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TEOS
Selected AbstractsElectrochemically-Induced Deposition of Amine-Functionalized Silica Films on Gold Electrodes and Application to Cu(II) Detection in (Hydro)Alcoholic MediumELECTROANALYSIS, Issue 19 2005Alain Walcarius Abstract Well-adherent amine-functionalized porous silica films have been deposited on gold electrodes by combining the self-assembly technology, the sol,gel process, and the electrochemical modulation of pH at the electrode/solution interface. A partial self-assembled monolayer of mercaptopropyl-trimethoxysilane (MPTMS) was first formed on disposable gold electrodes from recordable CDs (Au-CDtrodes). The so pretreated MPTMS-Au-CDtrodes were immersed in a stable sol solution (pH,3) containing (3-aminopropyl)-triethoxysilane (APTES) and tetraethoxysilane (TEOS). Polycondensation of the APTES and TEOS precursors was then achieved by applying a negative potential for a given period of time to generate a local pH increase at the electrode/solution interface and promote the deposition of the amine functionalized silica film adhering well to the electrode surface owing to the MPTMS monolayer acting somewhat as a "molecular glue". Various parameters affecting the electrodeposition process have been studied and the film permeability to redox probes in solution was characterized by cyclic voltammetry. The amine-functionalized silica film electrodes were then applied to the preconcentration of copper(II) species prior to their electrochemical detection by anodic stripping differential pulse voltammetry. Getting high sensitivity has however required the application of an electrochemical pre-activation step as the majority of the organo-functional groups were in the form of ammonium moieties (because the film was prepared from an acidic sol). This was achieved by applying a sufficiently negative potential to the electrode surface to reduce protons and increase consequently the amine-to-ammonium ratio within the film and, thus, the efficiency of the precocentration process. The resulting device was then optimized for copper(II) determination in hydroalcoholic medium, giving rise to a linear response in the 0.1,10,,M concentration range. [source] Hybrid silica monolithic column for capillary electrochromatography with enhanced cathodic electroosmotic flowELECTROPHORESIS, Issue 21 2006Jiwei Hu Abstract A hybrid silica monolithic stationary phase for RP CEC was prepared by in,situ co-condensation of (3-mercaptopropyl)-trimethoxysilane (MPTMS), phenyltriethoxysilane (PTES), and tetraethoxysilane (TEOS) via a sol,gel process. The thiol groups on the surface of the stationary phase were oxidized to sulfonic acids by peroxytrifluoroacetic acid. The introduced sulfonic acid moieties on the monoliths were characterized by a strong and relatively stable EOF in a broad pH range from 2.35 to 7.0 in CEC. Aromatic acids and neutral compounds can be simultaneously separated in this column under cathodic EOF. The CEC column exhibited a typical RP chromatographic mechanism for neutral compounds due to the introduced phenyl groups. [source] Drug Self-Templated Synthesis of Ibuprofen/Mesoporous Silica for Sustained ReleaseEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2006Fengyu Qu Abstract The synthesis of Ibuprofen/mesoporous silica has been achieved by a drug self-templated one-step co-condensation process. The drug template of Ibuprofen, a co-template of 3-aminopropyltriethoxysilane (APTES), and tetraethoxysiliane (TEOS) were self-assembled into Ibuprofen/mesoporous silica in a neutral aqueous reaction system. This drug/mesoporous silica was characterized by powder XRD diffraction, FTIR spectroscopy, N2 adsorption/desorption, TEM, and 29Si/MAS and 13C/MAS NMR spectroscopy. The Ibuprofen/mesoporous silica system gives a well-sustained release profile. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] In Situ Synthesis, Characterization of SiPMo-X, and Different Catalytic Properties of SiPMo-X and SiPW-XEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2006Chunfeng Shi Abstract SBA-15 frameworks with encapsulated Keggin type heteropolyacids (HPAs) were synthesized in situ under strongly acidic conditions (pH,<,0). During the hydrolysis of tetraethyl orthosilicate (TEOS), a P- and a Mo source were added into the initial sol,gel system to form Keggin type HPAs. The texture of the final products was studied by the N2 adsorption,desorption isotherms and transmission electron microscopy (TEM), and their structure was systematically characterized by X-ray diffraction (XRD), UV/Vis diffuse reflectance- (DRS), infrared- (IR), and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Characterization results suggest that the samples show very ordered hexagonal mesostructure, and the HPAs that are incorporated into the framework of meso-silica are insoluble during catalysis. Results of catalytic tests indicate that the materials demonstrated catalytic activity comparable with or even surpassing those of the bulk HPAs in catalytic tests implementing chemical reactions of bulky molecules (1,3,5-triisopropylbenzene cracking, esterification of benzoic acid with tert -butyl alcohol, and 2,3,6-trimethylphenol hydroxylation with H2O2). Additionally, some other properties, such as easy separation and stability when recycled, ensure their potential applications in the chemical industries. Here, we report not only the in situ synthesis and characterization of SiPMo-X, but also the difference in the catalytic properties of SiPMo-X and SiPW-X. