Silica Particles Research Articles

Nanoscale Effects in the Room-Temperature UV-Visible Photoluminescence from Silica Particles and Its Cancer Cell Imaging.

Silica nano/microparticles have generated significant interest for the past decades, emerging as a versatile material with a wide range of applications in photonic crystals, bioimaging, chemical sensors, and catalysis. This study focused on synthesizing silica nano/microparticles ranging from 20 nm to 1.2 μm using the Stöber and modified Stöber methods. The particles exhibited photoluminescence emission across a UV-visible range, specifically in the UV (∼290, ∼327, ∼339, and ∼377 nm), blue (∼450 nm), green (∼500 nm), yellow (∼576 nm), and red (∼634 nm) range of the electromagnetic spectrum. These emissions are due to radiative relaxation processes involving oxygen-deficient centers arising due to unrelaxed oxygen vacancies, strong interacting surface silanols, 2-fold coordinated silicon, self-trapped excitons, hydrogen-related species, strain-induced defects, and nonbridging oxygen hole centers excited via two-photon and single photon absorption. The increased PL intensity with a decreasing particle size was attributed to higher concentrations of defect sites in the case of smaller-sized particles. The MTT assay, AO/EB staining, and the DCFDA assay confirmed the biocompatible nature of silica particles in the HepG2 cell line. In addition, the cell viability assay in a normal cell line (HEK293) also showed no substantial cell death. Successful bioimaging of HepG2 cells was performed with silica nano/microparticles, which exhibited blue and green fluorescence, along with Hoechst33258 dye. Even though 20 nm-sized silica particles showed higher PL emission, particles sized above 20 nm showed better fluorescence in HepG2 cells, citing their potential in in vitro bioimaging applications.

Incorporation of Concrete Polishing Waste as a Partial Substitute for Cement in Mortar

This study examines concrete polishing waste (CFPW) potential as a partial cement substitute in mortar formulation. Concrete polishing waste, a by-product of the grinding and polishing of concrete surfaces, is mainly composed of fine particles of silica and calcium carbonate. The aim of the research was to assess this industry waste incorporation impact on various mortar properties. Four mixes containing different percentages of CFPW were tested for their physic-mechanical properties and environmental impact. The results show that increasing the CFPW percentage leads to higher porosity and shrinkage, as well as lower mechanical strength and density. However, a significant reduction in CO2 emissions was observed with CFPW incorporation (up to 29% reduction for 30% CPFW). Although CFPW use presents technical challenges, it offers an interesting opportunity to reduce mortars’ carbon footprint. The study concludes that moderate CFPW use can offer a balance between environmental benefits and performance, highlighting the need to optimize formulations to maximize benefits while minimizing compromises on mechanical properties.

Optimization Using Central Composite Design of the Response Surface Methodology for the Compressive Strength of Alkali-Activated Material from Rice Husk Ash

Alkali-activated materials are promising alternatives to cement. This study investigated the effects of the silica content, particle size, and replacement ratio of rice husk ash (RHA) on the compressive strength and the optimization of these parameters. Seventeen mixtures with different materials were tested to evaluate their compressive strengths. Three levels of particle size, silica content, and RHA replacement ratio were used. The effects of RHA characteristics on the compressive strength were investigated based on Archimedes porosity, pH, ignition loss, and X-ray diffraction. The experimental results reveal that the replacement ratio of RHA was p-values < 0.002, which affected the compressive strength compared with the particle size (p-values < 0.450) and silica content of the RHA (p-values < 0.017). It was confirmed that the optimum values of particle size, silica content, and replacement ratio of RHA were 50 µm, 90%, and 15 wt.%, respectively. After re-testing, the compressive strength of mortar made with the optimum values was 49.8 MPa. This increase in compressive strength was also found to be closely related to the porosity, pH, and ignition loss of the paste. It was confirmed that the replacement ratio of RHA increased with decreasing porosity and pH and increasing ignition loss, which was related to the formation of calcite and C-S-H.

