JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2007
Paul J. DesLauriers
Abstract SEC and on-line Fourier transform infrared spectroscopy analysis have been combined to study branching profiles from the Phillips Cr/silica catalyst. For the first time, catalyst and reactor variables have been shown to affect the overall level and distribution of branches in polyethylene copolymers. Branching profiles from various chromium catalysts have been shown to vary from highly concentrated in the low MW end, to uniformly distributed over all of the MW range. Activation temperature and the presence of titania were highly influential. These observations, which have been used to gain insight into the chemistry of Cr/silica, explain much of the catalyst behavior that has for decades been used to optimize polymer properties. Trends in ESCR, impact resistance, and other physical characteristics, which were long attributed to changes in MW distribution, can now be seen to also be due in large part to changes in the branching profile. This knowledge should be of value in designing future resins. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3135,3149, 2007 [source]

Synthesis and properties of crosslinked polyvinylformamide and polyvinylamine hydrogels in conjunction with silica particles

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2002
Torsten Meyer
Abstract Polyvinylamine hydrogels with silica particles encapsulated (PVAm/silica) were produced by a two-step synthesis. In the first step, polyvinylformamide/silica (PVFA/silica) hybrids were synthesized from vinylformamide (VFA) and 1,3-divinylimidazolidin-2-one (1,3-bisvinylethyleneurea, BVU), as the crosslinker, by radical copolymerization in silica/water suspensions using different compositions of VFA/BVU. The target product PVAm/silica was obtained by acidic hydrolysis of the PVFA/silica hydrogels in a second step. The chemical structures of both hydrogels, PVFA/silica and PVAm/silica, respectively, were revealed by solid-state 13C(1H) cross-polarity/magic-angle spinning NMR spectroscopy. Both hydrogels swelled significantly in water. The swelling capacity of the two systems was characterized by the correlation length , (or hydrodynamic blob size) of the network meshes with small-angle neutron scattering experiments. , is significantly larger for PVAm/silica than for PVFA/silica, which corresponds to the observed higher swelling capacity of this polyelectrolyte material. Furthermore, the swelling behavior of the hybrid hydrogels was quantitatively described in terms of free swell capacity, centrifuge-retention capacity, adsorption against pressure, and free swell rate as compared with values of the corresponding copolymer hydrogels. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3144,3152, 2002 [source]

Towards an understanding of adsorption behaviour in non-aqueous systems: adsorption of poly(vinyl pyrrolidone) and poly(ethylene glycol) onto silica from 2H, 3H-perfluoropentane

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 11 2005
Alison Paul
The adsorption behaviour of low molecular weight poly(ethylene glycol) (PEG 600) and poly(vinyl pyrrolidone) (PVP K25) to silica particles has been investigated at room temperature (21°C) in the partially fluorinated solvent 2H,3H-perfluoropentane (HPFP). PVP (absorbed amount, , = 12 mgg,1) was found to adsorb more strongly than PEG (, = 4 mgg,1). Both of these values were higher than observed in water. In a further distinction to the aqueous case, where PVP displaces PEG from the interface, no competitive adsorption effects were observed between these two polymers in HPFP, with the adsorbed amounts of each polymer being unchanged by the presence of the other. The stability of silica suspensions in HPFP was primarily dependent on the presence of PVP; PEG/silica systems were unstable, but PVP/silica and PEG/PVP/silica systems formed stable suspensions. All suspensions were destabilized by the addition of small (0.15 wt%) amounts of water. The observations made in this work would point to a flocculation phenomenon due to the addition of water, and not Ostwald ripening. The mechanism of this destabilization is likely to be water acting as a flocculation bridge between particles. [source]

Cationic Polymerization of 2-Vinylthiophene by Chloroarylmethanes as Surface Initiators on Silica and Consecutive Hydride Abstraction by Acceptors