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis of Monodisperse Silica Nanoparticles Dispersable in Non-Polar Solvents,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Eoin Murray Three synthetic routes to hydrophobic silica nanoparticles are compared in this paper. First, the established synthetic method based on the Stöber process was examined. Monodisperse colloidal silica particles with diameters of 15,25,nm were prepared via the hydrolysis of tetraethyl orthosilicate (TEOS) by aqueous ammonia in ethanol. The surfaces of these particles were rendered hydrophobic with octadecyltrimethoxysilane (ODTMS) after the reaction or, more conveniently, during the growth phase. Secondly, silica particles with diameters of 15,50,nm were prepared using a one-pot synthesis in which TEOS was hydrolyzed by an amino acid and the resulting particles were coated with ODTMS. Lastly a novel, direct approach to the synthesis of hydrophobic organosilica nanoparticles was developed using ODTMS as the single silica source. Hydrolysis of the ODTMS by aqueous ammonia in ethanol yielded monodisperse colloidal organosilica particles with diameters of 15,30,nm. [source] Controlling Photoactivity in Ultrathin Hematite Films for Solar Water-SplittingADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Florian Le Formal Abstract A promising route to increase the performance of hematite (,-Fe2O3) photoelectrodes for solar hydrogen production through water-splitting is to use an extremely thin layer of this visible light absorber on a nanostructured scaffold. However, the typically poor performance of ultrathin (ca. 20,nm) films of hematite has been the limiting factor in implementing this approach. Here, the surprising effect of a substrate pretreatment using tetraethoxysilicate (TEOS) is reported; it results in drastic improvements in the photoperformance of 12.5,nm thick films of hematite. These films exhibit a water oxidation photocurrent onset potential at 1.1,V versus the reversible hydrogen electrode (vs. RHE) and a plateau current of 0.63,mA cm,2 at 1.5,V vs. RHE under standard illumination conditions, representing the highest reported performance for ultrathin hematite films. In contrast, almost no photoactivity is observed for the photoanode with the same amount of hematite on an untreated substrate. A detailed study of the effects of the TEOS treatment shows that a monolayer of SiOx is formed, which acts to change the hematite nucleation and growth mechanism, increases its crystallinity, reduces the concentration of carrier trapping states of the ultrathin films, and suggests its further application to quantum-dot and extremely-thin-absorber (ETA)-type solar cells. [source] New supplying evaporation precursor method with CVDHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2009Motohiro Oshima Abstract We propose a novel system of chemical vapor deposition (CVD), i.e., flash boiling spray CVD (SF-CVD) to eliminate several kinds of problems, such as the decomposition of precursors in the supply line and evaporator. In this method, liquid precursors are supplied directly to the vacuum chamber through an injector, just like fuel for an automobile engine, without any vaporizers, so as to induce an unsteady and intermittent flash boiling spray in the chamber. However, it is necessary to keep the lowest ambient pressure possible because the saturated vapor pressure of the precursors is very low. Thus, this is very useful for modifying the saturated vapor pressure of the precursors. A technique of lowering the vaporization pressure is proposed by mixing a more saturated vapor-pressure organic solvent with a precursor. To determine the principles underlying FS-CVD, we first formed SiO2 film on the Si substrate. A mixed solution of tetraethylorthosilicate (TEOS) and n-pentane was used as the mixing solution. The film thickness distribution of SiO2 film on a 100-mm-diameter Si wafer was ±4% using this method. Furthermore, this method enabled us to control film with various thicknesses by optimizing the injection duration, cycle, and injection cycle per second. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20235 [source] Characteristics of CVD silicon oxide films: Effect of discharge form on formation and properties of filmsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2004Kazuhiro Ishimaru Abstract A silent discharge is one of the simplest methods for realizing a nonequilibrium plasma condition at atmospheric pressure. In this study, nonequilibrium plasma chemical reactions by this discharge have been applied to a remote plasma chemical vapor deposition (CVD) of silicon oxide films using tetraethylorthosilicate (TEOS) and oxygen. Film characteristics obtained by this CVD have been investigated for applications to advanced semiconductor devices. Conditions for depositing films with high quality have been investigated minutely. From these results, it has been clarified that silicon oxide films with high quality and excellent step coverage can be obtained by plasma excitation using pulsed silent discharge. It has also been clarified that films with similar characteristics can be obtained by plasma excitation using low-frequency AC silent discharge at subatmospheric pressure. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(2): 106,116, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20000 [source] Synthesis and characterization of novel polyimide/SiO2 nanocomposite materials containing phenylphosphine oxide via sol-gel techniqueJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Canan Kizilkaya Abstract In this article, a series of novel polyimide/silica (PI/SiO2) nanocomposite coating materials were prepared from tetraethoxysilane (TEOS), ,-glycidyloxypropyltrimethoxysilane (GOTMS), and polyamic acid (PAA) via sol-gel technique. PAA was prepared by the reaction of 3,3,,4,4,-benzophenone tetracarboxylic dianhydride (BTDA) and bis (3-aminophenyl) phenyphosphine oxide (BAPPO) in N -methyl-2- pyrrolidone (NMP). BAPPO was synthesized hydrogenation of bis (3-nitrophenyl) phenyphosphine oxide (BNPPO) in the presence of Pd/C. The silica content in the hybrid coating materials was varied from 0 to 20 wt %. The molecular structures of the composite materials were analyzed by means of FT-IR and 29Si-NMR spectroscopy techniques. The physical and mechanical properties of the nanocomposites were evaluated by various techniques such as, hardness, contact angle, and optical transmission and tensile tests. These measurements revealed that all the properties of the nanocomposite coatings were improved noticeable, by the addition of sol-gel precursor into the coating formulation. Thermogravimetric analysis showed that the incorporation of sol-gel precursor into the polyimide matrix leads to an enhancement in the thermal stability and also flame resistance properties of the coating material. The surface morphology of the hybrid coating was characterized by scanning electron microscopy (SEM). SEM studies indicated that nanometer-scaled inorganic particles were homogenously dispersed throughout the polyimide matrix © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Perfluorosulfonic acid,Tetraethoxysilane/polyacrylonitrile (PFSA-TEOS/PAN) hollow fiber composite membranes prepared for pervaporation dehydration of ethyl acetate,water solutionsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Hai-Kuan Yuan Abstract Preparation of organic-inorganic composite membranes and their pervaporation (PV) permeation and separation characteristics for the aqueous solution of ethyl acetate were described. Polyacrylonitrile (PAN) hollow fiber ultrafiltration membrane as support membrane, the mixtures of perfluorosulfonic acid (PFSA) and tetraethoxysilane (TEOS) by the sol-gel reaction as the coating solution, the PFSA-TEOS/PAN hollow fiber composite membranes by the different annealing conditions were prepared. The swelling of PFSA in ethyl acetate aqueous solutions was inhibited with addition of TEOS. The PFSA-TEOS/PAN composite membranes containing up to 30 wt % TEOS in coating solution exhibited high selectivity towards water, then the selectivity decreased and permeation flux increased with increasing the TEOS concentration more than 30 wt %. When the PFSA-TEOS/PAN composite membranes were annealed, the separation factor increased with increasing annealing temperature and time. Higher annealing temperature and longer annealing time promoted the crosslinking reaction between PFSA and TEOS in PFSA-TEOS/PAN composite membranes, leading to the enhanced selectivity towards water. For the PFSA/PAN and PFSA-TEOS/PAN composite membrane with 5 and 30 wt % TEOS annealed at 90°C for 12 h, their PV performance of aqueous solution 98 wt % ethyl acetate were as follows: the separation factors were 30.8, 254 and 496, while their permeation flux were 1430, 513 and 205 g/m2 h at 40°C, respectively. In addition, the PV performance of PFSA-TEOS/PAN composite membranes was investigated at different feed solution temperature and concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Pervaporation characteristics and structure of poly(vinyl alcohol)/poly(ethylene glycol)/tetraethoxysilane hybrid membranesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Li Yi Ye Abstract Poly(vinyl alcohol) (PVA) blended with poly(ethylene glycol) (PEG) was crosslinked with tetraethoxysilane (TEOS) to prepare organic,inorganic PVA/PEG/TEOS hybrid membranes. The membranes were then used for the dehydration of ethanol by pervaporation (PV). The physicochemical structure of the hybrid membranes was studied with Fourier transform infrared spectra (FT-IR), wide-angle X-ray diffraction WXRD, and scanning electron microscopy (SEM). PVA and PEG were crosslinked with TEOS, and the crosslinking density increased