Monodisperse Silica Particles Research Articles

Novel 3D-Printed Microfluidic Magnetic Platform for Rapid DNA Isolation.

This study presents a novel miniaturized device as a 3D-printed microfluidic magnetic platform specifically designed to manipulate magnetic microparticles in a microfluidic chip for rapid deoxyribonucleic acid (DNA) isolation. The novel design enables the movement of the magnetic particles in the same or opposite directions with the flow or suspends them in continuous flow. A computational model was developed to assess the effectiveness of the magnetic manipulation of the particles. Superparamagnetic monodisperse silica particles synthesized in-house are utilized for the isolation of fish sperm DNA and human placenta DNA. It was demonstrated that the proposed platform can perform DNA isolation within 10 min with an isolation efficiency of 50% at optimum operating conditions.

Characterizing stress development and cracking of ceramic particulate coatings during drying

AbstractDuring drying, liquid‐applied particulate coatings develop stress and are consequently prone to stress‐induced defects, such as cracking, curling, and delamination. In this work, the stress development and cracking of coatings, prepared from aqueous silica and zinc oxide particle suspensions, were characterized using cantilever beam deflection with simultaneous imaging of the coating surface. Drying uniformity was improved and lateral or edge‐in drying was discouraged by using thin silicone walls around the perimeter of the cantilever. Coatings prepared from larger monodisperse silica particles (D50 ∼ 0.9 µm) dried uniformly but had a high critical cracking thickness (>150 µm) that prevented simultaneous study of stress development and cracking. Coatings prepared from smaller silica particles (D50 ∼ 0.3 µm) cracked readily at low thicknesses but exhibited edge‐in drying that complicated the stress measurement data. This drying nonuniformity was connected to the potential for these small particles to accumulate at the coating surface during drying. Hence, the selection of particle size and density was critical to drying uniformity when characterizing stress development and cracking. Coatings prepared from suspensions of zinc oxide particles (D50 ∼ 0.4 µm) were well‐suited for these studies, with uniform drying stress peaking at ∼1 MPa. Characteristic features in the stress development data above and below the critical cracking thickness (53 µm) were identified, demonstrating that cantilever beam deflection is a useful tool for studying the effectiveness of crack mitigation methods and the fundamentals of coating fracture during drying.

Joint effects of gas bubbles and solid particles on sonochemical inhibition in sonicated aqueous solutions

Wastewater is a multicomponent and multiphase mixture. Gas bubbles and solid particles in the dispersed phase influence sonochemical efficiency during ultrasonic treatment of wastewater, sometimes unfavorably; however, the influencing factors and mechanisms remain unclear. In this paper, the influence of argon gas bubbles (1.2 mm) and monodisperse silica particles (0.1 mm) on sonochemical effects in an aqueous system using a horn-type reactor (20 kHz) is reported. Triiodide formation decreased with an increase in the volume fraction of either or both phases. The two phases started inhibiting sonoreactions as the total volume fraction approached 3.0–4.0 vol% compared to pure water. The effect of the gas-to-solid ratio is also considered. We propose an acoustic attenuation model, which incorporates the scattering effect of solid particles and the thermal effect of gas bubbles. The agreement between the modeling and experimental results demonstrates that the two phases are jointly responsible for sonochemical inhibition by increasing ultrasound attenuation. This enhances the understanding of sonochemistry in gas–solid–liquid systems and helps regulate gases and solids in sonochemical reactors.

Cibacron Blue F3GA ligand dye-based magnetic silica particles for the albumin purification.

