Submicron Silica Research Articles

Light-extraction enhancement and directional emission control of GaN-based LEDs by self-assembled monolayer of silica spheres

The light extraction of 1 × 1 mm(2) GaN-based blue light-emitting diodes (LEDs) was enhanced by a self-assembled monolayer (SAM) of silica submicron spheres. The silica spheres were synthesized with various spherical sizes via the ammonia-catalyzed hydrolysis and condensation of tetraethyl orthosilicate in water/ethanol solutions. Hexagonal closely-packed (HCP) silica sphere monolayer was formed onto the indium tin oxide layer of the LED by a spin coating process. The size effect of silica spheres on the light-extraction efficiency (LEE) of GaN-based LEDs was theoretically studied and their optimum size was determined. The simulation results showed that the use of silica spheres can improve the LEE by 1.1-1.32 times compared to the conventional LEDs. The light output power of the LED with 650-nm-thick SAM of HCP silica spheres was experimentally enhanced by 1.28 and 1.23 times under the injection currents of 100 and 350 mA, respectively. By employing the SAM of HCP silica spheres, the directional emission pattern was relatively converged, indicating a reasonable consistency with the simulation result.

Stability in Air of Silver and Silver Oxide Nanoparticle Shells Deposited Over Silica Spheres Without Using Coupling Agents

The deposition of silver nanoparticles on the surface of silica was carried out using our simple, robust and rapid chemical method without surface modification of silica or added coupling agents. The process was carried out at room temperature using water/methanol mixtures, tetraethyl orthosilicate as Si source and silver nanoparticles (NPs) in a single-pot reaction. Using EDS, XRD, HRTEM and High Angle Annular Dark Field (HAADF) STEM characterization techniques, we have found the coexistence of silver NPs and silver oxides NPs anchored to the surface of sub-micron silica spheres, with Ag NPs predominating sizes around 2-3 nm approximately, and Ag2O NPs sizes over 10 nm.

Flow injection chemiluminescence sensor using core-shell molecularly imprinted polymers as recognition element for determination of dapsone

This paper reports the preparation of dapsone (DDS) imprinted polymer layer-coated silica submicron particles (SiO(2)) combined with chemiluminescence (CL) toward analysis of tracing DDS in practical samples. To induce the selective occurrence of surface polymerization, the amino groups were first grafted at the surface of SiO(2) by the (3-aminopropyl)triethoxysilane (APTES). The molecularly imprinted polymers (MIP) were coated at the surface of modified SiO(2) by the graft copolymerization. After the removal of templates, recognition sites of DDS were exposed in the polymer layers. The DDS-imprinted products were characterized by FT-IR, SEM, TEM, dynamic adsorption, and static adsorption tests. The proximity between the thickness of MIP layer and the spatial size of DDS indicated that the imprinted sites almost situated at the surface of MIP, leading to rapid adsorption saturation within 90 min. The apparent maximum binding amount of MIP toward DDS was evaluated as 14.98 mg·g(-1), which was much higher than that of non-molecularly imprinted polymers. The CL sensor provided a wide linear range for DDS within 1.0 × 10(-6) to 1.0 × 10(-4) mol·L(-1) with a detection limit of 5.27 × 10(-7) mol·L(-1) and the relative standard deviation of 1.8 % (n = 11) by determinations of 5.0 × 10(-6) mol·L(-1) DDS. This method was applied to determine DDS in urine samples and satisfactory results were obtained.

Whole-body distribution of 14C-labeled silica nanoparticles and submicron particles after intravenous injection into Mice

We analyzed the whole-body distribution of 14C–ADP-labeled silica nanoparticles (14C–ADP–SiO2 nanoparticles) and submicron particles (14C–ADP–SiO2 submicron particles) after intravenous injection into ICR mice. The 14C–ADP–SiO2 nanoparticles and submicron particles were synthesized before the injection and the particle size was 19.6 and 130 nm, respectively. Similarly, the shape was spherical and the crystallinity was amorphous. After the synthesis, we injected mice with the 14C–ADP–SiO2 nanoparticles or the 14C–ADP–SiO2 submicron particles and dissected tissues after 1, 2, 4, 8 and 24 h. The radioactivity in the tissues was measured with a liquid scintillation counter. As a result, the retention percentage in bone, skin, lymph nodes, and the digestive mixture was at least twofold higher in the 14C–ADP–SiO2 nanoparticles-exposed mice, whereas the retention percentage in the kidney was statistically higher in the 14C–ADP–SiO2 submicron particles-exposed mice. Both types of 14C–ADP–SiO2 particles mainly translocated to the muscle, bone, skin, and liver, but hardly translocated to the brain and olfactory bulb. Furthermore, the 14C–ADP–SiO2 nanoparticles had a higher retention percentage (62.4 %) in the entire body at 24-h post-injection than did the 14C–ADP–SiO2 submicron particles (50.7 %). Therefore, we suggested that the 14C–ADP–SiO2 nanoparticles might be more likely than the 14C–ADP–SiO2 submicron particles to be retained in the body, and consequently they might be gradually accumulated by chronic exposure.

