共查询到20条相似文献,搜索用时 10 毫秒
1.
V. V. Serdobintseva D. V. Kalinin A. F. Danilyuk 《Reaction Kinetics and Catalysis Letters》1999,67(1):143-147
Structural ordering of monodispersed spherical silica particles (MSSP) occurs in ammonia stabilized concentrated suspensions
obtained by tetraethoxysilane (TEOS) hydrolysis in alcohol-aqueous solutions in the ammonia concentration range from 0.0001
to 0.0008 mol/L. MSSP interaction follows the DLFO (Deryagin, Landau, Ferway, and Overbeck) mechanism when electrostatic repulsive
forces between the particles predominate, and the structural ordering requires straightened conditions, which are provided
by suspension concentrating through MSSP gravitational precipitation. 相似文献
2.
Methods of estimating the degree of condensation of the surface silanol groups of silica due to its modification by silane coupling agents are reported.Also, a procedure for estimating the surface silanol groups for the pre- and post-modified silicas for the NIR 7326 cm–1 band is given.Using electron microscope studies and heats of immersion of silica surfaces, the silane effect on agglomeration of silica particles and, thus, on the physicochemical properties of its surface has been demonstrated. 相似文献
3.
Rubber compounds are filled with reinforcing fillers to improve their physical properties. Carbon black and silica have different surface chemistries to each other. Differences in properties of carbon black‐ and silica‐reinforced styrene‐butadiene rubber (SBR) compounds were studied. Variation of properties of carbon black‐ or silica‐filled compounds with the filler content was also investigated. The silica‐filled compounds without any coupling agent and dispering agent were prepared to investigate the influence of polar materials‐adsorption on the silica surface. Viscosity and crosslink density increased with increase of the filler content. Hardness, modulus, tensile strength, and wear property were improved more and more by increasing the filler content. Viscosity of the silica‐filled compound was higher than that of the carbon black‐filled one. Cure rate of the silica‐filled compound became slower as the filler content increased, while that of the carbon black‐filled one became faster. Difference in properties between the carbon black‐ and silica‐filled compounds were explained by the poor silica dispersion and the adsorption of cure accelerator on the silica surface. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
4.
Urbirajara Pereira Rodrigues Filho Yoshitaka Gushikem Fred Yukio Fujiwara Eduardo Stadler Valderez Drago 《Structural chemistry》1994,5(2):129-133
Pentacyanoferrate(II) absorbed on a silica gel surface previously modified with 3-aminopropyl and 3-imidazolylpropyl groups were characterized by13C MAS/NMR, FT-IR, Mössbauer spectroscopy, and cyclic voltammetry. FT-IR and13C MAS/NMR data indicated that the pentacyanoferrate(II) complex is bonded to the surface by the nitrogen atom of the functional group. The differences in the isomeric shifts, the quandrupole splittings and the midpoint potentials of the adsorbed complexes in comparison with the model complexes were attributed to the matrix polar effect—i.e., the interaction of the complex with polar groups on the silica surface. 相似文献
5.
6.
The paper presents the results of testing
the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates
with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan
NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified
silica. The test results were obtained with the use of a derivatograph, measurements
of flammability by the method of oxygen index, in air and also with the use
of a cone calorimeter. The effect of the modification on the zeta potential
was also examined.
A considerable reduction in the flammability
of nitrile rubber vulcanizates filled with silica can be obtained by the modification
of filler with bromine or iodine. All the vulcanizates containing modified
silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates
with bromine-modified silica makes it possible to obtain non-flammable polymeric
materials. They neither ignite nor glow under the action of a flame source
for 30 s.
The findings can be a rational basis for the synthesis
of modified silica that can act as active filler and effective flame-retardant
agent at the same time. 相似文献
7.
A. O. Litinsky V. N. Perminov G. Y. Vasiljeva 《International journal of quantum chemistry》2007,107(2):326-329
A model of molecular claster and nonempirical calculation schemes MP2/6‐31G*, MP4/6‐31G*, and MP2/DZVP2 were applied to study electronic and energy characteristics of the surface centers of different SiO2 modifications in rigid dehydroxidation conditions. It was established that depending on an angle α = Si′O′Si″ (where O′ is an oxygen atom of the nearest to the surface layer), O* atom corresponding with two surface Si atoms, could (i) form a chemical bond with one of the Si′ or Si″‐centers (an asymmetric configuration, α > 118° ÷ 120°); or (ii) be common for these centers (a symmetric configuration, α < 118° ÷ 120°). It was also established that when α > 132° ÷ 133°, the basic state was triple and at α < 132° ÷ 133°, it was single. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
8.
