Micro-sized Silica Particles Research Articles

Nanosized Particles of Synthetic Silicon Dioxide Delay the Regeneration of Gastric Ulcers Created by N-Methyl-N′-Nitro-N-Nitrosoguanidine and Induce Hyper-Trophic Gastritis-like Symptoms

Synthetically produced silicon dioxide used as a food additive exhibits nanoparticle size and shape during the early stages of manufacturing. Even when processed into food products, these nanoparticles are detected. Although processing food ingredients into nanoparticles can improve absorption rates or enhance texture, there are concerns about the specific biological effects of nanoparticles. In this study, three types of silica particles, including nanosized particles, were repetitively administered to the stomach using a gastric tube or exposed to a single injection into the submucosal layer of the stomach. Macroscopic and microscopic examinations did not reveal acute toxicity. However, when silica particles were administered to the stomach during the healing and regeneration process of gastric ulcers (induced by injecting the alkylating agent of N-Methyl-N′-Nitro-N-Nitrosoguanidine into the submucosal layer), silica particles with a diameter of 70 nm (SiNPs-70) delayed regeneration more strongly than microsized silica particles with diameters of 300 nm or 1000 nm (SiMPs-300, -1000). Furthermore, fibrosis for tissue regeneration spread throughout the entire mucosa of the stomach, resulting in hypertrophic gastritis-like symptoms. The frequency of this symptom was over 50% with SiNPs-70, 20% with SiMPs-300, and 0% with SiMPs-1000. Although the silica particles used in this study differ from actual samples found in food, the impact of particle size, particularly the effects unique to nanosize, was identified as toxicity in the stomach healing process.

Lightweight porous silica ceramics with ultra-low thermal conductivity and enhanced compressive strength

In recent years, the need for robust thermal protection for reusable spacecraft and vehicles has spurred strong demand for high-performance lightweight thermal insulation materials that exhibit high strength. Herein, we report silica porous ceramics prepared via the direct foaming technique with lightweight, ultra-low thermal conductivity and enhanced compressive strength. Silica particles (particle size: 500 nm and 2 μm) were used as the raw materials. The nano-sized silica particles were easily sintered, thereby improving the compressive strength of the ceramics, whereas the micro-sized silica particles maintained the pore structure integrity without deformation. The addition of nano-silica enhanced the compressive strength by 764% (from 0.039 to 0.337 MPa). In addition, the thermal conductivity of the ceramics was as low as 0.039 W m−1 K−1. Owing to these outstanding characteristics, these porous silica ceramics are expected to be employed as thermal insulation material in diverse fields, especially aerospace and space where weight is an important constraint.

Toward the Direct Synthesis of HDPE Powders for Powder Bed Fusion Based Additive Manufacturing

AbstractPowder bed fusion (PBF) suitable polyethylene particles are targeted by means of a direct synthesis, using a bisimino pyridine iron catalyst (BIP FeCl2) supported on microsized silica particles. An active support is generated by treating spray dried silica microparticles with a methyl aluminoxane activated BIP FeCl2 catalyst in toluene. Semibatch ethylene polymerization is mapped with respect to pressure, temperature, and reaction time to find optimal reaction parameters. The optimized synthesis leads to round polyethylene particles with a median size of ≈50 µm which have a sinter window of 8–15 °C and an unconfined yield stress (ffc) of 1.5 in a ring shear tester. The Young modulus of injection molded samples is in the range of 150–250 Pa with an elongation at break of about 30%. The powder flowability is improved by coating with nanosilica powder to an ffc of 3.8. Additivitation with carbon black allows to laser sinter the powder to solid parts in a small scale adapted setup for selective laser sintering (PBF/laser beam (LB)/P). Severe caking is preventing the preparation of CAD model conform parts. Commercial HDPE powder for PBF is additivated the same way to give substantially solid built parts, but with similar caking.

Increased Uptake of Silica Nanoparticles in Inflamed Macrophages but Not upon Co-Exposure to Micron-Sized Particles.

