Polycondensation Of Tetraethoxysilane Research Articles

Methyldiphenylsiloxane MQ Nanogels as Viscosity Regulators for Liquid Sealing Compositions

A new phenyl-containing MQ nanogel was obtained by the polycondensation of tetraethoxysilane and methyldiphenylethoxysilane in glacial acetic acid and characterized. Its effectiveness as a molecular thickener for siloxane oils was demonstrated. It was shown that its introduction into a poly(methylphenylsiloxane) liquid leads to an increase in the viscosity while maintaining the thermal and sealing characteristics.

Conservation of the Biocatalytic Activity of Whole Yeast Cells by Supported Sol – Gel Entrapment for Efficient Acyloin Condensation

In this study, an efficient and generally applicable 2nd generation sol – gel entrapment method was developed for immobilization of yeastcells. Cells of Lodderomyces elongisporus, Candida norvegica, Debaryomyces fabryi, Pichia carsonii strains in admixture with hollow silica microspheres support were immobilized in sol – gel matrix obtained from polycondensation of tetraethoxysilane. As biocatalysts in theselective acyloin condensation of benzaldehyde catalyzed by pyruvate decarboxylase of the yeast, the novel immobilized whole-cell preparations were compared to other states of the cells such as freshly harvested wet cell paste, lyophilized cells and sol – gel entrapped preparations without hollow silica microspheres support. Reusability and storability studies designated this novel 2nd generation sol – gel method as a promising alternative for solid formulation of whole-cells bypassing expensive and difficult downstream steps while providing easy-to-handle and stable biocatalysts with long-term preservation of the biocatalytic activity.

Preparation of acid-activated sepiolite/Rhodamine B@SiO2 hybrid fluorescent pigments with high stability

Rhodamine B (Rhb) supported on the acid activated sepiolite (AAS/Rhb), a kind of inorganic/organic composite fluorescent pigments was prepared. The AAS/Rhb was further coated with a layer of SiO2 by polycondensation of tetraethoxysilane (TEOS) with acetic acid as catalyst to prepare the AAS/Rhb@SiO2 pigments with high stability. The prepared materials were characterized by nitrogen adsorption-desorption, X-ray diffraction (XRD), scanning electron microscope (SEM), FT-IR spectra, thermogravimetric analysis (TGA), the excitation spectrum and emission spectrum, UV–Vis and transmission electron microscopy (TEM). The AAS/Rhb@SiO2 pigments have excellent stability against acid, alkali, organic solvent, thermal aging and UV irradiation.

Facile preparation of stable palygorskite/methyl violet@SiO2 “Maya Violet” pigment

Maya Blue pigment has attracted considerable attention owing to their extraordinary stability. The growing interest in this field has largely expanded the study of Maya Blue-like pigments. Inspired by Maya Blue, a stable palygorskite/methyl violet@SiO2 (PAL/MV@SiO2) “Maya Violet” pigment was fabricated via adsorption of MV by PAL, and then deposition of a layer of SiO2 on the surface by polycondensation of tetraethoxysilane (TEOS) in the presence of cetyltrimethylammonium bromide (CTAB). The weight ratio of MV to PAL is as high as 10%. The pigments were characterized by scanning electron microscopy and a variety of analytical techniques, e.g., Fourier Transform infrared spectroscopy and zeta potential. The results indicate that MV molecules are fixed onto the exterior surface, the grooves and at the entrances of the channels of PAL. The PAL/MV@SiO2 pigment shows excellent stability against chemical attacks, e.g., 0.1M HCl, 0.1M NaOH and various organic solvents. Different from Maya Blue, grinding and heating treatment are virtually ineffective in improving stability of the PAL/MV pigment. CTAB and the SiO2 layer formed on the surface of PAL/MV contribute greatly to the improved stability of the pigment due to shielding effect. The optimal CTAB/TEOS/ammonia/H2O molar ratio for the surface modification of PAL/MV is 0.24/1/2.89/495.

