Size control of nanostructured silica using chitosan template and fractal geometry: effect of chitosan/silica ratio and aging temperature

The uses of low cost, renewable, environmentally friendly chitosan biopolymer as the structural template to control the size of silica particles in the range of nanometer scales are attractive for their practical industrial applications. In this paper, the nanostructured silica was synthesized using sodium silicate as the silica source and chitosan as the template under mild conditions. Effects of chitosan/silica ratio and aging temperature on the formation and the control of nanostructured silica was investigated by using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), N₂-sorption measurement, and transmission electron microscopy (TEM). It was found that the silica products were composed of the aggregates of primary silica nanoparticles and nanostructured silica units. At low aging temperature, the size of nanostructured silica was decreased when increasing the chitosan/silica ratio from 0.1 to 0.4. In contrast, the reverse trend was observed at the chitosan/silica ratio of higher than 0.4. The increase of aging temperature led to the formation of larger primary silica nanoparticles and nanostructured silica, and also promoted the formation of silica/chitosan composites. The fractal dimension calculated using modified FHH method found the linear correlation at two different regimes which might reflect the aggregates of silica products at different length scales.     

Preparation of silica/perfluoroalkyl methacrylate polymer inorganic/organic particles in supercritical carbon dioxide

Silica/perfluoroalkyl methacrylate polymer (PHDFDMA) particles were prepared using various types of silica by polymerization in supercritical carbon dioxide. There are three steps in the fabrication of inorganic/organic hybrid composites: silane treatment, polymerization, and soxhlet extraction. After these steps, we observed the morphology of silica/PHDFDMA particles using field emission scanning electron microscope and transmission electron microscope. From these analyses, we can confirm that the silica/PHDFDMA core/shell particles were obtained when we used Ludox and silica gel as a silica template. On the other hand, core/shell particles were not formed when using fused silica and precipitated silica. In addition, to confirm the amount of polymer on silica, we performed an analysis using thermogravimetric analysis and electron probe micro-analyzer. In this case, PHDFDMA was approximately 20 wt.% on the silica gel and 40 wt.% on the Ludox, respectively. When using fused silica and precipitated silica as a template, amount of PHDFDMA on silica was maximum 5 wt.% and over 40 wt.%, respectively. From these results, to obtain enough PHDFDMA encapsulated silica particle, colloidal silica, Ludox is the best template in four different types of silica.     

Hybrids of colloidal silica and waterborne polyurethane

Waterborne polyurethane (WPU) was synthesized and followed by adding colloidal silica to prepare WPU-silica hybrids. The silica content in the hybrid thin films was varied from 0 to 50 wt%. The experimental results revealed that the viscosity of these hybrid solutions increased with increasing silica content and resulted in the aggregation of silica particle in the hybrid films. The latter result was evidenced by SEM examination. The effect of interaction between silica particle and urethane polymer chains is more significant with increasing silica content. The prepared hybrid films show much better thermal stability and mechanical properties than pure WPU. The optical transparence did not linearly decrease with increasing the silica fraction in the hybrid thin film. At below 20% silica content, the film transparence decreased with increasing silica content; the converse is true at above 20% silica content. These results showed that the prepared hybrid films demonstrated tunable transparence with the silica fraction in the films.     

Influence of silica fillers during the electron irradiation of DGEBA/TETA epoxy resins, part III: Solid-state NMR investigations

The influence of silica fillers on chemical modifications of diglycidyl ether of bisphenol A/triethylene tetramine (DGEBA/TETA) epoxy resins induced by electron beam irradiation has been studied by ¹³C CP-MAS (Cross Polarisation and Magic Angle Spinning) NMR. Four kinds of silica filler were investigated: a pure micrometric silica, a treated micrometric silica, a pure nanometric silica and a treated nanometric silica. On the unirradiated epoxy resins, the magnetization transfer curves reveal structural differences due to the kind of silica fillers. A decrease of the epoxy network rigidity in the presence of nanometric silica fillers is shown. During irradiation, the formation of phenolic ends and enamine functions is confirmed. The slowing of the magnetization transfer of the pure and treated micrometric silica filled epoxy resin reveals an important decrease of the rigidity of these resins. On the pure and treated nanometric silica filled epoxy resins, reactions of the reactive species created by the irradiation in the epoxy resin and the silica particles surface are shown.     