In the present review the findings concerning the effect of nanofillers to biodegradation and enzymatic hydrolysis of aliphatic polyesters were summarized and discussed. Most of the published works are dealing with the effect of layered silicates such as montmorillonite (unmodified and modified with organic compounds), carbon nanotubes and spherical shape additives like SiO2 and TiO2. The degradation of polyester due to the enzymatic hydrolysis is a complex process involving different phenomena, namely, water absorption from the polyesters, enzymatic attack to the polyester surface, ester cleavage, formation of oligomer fragments due to endo- or exo-type hydrolysis, solubilization of oligomer fragments in the surrounding environment, diffusion of soluble oligomers by bacteria and finally consumption of the oligomers and formation of CO2 and H2O. By studying the published works in nanocomposites, different and sometimes contradictory results have been reported concerning the effect of the nanofillers on aliphatic polyesters biodegradation. Most of the papers suggested that the addition of nanofillers provokes a substantial enhancement of polyester hydrolysis due to the catalyzing effect of the existed reactive groups (–OH and –COOH), to the crystallinity decrease, to the higher hydrophilicity of nanofillers and thus higher water uptake, to the higher interactions, etc. However, there are also some papers that suggested a delay effect of nanofillers to the polyesters degradation mainly due to the barrier effect of nanofillers and the lower available surface for enzymatic hydrolysis. 相似文献
9.
A. Krysztafkiewicz B. Rager M. Maik J. Szymanowski 《Colloid and polymer science》1994,272(12):1526-1535
Results of studies are presented on effect of new model compounds, applied to modify precipitated silica, on reinforcing of butadiene-styrene rubber vulcanizates filled with modified silica. Precipitated silica applied for the pur pose has been obtained according to our own procedure. Estimation of heats of immersion, mainly in benzene, has documented effect of model compounds involving hydrophobization of silica surface.For comparative reasons, results of strength tests have also been presented on vulcanizates of butadiene-styrene rubber filled with silica modified with a recognized coupling agent-mercaptosilane A-189. 相似文献
10.
M. Pilar Gonzlez-Marcos JosI. Gutirrez-Ortiz C. Gonzlez-Ortizde Elguea Juan R. Gonzlez-Velasco 《Journal of molecular catalysis. A, Chemical》1997,120(1-3):185-196
The reducibility of several nickel on silica systems prepared by incipient wetness impregnation and precipitation-deposition has been studied using TPR and TG. The analysis of the results has allowed us to determine the minimum drying and reduction temperatures for both impregnation and precipitation catalysts. From an analysis of the obtained results, together with X-ray diffraction and the study of the reduction degree, dispersion and nickel particle size of catalysts activated at different reduction temperatures, conclusions on the nickel surface chemical distribution have been derived. An optimal reduction temperature for the catalysts has been determined from activity considerations in the hydrogenation of sunflower seed oil. 相似文献
11.
Courtois J Szumski M Byström E Iwasiewicz A Shchukarev A Irgum K 《Journal of separation science》2006,29(1):14-24
Based on a survey of the literature on pretreatment of fused silica capillaries, 3 etching procedures and 11 silanization protocols based on the vinylic silane 3-((trimethoxysilyl)propyl) methacrylate (gamma-MAPS) were found to be most representative as a means of ensuring attachment of in situ prepared vinylic polymers. These techniques were applied to fused silica capillaries and the success in establishing the intended surface modification was assessed. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical state of the surface, providing information regarding presence of the reagent bound to the capillary. Wetting angles were measured and correlated with the XPS results. An adherence test was done by photopolymerization of a 2 mm long plug of 1,6-butanediol dimethacrylate in the prepared capillaries and evaluation of its ability to withstand applied hydraulic pressure. SEM was also performed in cases where the plug was released or other irregularities were observed. Finally, the roughness of the etched surface, considered to be of importance, was assessed by atomic force microscopy. Alkaline etching at elevated temperature provided a surface roughness promoting adhesion. The commonly used silanization protocols involving water in the silanization or washing steps gave inadequate surface treatment. The best silanization procedure was based on toluene as a solvent. 相似文献
12.
13.
Honami Hayashi 《Journal of Dispersion Science and Technology》2017,38(5):737-742
Two types of precipitated silica powders modified by poly (dimethylsiloxane) (PDMS) were suspended in benzyl alcohol and their rheological properties were investigated as a function of silica volume fraction, φ. The suspensions were classified into sol, pre-gel, and gel states based on the increase in φ. An increase in the degree of surface modification by PDMS caused gelation at higher φ. Plots of apparent shear viscosity against shear rate in the sol and pre-gel states of highly modified silica suspensions showed weak shear thickening behavior, while the same plots for silica suspensions with a low modification level exhibited shear thinning behavior. The dynamic moduli of hydrophobic suspensions in the pre-gel and gel states were dependent on the surface modification: the storage modulus G′ was larger than the loss modulus G″ in the linear region and these moduli increased with increasing φ, irrespective of the silica powder. The linear region of the φ range for the precipitated silica suspensions was wider than that for the fumed silica powders modified by PDMS suspended in benzyl alcohol, while the G′ value in the linear region for the precipitated silica suspensions was less than those for the fumed silica suspensions. 相似文献
14.