Silica nanoparticles (NPs) are widely used in various industrial and biomedical applications. Little is known about the cellular uptake of co-exposed silica particles, as can be expected in our daily life. In addition, an inflamed microenvironment might affect a NP’s uptake and a cell’s physiological response. Herein, prestimulated mouse J774A.1 macrophages with bacterial lipopolysaccharide were post-exposed to micron- and nanosized silica particles, either alone or together, i.e., simultaneously or sequentially, for different time points. The results indicated a morphological change and increased expression of tumor necrosis factor alpha in lipopolysaccharide prestimulated cells, suggesting a M1-polarization phenotype. Confocal laser scanning microscopy revealed the intracellular accumulation and uptake of both particle types for all exposure conditions. A flow cytometry analysis showed an increased particle uptake in lipopolysaccharide prestimulated macrophages. However, no differences were observed in particle uptakes between single- and co-exposure conditions. We did not observe any colocalization between the two silica (SiO2) particles. However, there was a positive colocalization between lysosomes and nanosized silica but only a few colocalized events with micro-sized silica particles. This suggests differential intracellular localizations of silica particles in macrophages and a possible activation of distinct endocytic pathways. The results demonstrate that the cellular uptake of NPs is modulated in inflamed macrophages but not in the presence of micron-sized particles.

Preparation of fluoroalkyl end-capped vinyltrimethoxysilane oligomer/micro-sized silica composites possessing superoleophilic/superhydrophobic characteristic: application to selective removal of aromatic compounds from aqueous methanol solution by using these composites

Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [RF-(CH2–CHSi(OMe)3)n-RF; n = 2, 3; RF = fluoroalkyl group: RF-(VM)n-RF] was found to undergo the sol–gel reaction in the presence of micro-sized silica particles under alkaline conditions to afford the corresponding fluorinated oligomer/micro-sized silica composites [RF-(VM-SiO3/2)n-RF/μ-SiO2]. The obtained composites were applied to the surface modification of glass to reveal a superoleophilic/superhydrophobic characteristic on the modified surface. In contrast, fluoroalkyl end-capped vinyltrimethoxysilane oligomer/silica nanocomposites [RF-(VM-SiO3/2)n-RF/n-SiO2], which were prepared in the presence of nanometer-sized silica particles under similar sol–gel reactions, provided an oleophobic/superhydrophobic property on the surface. RF-(VM-SiO3/2)n-RF/μ-SiO2 composites were applied to the solid-phase extraction sorbent to isolate the transparent colorless oil from water-in-oil (W/O) emulsion. These composite powders were also applicable to the effective removal of traditional organic dyes, such as rhodamine B, acid red 289, and fluorescein from aqueous methanol solution. Of particular interest, it was demonstrated that RF-(VM-SiO3/2)n-RF/μ-SiO2 composites, of whose micro-sized silica gel is surface-functionalized with amino units, can exhibit a similar superoleophilic/superhydrophobic characteristic on the composite surface, giving the selective removal of fluorinated phenol-type aromatic compounds from aqueous methanol solutions, although the removal ability for the corresponding non-fluorinated ones was not observed at all under similar conditions.

Energy-efficient and environment-friendly method to prepare monodispersed silica stationary phases for simultaneous separation of compound drugs

An energy-efficient and environment-friendly approach to prepare porous monodispersed micro-sized silica particles with methyltrimethoxysilane (MTMS) as the precursor is described. The particles were synthesized by a two-step hydrolysis/condensation procedure, with post-synthetic aging and calcination for methyl group removal. They show uniform spherical morphology, narrow particle size distribution (D90/10, 1.2–1.6), tailored particle size (3, 5, 7 μm) and mesopore structure (10, 13 nm), which can be directly used as packing materials for HPLC without size classification. C18, sulfonate, and C18/sulfonate mixed-mode stationary phases were produced by a green vapor deposition method based on the synthesized silica particles. The newly synthesized C18 phase exhibits mechanical stability, kinetic behavior and separation performance expected from the commercial C18 column. The C18/sulfonate phase exhibits prominent mixed-mode retention behavior which can be applied to the simultaneous separation of multiple substances in the compound drugs.

Improved Electromagnetic Interference Shielding Properties Through the Use of Segregate Carbon Nanotube Networks.

