单分散SiO2体系制备中TEOS水解动力学研究

采用一种与他人不同的萃取－冷冻分离－气相色谱法，跟踪形成单分散二氧化硅体系条件下正硅酯乙酯（TEOS）的水解过程，考察了温度（25～45℃）、氨浓度（0．5～0．2mol•L－1）、水浓度（6．0～15．0mol•L－1）等实验条件范围内，以上实验参数对TEOS水解速度的影响；并回归得到目前适用于在乙醇介质中氨催化下，形成单分散二氧化硅微粒常用实验条件范围内，唯一的较完整的水解动力学方程式．     

由硅酸酯合成单分散二氧化硅中碳的化学形态

单分散二氧化硅是指尺寸分布十分狭窄的二氧化硅颗粒．单分散颗粒在科学研究及工业应用中得到了广泛的应用［1］．单分散二氧化硅由正硅酸有机酯在氨催化下于醇溶液中水解缩合得到．硅酸酯的水解和缩合反应可用如下反应描述．总的反应式为：nSi（OR）4＋2nH20→nSiO2＋4nROH1956年Kolbe［2］发现正硅酸乙酯（TEOS）在碱催化下于乙醇溶剂中水解反应有时会形成均一颗粒二氧化硅以来，许多学者对这一反应体系进行了较为广泛的研究，提出了双分子缩合成核机理、单分子叠加生长机理、表面反应控制生长机理、扩散控制生长机理和微晶核团聚生…     

单分散酸性纳米二氧化硅的合成新方法

非极性有机溶剂中,乙酸和醇在没有酸性催化剂的情况下发生酯化反应,酯化生成的水水解TEOS(硅酸乙酯)合成单分散酸性纳米二氧化硅,粒径从数十纳米到数百纳米。TEM研究表明,溶剂的极性影响二氧化硅的形态,只有在非极性溶剂中才可以得到球形粒子,醇的种类和TEOS的浓度影响粒子的大小和粒径分布,利用FTIR和GC对TEOS的水解和二氧化硅形成过程进行研究。同时,文中提出了有机相在TEOS的酯化水水解、晶核的形成和生长的过程模型。     

单分散、大粒径聚苯乙烯微球的制备

以聚乙烯基吡咯烷酮为分散剂、偶氮二异丁腈为引发剂、醇／水混合物为分散介质进行了苯乙烯的分散聚合，讨论了初始单体浓度、分散剂用量、引发剂浓度、分散介质组成和反应温度等反应条件对所得聚合物颗粒直径和直径分布的影响．通过大量的试验，筛选出了较为理想的分散聚合的条件及配方，制备出了粒径为４８μｍ的单分散聚苯乙烯微球．然后，以分散聚合所制得的聚合物颗粒为种子，用动力学溶胀法制成了粒径增大近四倍的单分散、大粒径聚苯乙烯微球，并讨论了滴水速度和补加分散剂对溶胀的影响     

由硅溶胶生长单分散颗粒的研究

针对现行单分散二氧化硅颗粒制备方法的粒径预见性差、步骤繁琐、收率低等问题，研究了一种用硅溶胶作为种子，在氨、水和乙醇的混合溶液中通过水解正硅酸乙酯（TEOS）生长出单分散颗粒的简便方法．该方法仅在初始的悬浮液中滴加TEOS即可使种子正常生长，无须补充氨水以修正体系浓度的变化．最终的分散相浓度可达10％（质量分数）．可选择生长的粒径范围在1微米以内并可精确控制．所得颗粒粒径分布偏差优于Stber方法．讨论了种子数密度、生长环境和TEOS滴加速度对生长最终颗粒粒径分布偏差的影响     