New Submicron Silica Produced by the Fumed Process

Submicron silicas produced by fumed processes and their corresponding surface-modified counterparts are compared with respect to their applicability as external additives for electrophotographic toners. The principal metric for comparison is tribo-electrostatic charge (T-ESC) stability under extended activation periods. Experimental samples are surface-modified submicron silicas produced by a fumed process. These materials have sufficient hydrophobicity and can work as spacer particles to prevent the embedding of small particle size external additives. This spacer-attribute thereby eliminates problems with charge stability and flowability, especially under extreme environmental conditions, that can impact toner performance.

Effect of Annealing on Ag-Doped Submicron Silica Powder Prepared with Modified Stöber Method

Antibacterial silver can be used against such micro-organisms as bacteria and molds. When Ag nanoparticles are attached to an inorganic carrier, e.g., silica long-term antimicrobial functionality can be gained. Such Ag-SiO2particles are potential for water purification or bactericidal applications. In this work, submicron sized silica particles doped with Ag were prepared by the modified Stöber method. The as-prepared powder was air-dried and annealed for 75 minutes at 573, 673, 773, 873, 973, 1073, 1173, or 1273 K in air. The powders were studied by DSC/TGA, XRD, SEM, TEM and UV-vis methods. The as-prepared powder consisted of round silica particles having size around several hundred nanometers. XRD and SEM studies confirmed that the powder consisted of metallic silver nanoparticles on the submicron silica surface after annealing at 873 K or higher. According to the SEM study the silver particles had an average particle size between 19-400 nm depending on the annealing temperature. DSC was used to determine the phase transformation temperatures. After annealing the Ag-SiO2powder at 873 K the TEM study suggested that the silver had crystalline structure. The XRD studies confirmed that silver appeared as a FCC crystal structure. The UV-vis measurements of Ag-SiO2powder annealed at and below 773 K showed a steady increase in absorption with decreasing wavelength without absorption peaks. Annealing at 873 K and above resulted in a strong peak in between 404 nm and 416 nm. This peak can be attributed to the surface plasmon resonance of silver nanoparticles.

Double modes characterization and incident light angle tuning on the photonic band gap of SiO2 colloid crystal

AbstractPhotonic crystal of packed monodisperse silica submicron spheres were synthesized in this article. We investigated the optical properties of packed monodisperse silica submicron spheres by means of both optical transmission and reflection measurements. Research suggests that the two methods are consistent in essence, and the reflection mode is more suitable for colloidal crystal assembled of smaller colloidal spheres. Accurately tuning of photonic band gap by incident light angle was also studied in our article. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26156

Preparation of pore size controllable macroporous polymer beads

Macroporous polymer beads have been used in various fields, for example as solid supports in solid-phase organic synthesis and heterogeneous catalysts and as adsorbents in column chromatography. Their broad applications have stimulated many researchers to develop various kinds of macroporous polymer beads. However, despite all the efforts, it is still hard to control the porosity and pore size distributions within the polymer beads. In this study, we prepared pore size controllable macroporous poly(methyl methacrylate-co-methyl methacrylic acid) (PMMA-co-PMAA) beads. First, we prepared silica submicron particles embedded PMMA beads by the polymerization of methyl methacrylate monomer with mono-dispersed silica particles. Then, the silica NP embedded PMMA beads were hydrolyzed with sodium hydroxide to obtain a macroporous structure by removing the embedded silica particles. At the same time, part of the methyl methacrylate turned into methacrylic acid, which caused the PMMA beads to become PMAA-co-PMMA beads. Through this method, two types of beads having different pore sizes were prepared as a model study. The pore size of the beads could be easily controlled by adjusting the size of the silica particles.