Dye-ligand affinity chromatography is among the increasingly popular affinity chromatography based on molecular recognition for the purification of albumin. This study focuses on the binding of Cibacron Blue F3GA ligand dye with magnetic silica particles and purification by separation. Mono-disperse silica particles with bimodal pore size distribution were employed as a high-performance adsorbent for human serum albumin (HSA) protein purification under equilibrium conditions. The synthesized ligand-dye affinity based magnetic silica particles were characterized by electron spin resonance, Fourier-transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer, elemental analysis, and dispersive X-ray analysis. The HSA purification performance of the proposed material in the presence of a magnetic field was relatively investigated using magnetic-based particles with similar morphologies. The maximum adsorption capacity for HSA in an artificial plasma medium was defined as 48.6 mg/g magnetic silica particle. By using the designed magnetic silica particles, 1.0 M NaCl solution was successfully utilized for obtaining quantitative desorption with HSA. However, continued HSA purification performances of magnetic-based particles were significantly lower concerning the ligand-dye magnetic silica particles. The purity of the removed albumin was about 97%. The magnetic silica particles could be utilized many times without decreasing their protein adsorption capacities remarkably.

Synthesis of Monodisperse Silica Particles by Controlled Regrowth

The development of a simple and reproducible method for the synthesis of monodisperse silica particles is of considerable interest from the point of view of their numerous applications in photonics, biosensing, and biomedicine. When using the well-known Stober method, there is a continuous formation and growth of seeds, which leads to the synthesis of polydisperse colloids. In this work, we used the method of successive growth of silica particles obtained by hydrolytic condensation of tetraethylorthosilicate in an alcoholic-aqueous medium using an alkaline catalyst. It is shown that this technique makes it possible to obtain colloids with a particle size from 50 nm to 3 μm and a standard deviation of less than 5%. An additional advantage of the developed method of stepwise growth is the possibility to include fluorophores and SERS tags into the silica matrix.

Approach to achieve controlled particle size synthesis of non-polar functionalised siloxane particles using a one-pot synthesis

The homogeneous addition of functional silanes dissolved in a co-solvent such as ethanol has been shown to change particle growth mechanisms as well as control over particle size and dispersity, especially for non-polar silanes. Highly monodisperse size-controlled silica particles from 50 to over 1000 nm bearing thiol, vinyl, phenyl, propyl, cyanopropyl and chloropropyl R group functionality were synthesised directly from the corresponding single organosilane source. Observing particle growth over time revealed that it proceeded by a conventional Stöber process, where silane monomers and oligomers add to nucleation sites, resulting in particle growth. Scale-up of the homogeneous mixing approach produced gram quantities of particles without affecting size, size dispersion or functionality under good mixing. The presence and functionality of the surface R groups were confirmed by a simple second addition of reactive molecules to the particle synthesis liquor, resulting in theoretical maximum attachment densities.

Colloidal Crystal Films with Narrow Reflection Bands by Hot-Pressing of Polymer-Grafted Silica Particles.

Previous reports have shown that colloidal crystal (CC) films with visible Bragg reflection characteristics can be fabricated by the surface modification of monodisperse silica particles (SiPs) with poly(methyl methacrylate) (PMMA) chains, followed by hot-pressing at 150 °C. However, the reflection bands of the CC films were very broad due to their relative disordering of SiPs. In this report, we attempted to fabricate the CC films using SiPs surface-modified with poly(n-octyl acrylate) (POA) chains by hot-pressing. When the cast films of POA-grafted SiPs were prepared by hot-pressing at 100 °C, the reflection bands were narrow rather than those of CC films of PMMA-grafted SiPs. This can be ascribed to easy disentanglement of POA chains during the hot-pressing process, thereby enabling the formation of well-ordered CC structures. Moreover, the reflection colors of CC films could be easily tuned by controlling the molecular weight of POA chains grafted on the SiP surface.

