Preparation and properties investigation of PMMA/silica composites derived from silicic acid

Hybrid materials based on silicic acid and polymethyl methacrylate (PMMA) were prepared by in situ bulk polymerization of a silicic acid sol and MMA mixture. Silicic acid sol was obtained by tetrahydrofuran (THF) extraction of silicic acid from water. Silicic acid was prepared by hydrolysis and condensation of sodium silicate in the presence of 3.6 M HCl. As a comparative study, PMMA composites filled by silica particles, which were derived from calcining the silicic acid gel, were prepared by a comparable in situ polymerization. Each set of PMMA/silica composites was subjected to thermal and mechanical studies. Residual THF in PMMA/silicic acid composites impacted the properties of the polymer composites. With increase in silica content, the PMMA composites filled with silica particles showed improved thermal and mechanical properties, whereas a decrease in thermal stability and mechanical strength was found for PMMA composites filled with silicic acid dissolved in THF. With a better compatibility with polymer matrix, silicic acid sol shows better reinforcement than silica particles in PMMA films prepared via blending of the corresponding THF solutions. Copyright © 2008 John Wiley & Sons, Ltd.     

Hochauflösende Festkörper-NMR-Untersuchungen an Kieselsäuren. III Hochauflösende 29 Si-Festkörper-NMR-Untersuchungen an synthetischen siliciumreichen Kieselsäurehydraten

Solid-State High-Resolution N.M.R. Studies of Silicic Acids. III. Solid-State High-Resolution ²⁹Si-N.M.R. Studies of Synthetic Highly Siliceous Silicic Acid Hydrates Solid-state high-resolution ²⁹Si-N.M.R. experiments were used to study the structure of the silicate layers in three synthetic highly siliceous silicic acid hydrates obtained by cation exchange reactions from the synthetic sodium silicate hydrates ilerite, magadiite and kenyaite. For each of the studied samples two well-separated N.M.R. signals have been recorded which could be assigned to Q³ - (O?Si(OSi?)₃–) and Q⁴-(?Si(OSi?)₄–) units of the silicate layers of the corresponding silicic acid hydrate. On the basis of these results the same model was used to describe the structure of the silicate layers in the studied compounds which has been already used for the interpretation of the N.M.R. results in case of the synthetic sodium silicate hydrates. Compared with the sodium silicate hydrates in the studied silicic acid hydrates a somewhat large Q⁴/Q³-ratio and a high-field shifted Q³signal have been detected. These observations were attributed to structural changes which appeared as a result of the cation exchange reactions.     

Spectrophotometric determination of silicon in silicates by flow-injection analysis

A flow-injection spectrophotometric method has been developed for the accurate, continuous determination of silicon in silicate rocks. A rock sample solution is prepared by fusion with a 1:1 mixture of lithium carbonate and boric acid and subsequent dissolution of the cake in 1 M hydrochloric acid. The preparation technique is the same as that used for the determination of total iron, aluminium, calcium, titanium, and phosphorus in silicate rocks by flow-injection spectrophotometry. Because of the marked polymerization of silicic acid in acid solution, silicic acid is depolymerized in alkaline medium after a simple cation-exchange column filtration of the rock sample solution and then determined by a static or an FIA spectrophotometric method. The FIA system consists of two channels which carry the carrier solution and molybdate reagent, and allows the colour reaction to proceed under controlled conditions. The FIA system permits high throughput of 70 samples per hour. The procedure has been applied to a variety of standard silicate rocks of the U.S. Geological Survey and the Geological Survey of Japan, and gave satisfactory agreement with the recommended values.     

Analytical Properties of Gaize- and Silicate Glue-Based Xerogels with Immobilized Chrome Azurol S

A method is proposed for the synthesis of silicic acid xerogels based on opoka aluminosilicate (gaize) and silicate glue. The physicochemical properties of xerogels were studied. The complexation of Be(II) with immobilized Chrome Azurol S was studied by electronic absorption and diffuse-reflection spectrometry and solid-phase spectrophotometry. Test procedures were developed for determining Be(II) and Al(III) in waters and soils.     

The action of polysilicic acid on mixed monolayers of cholesterol and lecithins

Silicic acid produces marked expansion in dipalmitoyl lecithin films and in mixed cholesterol-dipalmitoyl lecithin films with more than 50 % phospholipid. In the presence of silicic acid, these films no longer exhibit a transition region between the liquid-expanded and liquid-condensed states. Mixed cholesterol-dilauroyl lecithin.films are also expanded by silicic acid. In the absence of silicic acid, the addition of cholesterol produces greater condensation in dilauroyl lecithin films than in films of dipalmitoyl lecithin, but the reverse is the case if the substrate contains silicic acid. These results have been interpreted in terms of a possible electrostatic interaction between negatively charged dissociated silicate ions and the positively charged trimethyl ammonium group of the choline fragment.     