苯基化硅胶的物理结构和表面性质的研究

本文利用苯基三氯硅烷和硅胶表面羟基反应制备了苯基化硅胶。测定了苯基化硅胶的物理结构、水蒸气吸附等温线、润湿热、差热分析(DTA)和红外光谱(IR)。结果表明,所有苯基化硅胶的真密度(dT)、比表面(S)和比孔体积(V)均减少, 而表观密度(dA)增加, 但苯基化对不同硅胶的平均孔半径(r)有不同的影响; 苯基化硅胶对水蒸气吸附, 对水、苯和环己烷的润湿热均显著减少; 苯基化硅胶的热稳定性大于甲基化硅胶, 甲基化硅胶的表面是高度憎水的, 但苯基化硅胶的憎水性则很弱。     

Synthesis and formation of hierarchical mesoporous silica network in acidic aqueous solutions of sodium silicate and cationic surfactant

Synthesis and formation of hierarchical mesoporous silica network in acidic aqueous solutions of commercial sodium silicate and cationic surfactant were studied by SEM, TEM, XRD and nitrogen adsorption-desorption methods. The formation process occurs through several steps, involving (1) formation of mesoporous silica nanoparticles; (2) aggregation of mesoporous silica nanoparticles into blocks; (3) growth of silica nanorods in closely-packed arrays by merging of silica nanoparticles; (4) separation of the nanorods to form 3D silica network; and (4) shrinking of the mesoporous silica network. The as-prepared 3D silica network exhibits bimodal morphology constituting mesoporous and macroporous phases.     

二氧化硅溶胶的形成与硅胶膜性能

采取溶胶-凝胶成膜技术,以正硅酸乙酯(TEOS)为原料,分别以水为溶剂NH3催化、乙醇为溶剂HCl催化和冰醋酸为溶剂各自制备出粒状结构、簇状结构和网状结构的二氧化硅溶胶,丙三醇作为添加剂与TEOS水解中间体以氢键结合控制二氧化硅溶胶形态,聚乙烯醇(PVA)与二氧化硅溶胶形成有机/无机互穿网络结构,易于成膜。热处理能使二氧化硅凝胶薄膜中的添加剂逸出并形成疏松结构,塑性形变使硅胶薄膜形成多孔、疏松、致密结构二氧化硅薄膜。实验表明,催化剂和溶剂效应直接影响着二氧化硅溶胶微观结构,从而影响着所形成的硅胶薄膜的微结构。多孔硅胶膜的平衡吸湿量是致密硅胶薄膜的3倍;而疏松结构的硅胶薄膜的吸湿量高于多孔硅胶薄膜的吸湿量,且其吸附速率明显大于多孔硅胶薄膜的吸附速率。     

Determination of crystalline silica in silica fume

Silica fume is formed as a by-product in the manufacture of silicon from quartzite. This paper describes an analytical method for the determination of crystalline silica in silica fume. The crystalline silica was determined after removal of amorphous silica from the fume. A gravimetric method was developed for the determination of the total crystalline silica in the fume, while the cascade impactor technique was used to determine the crystalline content in the -10 microm fraction. X-Ray diffraction, scanning electron microscopy and particle size distributions were used to validate the steps in the analytical procedure. The total crystalline silica content was found to vary from 2.7 to 8.6% with an RSD of +/-2%, while the crystalline silica content of the -10 microm fraction was 0.23 to 0.55% with an RSD of +/-10%. A knowledge of the crystalline silica content of silica fume is of great importance in the area of Occupational Health and Safety. The samples surveyed were shown to have levels of crystalline silica in the respirable fraction well within the draft guidelines for silica fume. It is proposed that this method be accepted as a standard method for the determination of crystalline silica in silica fume.     