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 12 2004
Susanne Höhne
Abstract Summary: 2-Vinylthiophene (2-VT) has been cationically polymerized using chloroarylmethane derivatives as the surface polymerization initiator on silica. By applying this procedure a soluble fraction of poly(vinylthiophene) (PVT) and PVT/silica composites can be simultaneously synthesized. The mass balance of the products (soluble fraction and hybrid particle fraction) depends significantly on temperature and 2-VT/silica ratio. The hydride abstraction reaction of PVT both in solution and immobilized on silica particle surface has been studied using 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ), tetrachloro-1,4-quinone (chloranile,=,ClA) and triphenylmethylium as reagents. The transformation process of PVT towards conjugated polymers has been studied with UV-vis spectroscopy and ESR spectroscopy. Cyclic voltammetry shows that chloranil is complexated with the formed polymer. Radical formation increases with increasing degree of conversion. The soluble fraction of the conjugated PVT sections formed is capable of reacting with each other as evidenced by GPC data. Structure of PVT/silica and resulting hybrid materials have been investigated by solid state 13C {1H} CP MAS NMR-spectroscopy showing a reaction of methine and methylene hydrogen atoms after treatment with DDQ or chloranil as hydride acceptors. For all poly-(2-vinylthiophene)/hydride acceptor systems studied, chloranil has been found to be the best reagent for the transformation of PVT towards conjugated polymers. Transformation of PVT in poly(2-ethinylthiophene) (PET) and PVT-PET copolymers. [source]

Simultaneous Determination of Cadmium, Lead, Copper and Mercury Ions Using Organofunctionalized SBA-15 Nanostructured Silica Modified Graphite,Polyurethane Composite Electrode

ELECTROANALYSIS, Issue 1 2010
Ivana Cesarino
Abstract A new sensor has been developed for the simultaneous detection of cadmium, lead, copper and mercury, using differential pulse and square wave anodic stripping voltammetry (DPASV and SWASV) at a graphite,polyurethane composite electrode with SBA-15 silica organofunctionalized with 2-benzothiazolethiol as bulk modifier. The heavy metal ions were preconcentrated on the surface of the modified electrode at ,1.1,V vs. SCE where they complex with 2-benzothiazolethiol and are reduced to the metals, and are then reoxidized. Optimum SWASV conditions lead to nanomolar detection limits and simultaneous determination of Cd2+, Pb2+, Cu2+ and Hg2+ in natural waters was achieved. [source]

Direct Electrochemistry of Cytochrome c at Gold Electrode Modified with Fumed Silica

ELECTROANALYSIS, Issue 20 2005
Hongjun Chen
Abstract Direct electrochemistry of horse heart cytochrome c (cytc) has been obtained at a gold electrode constructed by self-assembling fumed silica particles (FSPs) onto a silane monolayer. A pair of well-defined and nearly symmetrical redox peaks of cytc is obtained at the FSPs film modified gold electrode. Cyclic voltammetry (CV) and tapping-mode atomic force microscopy (AFM) are used to characterize the FSPs film modified electrode, showing that the FSPs can provide a favorable microenvironment for cytc and facilitate the direct electron transfer between the cytc and the gold electrode, which may propose an approach to realize the direct electrochemistry of other proteins. [source]

Selection of refractory for thermal oxidizers on gas streams containing fluorine

ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2002
Stanley C. Che
Thermal oxidizers for destruction of fluorine-containing chemicals are typically operated between 1,100° to 1,400° C. Fluorine is converted to hydrogen fluoride (HF) during the combustion process. At high temperatures, HF will react with almost all materials. Proper selection of the refractory material used by the thermal oxidizer is essential for long-term use, and to protect the metal shell from corrosion. Selection criteria should include analysis of chemical composition, physical properties, morphology, and bonding phases. A high alumina brick from a thermal oxidizer was analyzed after it had been in service for one year. The brick surface underwent significant changes of its chemical and micro-structural compositions. Silica in the mullite phase had reacted with HF, leaving only corundum. In the inner part of the brick, both mullite and corundum crystals still existed. Refractory selection guidelines are suggested. [source]

IR Laser-Induced Carbothermal Reduction of Silica

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2008
Markéta Urbanová
Abstract Pulsed IR-laser irradiation of silica in the presence of gaseous hydrocarbons (benzene or ethyne) results in carbothermal reduction of silica by hydrocarbon decomposition products and allows deposition of amorphous solids which were analyzed by FTIR, Raman, X-ray photoelectron and Auger spectra and by electron microscopy and revealed as nanosized carbon,silicon oxycarbide composites containing crystalline silica domains. The reported IR laser-induced process is the first approach to deposition of nanosized carbon,silicon oxycarbide composites. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