新型球形纳米空心SiO2的模板合成方法研究

以纳米碳酸钙颗粒为新颖的无机模板剂,硅酸钠为无机硅源,通过溶胶-凝胶法形成CaCO3／SiO2的核壳结构;随后通过高温煅烧、酸溶和干燥处理,合成出了具有高比表面积的球形纳米空心二氧化硅粒子．然后,分别采用TEM,SEM,EDS,XRD,FTIR和TG等测试手段对样品进行了分析和表征,并考察了不同合成条件,如反应温度、反应pH值、煅烧温度和包覆反应时SiO2／CaCO3的配比对纳米空心二氧化硅粒子的比表面积变化．实验结果表明：较高的反应温度如60～80℃,pn值9左右、SiO2包覆量为碳酸钙质量的10％,以及煅烧温度为700℃,有利于形成空心形貌较好、比表面较大的球形纳米空心二氧化硅。     

葡萄糖还原氢氧化铜制备球形氧化亚铜及其粒度控制研究

以Cu(OH)2为前躯体,用葡萄糖还原制备了不同粒径的单分散球形氧化亚铜粉末。利用扫描电镜和smileview软件对Cu2O粉末进行了表征分析,并通过上述分析考察了反应温度和反应物浓度等因素对Cu2O粉末粒径的影响。结果表明,随着反应温度与葡萄糖投加浓度的提高,颗粒粒径减小;而随着氢氧化钠投加浓度的提高,颗粒粒径增大;体系内最终颗粒密度n+∞或颗粒个数n与各影响因素的变化呈直线关系。最后根据晶体成核生长模型初步分析了反应条件对Cu2O颗粒粒径的影响机理。     

单分散聚苯乙烯微球的制备及影响因素研究

以聚乙烯吡咯烷酮为分散剂，无水乙醇为反应介质，偶氮二异丁腈为引发剂，采用分散聚合工艺，通过优化反应条件，制备出了粒径为5μm单分散（分散系数≤5％）聚苯乙烯微球。所制备的聚苯乙烯微球标准偏差δ＝0．16μm，分散系数ε＝0．02，且具有良好的球形度，表面非常光滑，无破损，无缺损。对影响单分散聚苯乙烯微球的因素进行了研究，结果表明：随着分散稳定剂用量的增加，聚苯乙烯微球的粒径减小；随着单体和引发剂用量的增加，聚苯乙烯微球的粒径增大。分散稳定剂和单体用量是影响聚苯乙烯微球粒径分布的两个主要因素。     

由硅溶胶生长单分散颗粒的研究

针对现行单分散二氧化硅颗粒制备方法的粒径预见性差、步骤繁琐、收率低等问题，研究了一种用硅溶胶作为种子，在氨、水和乙醇的混合溶液中通过水解正硅酸乙酯（ＴＥＯＳ）生长出单分散颗粒的简便方法。该方法仅在初始的悬浮液中滴加ＴＥＯＳ即可使种子正常生长，无须补充氨水以修正体系浓度的变化。最终的分散相浓度可达１０％（质量分数）。可选择生长的粒径范围在１微米以内并可精确控制。所得颗粒粒径分布偏差于Ｓｔｏｂｅｒ方法     

氨乙基氨丙基聚二甲基硅氧烷改性水性聚酯型聚氨酯的研究

由聚酯二元醇、异佛尔酮二异氰酸酯和二羟甲基丙酸合成聚氨酯预聚体，以氨乙基氨丙基聚二甲基硅氧(AEAPS)为扩链剂，制备了AEAPS改性聚氨酯水分散液。与未改性的聚氨酯水分散液相比，AEAPS改性聚氨酯水分散液的粒径增大，但粒径分布和表面张力基本不变，说明疏水的聚二甲基硅氧烷侧链被包裹于分散颗粒的内部；此外，改性聚氨酯水分散液的冻融稳定性显著增强。AEAPS改性聚氨酯水分散液成膜后，吸水率明显下降，水在膜表面的接触角增加，400℃时热失重下降，具有良好的疏水性和耐热性。     

反相微乳液法制备纳米SiO2的研究

在壬基酚聚氧乙烯5醚(NP-5)/环己烷/氨水的反相微乳液体系中，进行正硅酸乙酯(TEOS)的水解、缩合反应，得到粒径在30～50 nm的单分散纳米SiO₂胶体。红外光谱法(FTIR)及透射电子显微镜(TEM)观察证明了纳米SiO₂粒子的生成。反相微乳液体系相图的研究表明，水相为氨水比纯水有较窄的W/O型微乳区。氨水微乳液是碱催化TEOS水解、缩合制备纳米SiO₂粒子的适宜体系。当体系中TEOS的浓度增大时，粒子的粒径随之增大。降低NP-5     

