Large Silica Particles Research Articles

A near-infrared plasma membrane-specific AIE probe for fluorescence lifetime imaging of phagocytosis

Phagocytosis is a biological process that plays a key role in host defense and tissue homeostasis. Efficient approaches for realtime imaging of phagocytosis are highly desired but limited. Herein, an AIE-active near-infrared fluorescent probe, named TBTCP, was developed for fluorescence lifetime imaging of phagocytosis. TBTCP could selectively label the cell plasma membrane with fast staining, wash-free process, high signal-to-background ratio, and excellent photostability. Cellular membrane statuses under different osmolarities as well as macrophage phagocytosis of bacteria or large silica particles in early stages could be reported by the fluorescence lifetime changes of TBTCP. Compared with current fluorescence imaging methods, which target the bioenvironmental changes in the late phagocytosis stage, this approach detects the changes in the cell membrane, thus giving a faster response to phagocytosis. This article provides a functional tool to report the phagocytic dynamics of macrophages which may greatly contribute to the studies of phagocytic function-related diseases.

Controlling Factors of the Particle Size of Spherical Silica Synthesized by Wet and Dry Processes

We clarified the controlling factors of the particle size of the amorphous silica synthesized by wet and dry processes. In the wet process using methyl-trimethoxy-silane as a starting monomer, the obtained particle size can be easily controlled by changing the reaction time appropriately. However, to obtain larger particles, a relatively long time is needed. After the condensation reaction was conducted for 50h, the silica particles (D50: 3?m) were synthesized by calcination at 550oC in air. To synthesize larger silica particles, we used silica-seed particles (8?m) to obtain very large spherical silica particles (D50: 20?m). Thus, although the wet process needs a relatively long reaction time, it is very useful for synthesizing spherical silica particles with a wide range of particle size. In the dry process, we used methyl-trimethoxy-silane (MTMS), tetra-ethoxy-silane (TEOS), and octamethyl-cyclotetrasiloxane (OMCTSO) as the starting materials. In this process, the size of the silica particles was dominated by the molecular structure of the monomer, in particular, the number of silicon atoms contained in the monomer and the bulkiness of the substituent group. The largest silica particles were synthesized from OMCTSO, which contains the largest number of silicon atoms.

Controlling Factors of the Particle Size of Spherical Silica Synthesized by Wet and Dry Processes

We clarified the controlling factors of the particle size of the amorphous silica synthesized by wet and dry processes. In the wet process using methyl-trimethoxy-silane as a starting monomer, the obtained particle size can be easily controlled by changing the reaction time appropriately. However, to obtain larger particles, a relatively long time is needed. After the condensation reaction was conducted for 50h, the silica particles (D50: 3μm) were synthesized by calcination at 550oC in air. To synthesize larger silica particles, we used silica-seed particles (8μm) to obtain very large spherical silica particles (D50: 20μm). Thus, although the wet process needs a relatively long reaction time, it is very useful for synthesizing spherical silica particles with a wide range of particle size. In the dry process, we used methyl-trimethoxy-silane (MTMS), tetra-ethoxy-silane (TEOS), and octamethyl-cyclotetrasiloxane (OMCTSO) as the starting materials. In this process, the size of the silica particles was dominated by the molecular structure of the monomer, in particular, the number of silicon atoms contained in the monomer and the bulkiness of the substituent group. The largest silica particles were synthesized from OMCTSO, which contains the largest number of silicon atoms.