A New Donor-Stabilized Ditungsten Amido Alkoxido Species: Synthesis, Crystal Structure, Fluxionality, and Grafting onto Silica

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2007
Olivier Coutelier
Abstract A new dimeric tungsten(III) complex containing amidoand chelating pyridine,alkoxido ligands was synthesized through protonolysis of [W2(NMe2)6] by 2-(2-pyridyl)propan-2-ol and fully characterized by X-ray diffraction and infrared and NMR spectroscopy. Intramolecular exchange processes were studied by variable-temperature NMR spectroscopy. The compound was grafted onto dehydroxylated silica by protonolysis of an amido,tungsten bond, and the structure of the supported species was investigated by infrared and solid-state (bidimensional) NMR spectroscopy. The reactivity of the molecular and grafted species toward alkynes was probed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Drug Self-Templated Synthesis of Ibuprofen/Mesoporous Silica for Sustained Release

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2006
Fengyu 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]

High-Zirconium-Content Nano-Sized Bimodal Mesoporous Silicas

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2006
David Ortiz de Zárate
Abstract Silica-based nanoparticulated bimodal mesoporous materials with high Zr content (43 , Si/Zr , 4) have been synthesized by a one-pot surfactant-assisted procedure from a hydroalcoholic medium using a cationic surfactant (CTMABr = cetyltrimethylammonium bromide) as structure-directing agent, and starting from molecular atrane complexes of Zr and Si as hydrolytic inorganic precursors. This preparative technique allows optimization of the dispersion of the Zr guest species in the silica walls. The bimodal mesoporous nature of the final high surface area nano-sized materials is confirmed by XRD, TEM, and N2 adsorption,desorption isotherms. The small intraparticle mesopore system (with pore sizes around 2,3 nm) is due to the supramolecular templating effect of the surfactant, while the large mesopores (around 12,24 nm) have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. The basicity of the reaction medium seems to be a key parameter in the definition of this last pore system. The effects induced by the progressive incorporation of Zr atoms on the mesostructure have been examined, and the local environment of the Zr sites in the framework has been investigated by UV/Vis spectroscopy. Observations based on the consequences of post-treatments of the as-synthesized materials with HCl/ethanol mixtures corroborate that the atrane method leads to Zr-rich materials showing enhanced site accessibility and high chemical homogeneity throughout the pore walls. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Sol,Gel Coatings as Active Barriers to Protect Ceramic Reinforcement in Aluminum Matrix Composites,

ADVANCED ENGINEERING MATERIALS, Issue 1-2 2004
J. Rams
Silica obtained through a sol,gel process is used as a coating for ceramic reinforcements (SiC) in aluminium matrix composite materials. The interaction between molten aluminium and the coated particles during material casting can be controlled by means of the thermal treatment given to the coating. Wettability is increased because the coating reacts with molten aluminium, and the formation of the degrading aluminium carbide is inhibited. [source]

Organically Functionalized Mesoporous Silica by Co-structure-Directing Route

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Chuanbo Gao
Abstract This article provides a brief overview of functional mesoporous silica materials synthesized by the co-structure-directing route, which is distinct from conventional synthesis strategies. In these systems, organosilane serves as the co-structure-directing agent (CSDA), which provides critical interactions between the template and organic part of the organosilane to form mesostructures, thus retaining the organic groups on the pore surface after removal of the template by extraction. i) The formation of anionic-surfactant-templated mesoporous silicas (AMSs) has been achieved by the co-structure-directing route, which leads to a variety of mesostructures, porous properties and morphologies. ii) Other co-structure-directing systems for synthesizing mesoporous silicas have also been achieved, including systems using cationic surfactants and non-surfactants, and systems using DNA for constructing nanofibers and DNA,silica liquid crystalline complexes. iii) Evidence for the regular arrangement of functional groups on the pore surface resulted from the co-structure-directing effect has been discussed. Also included is a brief description of the application, future requirements, and trends in the development of mesoporous materials by the co-structure-directing route. [source]

Bioelectronics: Induced SER-Activity in Nanostructured Ag,Silica,Au Supports via Long-Range Plasmon Coupling (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Mater.
The picture shows a nanostructured layered silver-silica-gold electrode developed by J.-J. Feng, I. M. Weidinger, et al. on page 1954 where the underlying silver surface can be excited by laser light. The resulting surface plasmon resonance is transferred over a distance of up to 20 nm to the outer gold layer where attached proteins can be detected by surfaceenhanced Raman spectroscopy. [source]