We report the enhanced electromagnetic interference (EMI) shielding properties of hybrid carbon nanotube (CNT) composites consisting of more than two kinds of fillers through the use of segregate conducting networks. An excluded volume was created by micro-sized silica particles that concentrate the CNT network, resulting in improved electrical conductivity and microwave properties. To achieve the optimal dispersion of CNTs and silica particles, high shear force was applied to the pre-cured composite mixture via three-roll milling. Depending on the micro-silica content ratio, we observed improved electrical conductivity and EMI shielding properties. For a quantitative comparison to observe the excluded-volume effects, a CNT composite without micro-silica was measured in parallel with the other sample.

Dopamine Polymerization in Liquid Marbles: A General Route to Janus Particle Synthesis.

Coating a liquid with a particle shell not only renders a droplet superhydrophobic but also isolates a well-confined microenvironment for miniaturized chemical processes. Previously, we have demonstrated that particles at the liquid marble interface provide an ideal platform for the site-selective modification of superhydrophobic particles. However, the need for a special chemical reaction limits their potential use for the fabrication of Janus particles with various properties. Herein, we combine the employment of liquid marbles as microreactors with the remarkable adhesive ability of polydopamine to develop a general route for the synthesis of Janus particles from micrometer-sized superhydrophobic particles. We demonstrate that dopamine polymerization and deposition inside liquid marbles could be used for the selective surface modification of microsized silica particles, resulting in the formation of Janus particles. Moreover, it is possible to manipulate the Janus balance of the particles via the addition of surfactants and/or organic solvents to tune the interfacial energy. More importantly, owing to the many functional groups in polydopamine, we show that versatile strategies could be introduced to use these partially polydopamine-coated silica particles as platforms for further modification, including nanoparticle immobilization, metal ion chelation and reduction, as well as for chemical reactions. Given the flexibility in the choice of cores and the modification strategies, this developed method is distinctive in its high universality, good controllability, and great practicability.

Switch regulation of interleukin-1 beta in downstream of inflammatory cytokines induced by two micro-sized silica particles on differentiated THP-1 macrophages

To investigate the regulated role of IL-1β in initiating and maintaining inflammation, PMA-differentiated THP-1 macrophages were exposed to two micro-sized crystalline silica particles (Si3–5μm and Si1μm) from 3h to 24h, respectively. Cytotoxicity and inflammatory cytokines (IL-1β, TNF-α and IL-6) expressions measured showed that they were induced by both silica particles in positive dose-dependent manners. The levels of inflammatory cytokines induced by Si1μm were higher than those induced by Si3–5μm at low concentration. When pretreated with anti-human IL-1β, not only the high levels of IL-1β but also elevated TNF-α and IL-6 induced by both silica particles were remarkably blocked, especially Si1μm particle. In addition, recombinant human IL-1β protein could induce macrophages to strikingly augment TNF-α and IL-6 expressions. Our data suggest that IL-1β could play a critical role of switching regulation in the downstream inflammation induced by micro-sized silica particles.

Steam-enhanced regime for liquid hydrocarbons combustion: velocity distribution in the burner flame

The lab-scale burner device with proprietary design was used for combustion of diesel fuel in a steam-enhanced regime. This operation mode ensures drastic intensification of liquid hydrocarbon combustion due to supply of superheated steam jet to the combustion zone. The particle image velocimetry technique was used for study of velocity field in the burner flame. The method of seeding of flow zone with new kind of tracers (micro-sized silica particles produced from silicon oil added to liquid fuel) was tested.

Amino-bearing calixcrown receptor grafted to micro-sized silica particles for highly selective enrichment of palladium in HNO3 media