with increases in the TEOS content, annealing temperature, and time. The water permselectivity of the hybrid membranes increased with increasing annealing temperature or time; however, the permeation fluxes decreased at the same time. SEM pictures showed that phase separation took place in the hybrid membranes when the TEOS content was greater than 15 wt %. The water permselectivity increased with the addition of TEOS and reached the maximum at 10 wt % TEOS. The water permselectivity decreased, whereas the permeation flux increased, with an increase in the feed water content or feed temperature. The hybrid membrane that was annealed at 130°C for 12 h exhibited high permselectivity with a separation factor of 300 and a permeation flux of 0.046 kg m,2 h,1 in PV of 15 wt % water in ethanol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Preparation and applications of novel fluoroalkyl end-capped sulfonic acid oligomers,silica gel polymer hybridsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Kazuo Sasazawa Abstract Fluoroalkyl end-capped 2-methacryloxyethanesulfonic acid homo-oligomer [RF,(MES)n,RF] and 2-methacryloxyethanesulfonic acid,N,N -dimethylacrylamide co-oligomers [RF,(MES)x,(DMAA)y,RF] reacted with tetraethoxysilane (TEOS) under acidic conditions to afford RF,(MES)n,RF homo-oligomer,SiO2 polymer hybrid and RF,(MES)x,(DMAA)y,RF co-oligomer,SiO2 polymer hybrid, respectively. Thermogravimetric,mass spectra showed that the thermal stability of RF,(MES)n,RF homo-oligomer,SiO2 polymer hybrid was superior to that of traditionally well-known perfluorinated ion exchange polymers such as Nafion 112 (TR). The sol solutions of the fluorinated co-oligomer,SiO2 polymer hybrid were applied to the surface modification of glass to exhibit not only a strong oleophobicity imparted by fluorine but also a good hydrophilicity on the glass surface. On the other hand, RF,(MES)x,(DMAA)y,RF co-oligomer reacted with TEOS in the presence of a variety of silica nanoparticles (mean diameters: 11,95 nm) under alkaline conditions to afford fluoroalkyl end-capped oligomers,silica nanoparticles (mean diameters: 32,173 nm) with a good dispersibility and stability in methanol. Similarly, a variety of fluorinated oligomers containing sulfo groups,silica nanoparticles were prepared by the homo- and co-oligomerizations of fluoroalkanoyl peroxides with 2-methacryloxyethane sulfonic acid (MES) and comonomers such as N,N -dimethylacrylamide (DMAA) and acryloylmorpholine (ACMO) in the presence of silica nanoparticles. Interestingly, these isolated fluorinated particle powders were found to afford nanometer size-controlled colloidal particles with a good redispersibility and stability in aqueous and organic media such as methanol. These fluorinated nanoparticles containing sulfo groups were also applied to an excellent heterogeneous catalyst for Bronsted acid-catalyzed transformations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 110,117, 2007 [source] Synthesis of high fluorescent silica hybrid materials by immobilization of orange peel extract in silica-silsesquioxane matrixJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2009I. Lacatusu Abstract Sol,gel chemistry can be easily modified to the changing needs of society to produce fine-tuned sol,gel nanostructured materials for relevant applications. In this context, there is an increasing need for natural and versatile raw materials as well as biocompatible compounds that could be extensively used as biomarkers for bioimaging in diagnosis or therapy. Silica-based materials are widely used in the field of biomedicine due to their chemical inertness and biocompatibility. In the present paper, orange peel extract was immobilized inside inorganic silica and hybrid silica-silsesquioxane polymeric networks. Silica and organo-modified silica matrices were synthesized through a templated sol,gel route of TEOS and an organosilsesquioxane (octaisobutyltetracyclo[7.3.3.15,11] octasiloxane- endo -3,7-diol), with D -glucose as template, and for comparison a non-ionic surfactant (tetraethylene glycol mono-hexadecyl ether) was also used. The bioactive properties of the molecules from orange peel extract were preserved after immobilization in both silica and silica-silsesquioxane networks. Moreover, the fluorescence properties were amplified by 10,20 times more than the native orange peel extract. The structural properties of the final materials have been studied by FT-IR, UV,Vis-NIR, and fluorescence spectroscopy. Dynamic light scattering measurements and transmission electron microscopy were used to estimate the size and morphology of the hybrid materials with orange peel extract immobilized in silica networks. Copyright © 2009 John Wiley & Sons, Ltd. [source] A direct preparation of silica shell on polystyrene microspheres prepared by dispersion polymerization with polyvinylpyrrolidoneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2008Jinho Hong PS/silica core/shell structured microspheres were easily prepared in a simple process. Because of the acid-base interaction between the TEOS and seed particles prepared