Three-dimensional printing of photonic colloidal glasses into objects with isotropic structural color

Structural color is frequently exploited by living organisms for biological functions and has also been translated into synthetic materials as a more durable and less hazardous alternative to conventional pigments. Additive manufacturing approaches were recently exploited for the fabrication of exquisite photonic objects, but the angle-dependence observed limits a broader application of structural color in synthetic systems. Here, we propose a manufacturing platform for the 3D printing of complex-shaped objects that display isotropic structural color generated from photonic colloidal glasses. Structurally colored objects are printed from aqueous colloidal inks containing monodisperse silica particles, carbon black, and a gel-forming copolymer. Rheology and Small-Angle-X-Ray-Scattering measurements are performed to identify the processing conditions leading to printed objects with tunable structural colors. Multimaterial printing is eventually used to create complex-shaped objects with multiple structural colors using silica and carbon as abundant and sustainable building blocks.

Synthesis of Porous Hollow Organosilica Particles with Tunable Shell Thickness.

Porous hollow silica particles possess promising applications in many fields, ranging from drug delivery to catalysis. From the synthesis perspective, the most challenging parameters are the monodispersity of the size distribution and the thickness and porosity of the shell of the particles. This paper demonstrates a facile two-pot approach to prepare monodisperse porous-hollow silica particles with uniform spherical shape and well-tuned shell thickness. In this method, a series of porous-hollow inorganic and organic-inorganic core-shell silica particles were synthesized via hydrolysis and condensation of 1,2-bis(triethoxysilyl) ethane (BTEE) and tetraethyl orthosilicate (TEOS) in the presence of hexadecyltrimethylammonium bromide (CTAB) as a structure-directing agent on solid silica spheres as core templates. Finally, the core templates were removed via hydrothermal treatment under alkaline conditions. Transmission electron microscopy (TEM) was used to characterize the particles′ morphology and size distribution, while the changes in the chemical composition during synthesis were followed by Fourier-transform infrared spectroscopy. Single-particle inductively coupled plasma mass spectrometry (spICP-MS) was applied to assess the monodispersity of the hollow particles prepared with different reaction parameters. We found that the presence of BTEE is key to obtaining a well-defined shell structure, and the increase in the concentration of the precursor and the surfactant increases the thickness of the shell. TEM and spICP-MS measurements revealed that fused particles are also formed under suboptimal reaction parameters, causing the broadening of the size distribution, which can be preceded by using appropriate concentrations of BTEE, CTAB, and ammonia.

Clarification of regimes determining sonochemical reactions in solid particle suspensions

Although there has been extensive research on the factors that influence sonochemical reactions in solid particle suspensions, the role that solid particles play in the process remains unclear. Herein, the effect of monodisperse silica particles (10–100 μm, 0.05–10 vol%) on the sonochemical activity (20 kHz) was investigated using triiodide formation monitoring and luminol tests. The results demonstrate that, in the particle size range considered, the sonochemical yields were enhanced in dilute suspensions (0.05–1 vol%), while further particle addition in semi-dilute suspensions (1–10 vol%) decreased the yields. Two regimes, namely the site-increasing regime and sound-damping regime, are identified in respect of the enhancing and inhibiting effects of the particles, respectively, and their dependence on particle characteristics is analyzed. Both regimes are confirmed based on the cavitation erosion test results or cavitation noise analysis. The clarification of the two regimes provides a better understanding of the dominant factors controlling sonochemistry in the presence of solid particles, as well as a guide for sonochemical efficiency prediction.

Chain length of bioinspired polyamines affects size and condensation of monodisperse silica particles

Polyamines play a major role in biosilicification reactions in diatoms and sponges. While the effects of polyamines on silicic acid oligomerization and precipitation are well known, the impact of polyamines chain length on silica particle growth is unclear. We studied the effects of polyamine chain length on silica particle growth and condensation in a known, simple, and salt-free biphasic reaction system; with tetraethyl orthosilicate as organic phase and polyamine dissolved in the aqueous phase. The particles at various growth stages were characterized by Cryo- Transmission Electron Microscopy, Scanning Electron Microscopy, Thermogravimetric Analysis, Zeta Potential, and solid-state NMR analysis. Polyamines were found co-localized within silica particles and the particle diameter increased with an increase in polyamine chain length, whereas silica condensation showed the opposite trend. Particle growth is proposed to progress via a coacervate intermediate while the final particles have a core shell structure with an amine-rich core and silica-rich shell. The results presented in this paper would of interest for researchers working in the field of bioinspired materials.