Gravity effect of silica and polystyrene particles on deposition pattern control and particle size distribution on hydrophobic surfaces

Ring-like residual deposits are often observed after drying suspension droplets on surfaces. That introduces a crucial defect in practical applications, such as ink-jet printing that requires a uniform deposit. In this study, depositions after drying sessile/pendant droplets with silica/polystyrene particles were examined to identify the effect of gravitational sedimentation of particles on self-pinning and deposition pattern. The suspension droplet with larger polystyrene (or silica) particles would trigger the self-pinning at larger (or smaller) particle concentrations. The deposition pattern of pendant drops with silica particles is hill-like. This is due to the large density difference between silica and water to induce high sedimentation velocity, and the particles would precipitate and aggregate along the air–liquid interface to form a hollow shell deposit. The depositions for suspensions with bi-dispersed particles, the larger silica particles would accumulate at the bottom of the deposit due to the higher sedimentation velocity, in contrast to the well-mixed in the deposits for bi-dispersed polystyrene particles. The sedimentation and capillary flow velocities were calculated and discussed. These new findings reveal that the particle density (gravity effect) can be used to adjust the sedimentation velocity to control the deposition morphology and particle size distribution even to suppress the coffee-ring effect.

Noniridescent structural color from enhanced electromagnetic resonances of particle aggregations and its applications for reconfigurable patterns

Hypothesis: The conventional noniridescent structural colors refer to the coherent scattering of visible light by the short-range ordered structures assembled from the small colloids (100–250 nm). Our hypothesis is that noniridescent structural color can be generated by the random aggregations of large silica particles through the enhanced electromagnetic resonances.Experiments: The random aggregations of large silica particles (350–475 nm) were prepared through the infiltration of silica particles solution with the porous substrate. The mechanism of the structural color is investigated. Reconfigurable patterns are prepared.Findings: Dissimilar to the conventional noniridescent colors, the angle-independent colors of silica aggregations originate from the enhanced electromagnetic resonances due to the random aggregation of the particles. The colors (blue, green, and red) and corresponding reflection peak positions of the particle aggregations can be well controlled by simply altering the size of the silica particles. Compared to the traditional prints with permanent patterns, reconfigurable patterns with large-area and multicolor can be fabricated by the repeatedly selective spray of water on the substrate pre-coated with noniridescent colors. This work provides new insight and greenway for the fabrication of noniridescent structural colors and reconfigurable patterns, and will promote their applications in soft display, green printing, and anti-counterfeiting.

Systematic preparation of high‐quality colloidal silica particles by sol–gel synthesis using reagents at low temperature

AbstractWe propose a new approach to obtain monodisperse submicrometer‐sized colloidal silica particles prepared via a modified Stöber synthesis method, leading to high‐quality spherical particles with a narrow size distribution. The novelty of this work consists in setting, previously to the synthesis reaction, the initial temperature of the reagents at low values (6−14°C) in comparison to the constant laboratory room temperature, while fixing other experimental parameters such as humidity and reagent concentrations. A series of samples of monodisperse colloidal silica particles were prepared, with diameters ranging from 600 to 1000 nm and exhibiting quite narrow particle size distributions. According to our results, it was established that the initial temperature of the reagent solutions constitutes a remarkable parameter, affecting the particle size, shape, and monodispersity. This experimental approach even allows the size tunability for the synthesis of large spherical silica particles in a one‐step process. Moreover, in combination with spin‐coating deposition, the proposed technique greatly favors the formation of ordered arrays of monodisperse silica particles over silicon substrates in areas as large as several mm2. This is ideal for thermal insulators, photonic crystals, nanosphere lithography, and other engineering and industrial applications requiring high‐quality extended arrays of monodisperse silica particles.

Three phase corrosion of pipeline steel: Size effects of deposited solids under water droplets and an oil diffusion barrier