by dispersion polymerization, uniform silica shell was formed on the PVP-stabilized PS particles without additional PVP-coating process. [source] Nonaqueous synthesis of nanosilica in epoxy resin matrix and thermal properties of their cured nanocompositesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2006Tzong-Ming Lee Abstract Nonaqueous synthesis of nanosilica in diglycidyl ether of bisphenol-A epoxy (DGEBA) resin has been successfully achieved in this study by reacting tetraethoxysilane (TEOS) directly with DGEBA epoxy matrix, at 80 °C for 4 h under the catalysis of boron trifluoride monoethylamine (BF3MEA). BF3MEA was proved to be an effective catalyst for the formation of nanosilica in DGEBA epoxy under thermal heating process. FTIR and 29Si NMR spectra have been used to characterize the structures of nanosilica obtained from this direct thermal synthetic process. The morphology of the nanosilica synthesized in epoxy matrix has also been analyzed by TEM and SEM studies. The effects of both the concentration of BF3MEA catalyst and amount of TEOS on the diameters of nanosilica in the DGEBA epoxy resin have been discussed in this study. From the DSC analysis, it was found that the nanosilica containing epoxy exhibited the same curing profile as pure epoxy resin, during the curing reaction with 4,4,-diaminodiphenysulfone (DDS). The thermal-cured epoxy,nanosilica composites from 40% of TEOS exhibited high glass transition temperature of 221 °C, which was almost 50 °C higher than that of pure DGEBA,DDS,BF3MEA-cured resin network. Almost 60 °C increase in thermal degradation temperature has been observed during the TGA of the DDS-cured epoxy,nanosilica composites containing 40% of TEOS. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 757,768, 2006 [source] Synthesis and properties of silica/polystyrene/polyaniline conductive composite particlesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2005Chia-Fen Lee Abstract In this study, silica/polystyrene/polyaniline (SiO2/PS/PANI) conductive composite particles were synthesized by four sequential reactions. The nanosized SiO2 particles were synthesized from tetraethoxysilane (TEOS) by a sol,gel process with water as the solvent medium, followed by a surface modification with triethoxyvinylsilane; then the surface modified SiO2 particles were used as seeds to synthesize SiO2/PS composite particles with soapless seeded emulsion polymerization. Finally, the SiO2/PS particles were used as seeds to synthesize the SiO2/PS/PANI conductive composite particles. The sol,gel process of SiO2, the effect of surface modification, and several other factors that influenced polymerization of styrene in the soapless seeded emulsion polymerization will be discussed. Either potassium persulfate (KPS) or 2,2,-azobis(isobutyramidine) dihydrochloride (AIBA) was used as the initiator to synthesize the uniform SiO2/PS particles successfully, and the cross-section morphology of the SiO2/PS particles was found to be of a core,shell structure, with SiO2 as the core, and PS as the shell. The SiO2/PS particles were well dispersed in many organic solvents. In the following step to synthesize SiO2/PS/PANI conductive composite particles, sodium dodecyl sulfate (SDS) played an important role, specifically, to absorb aniline onto the surfaces of the SiO2/PS particles to carry out the polymerization of aniline over the entire surface of the particles. The conductivity of the SiO2/PS/PANI composite particles approached that of semiconductive materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 342,354, 2005 [source] Preparation and properties of high molecular weight polyethoxysiloxanes stable to self-condensation by acid-catalyzed hydrolytic polycondensation of tetraethoxysilaneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2003Yoshimoto Abe Abstract The acid-catalyzed controlled hydrolytic polycondensation of tetraethoxysilane (TEOS) provided polyethoxysiloxanes with weight-average molecular weights of 2300,11,700, which depended on the reaction molar ratios of the water, catalyst, and solvent to TEOS. They were soluble in common organic solvents and stable to self-condensation and were characterized with high silica contents of up to 67%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2250,2255, 2003 [source] Reduced-bore monolithic silica column modified with C8 -TEOS for reversed-phase electrochromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2004Qishu Qu Abstract Monolithic silica columns of 2.7 mm ID were prepared and derivatized with C8 -TEOS and TEOS by on-column sol-gel reaction. These C8 large diameter monolithic silica columns gave 21 000 theoretical plates for aromatic hydrocarbons in 60% acetonitrile and 40% Tris-HCl buffer. The surface areas as well as the separation reproducibility were improved on coating by the sol-gel approach. Joule heating was greatly reduced by using monolithic columns to which fine quartz sand had been added during column preparation. Since this is a preliminary investigation on a monolithic column with such a large inner diameter, the separation efficiency