Induced SER-Activity in Nanostructured Ag,Silica,Au Supports via Long-Range Plasmon Coupling

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Jiu-Ju Feng
Abstract A novel Ag,silica,Au hybrid device is developed that displays a long-range plasmon transfer of Ag to Au leading to enhanced Raman scattering of molecules largely separated from the optically excited Ag surface. A nanoscopically rough Ag surface is coated by a silica spacer of variable thickness from ,1 to 21,nm and a thin Au film of ,25,nm thickness. The outer Au surface is further functionalized by a self-assembled monolayer (SAM) for electrostatic binding of the heme protein cytochrome c (Cyt c) that serves as a Raman probe and model enzyme. High-quality surface-enhanced resonance Raman (SERR) spectra are obtained with 413,nm excitation, demonstrating that the enhancement results exclusively from excitation of Ag surface plasmons. The enhancement factor is estimated to be 2,×,104,8,×,103 for a separation of Cyt c from the Ag surface by 28,47,nm, corresponding to an attenuation of the enhancement by a factor of only 2,6 compared to Cyt c adsorbed directly on a SAM-coated Ag electrode. Upon immobilization of Cyt c on the functionalized Ag,silica,Au device, the native structure and redox properties are preserved as demonstrated by time- and potential-dependent SERR spectroscopy. [source]

Silica-Based, Organically Modified Host Material for Waveguide Structuring by Two-Photon-Induced Photopolymerization

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2010
Stefan Krivec
Abstract The three-dimensional fabrication of optical waveguides has gained increasing interest in recent years to establish interconnections between electrical components on a very small scale where copper circuits encounter severe limitations. In this work the application of optically clear, organically modified porous silica monoliths and thin films as a host material for polymeric waveguides to be inscribed into the solid host structure by two-photon-induced photopolymerization is investigated. Porosity is generated using a lyotropic liquid crystalline surfactant/solvent system as a template for the solid silica material obtained by a sol,gel transition of a liquid precursor. In order to reduce the brittleness of the purely inorganic material, organic,inorganic co-precursor molecules that contain poly(ethylene glycol) chains are synthesized and added to the mixture, which successfully suppresses macroscopic cracking and leads to flexible thin films. The structure of the thus-obtained porous organic,inorganic hybrid material is investigated by atomic force microscopy. It is shown that the modified material is suitable for infiltration with photocurable monomers and functional polymeric waveguides can be inscribed by selective two-photon-induced photopolymerization. [source]

Seasonal response of nutrients to reduced phosphorus loading in 12 Danish lakes

FRESHWATER BIOLOGY, Issue 10 2005
MARTIN SØNDERGAARD
Summary 1.,Concentrations of phosphorus, nitrogen and silica and alkalinity were monitored in eight shallow and four deep Danish lakes for 13 years following a phosphorus loading reduction. The aim was to elucidate the seasonal changes in nutrient concentrations during recovery. Samples were taken biweekly during summer and monthly during winter. 2.,Overall, the most substantive changes in lake water concentrations were seen in the early phase of recovery. However, phosphorus continued to decline during summer as long as 10 years after the loading reduction, indicating a significant, albeit slow, decline in internal loading. 3.,Shallow and deep lakes responded differently to reduced loading. In shallow lakes the internal phosphorus release declined significantly in spring, early summer and autumn, and only non-significantly so in July and August. In contrast, in deep lakes the largest reduction occurred from May to August. This difference may reflect the much stronger benthic pelagic-coupling and the lack of stratification in shallow lakes. 4.,Nitrogen only showed minor changes during the recovery period, while alkalinity increased in late summer, probably conditioned by the reduced primary production, as also indicated by the lower pH. Silica tended to decline in winter and spring during the study period, probably reflecting a reduced release of silica from the sediment because of enhanced uptake by benthic diatoms following the improved water transparency. 5.,These results clearly indicate that internal loading of phosphorus can delay lake recovery for many years after phosphorus loading reduction, and that lake morphometry (i.e. deep versus shallow basins) influences the patterns of change in nutrient concentrations on both a seasonal and interannual basis. [source]

