Fluoroalkyl-functionalized silica particles: synthesis, characterization, and wetting characteristics

Fluoroalkyl-functionalized silica particles for use in nonwetting surfaces were prepared by treatment of silica particles with fluoroalkyl-functional chlorosilanes. Both fumed and precipitated silica were studied, as well as the efficiency of surface coverage using mono-, di-, and trifunctional chlorosilanes. The most effective surface treatment was accomplished via the surface grafting of monofunctional chlorosilanes in the presence of preadsorbed dimethylamine under anhydrous conditions at room temperature. Confirmation of covalent attachment was accomplished via Fourier transform infrared (FT-IR) spectroscopy, while elemental analysis, thermogravimetric analysis, and nitrogen adsorption isotherms were used to determine grafting densities and additional key geometric characteristics of the grafted layer. The effect of residual silanol content on the moisture uptake properties of the modified silica particles was determined by measuring the water uptake of unbound particles, while liquid wetting properties were determined by dynamic contact angle analysis of elastomeric composites. Although residual silanol content was shown to effect wetting properties, results suggest that surface geometry dominates the performance of liquid-repellent surfaces. The potential use of fluoroalkyl-functionalized silica particles for hydrophobic and oleophobic applications is discussed.     

Comparative characterization of polymethylsiloxane hydrogel and silylated fumed silica and silica gel

Polymethylsiloxane (PMS) hydrogel (C(PMS)=10 wt%, soft paste-like hydrogel), diluted aqueous suspensions, and dried/wetted xerogel (powder) were studied in comparison with suspensions and dry powders of unmodified and silylated nanosilicas and silica gels using (1)H NMR, thermally stimulated depolarization current (TSDC), quasielastic light scattering (QELS), rheometry, and adsorption methods. Nanosized primary PMS particles, which are softer and less dense than silica ones because of the presence of CH(3) groups attached to each Si atom and residual silanols, form soft secondary particles (soft paste-like hydrogel) that can be completely decomposed to nanoparticles with sizes smaller than 10 nm on sonication of the aqueous suspensions. Despite the soft character of the secondary particles, the aqueous suspensions of PMS are characterized by a higher viscosity (at concentration C(PMS)=3-5 wt%) than the suspension of fumed silica at a higher concentration. Three types of structured water are observed in dry PMS xerogel (adsorbed water of 3 wt%). These structures, characterized by the chemical shift of the proton resonance at delta(H) approximately 1.7,3.7, and 5 ppm, correspond to weakly associated but strongly bound water and to strongly associated but weakly or strongly bound waters, respectively. NMR cryoporometry and QELS results suggest that PMS is a mesoporous-macroporous material with the textural porosity caused by voids between primary particles forming aggregates and agglomerates of aggregates. PMS is characterized by a much smaller adsorption capacity with respect to proteins (gelatin, ovalbumin) than unmodified fumed silica A-300.     

Preparation, characterization and biodegradation of biopolymer nanocomposites based on fumed silica

PLA and PCL based nanocomposites prepared by adding three different types of fumed silica were obtained by melt blending. Materials were characterized by means of Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Dynamic–Mechanical Thermal Analysis (DMTA).A good distribution of the fumed silica into both polymer matrices was observed. The highest thermo-mechanical improvements were reached by addition of the fumed silica with higher surface area. PLA and its nanocomposites were degraded in compost at 58 °C; at this temperature all samples presented a significant level of polymer degradation, but a certain protection action of silica towards PLA degradation was observed, whereas the addition of fumed silica did not show considerable influence on the degradation trend of PCL. These dissimilarities were attributed to the different degradation mechanism of the two polymers.     

Dendrimer modified silica gel for anion exchange chromatography: synthesis, characterization and application

The novel grafted silica supports were investigated. The anion exchanger was prepared by chemical modification of a bare silica gel surface. The support was coated with a polymeric moiety formed by condensation polymerization of primary amine with diepoxide. The synthesized copolymer of methylamine (MA) and 1,4-butanedioldiglycidyl ether (BDDE) exhibited a dendrimer structure. The prepared materials were characterized by elemental analysis, FT-IR spectroscopy and solid state (13)C and (29)Si NMR CP-MAS spectroscopy. The porous structure of the adsorbents was investigated using the low temperature nitrogen adsorption (LTNA) method. It allows determination of the influence of the topology of packing materials on their chromatographic properties. Imaging was also carried out on the surfaces of the synthesized materials by scanning electron microscopy (SEM). The obtained stationary phase was applied in ion chromatography for the separation of inorganic anions (F(-), Cl(-), NO(2)(-), Br(-), NO(3)(-), HPO(4)(2-), SO(4)(2-), ClO(4)(-)). Bicarbonate buffer was used as a mobile phase.     