Studies were performed on application of highly dispersed silicas, specially obtained in organic solvent medium, to processing of elastomers. Particular attention was paid to silica surface modification and to estimation of an extent of the surface modification. To this aim, near infrared techniques were used and heat effects associated with surface wetting with water and benzene were estimated. Application studies were also conducted on the use of modified silicas in butadiene-styrene rubber. 相似文献
15.
16.
J. Nawrocki 《Chromatographia》1988,25(5):404-408
Summary The paper is concerned with the structure of an organic layer bonded to the silica surface modified with silazanes. The changes
of the retention volumes of hydrocarbons is studied for the silicas modified with hexamethylcyclotrisilazane, hexamethyldisilazane
and their mixtures. It is shown that most of the carbon in the layer after hexamethylcyclotrisilazane modification is bonded
to the surface by Si−O−Si bonds. This fact supports the assumption of a fragmentation of the cyclosilane used for modification. 相似文献
17.
Surface properties of poly(cyclopentadiene)–silica hybrid particles (PCPD–silica) were studied by means of XPS and electrokinetic measurements. The surfaces of PCPD–silica particles exhibit two different areas with different properties: bare silica holes and PCPD patches. The PCPD chains contain different functional groups such as alcohol and carbonyl groups that were identified by XPS. The PCPD chains are grafted covalently onto the silica surface via Si–O–C bonds created by the reaction of silanol groups and active PCPD chains. The amount of Si–O–C was examinated by means of XPS. The Brønsted acidity of the residual silanol groups was determined by means of electro-kinetic measurements. It was found that the pK a values of the residual silanol groups increase with increasing polymer content on the particle surface. The surface acceptor strengths of the hybrid particles in non-aqueous liquids were investigated by the solvatochromic indicator bis(1,10-phenanthroline)-cis-dicyano-iron-II in 1,2-dichloroethane. 相似文献
18.
《Journal of separation science》2017,40(22):4320-4328
Monodisperse silica particles with average diameters of 1.9–2.9 μm were synthesized by a modified Stöber method, in which tetraethyl orthosilicate was continuously supplied to the reaction mixture containing KCl electrolyte, water, ethanol, and ammonia. The obtained silica particles were modified by self‐assembly with positively charged photosensitive diazoresin on the surface. After treatment with ultraviolet light, the ionic bonding between silica and diazoresin was converted into covalent bonding through a unique photochemistry reaction of diazoresin. Depending on the chemical structure of diazoresin and mobile phase composition, the diazoresin‐modified silica stationary phase showed different separation mechanisms, including reversed phase and hydrophilic interactions. Therefore, a variety of baseline separation of benzene analogues and organic acids was achieved by using the diazoresin‐modified silica particles as packing materials in ultra high performance liquid chromatography. According to the π–π interactional difference between carbon rings of fullerenes and benzene rings of diazoresin, C60 and C70 were also well separated by ultra‐high performance liquid chromatography. Because it has a small size, the ∼2.5 μm monodisperse diazoresin‐modified silica stationary phase shows ultra‐high efficiency compared with the commercial C18‐silica high‐performance liquid chromatography stationary phase with average diameters of ∼5 μm. 相似文献
19.
J. Sonnefeld 《Colloid and polymer science》1996,274(12):1137-1144
The influence of an acid treatment on the pore structure as well as on the surface charge density of porous silica was investigated. It is shown that this treatment causes only small changes of the pore structure. Positive values of the surface charge density at pH>4 are interpreted in terms of surface impurities consisting of Na+ ions resulting from the synthesis of the gel from sodium silicate solution. This effect is strongly influenced by the acid treatment. The surface charge density parameters were evaluated on the basis of the triple-layer model for the electrical double layer. Here two different mechanisms of counterion attachment in the inner Helmholtz plane are discussed. 相似文献
20.
The adsorption of codeine from aqueous solution onto colloidal silica and silica surface-modified with chemiadsorbed octadecyl dimethyl silane (ODDMS) or dimethyl silane (DMS) groups was studied in the presence of neutral electrolytes at different pH values. From codeine-hydrochloride solutions codeine cations are strongly bound to negatively charged silica surfaces. Inorganic salts (NaCl, NaNO3) reduce the adsorption of the organic cation. On silica modified by ODDMS (10% of surface silanol groups are occupied), codeine cations are adsorbed to a higher extent at pH 6, while at pH 8 the adsorbed amounts are lower than on the bare silica surface. Neutral electrolytes reduce codeine adsorption on the ODDMS modified silica. On the hydrophobic silica, completely covered by DMS groups, codeine adsorption is considerably lower than on the bare silica, but neutral salts increase the adsorption. The adsorption of codeine is compared with the adsorption of aggregating surfactant ions. Common and different features of their interactions with silica surfaces are outlined. 相似文献