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.

Effects of electrostatic interaction on rheological behavior and microstructure of concentrated colloidal suspensions

This research examined the effect of salt concentration on the viscosity behavior of concentrated colloidal suspensions of monodispersed silica particles in aqueous media and ethylene glycol. Silica particles with a lot of negative surface charge form three-dimensional ordered structures (colloidal crystals) in aqueous media or ethylene glycol due to electrostatic repulsion. These three-dimensional structures are distorted by shear, causing viscosity to decrease and shear thinning to occur. Adding salt increases the ionic strength within the suspension, thereby reducing the Debye length of the particle and weakening the electrostatic repulsion between particles. As a result, the viscosity at low shear rates and the shear thinning gradient decreases. However, if the salt concentration increases further, the ionic strength within the suspension will rise, virtually eliminating the Debye length of the particle. In this event, the electrostatic repulsion between the particles becomes extremely weak, and the microstructures will be formed in the aqueous media by hydrophobic interaction and van der Waals force between the particles. As a result, the viscosity at low shear rates and the shear thinning gradient becomes extremely large. In contrast, the behavior in an ethylene glycol differs from behavior in an aqueous media. In this case, the microstructures are not formed by hydrophobic interaction. Consequently, collisions between particles are promoted, causing shear thickening. This phenomenon provides further support to the hypothesis that shear thickening is caused by collisions between particles and suggests that shear thickening can be avoided by strengthening the electrostatic interaction between particles.

Microfluidic Production of Mechanochromic Photonic Fibers Containing Nonclose‐Packed Colloidal Arrays

Photonic fibers are important raw materials for structurally colored fabrics. In particular, the mechanochromic fibers potentially provide color‐tunable clothes, like chameleon skins. Herein, microfluidic jetting to continuously produce mechanochromic fibers in a controlled manner is used. The jet is produced by flow‐focusing the photocurable dispersions in a surfactant‐laden carrier fluid using microfluidic devices. The dispersions contain monodispersed silica particles in an elastomer‐forming resin. As the silica particles have repulsive interparticle potential in the resin, they spontaneously organize into a nonclose‐packed regular array, developing structural colors. The jet of the dispersions is photocured in situ by irradiation of ultraviolet at the exit of the microfluidic channel, continuously producing the photonic fibers. As the interparticle separation among silica particles is shortened along the radial direction by stretching the elastic fibers, the structural colors are dynamically blue shifted. Also, the original colors are reversibly recovered by relaxing the fibers as the deformation is fully elastic. The nonclose‐packed array of inelastic silica particles provides a wide range of color tuning and high reversibility. Moreover, microfluidic jetting enables the production of Janus fibers composed of two distinct color domains, which enriches the available structural colors through color mixing.

Evaluation of Potential of Uncoated Mesoporous Silica Particles for Drug Delivery Applications

The drug loading capability and inherent cytotoxicity of mesoporous silica particles are two prime considerations for targeted drug delivery applications. In current study, uncoated mesoporous silica (UMS) carrier particles were synthesized by sol-gel emulsion approach. The morphology and structure of UMS was thoroughly characterized using atomic force microscope (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET). The scanning electron microscopy (SEM) and dynamic light scattering (DLS) measurements reveal that mono dispersed silica particles have an average size of 250 nm with narrow size distribution. The pore size was measured as 47nm. Concentration dependent biocompatibility of UMS was evaluated using MTT assay with Hep-2c cancer cell line and cell viability of ~65% at concentrations of 7.5 nM was observed. Finally, the drug loading capability of UMS carrier was studied using ibuprofen as a model drug.

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.