高效液相色谱用硅质填料的进展

 对高效液相色谱用硅质填料的进展情况做了全面的评述。介绍了硅质填料的制备及化学修饰 ,评价了硅胶表面的物理表征 ,概括了硅质填料在高效液相色谱中的应用 ,并对我国的硅质填料前景进行了展望。     

Anchoring of polyacrylate onto silica and formation of polyacrylate/silica nanocomposite particles via in situ emulsion polymerization

Polyacrylate/silica nanocomposite latex particles were prepared by in situ emulsion polymerization of acrylate monomers initiated by 2,2′-azobis(2-amidinopropane)dihydrochloride (AIBA) adsorbed by silica nanoparticles. The anchoring of polyacrylate (ACR) onto silica nanoparticles was achieved through the physical absorption and chemical grafting reaction. The elution and HF etching experiments showed that most silica nanoparticles were encapsulated by ACR to form the raspberry-like ACR/silica nanocomposite latex particles. The silica nanoparticles with a greater grafting degree of ACR tended to locate in the bulk of the polymer, and the silica particle with a lower grafting degree would not be combined with polymer latex particles and always remained in water phase. The formation of the final ACR/silica nanocomposite latex particles included the anchoring of ACR onto silica primary particles, aggregation of silica primary particles to form the silica-containing latex particles, and the growth of latex particles.     

硅胶基质高效液相色谱填料研究进展

高效液相色谱(HPLC)不仅是一种有效的分析分离手段,也是一种重要的高效制备分离技术。色谱柱是HPLC系统的核心,不同性能的填料是HPLC广泛应用的基础。硅胶是开发最早、研究最为深入、应用最为广泛的HPLC固定相基质,其制备方法主要有喷雾干燥法、溶胶-凝胶法、聚合诱导胶体凝聚法及模板法等。近年来,亚2μm小粒径硅胶、核-壳型硅胶、双孔径硅胶、介孔性硅胶、有机杂化硅胶等新型硅胶应用于HPLC并取得了色谱分离技术的飞速发展,例如基于亚2μm填料的超高压液相色谱技术、基于核-壳型填料的快速分离技术、基于杂化硅胶填料的高温液相色谱技术等。硅胶经表面化学键合、聚合物包覆等有机改性可制得先进的大分子限进填料、温敏性填料、手性填料等,大大扩展了HPLC的应用范围。本文对液相色谱用硅胶的制备方法、改性与修饰方法以及硅胶基质固定相的评价方法加以系统综述,概述了新型硅胶在HPLC中的应用进展,并对硅胶基质填料的发展方向与应用前景进行了展望。     

高分散性SiO2/PMMA复合材料的制备与表征——纳米SiO2在MMA中的分散

用硅烷偶联剂3-(甲基丙烯酰氧)丙基三甲氧基硅烷(MPS)对分散于乙醇中的纳米SiO2进行偶联改性,再通过介质置换和原位本体聚合制得SiO2/甲基丙烯酸甲酯(MMA)单体分散液和SiO2/PMMA复合材料.红外光谱分析(FTIR)和热重分析(TG)结合洗提实验考察了SiO2表面MPS的偶联率和偶联效率,透射电镜(TEM...     

An improved methodology for adsorption characterization of unmodified and modified silica gels

An improvement in the adsorption characterization of the surface and structural properties of unmodified and modified mesoporous silica gels is presented. This improvement was achieved by selection of proper macroporous silica as the reference solid for adsorption characterization of porous silica gels. Experimental illustration is provided for unmodified and n-octyl-modified silica gels of different bonding density. The surface and structural properties of these silica gels were characterized by utilizing the standard adsorption data for both unmodified and octyl-modified LiChrospher Si-1000 macroporous silica gels. It was shown that the standard nitrogen adsorption data have an appreciable influence on the analysis of the pore size and surface properties of silica gels. This analysis can be improved by selecting the reference solid of the surface properties close to those of the silica gel studied.     

Rubber products prepared from silica modified by radiation-induced admicellar polymerization

Unmodified silica, silica modified with Si69, silica modified by thermal admicellar polymerization and silica modified by radiation-induced admicellar polymerization were applied as rubber reinforcement. Mechanical properties of these different rubber formulae were subsequently tested. The results revealed that the mechanical properties of rubber reinforced with silica modified by admicellar polymerization were superior to those reinforced with unmodified silica or silica modified with Si69. As for the silica modified by admicellar polymerization, cetyltrimethyl ammonium bromide (CTAB) proved to be the most effective surfactant, compared to dodecyltrimethyl ammonium bromide (DTAB) and tetradecyltrimethyl ammonium bromide (TTAB).     