Tuning the Thermal Relaxation of a Photochromic Dye in Functionalized Mesoporous Silica

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2009
Lea A. Mühlstein
Abstract In this study, it is shown that the kinetics of the back-switching reaction of a photochromic spirooxazine dye encapsulated in mesoporous silica materials can be significantly influenced both by the space available to the dye molecules and by the functionalization of the silica wall. Steric hindrance of the ring-closing process due to high dye content or small pore size leads to a slow fading speed of the irradiated dye species. Further, the density of surface silanol-groups present at the silica walls has an effect on the switching behavior of the dye because of their ability to stabilize the zwitterionic merocyanine isomers, thereby slowing the fading process from the open to the closed form. This stabilization effect is further enhanced in the presence of acidic functional groups, while, in contrast, basic functional groups reduce the stabilization of the open-from dye isomers, and thus a faster decay of the irradiated species is observed. Control over the fading speed of photochromic dyes is interesting for applications requiring a particularly fast or slow fading speed. [source]

Interfacial Polar-Bonding-Induced Multifunctionality of Nano-Silicon in Mesoporous Silica

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2009
Jung Y. Huang
Abstract The optoelectronic response of a material governs its suitability for a wide range of applications, from photon detection to photovoltaic conversion. To conquer the material limitations and achieve improved optoelectronic responses, nanotechnology has been employed to arrange subunits with specific size-dependent quantum mechanical properties in a hierarchically organized structure. However, building a functional optoelectronic system from nano-objects remains a formidable challenge. In this paper, the fabrication of a new artificially engineered optoelectronic material by the preferential growth of silicon nanocrystals on the bottom of the pore-channels of mesoporous silica is reported. The nanocrystals form highly stable interface structures bonded on one side; these structure show strong electron,phonon coupling and a ferroelectric-like hysteretic switching property. A new class of multifunctional materials is realized by invoking a concept that employs semiconductor nanocrystals for optical sensing and utilizes interfacial polar layers to facilitate carrier transport and emulate ferroelectric-like switching. [source]

Ordered Mesoporous Silica Derived from Layered Silicates

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2009
Tatsuo Kimura
Abstract Here, the development of ordered mesoporous silica prepared by the reaction of layered silicates with organoammonium surfactants is reviewed. The specific features of mesoporous silica are discussed with relation to the probable formation mechanisms. The recent understanding of the unusual structural changes from the 2D structure to periodic 3D mesostructures is presented. The formation of mesophase silicates from layered silicates with single silicate sheets depends on combined factors including the reactivity of layered silicates, the presence of layered intermediates, the variation of the silicate sheets, and the assemblies of surfactant molecules in the interlayer spaces. FSM-16-type (p6mm) mesoporous silica is formed via layered intermediates composed of fragmented silicate sheets and alkyltrimethylammonium (CnTMA) cations. KSW-2-type (c2mm) mesoporous silica can be prepared through the bending of the individual silicate sheets with intralayer and interlayer condensation. Although the structure of the silicate sheets changes during the reactions with CnTMA cations in a complex manner, the structural units caused by kanemite in the frameworks are retained. Recent development of the structural design in the silicate framework is very important for obtaining KSW-2-based mesoporous silica with molecularly ordered frameworks. The structural units originating from layered silicates are chemically designed and structurally stabilized by direct silylation of as-synthesized KSW-2. Some proposed applications using these mesoporous silica are also summarized with some remarks on the uniqueness of the use of layered silicates by comparison with MCM-type mesoporous silica. [source]

Tuning and Transcription of the Supramolecular Organization of a Fluorescent Silsesquioxane Precursor into Silica-Based Materials through Direct Photochemical Hydrolysis,Polycondensation and Micropatterning