was not so high as that presently achieved in normal capillary electrochromatography (CEC). However, use of the columns improved sample loadability and concentration detectability of electrochromatography, and semi-preparative separations could be performed. [source] A Study on the Effect of Template Chain Length on the Synthesis of Mesoporous Silica in An Acidic ConditionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Yang Yu-Xiang Hexagonal mesoporous silica materials were synthesized in an acidic medium using different chain length of the quaternary ammonium surfactants as a template. The effects of chain length on the physical property, morphology of mesoporous materials, and the temperature on synthesis of materials in CnTMBr,TEOS,HNO3,H2O (n=12,14,16,18) system were systematically studied. The synthesized products were characterized by X-ray diffraction patterns, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption analysis. It was found that degree of ordering, the d spacing values, and pore size all increase with an increase in the chain length of the template. The optimum synthesis temperature for mesoporous silica using C18TMBr,TEOS,HNO3,H2O system is slightly higher than the Krafft point. The temperature and pH can all affect the expandability of micelles, and so an increase in temperature and decrease in pH all lead to an increase in the pore size. It is also found that the shear flow and chain length are two key factors inducing the formation of millimeter-scaled silica ropes and micrometer-scaled rope fibers. [source] Superhydrophobic Silica Nanocomposite Coating by a Low-Temperature ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004Walid A. Daoud We successfully prepared transparent and durable superhydrophobic silica-coating films on cotton substrates at low temperatures. The coatings were produced via cohydrolysis and polycondensation of a hexadecyltrimethoxysilane (HDTMS), tetraethoxyorthosilcate (TEOS), and 3-glycidyloxypropyltrimethoxysilane (GPTMS) mixture. The hydrophobic properties of the nanocomposite coatings were determined using contact-angle and water-gain measurements. The water contact angle for the coated substrates was 141°, whereas, before coating, the contact angle was 0° because of the superhydrophilic nature of cotton. The nanocomposite coating has new applications in daily used materials, especially those with low heat resistance, such as textiles and plastics, and as an environmentally friendly water-repellent substitute for fluorine compounds. [source] New Process for the Preparation of Monodispersed, Spherical Silica ParticlesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002Ki Do Kim A new method is presented for preparing highly monodispersed silica particles using a two-stage semibatch/batch hydrolysis reaction of Si(OC2H5)4. The slower rate of hydrolysis of the tetraethylorthosilicate (TEOS) that occurred during the semibatch process resulted in larger silica particles with a higher yield and narrower size distribution. This was in direct contrast to the batch process. In addition, the ability of four different mixed processes to produce silica particles with good packing density, narrower particle-size distribution, and higher yield were evaluated. These were batch/batch (B-B), batch/semibatch (B-S), semibatch/batch (S-B), and semibatch/semibatch (S-S) processes. The S-S system produced the largest particles with the highest yields. The size of the silica particles obtained by the S-B method decreased with increasing reaction time, while the particles obtained by the B-S process had the best particle-size distribution and packing density. In conclusion, a mixed batch/semibatch system was the best way to produce an extremely narrow particle-size distribution and a good packing density. [source] Silica Reinforced Organic,Inorganic Hybrid Polyurethane Nanocomposites From Sustainable ResourceMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2010Deewan Akram Abstract Polyol/nanosilica organic,inorganic hybrids (Si/Lpol) were prepared through facile sol,gel chemistry. Tetraethoxyorthosilane (TEOS) and linseed polyol (Lpol) obtained by hydroxylation of linseed oil were used as inorganic and organic precursors, respectively. Si/Lpol was further treated with toluene-2,4-diisocyanate (TDI) to obtain silica embedded polyurethane (Si/LPU). The structure of the organic,inorganic hybrid was confirmed by FTIR, 1H NMR, and 13C NMR spectral analysis. The polyol/nanosilica network shows strong interaction with the remnant polyol backbone through hydrogen bonding, which also has bearing on Tg of polymers. Morphological studies of Si/LPU show the formation of uniform, spherical silica nanoparticles of 2,30,nm size embedded in the polymer matrix. Si/LPU was further reinforced with 2 and 5,wt.