Existing studies have examined either under deposit corrosion in bulk solutions or underoil droplet corrosion without deposits. Yet, neither of these scenarios represents the conditions existing within a diluted bitumen pipeline where underoil droplet corrosion occurs in tandem with under deposit corrosion. Herein, this industrially important 3-phase system – solid deposit, aqueous droplet, oil cover – is studied for the first time. In particular, the relationship between varying deposit particle size and underoil droplet corrosion is established. Scanning electron microscopy coupled with profilometry was used to monitor droplet corrosion over time for API-X100 pipeline steel covered with different sized silica particles underneath simulated diluted bitumen. A zero resistance ammeter was used to validate the observed corrosion from the immersion experiments. The data indicate that localized corrosion coupled with uniform corrosion occurred beneath the large (80% of the cumulative particle size distribution less than 540 µm) and small (80% of the cumulative particle size distribution less than 43 µm) silica covered underoil droplets on API-X100 pipeline steels after 24 h of exposure. The underoil droplet corrosion of silica covered steel has maximum localized penetration predominantly around the silica pile perimeter. With continued exposure, up to 240 h, the corrosion beneath the two sizes of silica continues to develop with a difference in rate. The maximum penetration rate (13.58±0.76 mm/year) of localized corrosion under the large silica particles was higher than that (10.02±0.87 mm/year) of the localized corrosion beneath the small silica particles.

Tetrabutylammonium bromide assisted preparation of monodispersed submicrometer silica particles

In this work, we demonstrate a new, facile approach for preparation of monodispersed, submicrometer silica particles via a tetrabutylammonium bromide (TBABr) assisted Stöber method. Sizes of the resulting silica particles increased from 0.39 to 1.08 μm with polydispersity lower than 5 % while the concentration of TBABr in the reaction media was elevated from 0 to 20.0 mM. The presence of TBABr molecules was able to effectively suppress the condensation rate of silanol monomers during the Stöber reaction, which, in turn, slowed the formation of silica seeds and thus accounted for growth of large silica particles. The use of tetraethylammonium bromide (TOABr), a quaternary ammonium agent with longer alkyl chains, instead of TBABr, yielded monodisperse silica particles more hydrophobic in character, making it feasible to tailor the surface properties of the as-prepared silica particles.

Improved Packing Model for Functionally Graded Sand-Fines Mixtures—Incorporation of Fines Cohesive Packing Behavior

Binary soil mixture, containing large silica particles (sand) mixed with variable content of very fine silt or clay, is an example of a functionally graded material that is important for several science and engineering applications. Predicting the porosity (or void ratio), which is a fundamental quantity that affects other physical properties, of such material as function of fines (clay or silt) fraction can be significant for sediment research and material design optimization. Existing analytical models for porosity prediction work well for binary mixed soils containing multi-sized non-cohesive particles with no clay, while such models frequently underestimate the porosity of sand-clay mixtures. This study aims to present an analytical model that accurately predicts the porosity of mixed granular materials or soils containing sand and very fine silt or clay (cohesive particles). It is demonstrated that accounting for the cohesive nature of very fine particles, which exists due to the effect of inter-particle forces, is a major missing aspect in existing packing models for mixed soils. Consequently, a previously developed linear packing model is modified so that it accounts for fines cohesive packing in sand-fines mixtures. The model prediction is validated using various experimental published data sets for the porosity of sand-fines mixtures. Improvement in the prediction of permeability and maximum packing dry density when incorporating cohesive packing behavior is discussed. The current model also provides important insights on the conditions under which, the lowest permeability and maximum packing state are expected.

Tetraethylorthosilicate-containing barrier dispersion coatings—Mechanism of action

We demonstrate the use of tetraethylorthosilicate (TEOS) as a silica precursor for water barrier poly(styrene-butadiene) latex dispersion coating applications. The TEOS is adsorbed at the surface interface by the latex particles in the aqueous dispersion due to the hydrophobic nature of the surface and the TEOS. It then undergoes hydrolysis and condensation to the silica phase in the interstitial sites in the partially dry close-packed polymer structure. The fully cured film exhibits a greater degree of coalescence than films prepared from the unmodified latex binder. Large discrete silica particles are not formed within the cured film; rather the films contain homogenous silica dispersion with a probable particle size no larger than 10 nm. This higher degree of coalescence results in improvements in water vapour barrier performance from 121 – 20 g m−2 d−1, with direct water barrier performance (Cobb 120 s) improving from 25 to < 2 g m−2, compared to the silica-free film.