Effect of electrolyte in silicone oil-in-water emulsions stabilised by fumed silica particles

Partially hydrophobised fumed silica particles are used to make silicone oil-in-water emulsions at natural pH of the aqueous phase. The stability and rheological properties of the emulsions and suspensions are studied at NaCl concentrations in the range 0-100 mM. It is found that all emulsions are very stable to coalescence irrespective of the NaCl concentration. However, a strong effect of electrolyte on the creaming and rheological properties is observed and linked to the particle interactions in aqueous suspensions. The creaming rate and extent are large at low electrolyte concentrations but both abruptly decrease at salt concentrations exceeding the critical flocculation concentration of the suspension (approximately 1 mM NaCl). The drastic improvement of the stability to creaming is attributed to the formation of a visco-elastic three-dimensional network of interconnected particles and emulsion droplets.     

Fumed silica synthesis. Influence of hydrogen chloride on the fumed silica particle formation process

Interaction of silicon dioxide molecule up to the small silica protoparticle and primary particle formation, and influence of hydrogen chloride (HCl), water (H₂O) and inert molecules (nitrogen N₂) “under flame condition” and “after cooling” on structure and properties of fumed silica were investigated by quantum-chemical simulations. An attempt to give definition of surface concept on atomic level was made.     

Hard structured particles: suspension synthesis, characterization, and compressibility

Hard interactions are developed on three grades of fumed silica by eliminating interparticle forces and sterically stabilizing the particles by attaching an organic coating to the surface of the particles, suspending them in an index-matching solvent and screening the electrostatics. These hard-structured particles are studied to understand the effects of the particle's microstructure on suspension properties without the influence of interparticle forces other than volume exclusion, Brownian, and hydrodynamic interactions. Light and X-ray scattering studies of low-volume-fraction suspensions suggest that the fumed silicas consist of primary particle of radius of gyration R(g1) approximately equals 16 nm and aggregate size R(g2) approximately 50 nm and mass fractal dimension D(f) approximately equals 2.2. Osmotic compressibilities of these suspensions are measured as a function of particle concentration exploring the packing mechanism of fumed silica. While there is minimal detectable change in the primary particle size, R(g2) varies by approximately 15%, providing insight into how suspension properties are related to particle size. As expected of hard particles with the same microstructure, the concentration dependence on the osmotic pressure superimposes with volume fraction of solids. The comparison of fumed-silica-suspension measurements to the known behavior of hard-sphere suspensions demonstrates the effects of particle geometry on suspension properties with indications of interpenetration of the fumed silica due to their open geometry.     

Biochemical and biomedical application of monodisperse polymer particles

Macroporous particles with large pores are used for size exclusion chromatography of carbohydrates with very high molecular weights. Macroporous particles of different sizes are used for multiple immunofluorometric analysis by flow cytometry. Porous magnetic particles with protein A coupled to the surface of the pores combine a high capacity in binding of IgG with easy handling of the particles. Magnetic beads with boronic acid coupled to the surface are applied for selective isolation of subclasses of cells. The beads are detached from the cells by addition of sorbitol, leaving free, pure cell fractions in good yield. The use of magnetic particles in molecular biology is described.     

Dispersion stability and rheological behavior of suspensions of polystyrene coated fumed silica particles in polystyrene solutions

Polystyrene coated silica（SiO₂@PS） core-shell composite particles with averaged diameter of about 290 nm were prepared by in situ emulsion polymerization of styrene on the surface ofγ-methacryloxypropyltrimethoxysilane grafted SiO₂ nanoparticles of 20-50 nm in diameter.Rheological behavior and dispersion stability of SiO₂@PS suspension in 10 wt%PS solution were compared with suspensions of untreated SiO₂ and silane modified SiO₂ nanoparticles.Suspensions of the untreated and the silane modified SiO₂ exhibited obvious shear thinning.The SiO-2@PS suspension exhibits shear viscosity considerably smaller than suspensions of untreated and silane modified SiO₂ at low shear rates.Transmission electron microscopy showed that the composite particles can uniformly and stably disperse in PS solution compared to other suspensions,implying that the PS shell can effectively enhance the particle compatibility with PS macromolecules in solution.     

Preparation of a dual-functionalized fumed silica nanoparticle catalysis for synthesis of azaluorenone derivatives

Research on Chemical Intermediates - A dual-functional silica-based catalyst was prepared by treating fumed silica with amino-containing silane then 1,4-butane sultone. The presence of functional...     

Metal oxide nanoparticles: synthesis, characterization and application

The synthesis of metal oxide nanoparticles is described in terms of precursor formation, nucleation, growth, and aging processes. The main parameters governing these processes are the solution properties, including the solvent viscosity, dielectric constant and the presence of adsorbing anions, the solubility of the metal oxide, and the metal oxide surface energy.     

