介孔二氧化硅的合成与表征

采用溶胶凝胶法,在酸性条件下用Na2SiO3作为硅源,在碱性条件下用TEOS作为硅源,合成了介孔二氧化硅。小角X衍射表明在酸性条件下,十六烷基三甲基溴化铵(CTAB)的浓度为0.01mol/L,Na2SiO3的浓度为0.1mol/L时,合成二氧化硅的介孔结构明显。碱性条件下,TEOS浓度为5%~10%(体积比)时,得到明显介孔结构的二氧化硅。     

Silicate-based polymer-nanocomposite membranes for polymer electrolyte membrane fuel cells

Proton-exchange membrane fuel cells have emerged as a promising emission free technology to fulfill the existing power requirements of the 21st century. Nafion^® is the most widely accepted and commercialized membrane to date and possesses excellent electrochemical properties below 80 °C, under highly humidified conditions. However, a decrease in the proton conductivity of Nafion^® above 80 °C and lower humidity along with high membrane cost has prompted the development of new membranes and techniques. Addition of inorganic fillers, especially silicate-based nanomaterials, to the polymer membrane was utilized to partially overcome the aforementioned limitations. This is because of the lower cost, easy availability, high hydrophilicity and higher thermal stability of the inorganic silicates. Addition of silicates to the polymer membrane has also improved the mechanical, thermal and barrier properties, along with water uptake of the composite membranes, resulting in superior performance at higher temperature compared to that of the virgin membrane. However, the degrees of dispersion and interaction between the organic polymer and inorganic silicates play vital roles in improving the key properties of the membranes. Hence, different techniques and solvent media were used to improve the degrees of nanofiller dispersion and the physico-chemical properties of the membranes. This review focuses mainly on the techniques of silicate-based nanocomposite fabrication and the resulting impact on the membrane properties.     

纳米级微孔SiO_2玻璃材料制备技术研究Ⅱ.纳米级微孔SiO_2玻璃体材的研制

采用溶胶－凝胶法，以正硅酸乙酯为原料，在酸催化下，用草酸作化学添加助剂（ＤＣＣＡ），着重研究了草酸用量对产品性能的影响，在此基础上，成功地研制出本体尺寸较大的纳米级微孔玻璃体材，其孔径分布主要范围在１～２ｎｍ之间，比表面积可达２１５．３９ｍ２／ｇ，密度几乎为石英玻璃的１／２，在紫外－可见光区透光性好，是一种很好的功能性纳米级基质材料。     

Porous inorganic materials

The field of porous, inorganic materials is experiencing explosive growth, as is shown by more than 6000 literature citations since 1994 along with numerous recent symposia and workshops that have been devoted to this topic. Much of the recent interest has been fueled by new synthetic strategies, such as ‘supramolecular templating’, that have enabled precise engineering of pore size, shape, and connectivity on the mesoscopic scale. In general, template-based approaches involving the cooperative organization of organic—inorganic assemblies as intermediates are emerging as a promising conceptual basis for future developments in the field of porous inorganic materials, such as the synthesis of hierarchical morphologies that mimic the intricate structures found so often in nature.     

Small-angle X-ray scattering investigations of fractal dimensions of hybrid inorganic organic network (ceramers) based on tetraethylorthosilicate and polytetramethylene oxide

Over the last 2 years the sol gel technique has become very popular because of its ability to yield multicomponent inorganic glasses at low temperatures. More recently techniques to incorporate functionlized organic species into a sol gel network of metal alkoxides have been developed and studied in our laboratory as well as others. Most of these studies have focussed on the structure-property behavior of these materials, with an emphasis on understanding the properties in terms of the level of microphase separation that occurs during the network buildup in these systems. While much has been gained in this respect, the desire exists to characterize better the structure of the inorganic phase in such systems, and in this respect, utilization of small-angle X-ray scattering profiles can provide information about this structure through fractal analysis. The work discussed here focuses specifically on the fractal character of specific ceramer materials produced as a result of the reaction between tetraethylorthosilicate and end-functionalized polytetramethylene oxide. It is shown that the cosolvent system utilized to compatibilize the reactants plays a very important role in development of the structure of the inorganic phase in these hybrid materials.     

有机硅改性涂料的开发现状

概述了国内高功能建筑涂料的开发现状,着重介绍了溶剂型有机硅改性丙烯酸酯涂料,水性有机硅改性丙烯酸酯乳胶涂料及陶瓷复合含硅弹性涂料,并介绍了硅氧烷聚酯卷材涂料。     

High pressure enhances activity and selectivity of Candida rugosa lipase immobilized onto silica nanoparticles in organic solvent

High hydrostatic pressure has been increasingly utilized to improve functions of enzymes, and most of such studies are currently focused on free enzymes in aqueous solution or organic solvent. In this work, Candida rugosa lipase (CRL) was immobilized onto silica nanoparticles and its activity and enantioselectivity in organic solvent were evaluated at high pressures under different water activities. The application of high hydrostatic pressures (50–200 MPa) led to improved activities of immobilized CRL for transesterification of (R)-1-phenylpropan-2-ol with vinyl acetate by 4–6 folds. Additionally the immobilization of CRL resulted in a significant change of selectivities, shifting the enantiomeric excess from the (R)- towards (S)-1-phenylpropan-2-yl acetate product at atmospheric pressure. The application of high pressures led to either enantiomeric excess towards (R)-1-phenylpropan-2-yl or no enantiomeric selectivity, depending on the water activities in the organic solvent and the level of pressures. The interesting behaviour of immobilized CRL under high pressures offers new opportunities to modulate enzyme functions through combination of high pressures and enzyme immobilization.     

单分散二氧化硅形成过程中TEM观察和形成机理

利用透射电子显微镜（TEM）首次观察到了生长过程中的单分散二氧化硅颗粒内部结构.在生长初期,单分散二氧化硅由结构疏松的絮状SiO₂组成;而在生长过程的中后期由结构密实的SiO₂组成．基于TEM观察结果和生长过程中其它现象的研究,提出了单分散二氧化硅形成机理,利用该基理对一些实验现象进行了分析和讨论．     

常压化学气相渗透制备Nextel 480/SiO_2复合材料

连续氧化物纤维增韧的氧化物陶瓷基复合材料与 Si C等非氧化物复合材料相比易加工 ,能满足航空部件的精度要求 ,而且高温抗氧化[1] ,已成为陶瓷基复合材料的研究热点。Si O2 陶瓷具有良好的耐烧蚀性能和稳定的高温介电性能 ,是导弹弹头和天线窗理想的介电 -防热材料。目前 ,以三向石英纤维及高硅氧布增韧的氧化硅陶瓷基复合材料均采用硅溶胶多次循环浸渍烧结制成 ,以 C纤维增韧的氧化硅陶瓷基复合材料采用氧化硅浆料涂刷热压制成 ,并已经得到了应用[2 ] 。但是 ,尚未见有采用化学气相渗透的方法制备氧化硅基复合材料的报道 ,而化学气相渗…     

纳米尺寸硅树脂的制备及性能

以正硅酸乙酯，甲基三乙氧基硅烷，二甲基二乙氧基硅为主要原料，在酸催化下，在醇溶液中水解、缩合，制得硅树脂，产物用TEM，IR，SEM表征，结果表明，硅树脂胶粒粒径50－100nm，硅树脂的成膜性能优良，基于铜片的硅树脂膜附着力为1级，冲击强度等于或大于500N.cm。