Preparation and characterization of silica aquasols

Aquasols containing silica nanoparticles with diameters of 75 to 95 nm were obtained directly by hydrolysis of 2 wt.% tetraethoxysilane (TEOS) in water in the presence of a non-ionic surfactant. The reaction was catalyzed by hydrochloric acid, ammonia, or sodium hydroxide. The particle size, which mainly depends on the concentration of TEOS in water, was determined by dynamic light scattering (DLS). Whereas the catalysts have almost no influence on the particle size, they very strongly affect the morphology of the silica particles formed. The dried SiO(2) particles obtained via the HCl-catalyzed reaction have film-forming properties and show no measurable BET surface area. SiO(2) particles prepared with ammonia as catalyst form nanoporous films on glass, and the BET surface area of the freeze-dried particles is 540 m(2)/g. Using sodium hydroxide as catalyst results in some agglomeration of uniform spherical particles with a BET surface area of 237 m(2)/g. (29)Si MAS NMR investigations of the freeze-dried particles provide information about the degree of condensation and the ratio of "free" hydroxyl groups. The silica aquasols described have a surprisingly high hydrophilizing effect on hydrophobic fibers (PP, PET). Silica nanoparticles of comparable diameters, prepared by the "St?ber method", dispersed in alcohol do not show any hydrophilizing properties worth to mention.     

Aerial Oxidation of Tetraethyl Silicate and Effect on Ammonia Catalyzed Hydrolysis

Colloidal suspensions of SiO2 in ethanol prepared by the ammonia catalyzed hydrolysis of tetraethyl silicate (TEOS) in ethanol have been routinely used for over 10 years to prepare antireflective (AR) coatings on the fused silica transmissive optical components of high power fusion lasers. Very high purity coatings are required to avoid laser damage and these are obtained when the TEOS is fractionally distilled under N2 prior to use.Recently we found that products from aerial oxidation of distilled TEOS, had a significant effect on the particle size of our coating suspensions to the detriment of the optical performance. We require particle sizes less than 20 nm to avoid light loss due to scatter and contaminated TEOS gave suspensions with much higher particle sizes. Oxidation products were identified by GC mass spectroscopy and included acetaldehyde, acetic acid, silicon acetates and reaction products of these compounds with ethanol.Acetic acid and silicon acetates were found to be the major cause of large particle formation. These could be removed by careful redistillation preferably in the presence of a small quantity of magnesium ethoxide. Storage in sealed containers under N2 avoided further problems.     

Solvent Effects on Particle Formation in Hydrolysis of Tetraethyl Orthosilicate

Particle formation in ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) was studied in aqueous solvents that contained ethanol, 1-propanol or 1-butanol. The reactions were performed at a TEOS concentration of 0.2 kmol/m³, a H₂O concentration of 5 kmol/m³ and a NH₃ concentration of 1 kmol/m³. Average particle size was the largest for 1-butanol and the smallest for ethanol. No specific relation of the average diameter to hydrolysis rate was observed in the reactions. Difference in dielectric constant of the solvent and particle surface potential in the reactions indicated that the magnitudes of interparticle repulsion in the solvents corresponded with the order of the average particle sizes. This suggested that the particle sizes were dominated by the interparticle repulsion.     