A simple and compact blue diode laser powered excitation source for fluorescence detection in capillary electrochromatographic microchip separation

A simple and compact fluorescence excitation source was prepared using a 405nm blue laser diode module and characterized in capillary electrochromatographic or capillary electrophoretic microchip separation. An inexpensive blue laser diode module with a tiny focusing lens was simply mounted at the center of an aluminum block on a miniature linear motion guide for heat dissipation and position control. A slit unit has a series of fifteen laser-machined slits with 1mm space along the direction of the separation channel of the microchip above this unit. The laser beam was focused through a slit with 50μm width to the separation channel at the position of a desired length. Although the excitation source unit was connected to a simple current controlled power supply, it was stable with 0.1% drift per hour and 1.3% (1σ) fluctuation in intensity. This simple excitation source can be prepared easily with inexpensive minimum optical components and mounted with a microchip on the stage of an ordinary fluorescence microscope for daily separation studies using a CE or CEC microchip. The applicability of the excitation source was evaluated with FITC-amino acid derivative mixtures using a polymer based CEC microchip packed fully with submicron silica beads in its microchannel.

Uptake and intracellular localization of submicron and nano-sized SiO2 particles in HeLa cells

Engineered amorphous silica nanoparticles (SiO(2)-NPs) are widely used in dyes, varnishes, plastics and glue, as well as in pharmaceuticals, cosmetics and food. Novel composite SiO(2)-NPs are promising multifunctional devices and combine labels for subsequent tracking and are functionalized e.g. to specifically target cells to deliver their cargo. However, biological and potential toxic effects of SiO(2)-NPs are insufficiently understood. The aim of this study was to determine the uptake and fate of SiO(2)-NPs in mammalian cells. Also, silica submicron particles (SiO(2)-SMPs) were included in the studies in order to identify effects, which are only observed for nano-sized SiO(2) particles. Fluorescently labelled SiO(2)-NPs (nominal size 70 nm) and SiO(2)-SMPs (nominal size 200 and 500 nm) were used to examine cytotoxicity, cellular uptake and localization in human cervical carcinoma cells (HeLa). Particle uptake and intracellular localization in mitochondria, endosomes, lysosomes and nuclei were studied by wide field and confocal laser scanning fluorescence microscopy. Physicochemical characterization of SiO(2)-NPs by transmission electron microscopy and dynamic light scattering revealed a spherical morphology and a monodisperse size distribution. In the presence of serum, all SiO(2) particles are non-toxic. However, in the absence of serum SiO(2)-NPs but not SiO(2)-SMPs are highly toxic. SiO(2) particles, irrespective of size, were detected in the cytosol and accumulated in endosomal compartments of HeLa cells. No accumulation of SiO(2) particles in nuclei or mitochondria of HeLa cells could be observed. In contrast to SiO(2)-SMPs, SiO(2)-NPs are preferentially localized in lysosomes.

Designing photonic band gaps in SiO<sub>2</sub>-based face-centered cubic-structured crystals

We designed face-centered cubic-structured (fcc) photonic crystals whose lattice parameters were tuned by varying the size of the constituent spherical silica particles in the range 100 to 520 nm. From wide-angle optical transmission investigations and Gaussian fitting of the absorbance spectra over UV-Vis-Near IR range, we found that in these crystals the Bragg wavelengths of the photonic band gaps (PBGs) corresponding to the reflected crystal planes linearly increase with the size of the spheres as expected. From this data, the average refractive index along the different crystal planes of the fcc structure was found to be in the 1.24 to 1.32 range. The Bragg wavelengths were tuned between 400 and 1100 nm. Thus, photonic crystals of the same structure can be designed to tune the Bragg wavelengths of PBGs by selecting the sphere size. These studies open up possibilities to design a new class of "smart" photonic crystals consisting of dielectric entities of sub-micron silica spheres with added functionality from magnetic or piezoelectric nanoparticles embedded in them.

Surface roughness and EDS characterization of a Y-TZP dental ceramic treated with the CoJet™ Sand

Objectives (1) To determine the surface roughness and material loss of a Y-TZP ceramic before and after tribochemical grit blasting and (2) to characterize the changes in elemental surface composition and the phase transformations after tribochemical treatment. Methods Machined bar shaped specimens (Zeno, Wieland) were subdivided into three groups. After grit blasting for 10, 20 and 30 s respectively, half of the specimens of each group were ultrasonically cleaned in ethanol for 10 min. The other half was rinsed with a water spray. Surface roughness was measured using an electro-mechanical profilometer. The elemental composition of the samples was obtained by energy dispersive X-ray spectroscopy (EDS). X-ray diffraction (XRD) was used for phase transformations determination. Results The median Ra increased significantly from 0.24 to 0.32–0.38 μm after grit blasting. Augmentations were also noted for R max, R v and R p. The highest roughness parameters were, obtained for water sprayed specimens and samples abraded for 30 s. Loss of material ranged between 1 and 3 μm for 30 s grit blasting. Tetragonal and cubic phases were identified in ‘as machined’ specimens. Grit blasting resulted in domain switching and lattice deformations. The elemental composition comprised Si and Al. The duration of grit blasting did not significantly, influence the atomic percentages of Si or Al. Significantly lower values for both Si and Al were noted, after ultrasonic cleaning. Significance Grit blasting with CoJet™ Sand resulted in an increase of surface roughness, a removal of maximum 3 μm of material and coated the surface with submicron silica and alumina particles.