Perfluoropolyether Segmented Polybutadiene Urethanes With Improved Dispersion of Silica Particles: A Surrogate Methodology for Additive Manufacturing of Composite Binders

ABSTRACTFluorinated hydroxy‐terminated polybutadiene (F‐HTPB) urethane binders were prepared by the incorporation of a perfluoropolyether (PFPE) diol (Fluorolink E10H (FL)) as a terpolymer system. Rheology measurements at 25°C showed a steady decrease in viscosity with increased cure rates at the gelation time with increasing molar loadings of FL. The optimized F‐HTPB urethane binder was then formulated with fluorinated silica particles (F‐SP) that were successfully modified with a monolayer of perfluoropolyether bound carboxylic acids using Krytox 157 FSH. Loadings up to 20 wt% F‐SPs were prepared with no phase separation demonstrating the interfacial compatibility of the fluorine‐rich PFPE domains of the binder and the silica particle surface while lowering the viscosity at full cure. These rheology measurements suggest the fluorinated binder composite formulations would advance their application as practical drop‐in feed stocks for reactive in situ additive manufacturing techniques at room temperature. This work also includes comprehensive analysis of the particles and composite formulations to include infrared spectroscopy, surface wettability measurements, calorimetry, and thermal gravimetric decomposition analysis.

Zr-doped mesoporous silica (Zr-MSS) for improved mechanical stability and biocompatibility of dental composite resins.

Mesoporous silica particles are of great interest in the field of dental composites as functional inorganic fillers due to their unique interconnected pores which can form micromechanical interlocking at the filler-resin interfaces. However, the degradation of mesoporous silica is fast in wet environments, leading to the poor mechanical stability of dental composites. Here, we synthesized Zr-doped mesoporous silica spheres (Zr-MSS) to increase the chemical stability of the particles. The particles were formulated with dental resins (Bisphenol A glycerolate dimethacrylate/triethylene glycol dimethacrylate, 50/50, wt%) to evaluate the performance of dental composites. Dental composites filled with different amount of Zr-MSS (15, 20, 25 and 30wt%) and their bimodal fillers with nonporous silica spheres (NSS) at a total filler loading of 60wt% (mass ratios of Zr-MSS: NSS=10:50) were prepared. Neat resin matrix and samples filled with mesoporous silica spheres (MSS) were used as control. The results showed that the decrease percentage of flexural strength of dental resins with Zr-MSS was the lowest, which was between 3.4 and 6.8%. It was between 20.8 and 35.5% for those with MSS. Further studies revealed that the incorporation of Zr into mesoporous fillers did not affect their light curing ability of dental composites. Not only that, cell proliferation on the dental composites with Zr-MSS was promoted, suggesting improved biocompatibility of the restorations. These indicated that the prepared Zr-MSS would be promising functional fillers for dental composite resins.

Evaluation of Ceramic Membrane Filtration for Alternatives to Microplastics in Cosmetic Formulations Using FlowCam Analysis.

The rapid expansion of the cosmetics industry has significantly increased the adoption of alternative microplastics in response to increasingly stringent global environmental regulations. This study presents a comparative analysis of the treatment performance of silica powder and cornstarch-common alternatives for microplastics in cosmetics-using ceramic membrane filtration combined with flow imaging microscopy (FlowCam) to analyze particle behavior. Bench-scale crossflow filtration experiments were performed with commercially available alumina ceramic membranes. By analyzing high-resolution images from FlowCam, the transport and retention behaviors of the two microplastic alternatives were examined by comparing their morphological properties. Despite their similar particle sizes, the cornstarch demonstrated a higher removal efficiency (82%) than the silica (72%) in the ceramic membrane filtration due to its greater tendency to aggregate. This increased tendency for aggregation suggests that cornstarch may contribute to faster fouling, while the stability and uniformity of silica particles result in less fouling. The FlowCam analysis revealed that the cornstarch particles experienced a slight increase in circularity and compactness over time, likely due to physical swelling and aggregation, while the silica particles retained their shape and structural integrity. These findings highlight the impact of the morphological properties of alternative microplastics on their filtration behavior and fouling potential.