The structure effect upon gallic acid re-binding in molecularly imprinted organosilica

This paper debates the effect of the stabilizer (vinyl benzyl trimethyl ammonium chloride—VBTAC or cetyl trimethyl ammonium chloride—CTAC) and the structure (typical SiO2 matrix or inorganic–organic interpenetrated matrix) influence in molecular imprinting of gallic acid-polyphenol class of templates. For this purpose, gallic acid-imprinted particles were obtained via typical polycondensation sol–gel reactions and via sol–gel/radical polymerization concurrent reactions of tetraethoxy silane (TEOS) and aminopropyl ethoxy silane (APTES) or vinyl triethoxy silane (VTES), respectively. The influence of the mesophase formation and stabilizer nature upon the re-binding of gallic acid was investigated using thermal, infrared and morphology measurements. Adsorption assays of organosilica particles were well correlated with their physical properties. Unlike the polycondensation of TEOS with APTES in the presence of CTAC, concurrent radical polymerization of VBTAC consumed the vinyl functionalities of VTES, decreasing the capacity of VBTAC to mediate the mesophase formation and the capacity of VTES to coordinate template molecules; hence, both the binding capacity and the “memory” effect of the interpenetrated organosilica structure were significantly affected.

Novel slurry containing graphene oxide-grafted microencapsulated phase change material with enhanced thermo-physical properties and photo-thermal performance

In this work, a new microencapsulated phase change material, paraffin@ silica (SiO2)/graphene oxide (GO), is prepared by two steps: engulfing paraffin with silica by in situ hydrolysis and poly condensation of tetraethoxysilane and the modification of the SiO2 shell with GO. The paraffin@SiO2/GO composite is composed of spherical capsules with diameters of ~20um. Raman spectrometer analysis verifies the embedding of GO in the SiO2 shell. The melting and freezing temperatures of the composite are very close to those of paraffin. Based on the melting and freezing enthalpy of the composite, the encapsulation ratio of paraffin is calculated to be 50.8% in the paraffin@SiO2 composite and 49.6% in the paraffin@SiO2/GO composite. It is shown that the paraffin@SiO2/GO composite exhibits enhanced thermal stability and excellent thermal reliability. The phase change slurry prepared by dispersing the paraffin@SiO2/GO composite in water shows higher thermal conductivity and heat capacity along with remarkable photo-thermal conversion performance, making it potential for use as the heat transfer fluid in direct absorption solar collectors. The high heat storage capability and excellent photo-thermal conversion performance of the paraffin@SiO2/GO composite enable it to be a potential material to store solar energy in practical applications.

Adsorption properties of xerogel prepared from mixed titanium and silicon alkoxides

Low-temperature nitrogen adsorption-desorption isotherms have been measured for samples of silica, titanium dioxide, and a TiO2/SiO2 composite xerogel prepared via acid hydrolysis and polycondensation of tetraethoxysilane, titanium isopropoxide, and a mixture thereof, respectively, in the presence of cetylpyridinium chloride at different Ti/Si molar ratios. It has been shown that nitrogen adsorption isotherms for silica are of type I and indicate the formation of micropores, while those for titanium dioxide and the TiO2/SiO2 composite are of type IV, which is characteristic of mesoporous adsorbents.

Learning from ancient Maya: Preparation of stable palygorskite/methylene blue@SiO2 Maya Blue-like pigment

A facile method for the preparation of stable palygorskite/methylene blue@SiO2 (PAL/MB@SiO2) Maya Blue-like pigment was reported. The PAL/MB pigment was prepared via adsorption of MB by PAL, which was further coated with a layer of SiO2 by polycondensation of tetraethoxysilane (TEOS) with acetic acid (HAc) as the catalyst to form the PAL/MB@SiO2 pigment. The weight ratio of MB to PAL, ball milling time and heating temperature play important roles in affecting stability of the PAL/MB pigment. The MB content in the PAL/MB pigment is up to 12%, which is higher than all the state-of-the-art Maya Blue-like pigments. The MB molecules can only be adsorbed onto the external surface, the grooves and the openings of the channels of PAL, but cannot enter the channels according to the BET, zeta potential, FTIR and XRD analyses. Owing to the fact that the stability of the PAL/MB pigment is not very high, a layer of SiO2 is introduced to shield the MB molecules and further improve the stability. The PAL/MB@SiO2 pigment shows excellent stability against elution, thermal aging and intensive UV irradiation. A TEOS/HAc/H2O molar ratio of 1/2/140 in forming the SiO2 layer is greatly helpful to improve the stability.