Sparsely-distributed silica/PMMA composite particles prepared by static polymerization in aqueous silica dispersion

Silica/poly(methyl methacrylate) (PMMA) composite particles, in which silica particles are sparsely distributed in the surface of PMMA particles, were formed by static dispersion polymerization of methyl methacrylate (MMA) in aqueous dispersions of submicron silica particles. The silica-modified PMMA particles were constructed via Pickering emulsion-like silica/PMMA aggregation based on weak interaction between PMMA and silica. The morphology of the composite particles is governed by the adsorption/partition equilibrium of PMMA with the silica surface.

Classification of Submicron Silica Particles Using Electrophoretic Phenomenon

The effect of pH, and the concentration of KNO3 and LiNO3 on the electrophoretic mobility and zeta potential of fine silica particles having a different median particle size were studied in order to classify submicron silica particles by electrophoretic phenomenon. The silica particles of 0.05 μm or abradant silica particles (median diameter: 0.067 μm) and silica particles of 0.5 μm were classified by a batch and continuous classification equipment designed in our laboratory. The absolute values of electrophoretic mobility and zeta potential of silica particles are found to be increased with increasing pH. Electrolytes containing cations with different hydration number were added to the particles of 0.05 and 0.5 μm. The electrophoretic mobility of 0.05 μm particles in KNO3 solution is higher than that in LiNO3. On the other hand, electrophoretic mobility of 0.5 μm particles has almost the same value by the addition of two kinds of electrolytes. These results imply that electrophoretic effect works to smaller particles, while do not act large particles. The electrophoretic mobility decreases when the particle size becomes smaller because of strongly acting asymmetric effect and electrophoretic effect. On the other hand, the electrophoretic mobility decreases with increasing a particle size due to the resistance force with viscosity, when the particle size is larger than 1 μm. It is found that the electrophoretic mobility of particles mainly depends on the particle size. In the case of a batch type classification equipment, classification of fine and coarse particles is advanced by applying weak electric field for long period. Classification of fine and coarse particles with a continuous classification equipment shows the possibility of classification using electrophoretic phenomenon.

Influence of inlet flow rate, pH, and beads mill operating condition on separation performance of sub-micron particles by electrical hydrocyclone

Experimental studies have been carried out about the separation performance of a special electrical hydrocyclone. In this study, effect of inlet flow rate, applied electrostatic potential, pH, and beads mill operating condition on separation performance of a special electrical hydrocyclone were investigated. A 0.5 wt% suspension of sub-micron silica dispersed by the beads mill was used as the test powder. A 20 mm electrical hydrocyclone in diameter with 20% of underflow was examined. A negative center electrode was vertically inserted inside the conical section and the potential difference up to 100 V was applied between the conical wall and the center electrode in the hydrocyclone. By use of beads mill, it was found that the negative values of zeta potential increases with the increase of the particles diameter. It was found that the separation performance of the electrical hydrocyclone increases significantly with the decrease of inlet flow rate and increase of the electrostatic potential, while the separation performance shows a less significant increase as the pH of suspension increases. Under several times of milling by use of the same beads, the values of zeta potential were not constant. The negative zeta potential of suspension attains the highest value under six times of milling by use of the same beads. A new model, based on the diffusive mass transfer equation in the conical section of the electrical hydrocyclone has been developed, and compared to the experimental results. It is found that the calculated results by the new model shows a qualitative agreement with the experimental results.