NIR-Reflective Black Photonic Films Designed for Effective LiDAR Recognition.

Conventional dark-tone paints absorb both visible light and near-infrared (NIR) wavelengths, posing a challenge for light detection and ranging (LiDAR) recognition in autonomous driving. To overcome this issue, various chemical and structural coating materials have been explored to selectively reflect NIR. In this study, we newly propose colloidal photonic crystals with a stopband in the NIR range, fabricated through the spontaneous formation of crystalline arrays of silica particles dispersed in a photocurable resin, as a potential solution. The stopband position is finely adjusted by controlling the volume fraction of particles, and the translucent films are rendered black by incorporating carbon black nanoparticles into the interstitial regions. By optimizing the concentration of carbon black, we achieve a balance of low visible light and high LiDAR intensity. These black photonic films demonstrate superior LiDAR intensity compared to commercial dark-tone paints and perform on par with the perylene black-deposited white coating, one of the most promising LiDAR-assistive materials currently available, under normal reflection conditions. Additionally, the photonic films are highly durable, thermally stable, nontoxic, and environmentally friendly, making them promising candidates for LiDAR-assistive coatings.

Two-Dimensional Square Lattice of Colloidal Particles Formed by Electrostatic Adsorption in Confined Space.

In this study, we demonstrate a novel and efficient fabrication methodology for nonclose-packed, two-dimensional (2D) colloidal crystals exhibiting square lattice structures. In our recent work, we detailed the formation of 2D colloidal crystals via the electrostatic adsorption of three-dimensional (3D) charged colloidal crystals onto oppositely charged substrates. These 3D colloidal crystals possessed a face-centered cubic (FCC) lattice structure with their (111) planes aligned parallel to the substrate, facilitating the formation of 2D crystals with triangular lattice arrangements upon adsorption. This work presents the synthesis of 2D crystals with square lattices─a configuration widely used in photonics. We prepared 3D colloidal crystals of silica particles with four-fold symmetry in a micrometer-scale gap between two coverslips. The bottom glass surface is modified with a cationic silane coupling reagent, aminopropyltriethoxysilane, generating pH-responsive charge characteristics with an isoelectric point (iep) near pH 8. When the pH is greater than iep, the surface is charged negatively. As pH decreases below iep, the sign of the surface charge reverses to positive. Controlled pH lowering below the iep induces adsorption of the lowermost lattice plane of 3D crystals onto the substrate, yielding 2D crystals with a distinct square lattice. We further synthesized three-layer body-centered cubic (BCC) structures by stacking alternating layers of the 2D square lattices of silica and polystyrene particles. By aligning the refractive index of the surrounding medium (aqueous solution of ethylene glycol) with that of silica particles, we successfully fabricated a structure that is optically identical to a simple cubic lattice. These findings advance the development of 2D crystalline materials for photonic and plasmonic applications.

Understanding the Kinetics of CO2 Hydrate Formation in Dry Water for Carbon Capture and Storage: X-ray Diffraction and In Situ Raman Studies.

Hydrate-based carbon capture and storage (HBCS) is a sustainable and promising approach to combating global warming by utilizing water, which is a ubiquitous resource. Here, we report a comprehensive study of CO2 hydrate formation in dry water (DW), a water-in-air dispersion confined in silica particles, for improving the kinetics of hydrate growth. Utilizing a combination of a home-built high-pressure reactor, in situ Raman spectroscopy, and powder X-ray diffraction (PXRD), we elucidate the crystal structure, growth dynamics, and morphology of CO2 hydrates formed in DW, with and without the kinetic hydrate promoter, l-tryptophan. Our analysis reveals that CO2 forms structure I (sI) hydrate in DW, with hydrate growth occurring both on and beneath the silica shell. This results in a substantial increase in CO2 uptake─approximately 2.8 times higher than that observed in pure water (∼134 v/v compared to ∼48 v/v). Moreover, incorporation of l-tryptophan in DW formation markedly accelerates the DW-CO2 hydrate formation process, reducing both the induction time and the time required to achieve 90% gas uptake at 274.65 K. These findings offer crucial insights into the formation of CO2 hydrate in DW, highlighting its potential to improve the efficiency and scalability of HBCS technologies.