Interaction and Microstructure of Polyurethane/Silica Hybrid Films Prepared by Sol-Gel Process

The polyester/silica hybrid resins and their hybrid polyurethanes were prepared via in situ (IS) or blending (BL) method using different silica sols. The effects of preparation methods, silica type and content on the interaction and microstructure of polymer/silica hybrid materials were investigated by FTIR, viscosity measurement, TGA, DMA and SAXS, respectively. It was found that both IS and BL methods formed agglomerates of silica-rich phases and primary silica-rich phases in the hybrid films, but the former caused stronger interaction between silica and polymer than the latter, resulting in much bigger agglomerates and compacter structure. The ethoxy group at silica was favorable for enhancing the interaction between silica phase and polymer, even between silica phases as well. The interaction between silica phase and polymer caused increasing viscosity, modulus and Tg, while the interaction between silica phases themselves increased the extent of micro-phase separation, especially for the hybrid films prepared by IS method.     

单分散SiO2/PS复合粒子的制备

聚合物包覆无机物的核一壳结构复合粒子研究长期以来受到关注,源于其应用广泛．根据表面性质要求对无机相或者有机相表面进行功能化,可使得到的复合粒子与不同的应用体系相匹配．这类聚合物包覆无机物的有机／无机复合粒子,已在光学器件、分离、药品、农业、涂料等很多领域有广泛和潜在应用．本文制备这类复合粒子用于石油工业模型催化剂和助剂．     

Stoeber二氧化硅溶胶中氨水的去除方法

通过pH值、电导率和二氧化硅解离量的测定，研究了Stfber二氧化硅溶胶的提纯过程．发现离心水洗很难完全去除体系中的氨水并且残留的氨水会影响二氧化硅粒子的化学稳定性．对二氧化硅溶胶进行酸处理后再提纯，可以大大加速提纯过程并消除氨水对二氧化硅粒子化学稳定性的影响。     

Silica dispersion and properties of silica filled ESBR/BR/NR ternary blend composites by applying wet masterbatch technology

Silica is used as a reinforcing filler in the rubber product such as a tire. When silica contents increased in the composite, deterioration of the processability and silica dispersion in silica-rubber composites cannot be overcome only by adding a silane coupling agent. Therefore, silica wet-masterbatch (WMB) technology is considered for manufacturing highly silica filled composites. Herein, we investigated silica dispersion, cure behavior, mechanical properties, abrasion characteristics, and viscoelastic properties of 3 types of WMB blend composites. Up to 82% improvement in silica dispersion was determined by the Payne effect and confirmed by atomic-force microscopy. The tensile strength and elongation at break increased and tan δ at 60 °C decreased by improving silica dispersion. The silica WMB is suitable for manufacturing highly silica filled composites.     

Crystallization of inorganic silica based on interaction between polyimide and silica by sol–gel method

Crystalline silica in cristobalite phase was successfully prepared at a relatively low temperature of 800 °C by calcinating polyimide/silica hybrid films under ambient air. X-ray photoelectron spectroscopy measurements show that the product is silica after calcination. It is found that the crystallinity is dependent on the removing rate and the strength of the interaction between polyimide and silica. The presence of polyimide plays an important role in the growth of silica. Calcination to remove polyimide with rapid heating results in lower crystallinity compared with calcination with slow heating. For samples with the same content of silica, the crystallinity changes with the strength of the interaction between polyimide and silica molecules.     

Influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles

The experimental results on the influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles were reported. The spherical silica nanoparticles have been synthesized using polyethylene glycol (PEG) as the surfactant and oil shale ash (OSA) as a new silica source. In order to identify the optimal condition for producing the best quality silica nanoparticles with the good dispersion and uniformity, the effects of surfactant surface coverage and aging time were investigated. It was found that the particle size and distribution of silica nanoparticles depend on the concentration of PEG in dispersion. At relatively low concentration, 0–2 wt.%, the existing PEG is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the PEG concentration increases to 3 wt.%, self-assembled PEG layer on the surface stabilizes the initially formed silica nanoparticles and the silica particles with average diameter of 10 nm are uniformly distributed. With further increasing the concentration of PEG, the number of PEG aggregates increases and silica nanoparticles are mainly formed inside the entangled PEG chains, resulting in an observation of clusters of silica nanoparticles. Moreover, it was found that as the aging time increased, the shape of silica nanoparticles becomes regular and the particle size distribution becomes narrow.