Fluorescent magnetic nanoparticles for cell labeling: Flux synthesis of manganite particles and novel functionalization of silica shell

Novel synthetic approaches for the development of multimodal imaging agents with high chemical stability are demonstrated. The magnetic cores are based on La0.63Sr0.37MnO3 manganite prepared as individual grains using a flux method followed by additional thermal treatment in a protective silica shell allowing to enhance their magnetic properties. The cores are then isolated and covered de novo with a hybrid silica layer formed through the hydrolysis and polycondensation of tetraethoxysilane and a fluorescent silane synthesized from rhodamine, piperazine spacer, and 3-iodopropyltrimethoxysilane. The aminoalkyltrialkoxysilanes are strictly avoided and the resulting particles are hydrolytically stable and do not release dye. The high colloidal stability of the material and the long durability of the fluorescence are reinforced by an additional silica layer on the surface of the particles. Structural and magnetic studies of the products using XRD, TEM, and SQUID magnetometry confirm the importance of the thermal treatment and demonstrate that no mechanical treatment is required for the flux-synthesized manganite. Detailed cell viability tests show negligible or very low toxicity at concentrations at which excellent labeling is achieved. Predominant localization of nanoparticles in lysosomes is confirmed by immunofluorescence staining. Relaxometric and biological studies suggest that the functionalized nanoparticles are suitable for imaging applications.

Dendritic silica nanoparticles synthesized by a block copolymer-directed seed-regrowth approach.

A facile seed regrowth method is presented for the preparation of a new type of colloidal dendritic silica nanoparticles (DSNPs) with unique Konpeito-like morphology and high surface area (∼400 m(2) g(-1)). Growth of silica nanoprotrusions on the surfaces of colloidal silica nanoparticles proceeds by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in the presence of a PEO-PPO-PEO-type block copolymer (Pluronic F127) under controlled pH conditions. The polymers adsorbed on the seed surface play a crucial role in the formation of DSNPs. DSNPs with controllable size (28-85 nm) and narrow size distributions can be obtained by using monodisperse silica nanoparticles with various sizes as seeds. The surface morphology of DSNPs is tunable by changing the concentration of TEOS. Additionally, novel dendritic silica nanochains are prepared using one-dimensionally assembled silica nanoparticles as the seeds.

BMIm-PF6@SiO2 Microcapsules: Particulated Ionic Liquid as A New Material for the Heterogenization of Catalysts

A method for the preparation of silica microcapsules containing a high loading of ionic liquids (ILs) is described. The method paves the way to the conversion of ionic liquids into particulated materials, which results in ILs with new properties without changing their molecular structures. The synthesis of these new materials is based on the emulsification of ionic liquids in water, using surfactants or dispersants, and the resulting ionic liquid droplets are then confined in a silica shell formed via interfacial hydrolysis and polycondensation of tetraethoxysilane. This material can be isolated by centrifugation, followed by drying to yield a fine powder of ionic liquid-silica microcapsules, which are water and organic solvents redispersible. These new materials are utilized in the heterogenization of palladium catalyst and then applied in the hydrogenation of alkynes. The catalyst shows chemoselectivity in the hydrogenation of internal alkynes such as 4-octyne. Comparative studies have shown that the sa...

Hydrophilic nature and sorption-diffusion properties of nanocomposite hybrid polysulfone films

Hybrid nanocomposite films containing silica (≥11.4 wt.%) or titania (≥18.8 wt.%) in the polymer matrix were prepared by the sol-gel method using the hydrolytic polycondensation of tetraethoxysilane and tetrabutoxysilane in a THF solution of aromatic polymer, polysulfone (PSF). The influence of the oxide nature and the film composition on the structure, the interaction of the polymer with oxides, hydrophilicity, and sorption-diffusion properties of the hybrid films were studied by FTIR spectroscopy, atomic force microscopy, dynamic light scattering, and a complex of other physicochemical methods. The absence of chemical or intermolecular hydrogen bonds between the polymer and oxide particles in the PSF films was shown. The average size of the oxides (SiO2, ∼20 nm; TiO2, ∼90 nm) in the films and roughness of their surface (∼0.2–0.8 nm) were determined. The introduction of oxides into the polymer matrix increases the hydrophilic properties and the ability of the PSF films to swell in water; the diffusion coefficients of water and permeability of water vapor in the PSF films also increase. Titania also induces a more considerable change in the structure of the polymer matrix and more strongly affects the sorption-diffusion properties of the hybrid films in aqueous solutions of THF. All prepared nanocomposite films PSF/SiO2 and PSF/TiO2 are capable of extracting an organic component from aqueous solutions and can be used as sorbents and membrane films for the removal of organic substances from the aqueous medium.

