using NH₄OH base-catalysis. Addition of PEG to the SiO₂-system increases the average particle size and most frequent pore diameter of the resultant gels while their total surface area decreases. The viscosity of the sol increases with PEG concentration and passes through a maximum with increasing molecular weight at PEG 200. Results obtained indicate a definite interaction of the polymer with SiO₂ and that this interaction is not as a result of direct formation of Si– O– C linkage, but is more likely to be due to hydrogen bonding between the hydrated PEG and the Si– O– Si network. Structure-process correlations are considered.