Synthesis of submicrometer-sized titania spherical particles with a sol-gel method and their application to colloidal photonic crystals

A synthetic method for preparing submicrometer-sized titania particles is proposed, which is based on hydrolysis of titanium alkoxide with the use of a cosolvent and an amine catalyst for alkoxide hydrolysis. The preparation was performed with different amines of ammonia, methylamine (MA), and dimethylamine (DMA) in different solvents of ethanol/acetonitrile, ethanol/methanol, ethanol/acetone, ethanol/acetonitrile, and ethanol/formamide for 0.1-0.3 M water and 0.03 M titanium tetraisopropoxide (TTIP) at temperatures of 10-50 degrees C. The use of the ethanol/acetonitrile solvent with MA was required for preparing monodispersed, spherical particles. The number average of the titania particle sizes and their coefficient of variation were varied from 143 to 551 nm and from 5.7 to 20.6%, respectively, with reaction temperature and concentrations of water and MA. Colloidal crystals of titania particles fabricated with a sedimentation method revealed reflection peaks attributed to Bragg's diffraction. Annealing at 100-1000 degrees C led to shrinkage and crystallization of titania particles followed by an increase in the refractive index of titania particles.     

A Generalized Model for Describing Particle Formation in the Synthesis of Monodisperse Oxide Particles Based on the Hydrolysis and Condensation of Tetraethyl Orthosilicate

A generalized model considering reaction and diffusion processes as rate determining steps is proposed for the formation of particles from hydrolysis and condensation of tetraethyl orthosilicate (TEOS). Reaction rate constant is assumed to be proportional to contact-surface area of two particles. Diffusion rate constant is given by Fuchs' stability theory with interparticle potential containing van der Waals attraction and electrostatic repulsion. To examine the validity of the model, ammonia-catalyzed reactions of TEOS were carried out in an ethanol-water solution at a water concentration of 11 mol/dm(3), an ammonia concentration of 1.0 mol/dm(3), and TEOS concentrations of 0.2 and 0.4 mol/dm(3) in the presence and in the absence of electrolytes. The experiments included competitive particle growth and seeded and nonseeded reactions. The model quantitatively expressed the results of the competitive growth experiments in which particles with different sizes grew at the same rate. The model gave the expected trend for the effect of ionic strength on particle sizes in the nonseeded reaction and the suppression of secondary particles in the seeded reaction by the addition of an electrolyte KCl. Good estimation was also obtained for transient particle size distributions in the nonseeded reaction and the seeded reaction in which secondary particles were generated. Copyright 2000 Academic Press.     

A novel method for synthesis of silica nanoparticles

A sequential method has been used, for the first time, to prepare monodisperse and uniform-size silica nanoparticles using ultrasonication by sol-gel process. The silica particles were obtained by hydrolysis of tetraethyl orthosilicate (TEOS) in ethanol medium and a detailed study was carried out on the effect of different reagents on particle sizes. Various-sized particles in the range 20-460 nm were synthesized. The reagents ammonia (2.8-28 mol L(-1)), ethanol (1-8 mol L(-1)), water (3-14 mol L(-1)), and TEOS (0.012-0.12 mol L(-1)) were used and particle size was examined under scanning electron microscopy and transmission electron microscopy. In addition to the above observations, the effect of temperature on particle size was studied. The results obtained in the present study are in agreement with the results observed for the electronic absorption behavior of silica particles, which was measured by UV-vis spectrophotometry.     

Preparation of large monodispersed spherical silica particles using seed particle growth

To obtain large-sized, monodispersed spherical particles of silica by sol precipitation, a seed particle growth method was attempted. The formation of secondary particles during seed particle growth causing a multimodal distribution of particle size was suppressed via fine adjustment of the reaction conditions, such as TEOS, ammonia, and water concentrations, as well as operational conditions such as feeding time and agitation speed. Among the reaction conditions, an increase of TEOS concentration promoted secondary particle formation, resulting in bimodal particle distribution. However, secondary particle formation was depressed with increasing ammonia and water concentrations. In addition, long feeding time (low feed flow rate) and rigorous agitation significantly reduced secondary particle formation because they contributed to the slow generation of supersaturation and rapid seed particle growth, respectively.     

Preparation and properties of uniform coated colloidal particles. VII. Silica on hematite

Spindle-type hematite particles of narrow size distribution were coated with uniform layers of silica by hydrolysis of tetraethylorthosilicate (TEOS) in 2-propanol. The effects of the reaction time and initial concentrations of ammonia and water on the thickness of the silica shell were investigated and the rate of the coating process, in terms of the TEOS concentration, was evaluated.