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
Xavier Sallenave
Abstract A new fluorescent silsequioxane precursor with tuned optical properties and controlled aggregation properties is designed. The two cyclohexyl moieties introduced in the molecular structure allow the formation of very good quality films. The J-aggregated structure is transcribed into the solid by photoacid-catalyzed hydrolysis,polycondensation. Aggregation of the chromophores is reduced and highly fluorescent materials are obtained. The photoacid generator lies on the surface of the homogeneous layer of the sol,gel precursor. This phase separation presents several advantages, including UV protection of the chromophore and easy removal of the PAG. The first example of chemical amplification in the photolithography of the conjugated silsesquioxane precursor is demonstrated. As hydrolysis,polycondensation could be achieved in a controlled way by UV exposure, chemically amplified photolithography is achieved by irradiating a composite film (,110,nm thick) on silicon wafer by using a copper TEM grid as shadow mask. The pattern is produced uniformly on a miscroscopic scale of 3,mm, the photopatterned pixels remaining highly fluorescent. The sizes of the photolithographed pixels correspond to the sizes of the rectangular holes of the 300,×,75 mesh grid (hole: 63,<$>,<$>m,×,204,<$>,<$>m). [source]

Designed Fabrication of Silica-Based Nanostructured Particle Systems for Nanomedicine Applications,

ADVANCED FUNCTIONAL MATERIALS, Issue 23 2008
Yuanzhe Piao
Abstract Suitably integrating multiple nanomaterials into nanostructured particle systems with specific combinations of properties has recently attracted significant attention in the research community. In particular, numerous particle systems have been designed and fabricated by integrating diverse materials with monodispersed silica nanoparticles. One or more distinct nanomaterials can be assembled on, encapsulated within, or integrated both inside and on the surface of silica nanoparticles using different chemistries and techniques to create multifunctional nanosystems. Research on these particle systems for biomedical applications has progressed rapidly during recent years due to the synergistic advantages of these complexes compared to the use of single components. This feature article surveys recent research progress on the fabrication strategies of these nanoparticle systems and their applications to medical diagnostics and therapy, thereby paving the way for the emerging field of nanomedicine. [source]

Hydrophobic Functional Group Initiated Helical Mesostructured Silica for Controlled Drug Release,

ADVANCED FUNCTIONAL MATERIALS, Issue 23 2008
Lei Zhang
Abstract In this paper a novel one-step synthetic pathway that controls both functionality and morphology of functionalized periodic helical mesostructured silicas by the co-condensation of tetraethoxysilane and hydrophobic organoalkoxysilane using achiral surfactants as templates is reported. In contrast to previous methods, the hydrophobic interaction between hydrophobic functional groups and the surfactant as well as the intercalation of hydrophobic groups into the micelles are proposed to lead to the formation of helical mesostructures. This study demonstrates that hydrophobic interaction and intercalation can promote the production of long cylindrical micelles, and that the formation of helical rod-like morphology is attributed to the spiral transformation from bundles of hexagonally-arrayed and straight rod-like composite micelles due to the reduction in surface free energy. It is also revealed that small amounts of mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, and phenyltrimethoxysilane can cause the formation of helical mesostructures. Furthermore, the helical mesostructured silicas are employed as drug carriers for the release study of the model drug aspirin, and the results show that the drug release rate can be controlled by the morphology and helicity of the materials. [source]

Multiple Functionalization of Mesoporous Silica in One-Pot: Direct Synthesis of Aluminum-Containing Plugged SBA-15 from Aqueous Nitrate Solutions,

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2008
Y. Wu
Abstract Aluminum-containing plugged mesoporous silica has been successfully prepared in an aqueous solution that contains triblock copolymer templates, nitrates, and silica sources but without using mineral acid. The acidity of the solution can be finely tuned from pH 1.4 to 2.8 according to the amount of the introduced aluminum species which ranged from an Al/Si molar ratio of 0.25/1 to 4.0/1. The aluminum nitrate additive in the starting mixture, along with the weak acidity produced by the nitrates, contributes to the formation of plugged hexagonal structures and the introduction of different amounts of aluminum species into the mesostructure. Characterization by X-ray diffraction, transmission electron microscopy, and N2 sorption measurements show that the Al-containing plugged silicas possess well-ordered hexagonal mesostructures with high surface areas (700,860 m2,g,1), large pore volume (0.77,1.05 cm3,g,1) and, more importantly, combined micropores and/or small mesopores in the cylindrical channels. Inductively coupled plasma,atomic emission spectrometry results show that 0.7,3.0 wt,% aluminum can be introduced into the final samples. 27Al MAS NMR results display that about 43,60% aluminum species are incorporated into the skeleton of the Al-containing silicas and the amount of the framework aluminum increases as the initial added nitrates rises. Scanning electron microscopy images reveal that the directly synthesized Al-containing plugged silica has a similar morphology to that of traditional SBA-15. Furthermore, the Al-containing plugged samples have excellent performances in the adsorption and the catalytic decomposition of isopropyl alcohol and nitrosamine. Finally, the direct synthesis method is used to produce plugged mesoporous silicas that contain other metals such as chromium and copper, and the resultant samples also show good catalytic activities. [source]