Thermal activation of polyethylene@silica particles: towards ceramic surfactants

The fabrication of “switch-on” amphiphilic submicrometer hybrid particles of cross-linked polyethylene (XPE)@silica is described. The synthesis of the particles is based on the simultaneous cross-linking of PE and the polycondensation of tetraethoxysilane in hot, surfactant-stabilized O/W micelles. Thermal activation of the particles results in particles with amphiphilic behavior. It is proposed that the thermal activation triggers partial phase-separation which pushes some of the PE chain to the surface, in a heterogeneous way. By this, on each particle two halves can be identified which differ in their degree of hydrophobicity (“Janus” structure), thus giving rise to the surfactant activity. The particles were intensively characterized before and after the thermal activation and their amphiphilic behavior was demonstrated. By the approach described in the paper it is in principle possible to design a library of functionalities out of a single surface active agent species. This was demonstrated by the thermal activation of functionalized composite particles of dyes@XPE@silica and of the triple hybrid Ag@XPE@silica. Full material characterization is provided, including SEM, TGA, surface area analysis, antibacterial tests and zeta potential measurements.

Synthesis and characterisation of π-conjugated polymer/silica hybrids containing regioregular ionic polythiophenes

Highly regioregular poly{3-[n-(1-methylimidazolium-3-yl)alkyl]thiophene-2,5-diyl bromide} (n = 4, 6, 8) (10–12) has been prepared by reaction of poly[3-(n-bromoalkyl)thiophene-2,5-diyl] (n = 4, 6, 8) (7–9) with 1-methylimidazole. Acid-catalyzed hydrolysis and polycondensation of tetraethoxysilane (TEOS) were carried out in the presence of these polymers. The strong ionic interactions between the imidazolium moieties of the polythiophene and the charged silanol groups enabled the homogeneous dispersion of the polythiophene within silica. The resulting composite materials were characterised by SEM, TEM and tapping mode atomic force microscopy (TM-AFM). The optical and thermal properties were investigated by UV and TGA measurements.

Enzyme encapsulation in silica particles prepared using enzyme-assisted sol-gel reactions in ionic liquids

Several studies have demonstrated the use of biomimetic approaches in the synthesis of a variety of inorganic materials. In this study, a low-temperature and natural pH procedure for the synthesis of silica was developed using hydrolytic enzymes. For the preparation of silica particles at room temperature and pH 7, a screening test for enzyme-catalyzing direct hydrolysis and polycondensation of tetraethoxysilane by using 5 types of hydrolases; pepsin, trypsin, esterase, and two lipases were chosen as biocatalysts; moreover, these enzymes can promote the precipitation of silica within 3 days. The 29Si nuclear magnetic resonance (NMR) measurements indicated that the enzyme activity in ionic liquids was higher than that in aqueous buffer solutions, and that the obtained silica particles were highly polycondensed. Under ionic liquid conditions, it was observed that enzymes were effectively encapsulated in the sol–gel silica material. In addition, for siloxane bond formation the catalytic activity of silica–enzyme composites was higher than that of free solution enzymes.

Helical silica nanotubes: Nanofabrication architecture, transfer of helix and chirality to silica nanotubes

AbstractA series of neutral gelators and cationic amphiphiles derived from 1,2 diphenylethylenediamine (I) and 1,2-cyclohexanediamine (II) was synthesised. Helical silica nanotubes were prepared utilising these organic gelators through sol-gel polycondensation of tetraethoxy silane, (TEOS-silica source). Right- and left-handed helical nanotubes respectively were obtained from a 1: 1 mass mixture of optically active, (1S,2S)-III-(1S,2S)-V neutral gelator and (1S,2S)-IV-(1S,2S)-VI cationic amphiphile and a 1: 1 mass mixture of optically active, (1R,2R)-III-(1R,2R)-V neutral gelator and (1R,2R)-IV-(1R,2R)-VI cationic amphiphile, indicating that the handedness of the helical nanotubes varied with the change in the neutral gelator precursors used. The nanotubes were characterised by SEM images.