Separation performance of sub-micron silica particles by electrical hydrocyclone

Separation performance of sub-micron particles by use of a special electrical hydrocyclone was studied. The effects of feed suspension waiting time, applied electrostatic potentials, and the feed suspension concentration, on the separation performance of the electrical hydrocyclone were investigated. An aqueous suspension of sub-micron silica particles with median diameter of about 0.2 µm was used as the test powder. A 20 mm diameter of electrical hydrocyclone operated at 20% of the underflow ratio was used. A negative center wire electrode was inserted vertically inside the conical section, and electrostatic potentials up to 100 V were applied in this electrical hydrocyclone. It was found that the 50% cut size of the electrical hydrocyclone increased with the increase of the feed suspension waiting time after a particle dispersion process by the beads mill. The classification of the sub-micron particles occurred under applied electrostatic potentials greater than about 40 V, while better classification performance was obtained with the increase of the applied electrostatic potentials. The 50% cut size decreased with the increase of the feed suspension concentration up to 1.5 wt.%, and further increasing of the concentration led to the increase of 50% cut size. A simple model based on the time of flight model, was developed in order to predict the 50% cut size of the electrical hydrocyclone. The model results qualitatively agreed with the experimental results. It was found that classification the sub-micron particles is possible by use of the special electrical hydrocyclone proposed in this study.

Dispersibility in organic solvents of nanosized silica particles used in semiconductor package substrates

This study examined the influence of different types of silane coupling agents on the dispersion of nanosilica particles with diameters of ca. 10 nm and 25 nm in two organic solvents, methylisobutylketone (MIBK) and cyclohexanone (CXN). The nanosilicas were prepared by the sol–gel process, and the following coupling agents were used: 3-glycidylpropyltrimethoxysilane (EpoSi), N-phenyl-3-aminopropyltrimethoxysilane (AmiSi), 3-mercaptopropyltrimethoxysilane (MerSi), and alkyltrimethoxysilane (AlkSi). While the 25-nm silica particles displayed dispersibility similar to that of submicron silica particles (ca. 150 nm and 250 nm), the dispersibility of the 10-nm silica particles proved to be dependent on the combinations of the agents and solvents; for example, EpoSi and MerSi were found to be suitable agents for MIBK and CXN, respectively. The slurries were also subjected to heating at 40 °C for 24 h, which resulted in a considerably higher stability of the dispersion state when CXN was employed as the solvent, regardless of which silica coupling agents were used. FTIR measurement revealed the presence of unreacted free Si–OH at 3740 cm −1 for some nanosilicas. Combustion of the organic moieties introduced onto the silica surfaces also proved that the amount of organic groups present in a unit surface area of the nanosilicas were only 1/3 or 1/2 of that found on submicron silicas. From these observations, the low dispersibility of the nanosilicas was inferred to be due to the imperfect coverage of the silanol groups by the silane coupling agents.

Textile with silver silica spheres: its antimicrobial activity against Escherichia coli and Staphylococcus aureus

The aim of this study was to investigate antimicrobial activity of textiles doped with silver in different forms. Three types of textiles were prepared and examined: textiles doped with commercially available Ag nanoparticles, textiles doped with commercial colloidal silver and textiles doped with silver silica SiO2/Ag spheres. The specimens of silica submicron spheres were synthesized by the sol–gel method as a matrix for biological active silver. The results of microbiological tests revealed that among three kinds of Ag doped textiles only these doped with SiO2/Ag spheres are bacteriostatically active. During the experiments minimal inhibiting bacteria growth concentration of active SiO2/Ag spheres added to textiles was determined.

2H NMR Studies of Polymer Multilayer Capsules, Films, and Complexes

The chain dynamics of aqueous suspensions of polyelectrolyte complexes, supported multilayers deposited on submicron silica colloids, and hollow capsules were characterized by wide-line 2H NMR spectroscopy (DNMR) as a function of layer number, temperature, and ionic strength. The strong polyelectrolytes, poly(diallyldimethyl ammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) were employed with selective deuteration of the PDADMAC methyl group. DNMR line-shape analyses showed that there is enhanced chain mobility in the systems with excess positive monomer units, that is, supported multilayers and capsules capped with PDADMAC. Selective deuteration of the first, fifth, and ninth layers confirms that the alternation in chain mobility with the capping layer is a through-film effect. Differential scanning calorimetry (DSC)-detected phase transitions were found to occur between 32 and 45 °C for the PSS/PDADMAC complexes, supported multilayers, and capsules. Whereas the glass transitions of bulk-state polymers are detected by DNMR typically 30 to 40° above the DSC-detected Tg, the onset of fast chain motion for the water-saturated polyelectrolyte complexes and supported multilayers coincides with calorimetric transitions.

Selection rules for Brillouin light scattering from eigenvibrations of a sphere

Selection rules governing Brillouin light scattering from the vibrational eigenmodes of a homogeneous, free-surface submicron sphere have been derived using group theory. The derivation is for the condition where the sphere diameter is of the order of the excitation light wavelength. Well-resolved spectral data obtained from Brillouin light scattering from submicron silica spheres provide experimental verification of the selection rules.