-% fumed silica (FS-Si/LPUs); their morphology revealed a carpet layer formation on top of Si/LPU. Thermogravimetric analysis showed improved thermal stability of Si/LPU and FS-Si/LPUs. The polymers exhibit mild to moderate antibacterial behavior against E. coli and S. aureus, respectively, and will pave way in plethora of biological and chemical applications as coating materials. [source] Preparation and Characterization of Hybrid Nanocomposites Coated on LDPEMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2006Laura Mazzocchetti Abstract Summary: Hybrid organic-inorganic nanocomposites containing hyperbranched structures were prepared through a dual-curing process, which involves photopolymerization and condensation alkoxysilane groups. In particular, an oligomer containing PEO units and ,,, -methacrylate groups was used together with a HBP bearing acrylic groups as the organic phase precursors. MEMO, as the organic-inorganic linker, and TEOS, as inorganic phase precursor, were also employed. The kinetics of both photopolymerization and condensation reactions were investigated by double bond conversion analysis (via FT-IR) and weight loss determination, respectively. The mobility of the organic phase was studied by means of DSC and DMTA and correlated with hybrid composition. TEM analyses performed on microtomed film slices indicated the formation of nanoscale silica domains. Hybrids were coated onto an LDPE film previously subjected to a plasma treatment, and substrate-coating interfacial adhesion was investigated through stress-strain and DMTA experiments. Reaction scheme showing the insertion of furanic units in copolyester chains by ester interchange reaction. [source] Photophysical Properties of Terbium Molecular-based Hybrids Assembled with Novel Ureasil LinkagesPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Bing Yan Three silica-based organic,inorganic hybrid systems composed of hydroxyl aromatic derivatives (2-acetylphenol [HAP], 2-hydroxy-3-methylbenzoic acid [HMBA], 3-hydroxy-meta-phthalic acid [HMPHTH] complexes) were prepared via a sol,gel process. The active hydroxyl groups of the three ligands grafted by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) through hydrogen transfer addition reaction were used as multi-functional bridge components, which can coordinate to Tb3+ with carbonyl groups, strongly absorb ultraviolet light and effectively transfer energy to Tb3+ through their triplet excited state, as well as undergo polymerization or crosslinking reactions with tetraethoxysilane (TEOS), for anchoring terbium ions to silica backbone. NMR, FT-IR, UV,vis absorption, luminescence spectroscopy was used to investigate the obtained hybrid material. UV excitation in the organic component resulted in strong green emission from Tb3+ ions due to an efficient ligand-to-metal energy transfer mechanism. [source] Coloured inorganic-organic films on glassPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007K. Cholewa-Kowalska Abstract Two kinds of inorganic-organic hybrid materials (A and B class) were obtained in the form of thin films on glass. As starting materials were used: PhTES + TEOS (A class); PhTES + GPTMS + TBA (B class). Hybrid materials were coloured using ORASOL type dyes. The coloured coatings were put on glass by dip-coating technique. The structure of hybrid matrix was examined by spectroscopic methods: FTIR, 29Si MAS NMR, 27Al MAS NMR. On this base structural units of hybrid were identified. UV/VIS spectra of thin films were measured directly after obtainment as well as after thermal and chemical treatment of samples. It has been found that UV/VIS spectra originate from electron transitions between ligands and transition metal ions. The coloured centres in hybrid matrix show good thermal and chemical resistance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Atmospheric Pressure Plasma Deposition of Adhesion Promotion Layers on AluminiumPLASMA PROCESSES AND POLYMERS, Issue S1 2009Philipp Bringmann Abstract The paper presents investigations on the deposition of plasma polymerised films at atmospheric pressure as a pretreatment for painting and adhesive bonding of aircraft aluminium structures. Two different plasma jet sources are employed, one based on a controlled arc discharge and air as process gas, and another based on a dielectric barrier discharge (DBD) and He as plasma gas. The organosilicon precursors HMDSO, TEOS and OMCTS are used with both plasma sources. Deposition in the arc discharge plasma jet leads to almost carbon-free silica coatings, whereas coatings deposited with the DBD jet source contain a high amount of carbon, varying with precursor type. The obtained results of corrosion investigations and adhesion tests are promising, as some representative aircraft industry requirements could be achieved. However, the investigations show a strong dependency on the used precursor and type of polymer (paint or adhesive) applied on the plasma polymerised film. [source] Preparation and properties of silicone-containing poly(methyl methacrylate) gelsPOLYMER INTERNATIONAL, Issue 11 2005Hamid Javaherian Naghash Abstract Poly(methyl methacrylate) (PMMA) gels with varying amounts of silicone and solvent and constant amounts of crosslinker were prepared by solution free radical crosslinking copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) comonomer systems. They were then studied in