Fumed silica synthesis: from molecules,protoparticles and primary particles to aggregates and agglomerates

Basing on quantum chemical simulations (semi‐empirical methode PM3) and vibration spectroscopy (Infrared (IR) and inelastic neutron scattering (INS)) and using other experimental data, a model of the formation of fumed silica particles is proposed, leading from initial molecules, via protoparticles and primary particles up to aggregates and agglomerates. Also, defintions of products in the flame process steps are suggested, from a chemical point of view. This process may be described as a sequence of states: Molecules ⇒ (molecular clusters = protoparticles) ⇒ primary particles ⇒ aggregates ⇒ agglomerates     

Lab-on-a-bubble: synthesis, characterization, and evaluation of buoyant gold nanoparticle-coated silica spheres

This paper describes the development and preparation of a new class of materials for surface-enhanced Raman scattering (SERS) consisting of gold nanoparticles coated onto hollow, buoyant silica microspheres. These materials allow for a new type of molecular assay designated as a lab-on-a-bubble (LoB). LoB materials serve as a convenient platform for the detection of analytes in solution and offer several advantages over traditional colloidal gold and planar SERS substrates, such as the ability to localize and concentrate analytes for detection. An example assay is presented using the LoB method and cyanide detection. Cyanide binds to SERS-active, gold-coated LoBs and is detected directly from the corresponding SERS signal. The abilities of LoBs and a gold colloid to detect cyanide are compared, and in both cases, a detection limit of ~170 ppt was determined. Differences in measurement error using LoBs versus gold colloid are also described, as well as an assay for 5,5'-dithiobis(2-nitrobenzoic acid) that shows the benefit of using LoBs over SERS analyses in colloids, which are often plagued by particle aggregation.     

Silver and gold nanoparticles in silica matrices: synthesis,properties, and application

Methods of synthesis, optical characteristics, morphology, and catalytic and bactericidal characteristics of composite materials based on silica (films and powders) containing nanoparticles of silver, gold, and their binary compounds with alloy or core–shell structure are examined. The photochemical reduction of Au³⁺ and Ag⁺ with a photocatalyst (a film of SiO₂ with adsorbed benzophenone) makes it possible to generate stable nanoparticles of gold and silver in solutions for subsequent introduction into adsorbents and catalysts. Examples of the use of nanosized composites in catalysis and in microbiological experiments are presented.     

Microfluidic synthesis of multifunctional Janus particles for biomedical applications

Multifunctional Janus particles have a variety of applications in a wide range of fields. However, to achieve many of these applications, high-throughput, low-cost techniques are needed to synthesize these particles with precise control of the various structural/physical/chemical properties. Microfluidics provides a unique platform to fabricate Janus particles using carefully controlled liquid flow in microfluidic channels to form Janus droplets and various types of solidification methods to solidify them into Janus particles. In this Focus article, we summarize the most recent representative works on Janus particle fabrication in microfluidics. The applications of Janus particles in biomedical areas are emphasized. We believe that microfluidics-enabled multifunctional Janus particles could resolve multiple prevalent issues in biomedicine (e.g., disease monitoring at an early stage, high-throughput bioassays, therapeutic delivery) if persistent effort and collaboration are devoted to this direction.     

Quantitative analysis and characterization of biofunctionalized fluorescent silica particles

A strategy for the production and subsequent characterization of biofunctionalized silica particles is presented. The particles were engineered to produce a bifunctional material capable of both (a) the attachment of fluorescent dyes for particle encoding and (b) the sequential modification of the surface of the particles to couple oligonucleotide probes. A combination of microscopic and analytical methods is implemented to demonstrate that modification of the particles with 3-aminopropyl trimethoxysilane results in an even distribution of amine groups across the particle surface. Evidence is provided to indicate that there are negligible interactions between the bound fluorescent dyes and the attached biomolecules. A unique approach was adopted to provide direct quantification of the oligonucleotide probe loading on the particle surface through X-ray photoelectron spectroscopy, a technique which may have a major impact for current researchers and users of bead-based technologies. A simple hybridization assay showing high sequence specificity is included to demonstrate the applicability of these particles to DNA screening.     

Synthesis and characterization of colloidal fluorescent mesoporous silica particles

Mesoporous silica particles with narrow size distribution were obtained by a seeded growth process. Depending on the size of seeds and on the time of addition of reactants, the size of particles can be varied between 300 and 1000 nm. In a second step the dye fluorescein isothiocyanate can be embedded. The structure of these new silica particles with low density was investigated by SEM, XRD, BET, and confocal microscopy.     

Corn oil based poly(urethane-ether-amide)/fumed silica nanocomposite coatings for anticorrosion application

Poly(urethane-ether-amide) (PUIEtA) nanocomposite coatings on mild steel were prepared by using corn oil, isosorbide and isophorone diisocynate and fumed silica. The syntheses steps were confirmed by FTIR, ¹H NMR and ¹³C NMR spectroscopy techniques. The morphology of PUIEtA nanocomposite coating was studied by SEM-EDX, that confirmed the presence of nanosilica and thermal behavior was studied by DSC/TGA analysis. The anticorrosion performance of PUIEtA coating systems on mild steel, exposed to 3.5?wt% NaCl solution, was evaluated using electrochemical impedance spectroscopy. Scratch hardness, pencil hardness, adhesion, and bending test were performed in order to investigate the performance of nanocomposite coating on mild steel substrate. It was found that PUIEtA-fumed silica nanocomposite coating could provide much better protection than PUIEtA. PUIEtA-3 nanocomposite coating can be safely used up to 200?°C.