Palladium recovery in HNO3-containing radioactive waste is of great value due to its considerable amount and benign radioactivity level. In this study, a new calixcrown receptor decorated with amino ligands (soft N donors) was synthesized for the selective extraction of Pd(II) in HNO3 media. A high distribution ratio (D) of 278.6 was obtained within 10min in solvent extraction. Moreover, the calixcrown receptor was covalently grafted to micro-sized silica particles to obtain a novel solid phase extraction (SPE) material (labeled as ACGSi). Detailed batch and column experiments revealed that the ACGSi material had fast kinetics and favorable adsorption capacity towards Pd(II) in HNO3 solutions. Parameters influencing the adsorption ability such as contact time, acidity and initial metal concentration were fully evaluated. Kinetic equations (pseudo-first/second-order) and adsorption isotherm models (Langmuir and Freundlich models) were employed to fit the experimental data for inspecting the adsorption mechanism. On this basis, a facile chromatographic process was proposed for the selective enrichment and recovery of palladium in simulated high level liquid waste (HLLW). A recovery rate of 99.3% was obtained. The amino-decorated calixcrown extractant as well as the functionalized SPE material is believed to be promising to find applications in palladium separation from radioactive liquid wastes.

Effect of aqueous phase structuring on the properties of model emulsion films stabilized with solid microsized particles

The thickness and stability of emulsion films stabilized with microsized silica particles are studied. The stabilization mechanism is shown to be realized via the formation of a thixotropic gel in a dispersion medium.

Nano-sized silica supported Me2Si(Ind)2ZrCl2/MAO catalyst for ethylene polymerization

Nano-sized and micro-sized silica particles were used to support a zirconocene catalyst [racemic-dimethylsilbis(1-indenyl)zirconium dichloride], with methylaluminoxane as a cocatalyst. The resulting catalyst was used to catalyze the polymerization of ethylene in the temperature range of 40–70°C. Polyethylene samples produced were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Nano-sized catalyst exhibited better ethylene polymerization activity than micro-sized catalyst. At the optimum temperature of 60°C, nano-sized catalyst's activity was two times the micro-sized catalyst's activity. Polymers obtained with nano-sized catalyst had higher molecular weight (based on GPC measurements) and higher crystallinity (based on XRD and DSC measurements) than those obtained with micro-sized catalyst. The better performances of nano-sized catalyst were attributed to its large external surface area and its absence of internal diffusion resistance. SEM indicated that polymer morphology contained discrete tiny particles with thin long fiberous interlamellar links. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Promotion of allergic immune responses by intranasally-administrated nanosilica particles in mice

With the increase in use of nanomaterials, there is growing concern regarding their potential health risks. However, few studies have assessed the role of the different physical characteristics of nanomaterials in allergic responses. Here, we examined whether intranasally administered silica particles of various sizes have the capacity to promote allergic immune responses in mice. We used nanosilica particles with diameters of 30 or 70 nm (nSP30 or nSP70, respectively), and conventional micro-sized silica particles with diameters of 300 or 1000 nm (nSP300 or mSP1000, respectively). Mice were intranasally exposed to ovalbumin (OVA) plus each silica particle, and the levels of OVA-specific antibodies (Abs) in the plasma were determined. Intranasal exposure to OVA plus smaller nanosilica particles tended to induce a higher level of OVA-specific immunoglobulin (Ig) E, IgG and IgG1 Abs than did exposure to OVA plus larger silica particles. Splenocytes from mice exposed to OVA plus nSP30 secreted higher levels of Th2-type cytokines than mice exposed to OVA alone. Taken together, these results indicate that nanosilica particles can induce allergen-specific Th2-type allergic immune responses in vivo. This study provides the foundations for the establishment of safe and effective forms of nanosilica particles.

Interaction Forces between Microsized Silica Particles and Weak Polyelectrolyte Brushes at Varying pH and Salt Concentration

The AFM colloidal probe technique was used to measure the interaction between microsized silica spheres and annealed polyelectrolyte brushes made of poly(acrylic acid) (PAA) and poly(2-vinyl pyridine) (P2VP) in KCl solutions of various pH values and salt concentrations. The interaction energy showed a distance dependence that was affected strongly by the swelling and the electric properties of the brushes. Between PAA brushes and silica particles, a repulsive interaction has been observed for all pH values and salt concentrations reflecting the swelling of the brush with varying pH value and the transition from osmotic to salted brush regime with increasing KCl concentration. Force measurements between P2VP brushes and silica particles revealed a much more complex behavior: a steric repulsion by the swollen brush at low pH values, a complex interplay of attractive and repulsive forces at intermediate pH values and a short-ranged attraction between the collapsed brush and the silica particle at basic pH values and high salt concentrations. The results are interpreted in comparison with the Alexander de Gennes model and zeta potential and ellipsometric measurements.