Stimuli-Responsive Structural Colored Gel That Exhibits the Three Primary Colors of Light by Using Multiple Photonic Band Gaps Acquired from Photonic Balls.

A material that can capture changes in environmental stimuli as a color change can be used to develop sensors and displays. By producing an ordered structure in a polymer gel that reflects particular wavelengths of light, we can express the volume change that occurs based on the environment as the change in the wavelength of reflected light, i.e., structural color. To date, many systems have been developed to change the hue of the structural color as a function of temperature, pH, substance, applied force, and so on. However, as is expected from the principle of optical interference, the gel usually shows a red-shift with increasing volume. In this study, we propose a method for preparing structurally colored stimuli-responsive polymer gels that display appropriate color changes according to changes in environmental stimuli. For this purpose, we employ the photonic balls, which are spherical colloidal crystals consisting of monodisperse silica particles, as templates. By combining the wavelength-selective reflection generated from different photonic band gaps of the photonic balls, we succeeded in developing porous stimuli-responsive polymer gels that exhibited various types of color change, which are not observed in conventional systems.

A PTFE helical capillary microreactor for the high throughput synthesis of monodisperse silica particles

We propose a simple and inexpensive SiO2 submicron particle synthesis method based on a PTFE helical capillary microreactor. The device is based on Dean flow mediated, ultrafast mixing of two liquid phases in a microfluidic spiral pipe. Excellent control of particle size between 100 nm and 600 nm and narrow polydispersity can be achieved by controlling the device and process parameters. Numerical simulations are performed to determine the optimal device dimensions. In the mother liquor the silica particles exhibit zeta potentials < −60 mV, rendering them very stable even at high particle volume fractions. The current device typically produces around 0.234 g/h of the silica particles.

Classification of regimes determining ultrasonic cavitation erosion in solid particle suspensions

Although the factors that influence ultrasonic cavitation erosion in solid particle suspensions have been extensively studied, the role that solid particles play in the cavitation process remains poorly understood. The ultrasonic cavitation erosion of AISI 1045 carbon steel was studied in the presence of monodisperse silica particles (10–100 μm, 0.5–20 vol%) suspended in transformer oil. Based on our results, we propose an overview of the possible influencing mechanisms of particle addition for specific particle sizes and concentrations. Four major regimes, namely a viscosity-enhancing regime (V), a particle-impinging regime (I), a particle-shielding regime (S), and a nuclei-adding regime (A) are identified, and their dependence on suspended particle characteristics is analyzed. The VISA regimes, in essence, reflect the viscous and inertial effects of suspended particles, and the way in which particle–particle interactions and heterogeneous nucleation affect erosion. This regime-based framework provides a better understanding of the dominant factors controlling the erosive wear caused by cavitation in the presence of solid particles, and provides a guide for erosion prediction and prevention.

Position Dependence of Emission Wavelength of a SiO2 Colloidal Photonic-Crystal Laser

In this paper, a wavelength tunable colloidal-crystal laser with monodispersed silica particles was demonstrated. Silica particles were synthesized through the modified Stöber process and self-assembled into the colloidal photonic-crystal structure, which was then used to form the optic cavity of a wavelength tunable laser device. Due to Bragg’s diffraction of the colloidal photonic-crystal and the coffee ring effect, the forbidden energy gap of light varied with different lattice sizes at different positions of the colloidal photonic-crystal. When the pumping pulsed laser irradiated on the gain medium of the sample, the fluorescence was restricted and enhanced by the colloidal photonic-crystal. Lasing emission with a single peak occurred when the energy of the pumping laser exceeded the threshold energy. The threshold energy and the full-width at half-maximum (FWHM) of the proposed laser were 7.63 µJ/pulse and 2.88 nm, respectively. Moreover, the lasing wavelength of the colloidal photonic-crystal laser could be tuned from 604 nm to 594 nm, corresponding to the various positions in the sample due to the coffee ring effect.