benzene at a total monomer concentration of 3.5 mol L,1 and 70 °C. The conversion of monomer, volume swelling ratio, weight fraction and gel point were measured as a function of the reaction time, silicone concentration and benzene content up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in benzene, gel fraction and Fourier-transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by SEM. Based on the obtained results, it was concluded that the FTIR data did not have the capacity to show the presence of the VTES or TEOS moiety in these kinds of copolymers. On the other hand, the variation of weight fraction of gel, Wg, and its equilibrium volume swelling ratio in benzene, qv, exhibited the same behaviour as that of MMA/EGDM copolymers. Also, the dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percent of conversion and gel fraction. Finally, TEOS is not an ideal silicone compound for reaction in the MMA/EGDM copolymerization system, whereas VTES is a suitable silicone comonomer for this system and it has been proved useful. Copyright © 2005 Society of Chemical Industry [source] Preparation and characterization of mesoporous materials based on silsesquioxane by block copolymer templating,POLYMER INTERNATIONAL, Issue 11 2002Byeong-Gyu Park Abstract Nanoporous materials were prepared by using silsesquioxane containing three alkoxy groups and a non-hydrolysable organic moiety. The influences of pH and precursor ratios of silsesquioxane and tetraethyl orthosilicate (TEOS) on the preparation of organo-modified periodic mesoporous materials were investigated. These materials were characterized using small angle X-ray scattering, infrared spectroscopy and thermogravimetric analysis. A non-ionic triblock copolymer was used as a structure-directing agent to provide large pores with a high density of silanol groups. It was found that silsesquioxanes could form ordered nanoporous materials in the presence of TEOS by controlling the pH and the co-precursors ratio, despite their structural irregularity. © 2002 Society of Chemical Industry [source] Modification of mesostructure base on composition of silica materials and their applications to pH sensing,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2006Eun-Hee Kang Abstract This study induced a chemical combination of fluoresceinamine (FA) and (3-chloropropyl)triethoxysilane (CP-TEOS) in the presence of tetraethyl orthosilicate (TEOS) which is able to maintain the shape of the mesostructure without prior removal of the surfactant. The sol-gel derived silica films were controlled by the reaction time and molar ratios of TEOS and CP-TEOS, and characterized in terms of response to pH, pKa values, effects of oxidation number, leaching, and scanning electron microscopy (SEM) imaging. The conclusions include the effect on molar ratios and the choice of reaction time. The results of this study are summarized as follows: (1) increasing the molar ratio of TEOS, the mesostructure of these films exhibited not only perfect single-crystal morphology but also a hexagonal morphology; (2) the most suitable molar ration in this synthesis is the ratio of 1:1 (the molar ratio of TEOS and CP-TEOS); (3) the reaction time for this system should be controlled at least to over 6,hr in order to maintain high intensity absorbance against a minimum of indicator quantity. Leaching-out is more pronounced for films used directly after preparation and varies for different molar ratios. The long-term implication of leaching-out on sol-gel based pH sensors is discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] Efficient on-chip proteolysis system based on functionalized magnetic silica microspheresPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 14 2007Yan Li Abstract An easily replaceable enzymatic microreactor has been fabricated based on the glass microchip with trypsin-immobilized magnetic silica microspheres (MS microspheres). Magnetic microspheres with small size (,300,nm in diameter) and high magnetic responsivity to magnetic field (68.2,emu/g) were synthesized and modified with tetraethyl orthosilicate (TEOS). Aminopropyltriethoxysilane (APTES) and glutaraldehyde (GA) were then introduced to functionalize the MS microspheres for enzyme immobilization. Trypsin was stably immobilized onto the MS microspheres through the reaction of primary amines of the proteins with aldehyde groups on the MS microspheres. The trypsin-immobilized MS microspheres were then locally packed into the microchannel by the application of a strong field magnet to form an on-chip enzymatic microreactor. The digestion efficiency and reproducibility of the microreactor were demonstrated by using cytochrome c (Cyt-C) as a model protein. When compared with an incubation time of 12,h by free trypsin in the conventional digestion approach, proteins can be digested by the on-chip microreactor in several minutes. This microreactor was also successfully applied to the analysis of an RPLC fraction of the rat liver extract. This opens a route for its further application in top-down proteomic analysis. [source] | |||||||||||||||||||||||||||||||