Effects of mixed ultrafine colloidal silica particles on chemical mechanical polishing of sapphire

The effects of ultrafine colloidal silica particles adsorbed on the surfaces of large silica particles in slurries used for the chemical mechanical polishing of sapphire were studied. Sapphire wafers were polished using hybrid silica particles that were composed of a mixture of ultrafine (4 nm) colloidal silica particles and large (20, 55, and 105 nm) silica particles. Dynamic light scattering results showed that the hybrid particles became larger after mixing. Transmission electron microscopy images revealed that the ultrafine particles adhered to the surfaces of the large particles and that the surface shape of the hybrid particles were changed by the mixing process. Atomic force microscopy and polishing results showed that the surface roughnesses and material removal rates of sapphire substrates were improved by using the hybrid particles. The coefficient of friction between the surface of the sapphire substrate and the hybrid particles was higher than that obtained using single-sized particles. These results confirm that the hybrid silica particles enhanced the performance of sapphire polishing.

Foam and thin films of hydrophilic silica particles modified by β-casein

HypothesisFoaming properties of particle dispersions can be modified by addition of amphiphiles. The molar ratio between particles and amphiphiles will influence the wetting properties of the particles as well as the bulk concentration of the amphiphiles. This will have an effect on air/water interfacial composition as well as on the thin film and foam stability of the mixed system. ExperimentsIn this research foams and thin films of hydrophilic silica particles in presence of β-casein (β-CN) were investigated with different particle sizes and varying β-CN/silica weight ratios (between 1:10 and 1:100). Samples were characterized for particles size, morphology as well as contact angle and related to their foaming, interfacial, and thin film properties. FindingsA threshold weight ratio of β-CN/silica was found to be 1:50 for foam stabilization with mixtures containing silica particles no larger than 1 μm and 1:30 for film stabilization with mixtures containing larger particles. At the interface, the modified silica particles were rather diluted without much interaction for surface compressions up to 30%. Large silica particles (0.0015% β-CN, Csilica ≤ 0.15%) were dragged to the periphery of the thin liquid films but no decrease of the inner film draining rate by a decrease of capilary pressure gradient across the film was observed. The depletion of β-casein in the bulk by particles played a major role in foam destabilization.

In-situ synthesis and textural evolution of the novel carbonaceous SiC/mullite aerogel via polymer-derived ceramics route

Abstract A novel carbonaceous SiC/mullite composite aerogel is derived from catechol-formaldehyde/silica/alumina hybrid aerogel (CF/SiO 2 /AlOOH) via polymer-derived ceramics route (PDCR). The effects of the reactants concentrations on the physicochemical properties of the carbonaceous SiO 2 /Al 2 O 3 aerogel and SiC/mullite aerogel are investigated. The mechanism of the textural and structural evolution for the novel carbonaceous SiC/mullite is further discussed based on the experimental results. Smaller reactants concentration is favorable to formation of mullite. Reactants concentration of 25% is selected as the optimal condition in considering of the mullite formation and bulk densities of the preceramic aerogels. Spherical large silica particles are also produced during heat treatment, and amorphous silica is remained after this reaction. With further heat treatment at 1400 °C, silicon carbide and mullite coexist in the aerogel matrix. The mullite addition decreases the temperature of SiC formation, when compared with the conventional methods. However, after heat treatment at 1450 °C, the amount of mullite begins to decrease due to the further reaction between carbon and mullite, forming more silicon carbide and alumina. The carbonaceous SiC/mullite can be transferred to SiC/mullite binary aerogel after carbon combustion under air atmosphere. The carbonaceous SiC/mullite has a composition of SiC (31%), mullite (19.1%), SiO 2 (14.4%), and carbon (35%). It also possesses a 6.531 nm average pore diameter, high surface area (69.61 m 2 /g), and BJH desorption pore volume (0.1744 cm 3 /g). The oxidation resistance of the carbonaceous SiC/mullite is improved for 85 °C when compared with the carbon based aerogel.