Preparation of polysiloxanes from silicic acid. X. Preparation and properties of allyldimethylsilylated silicic acids

In order to obtain polysiloxanes capable of forming a film, the preparation and properties of allyldimethylsilylated silicic acid was investigated. The reaction in variable molar ratios of allyldimethylchlorosilane to silicic acid gave partially silylated silicic acids with different degrees of silylation. They provided not only fibrous polysiloxanes but also films from concentrated polymer solutions. Spinnability and film formation depended on the solvent, degree of silylation, molecular weight, and allyl group.     

Oligo-lysine Induced Formation of Silica Particles in Neutral Silicate Solution

Introduction Theformationofsilicastructuresunderthecontrol ofalivingorganism(biosilification)isawidespread phenomenoninnature,whichisfoundinmanylife formssuchasdiatoms,spongesandgrasses,etc.[1,2].Themostattractiveaspectofbiosilificationisthatex quisitestr…     

CO2对硅酸钠-丙烯酰胺溶液聚合行为及产物性质的影响

研究了不同CO2分压下低浓度丙烯酰胺(AM)在硅酸钠溶液中的聚合反应行为, 用环境扫描电子显微镜、流变仪及激光粒度仪等研究了产物的微观结构及其流变特性. 结果表明, 随着CO2浓度的增加, 产物的储能模量增加, 即黏弹性增大; 反应后生成的硅酸凝胶镶嵌在聚丙烯酰胺高分子凝胶网格中形成了复杂的网状结构. 在超声波作用下, 硅酸凝胶颗粒从体系中脱离, 检测到的颗粒粒径范围在280~900 nm之间, 且随着超声时间的增加, 颗粒的平均粒径减小. 结果表明, CO2的存在使得AM及交联剂的分子扩散速度增加, 提高了AM分子之间及其与交联剂分子的接触几率, 从而提高了产物的分子量.     

Sodium silicate route to coat polymer particles with silica

This paper presents a low-cost method to coat polymer particles with silica nanoparticles from inexpensive sodium silicate solution, which is a less-common precursor compared with tetraethyl orthosilicate for coating of polymer particles. The method is based on deposition of active silicic acid in the presence of polymer particles, prepared by emulsion polymerization of styrene involving poly(N-vinyl-2-pyrrolidone), under conditions that a dilute silica sol can be formed from this active silicic acid. The whole process was conducted in aqueous media. The effects of different reaction parameters, such as reaction temperature, amount of active silicic acid and solution pH, on the morphology and size of composite particles were investigated.     

Study of silica gel and copper silicate gel solubilities in high performance liquid chromatography

Summary After summarizing published results on silica gel and alkyl-bonded silica gel solubilities, the experimental solubility of unmodified silica and copper silicate gel (used in ligand exchange chromatography) in watermethanol-ammonia and water-acetonitrile-ammonia mixtures are given. These results demonstrate that silica gel solubility, measured by a static method, varies greatly with the water volume fraction of a ternary mixture. Curiously, no influence from the organic nature of the solvent was demonstrated. This observation is inconsistent with the fact that the copper silicate gel used in ligand-exchange chromatography with water-methanol-ammonia as mobile phase is attacked more rapidly than with water-acetonitrile-ammonia.An explanation based upon the variations of acid-base properties of silicic acid versus mobile phase dielectric constant values in conjunction with the methanol protophilic properties is proposed. Finally, it is shown that chromatographic columns filled with copper silicate gel have lifetimes of several months, if they are used with a procolumn (of copper silicate gel) and with acetonitrile as organic solvent with a volume fraction greater than 0.5 in the mobile phase.     

聚甲基丙烯酸甲酯/二氧化硅杂化材料制备与性能

溶胶-凝胶;聚硅酸;聚甲基丙烯酸甲酯/二氧化硅杂化材料制备与性能     

Synthesis of magnesium silicate by heat treatment of sols and mechanical activation of solid components

A layered magnesium silicate, an analog to natural talc, was synthesized by mechanical treatment of a mixture of magnesium hydroxide and hydrated silicic acid powders, as well as by heat treatment of aqueous dispersions containing magnesium hydroxide particles and silica sols prepared from different precursors.     

Verteilung des Kieselsäure-Brenzcatechin-Komplexes zwischen wäßrigen Lösungen und organischen Lösungsmitteln

The extraction of silicic acid as catechol complex by different organic solvents in presence of various organic bases has been studied. The influence of pH as well as of catechol und diphenylguanidine concentrations was tested. Ca. 100% extraction of silicic acid can be achieved at pH 9.2–9.3 by nitrobenzene, if the concentration of catechol in the aqueous phase is 0.5 M and that of diphenylguanidine in the organic phase > 0.25 M.     