Morphology dependence of 1,2-diphenylethylenediamine-derived organogelator templates in solvents and their influence in the production of nanostructured silica

AbstractThe 1,2-diphenylethylenediamine-based neutral or cationic organogelator-templates, currently employed in the production of silica nanomaterials, were initially evaluated for their versatile gelation ability and found to be gelled in the majority of organic solvents tested. Scanning electron microscope and transmission electron microscope, images of neutral organogels made from different solvents revealed that they assembled into a plate-shaped, or rod-shaped morphology, respectively in ethanol or butan-1-ol and in acetonitrile or tetrahydrofurane. Similarly, a 1: 1 mixture (mass) of neutral and cationic gelators formed different morphologies in the solvents tested. Sol-gel polycondensation of tetraethoxy silane using either individual gels (neutral or cation) or a 1: 1 mixture of gels was explored. The experimental results and the scanning electron microscopy and transmission electron microscopy images revealed that silica nanotubes with an inner diameter of 82 nm and an outer diameter of 620 nm were obtained from the 1: 1 mixture of neutral and cationic gelator in ethanol, whereas silica nanoparticles were obtained using gels made in the other solvents tested.

Preparation and structure of chitosan-silica organic-inorganic hybrid films

Organic-inorganic hybrid films are prepared via the hydrolysis and polycondensation of tetraethoxysilane in chitosan solutions. It is shown that the composition of reagents, the time of synthesis, the crosslinking of chitosan macromolecules via amino groups by glutaric aldehyde, and the conditions of drying affect structurization of the resulting films. With the use of optical polarization microscopy and atomic force microscopy, it is found that the films contain silica particles with a wide size distribution. The crosslinking of the chitosan matrix by glutaric aldehyde results in the predominant formation of inorganic nanoparticles in the films. A good sorption capacity of the films for copper ions in solutions is found. It increases by a factor of 1.7 as the content of the silica in the films increases to 30 wt %.

Synthesis structure and stability of amino functionalized PEGylated silica nanoparticles

Amino functionalized PEGylated silica nanoparticles were prepared by one pot-procedure, based on ammonia catalysed hydrolysis and polycondensation of Tetraethoxysilane (TEOS) and 3-Aminopropyltriethoxysylane (APTS), in alcohol medium (ethanol) (Stöber method), containing PEG 5000 monomethyl ether. Particles size was studied using Transmission Electron Spectroscopy (TEM). PEGylation and amino functionalization was investigated through FT-IR and Thermogravimetric analysis (TG). The structure of nanoparticles consists of nanosilica (a few nanometers in size) dispersed into a PEG matrix, produced by entanglement of PEG chains. The stability of the water colloidal suspension depends on the PEG/silica mass ratio, that changes with PEG concentration in the reaction batch. By properly selecting the PEG concentration, nanoparticles smaller than 150 nm were obtained, stable towards aggregation in water media up to 6 months. The observed need of an optimal PEG/silica mass ratio for long-term stability can be explained on the basis of particles structure and assuming that both steric and electrostatic effect concur to stabilisation.

Cross-linked polyethylene@silica: the first full interpenetrating network hybrid particles

Sub-micron hybrid particles, where the two components are cross-linked polyethylene (PE) and silica, were prepared by the simultaneous cross-linking of PE and polycondensation of tetraethoxysilane in hot, surfactant-stabilized O/W micelles. The resulting material is new from two points of view: it is a previously unknown hybrid material made of the simplest organic and inorganic cross-linked polymers—cross-linked PE and silica; and the particles are the first full interpenetrating network (IPN) hybrid particles. Two PE cross-linkers are compared. Full material characterization is provided, including SEM, TGA, surface area analysis, solid-state NMR, thermoporosimetry, PE-leaching experiments and zeta potential measurements.