Recent Progress on Silica Coating of Nanoparticles and Related Nanomaterials

ADVANCED MATERIALS, Issue 11 2010
Andrés Guerrero-Martínez
Abstract In recent years, new strategies for silica coating of inorganic nanoparticles and organic nanomaterials, which differ from the classical methodologies, have emerged at the forefront of materials science. Silica as a coating material promises an unparalleled opportunity for enhancement of colloidal properties and functions by using core,shell rational designs and profiting from its synthetic versatility. This contribution provides a brief overview of recent progress in the synthesis of silica-coated nanomaterials and their significant impact in different areas such as spectroscopy, magnetism, catalysis, and biology. [source]

Formation of Porous SiC Ceramics by Pyrolysis of Wood Impregnated with Silica

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2006
Kateryna Vyshnyakova
Biomorphous ,-SiC ceramics were produced at 1400°C from pine wood impregnated with silica. This one-step carbothermal reduction process decreases the cost of manufacturing of SiC ceramics compared with siliconization of carbonized wood in silicon vapor. The synthesized sample exhibits a 14 m2/g surface area and has a hybrid pore structure with large 5,20 ,m tubular macropores and small (<50 nm) slit-shaped mesopores. SiC whiskers of 20,400 nm in diameter and 5,20 ,m in length formed within the tubular pores. These whiskers are expected to improve the filtration by removing dust particles that could otherwise penetrate through large pores. After ultrasonic milling, the powdered sample showed an average particle size of ,30 nm. The SiC nanopowder produced in this process may be used for manufacturing SiC ceramics for structural, tribological, and other applications. [source]

A Room Temperature Ionic Liquid (RTIL)-Mediated, Non-Hydrolytic Sol,Gel Methodology to Prepare Molecularly Imprinted, Silica-Based Hybrid Monoliths for Chiral Separation,

ADVANCED MATERIALS, Issue 24 2006
H.-F. Wang
Silica-based hybrid molecularly imprinted polymer (MIP) monoliths with good chiral recognition ability are synthesized (see figure) using a novel method, a room temperature ionic liquid (RTIL)-mediated, non-hydrolytic sol,gel technique. The approach avoids the cracking and shrinking of the bed during drying, which is commonly associated with conventional sol,gel processing, overcomes the shortcomings associated with conventional organic-polymer-based MIP matrices, and offers improved selectivity. [source]

Control of Morphology and Helicity of Chiral Mesoporous Silica,

ADVANCED MATERIALS, Issue 5 2006
H. Jin
Chiral ordered mesoporous silica has been synthesized by using a chiral surfactant (N -myristoyl- L -alanine sodium salt) as a template, 3-aminopropyltriethoxysilane as a co-structure directing agent, and tetraethoxylsilane as an inorganic source. The helicity and the morphology of the mesoporous silica are determined by the stirring rate during the chiral surfactant self-assembly (see Figure), providing new insight into the chiral self-assembly of molecules. [source]

Multiply Shaped Silica Mediated by Aggregates of Linear Poly(ethyleneimine),

ADVANCED MATERIALS, Issue 7 2005
J.-J. Yuan
A new method for biomimetic silica fabrication is reported. Organized poly(ethyleneimine) rapidly catalyzes and directs the shape of silica in the hydrolysis of tetramethoxysilane under ambient conditions. The resultant silica displays a diversity of controllable morphologies, such as flower, plate, bundle, leaf, and sphere (see Figure, scale bar represents 1,,m). [source]

Ordered Mesoporous Carbon Hollow Spheres Nanocast Using Mesoporous Silica via Chemical Vapor Deposition,

ADVANCED MATERIALS, Issue 11 2004
D. Xia
Hollow spheres of well-ordered mesoporous carbon (see Figure) may be obtained via a simple chemical vapor deposition route, which utilizes mesoporous silica SBA-15 as a solid template and suitable organic compounds (e.g., styrene) as the carbon source. [source]