Silicate complexes of sugars in aqueous solution

Certain sugars react readily with basic silicic acid to form soluble 2/1 (sugar/silicic acid) silicate complexes. Failure of monohydroxy compounds to give soluble products under these conditions indicates that the sugar silicates are chelates: five-membered diolato rings. Only furanose forms react. Pyranose sugars are stable under these conditions. Because all glycosides fail to react with silicic acid under these conditions, reaction appears to involve the anomeric position (C1 in aldoses, C2 in ketoses), which has a more acidic hydroxy group. Reaction is completed only when the anomeric hydroxy group is cis to an adjacent hydroxy group. The appropriate furanose form must have sufficient natural abundance and solubility to provide an observable product, as measured by (29)Si and (13)C NMR spectroscopy. These structural and practical constraints rationalize the successful reaction of the monosaccharides ribose, xylose, lyxose, talose, psicose, fructose, sorbose, and tagatose and the disaccharides lactulose, maltulose, and palatinose. Glucose, mannose, galactose, and sucrose, among others, failed to form complexes. This high selectivity for formation of sugar silicates may have ramifications in prebiotic chemistry.     

Über den Abbau von Kieselsol,Kieselgel und Aerosil in wäßrigen Tetramethylammoniumhydroxidlösungen

On the Degradation of Silicic Acid Sols, Silicic Acid Gel, and Aerosil in Aqueous Tetramethylammonium Hydroxide Solutions Investigations by trimethylsilylation and molybdate methods show that the degradation rate of silicic acid sols in tetramethylammonium (TMA) hydroxide solution depends on their average particle size. Under equivalent conditions (TMA/Si = 1, C = ～1,4 M, T: 25°C) the degradation of a silicic acid sol, silicic acid gel, and Aerosil takes place with different rates, which correlate with the specific surface of the investigated SiO₂ products. Regardless of the SiO₂ source the silicate anions of the three solutions are built up from the same types. During degradation the solutions with the same chemical composition show a similar anion distribution, which differs from analogous TMA-silicate solutions, the anions of which are in an equilibrium state.     

Critical study of the interference of silicic derivatives on fluoride determination

Several physical properties of various silicic derivatives are examined in order to elucidate an interference with fluoride during codistillation of hexafluorosilicic acid with superheated steam.The stated interference cannot be explained by the granulometry or by the specific surface area of the interfering derivatives but their porous structure: a nonporous adsorbent (silica) does not interfere; a porous adsorbent (silicic acid and silica gel) is liable to interfere when its pores reach a definite size, approximately a diameter of 50 Å.The occurrence of imprisonment of some fluoride anions in the pores of the interfering silicic derivatives is suggested.     

对硅酸聚合机制反应级数的验证

用胶凝法研究酸化了的不同摩尔比 (Si O2 /Na2 O)的硅酸钠溶液的胶凝速度 ,发现在恒盐条件下 ,硅酸胶凝速度常数是 2 ,这个结果和我们过去所提出的硅酸聚合机制符合一致。     

Preparation and constitution of the Crystalline Silicic Acid Trimethylsilyl Ester [(CH3)3Si]6Si6O15

A new crystalline compound has been synthesized by trimethylsilylation of tetraethylammonium silicate which was identified by means of gas chromatography, mass spectrometry, ²⁹Si NMR and X-ray analysis to be a eage-like double three-ring silicic acid trimethylsilyl ester containing six inequivalent SiO₄ tetrahedra and trimethylsilyl groups.     

Anionenstrukturen in Alkalisilicatschmelzen

Silicate Anions in Alkali Silicate Melts Melts of alkali silicates with molar ratios of alkali (Li, Na, K, Cs) to silicon between R = 4.0 and ca. 2.0 were prepared, quenched and worked up to the trimethylsilyl silicic acid esters. These were identified by comparison to the GC and silicon-29 NMR data of trimethylsilyl silicic acid esters from other sources. It was found that with cations of Li and Na mostly linear silicates were formed. But with the cations of K and Cs a considerable amount of the cyclic species Si₆O₉^6? was present. Branched silicates were of minor importance only. Besides the alkali silicon ratio, the temperature of the melt before quenching influences the composition of the silicate mixture.     

The composition and thermal behavior of nanodispersed silica synthesized by micellar technology

Morphology, particle size, and thermal behavior of silicic acid synthesized as gel by micellar technology were determined. It was found that the micellar synthesis using a smaller-molecule solvent, organic acid with shorter hydrocarbon (hydrophobic) part, as surfactant and silicate with smaller-radius cation yields silica gel with smaller particle size and, as consequence, increases silica dispersity. The differential thermal analysis of the synthesized silica gel showed that for samples with lesser particle size the phase transition temperatures are decreased by about 30–100°C.