Synthesis and characterization of polyaniline-silica composites: Raspberry vs core-shell structures. Where do we stand?

The synthesis of polyaniline-silica composites has been reinvestigated in view of the opposing results found in the literature. Firstly, we synthesized silica particles with tunable size using the Stöber process. These silica particles have been fully characterized before being used as solid support for the polymerization of aniline. This polymerization was performed according to a published procedure where the pH of the reaction mixture was below the pKa of aniline but at a value where the silica particles surface was still slightly negatively charged. The objective of this procedure was to favor electrostatic interactions between anilinium cations and the silica surface to lead to the formation of silica-polyaniline core-shell particles. Several sets of nanocomposites were prepared under different experimental conditions (oxidant/aniline ratio, silica concentration, temperature, silica particles diameters). The study evidenced that under all the conditions used the formation of core-shell nanoparticles is impossible. However, using different particle sizes, noticeable morphological differences were observed. The use of large silica particles led to the formation of non-uniform polyaniline-silica composites whereas the use of smaller particles always led to raspberry-like morphology as reported by other groups in highly acidic media. The difference in morphology led to different electrical properties with electrical conductivities measured at room temperature ranging from 1.6×10−3 to 2.5×10−5S cm−1.

The Effect of Silica Abrasive Particle Sizes in Polyester Based Composite on the Tribological Properties of Ti64

Investigation of the tribological characteristics of Ti6Al4V (Ti64) was performed by using a pin-on-disc tribometer. Polymer composites composed of a polyester resin matrix and silica abrasives with two different particle sizes were used as the counterface pin material. The macro and micro surface features on the wear track in relation to different abrasive particle sizes were analyzed by using optical microscope and scanning electron microscope. The wear depth was monitored by utilizing surface profiler and the change in hardness of Ti64 was measured by using Vickers hardness tester before and after the test. The effect of sliding speeds on the coefficient of friction was also studied. During sliding against Ti64 substrate, the results showed lower coefficient of friction, smoother surface features, and lower wear rate for the case of the polymer composite pin with smaller silica particles size when compared to that of polymer composite pin with larger silica particles size. The higher sliding speed generated more wear debris, much deeper wear depth, and wider wear track on Ti64 substrate.

Analytical on mixed colloidal silica particle in slurry of sapphire Chemical Mechanical Polishing

Mixed colloidal silica particles as abrasive in slurries have been proposed to improve and realize a high removal rate and smooth surface without subsurface damage, on sapphire chemical mechanical polishing (CMP). Mixed silica particles were fabricated by different sizes of nano-silica particle with the range of pH 7-13. The characteristics of the mixed large and small silica particles has been observed. Dynamic light scattering (DLS) spectra results revealed that the structure of the mixed particle, the small particle at the size of 4 nm are adsorbed on the large silica particles and increase in the size of the abrasive particles. Furthermore, we found that pH value affected to abrasive particle size. In these cases, our polishing tests results show that material removal rate (MRR) of the sapphire CMP totally increase. This confirmed that mixed particles could produce a higher MRR than single colloidal silica slurry. Finally, the mechanism of sapphire removal was discussed.