Scouring-ball effect of microsized silica particles on operation stability of the membrane reactor for acetone ammoximation over TS-1

A ceramic membrane reactor system was developed for the continuous ammoximation of acetone to acetone oxime over titanium silicalites-1 (TS-1) catalysts. The effects of catalyst concentration and microsized silica particles on the performances of the membrane reactor system were examined in detail. For the membrane reactor system the optimal catalyst concentration is 17.0 g L −1, obviously higher than the one obtained from the previous experiments in a batch glass reactor, because the strong adhesion of TS-1 catalyst particles on the surface of the pipeline, the tank and the membrane leads to the decrease of effective catalyst concentration. Adding the microsized silica particles can effectively inhibit the decrease of TS-1 catalysts concentration in reaction slurry and improve the operation stability of the membrane reactor system significantly, benefiting from the scouring effect and the attachment of TS-1 particles on the surfaces of larger silica particles. According to the estimation of hydrodynamic forces acting on particles, microsized silica particles are hard to deposit on the contact surfaces at the studied conditions and therefore a longer stable operation of the membrane reactor system has been achieved.

Observation of silane coupling agents adsorbed on silica by solid state 1H NMR under fast magic angle spinning

The spectroscopy of the adsorbed silane coupling agent on micro-sized silica particles was observed by 1H solid state NMR (SSNMR) under fast magic angle spinning (MAS). We found that this is a fast and effective way to characterize the structure and dynamics of the thin layer of coupling agent on the surface of micro-sized silica. Compared with conventional 29Si NMR spectroscopy and other methods, the present proton solid state NMR is a promising method to characterize the adsorbed layer on micro-sized silica.

Ethylene polymerization over a nano-sized silica supported Cp2ZrCl2/MAO catalyst

Nano-sized and micro-sized silica particles were used to support Cp2ZrCl2/MAO catalyst for ethylene polymerization. Nano-sized catalyst exhibited much better ethylene polymerization activity than micro-sized catalyst. At the optimum temperature of 60 °C, nano-sized catalyst’s activity was 4.35 times the micro-sized catalyst’s activity, which was attributed to the large specific external surface area, the absence of internal diffusion resistance, and the better active site dispersion for the nano-sized catalyst. Polymers produced were characterized with SEM, XRD, DSC, and densimeter. SEM indicated that the resulting polymer morphology contained discrete tiny particles and thin long fiberous interlamellar links.

Influence of electrical stress voltage on cathode degradation of organic light-emitting devices

Our in situ experimental observations of the influence of electrical stress voltage on organic light-emitting device growth in dark spot areas are presented. We demonstrate the use of microsized silica particles to create uniformly sized defects on the protective layer. This is an efficient way to control the location and the number of dark spots. The growth in dark spot area was studied at different driving voltages from 0 up to 11 V. Dark field microscopy was used to monitor the dark spot size below the turn-on voltage. The bright field was used at or above the turn-on voltage. Our observations indicate that dark spot growth was strongly affected by the electrical stress voltage. A linear growth rate with respect to the voltage was observed with a fitting parameter better than 99.7% when the device is driven above the turn-on voltage. We interpret the dark spot growth in terms of the diffusion of moisture and oxygen accompanied by cathode layer chemical and physical changes.

P‐49: Dependence of Dark Spot Growth on Electrical Stressing Voltage in OLED Devices

AbstractThe formation of dark spot in OLED devices has long been identified as pinholes on the protective layer that creates pathways for water or oxygen permeation and causes the cathode delamination and chemical change. In this work, we demonstrate that using micro‐sized silica particles to create uniform sized defects on protective layer is an efficient way of controlling the location and the number of dark spots. The dark spot growth was then studied at different driving voltage in the range from turn on voltage to about 11V, dark field microscopy was used to observe dark spot growth behaviour when device is driven lower than turn on voltage. Our observations indicate that the growth was strongly affected by the electrical stressing voltage. In other words, the chemical and physical changes reflected by the growth are speeded up with the increasing driving voltage. We discuss possible mechanisms for these degradation processes also.