Double cross-linking PVA-SiO2 hybrid membranes for alkali recovery

Abstract Non-charged PVA-SiO2 hybrid membranes are prepared through sol-gel process among polyvinyl alcohol (PVA) and double cross-linking agents, which are selected from four types of alkoxysilanes including tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), γ-aminopropyl triethoxysilane (APTEOS) and methacryloxypropyl trimethoxy silane (MPS). The double cross-linking agent can combine their advantages including different hydrolysis rates of OC2H5 and OCH3 groups, high compatibility of NH2, and polymerizable C C bonds. The NH2 group from APTEOS can enhance membrane homogeneity, thermal stability and flexibility due to its compatibility with PVA–OH groups. The membranes have high selectivity (62–101) but low permeability in diffusion dialysis process for separating NaOH/Na2WO4 solution. Single type of Si(OCH3) groups produces large silica particles (1.5–5μm), which reduce membrane stability but enhance permeability. The membrane has low strength and flexibility, and high swelling degrees in 65 °C water (373–408%) and weight loss percentage in 65 °C NaOH solution (25.8–28.7%). The permeability can reach up to 0.0076–0.0092 m/h but the selectivity is only 23.7–25.0 at 20–40 °C. The combination of Si(OCH3) and Si(OC2H5) groups (TEOS and MPS) can obtain high strength and flexibility (20.3 MPa, 571%), acceptable swelling degrees (232–279%) and balanced permeability and selectivity (0.0043–0.0071 m/h, 45–110). Hence, double cross-linking agents can be combined to prepare optimized neutral membranes for diffusion dialysis.

Formation of organic–inorganic nanomatrix structure with nanosilica networks and its effect on properties of rubber

Abstract Graft-copolymerization of vinyl monomer containing silica precursor, p -styryltrimethoxysilane, onto natural rubber microparticles was performed in latex stage to form three-dimensional networks of nanosilica. After the latex was cast into a film, morphology observation by transmission electron microscopy showed that the natural rubber microparticles were dispersed in organic–inorganic nanomatrix consisting of vinyl polymer and silica nanoparticles. In particular, generation of large silica particles was prevented by slow rate of hydrolysis and condensation of silicon alkoxides for p -styryltrimethoxysilane and the nanosilica networks were formed. The nanomatrix structure with the nanosilica networks increased tensile strength of the rubber, and destruction of the structure decreased the strength. Master curves of dynamic moduli of the rubber showed that the value of storage modulus at rubbery plateau region was high and it was almost flat at low-frequency region because of the nanosilica networks.

Immobilization of silver nanoparticle-decorated silica particles on polyamide thin film composite membranes for antibacterial properties

We present a new strategy to strongly and effectively immobilize silver nanoparticles (AgNPs) on polyamide thin film composite membranes to endow antibacterial activity. This method relies on the immobilization of relatively large silica particles (SiO2, ~400nm in diameter), where AgNPs of ~30nm in diameter are tightly and densely bound (AgNP@SiO2), on the membrane surface using cysteamine as a covalent linker. The formation of multiple Ag–S chemical bonds between a “bumpy” AgNP@SiO2 and the rough membrane surface provides a great leaching stability of AgNPs and AgNP@SiO2. AgNP@SiO2 particles were well distributed over the entire membrane surface without severe aggregation. The surface coverage of the membrane by AgNP@SiO2 was tuned by adjusting the deposition time and AgNP@SiO2 particle concentration. The AgNP@SiO2-immobilized membrane showed excellent antibacterial properties against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, even with a relatively low particle coverage. Importantly, the separation performance (water flux and salt rejection) of the membrane was not impaired by particle immobilization. These beneficial effects are attributed mainly to the sparse and good distribution of AgNP@SiO2, which can reinforce the antibacterial activity of AgNPs while having a negligible impact on the hydraulic resistance.

Construction of an Interconnected Nanostructured Carbon Black Network: Development of Highly Stretchable and Robust Elastomeric Conductors

In the present work, a strong filler–filler network of conductive carbon black was strategically established in an elastomer matrix, which leads to a unique combination of electrical and mechanical properties. The novelty of our composites was the development of a strong percolated morphology of nanostructured conducting carbon black particles by the incorporation of relatively large nonreinforcing spherical silica particles, inside the soft elastomer matrix. This technique allowed us to fabricate solution styrene butadiene rubber (S-SBR) composites with outstanding electrical conductivity of 40 S/m, tensile strength ∼10 MPa, and extensibility up to 200%. Furthermore, the electrical conductivity was strain-independent up to 50% elongation strain. The electrical conductivity was found to be unaltered after 2000 loading–unloading cycles. This is the first ever report of a robust elastomeric system with such high electrical conductivity where all the basic ingredients used were selected from well-known comme...