Full-Spectrum Mechanochromic Photonic Films with Large Interparticle Distance.

Non-close-packed crystalline arrays of colloidal particles in an elastic matrix exhibit mechanochromism. However, small interparticle distances often limit the range of reversible color shifts and reduce reflectivity during a blueshift. A straightforward, reproducible strategy using matrix swelling to increase interparticle distance and improve mechanochromic performance is presented. Photonic composites are initially prepared with silica particle arrays embedded in an elastomer matrix at volume fractions of 0.35-0.5. To increase interparticle distance, the composites are immersed in an elastomer-forming monomer, causing the matrix to swell, followed by photopolymerization, thereby producing liquid-free composites. The degree of swelling is controllable up to 3.16, depending on monomer choice, matrix volume fraction, and crosslinking density. The process can be repeated to further increase swelling up to 10.36. This method can reduce the volume fraction of silica particles from 40% to 3.8%, while interparticle distance increases from 53 to 257nm. The swollen photonic composites exhibit a full visible spectrum under compression, while minimizing reflectivity loss. This allows red-colored photonic composites to be transformed into vivid multicolor patterns when compressed with stamps featuring spatial height variations.

TNF-alpha mediates airway hyperreactivity in silicotic mice: Effect of thalidomide treatment.

Inhalation of crystalline silica particles causes silicosis, which is a severe inflammatory lung disease that is associated with granulomatous and fibrotic responses. We investigated whether silica-induced silicosis might promote airway hyperreactivity (AHR) and the role of TNF-α and thalidomide in this process. Mice received an intranasal instillation of silica particles (1.25, 5, and 10 mg/mouse) and given methacholine on days 2, 7, and 28 after provocation or 5-HT challenges on day 7 after provocation. AHR was assessed using invasive whole-body plethysmography. Lung-tissue samples were collected for TNF-α measurements and histological analyses. Thalidomide was given orally from days 21-27 after silica administration. We found that following aerosolised methacholine or 5-HT treatment, a state of AHR was induced with silica-particle amounts of 5 and 10 mg/mouse, but not 1.25 mg/mouse. The effect was apparent within 2 days and remained for at least 28 days. Silica-particle amounts of 5 and 10 mg/mouse also induced significant granuloma response correlating with the silica required to induce AHR. In addition, a parallel was also observed between the elevation of lung tissue levels of TNF-α and AHR. Notably, silica-induced granulomatous and AHR responses were abolished in TNFR1-/- mice compared to wild-type mice. Moreover, the blockade of ongoing TNF-α generation by thalidomide prevented both events. Our findings suggest that exposure of mice to silica particles leads to a granulomatous lung response marked by non-specific AHR induced by TNF-α. In addition, the results indicate that thalidomide can control silica-induced pathological features of the lungs by blocking TNF-α generation.

Enabling tumor-specific drug delivery by targeting the Warburg effect of cancer.

Metabolic reprogramming of tumor cells is an emerging hallmark of cancer. Among all the changes in cancer metabolism, increased glucose uptake and the accumulation of lactate under normoxic conditions (the "Warburg effect") is a common feature of cancer cells. In this study, we develop a lactate-responsive drug delivery platform by targeting the Warburg effect. We design and test a gold/mesoporous silica Janus nanoparticle system as a gated drug carrier, in which the gold particles are functionalized with lactate oxidase and the silica particles are capped with α-cyclodextrin through surface arylboronate modification. In the presence of lactate, the lactate oxidase generates hydrogen peroxide, which induces the self-immolation reaction of arylboronate, leading to uncapping and drug release. Our results demonstrate greatly improved drug delivery specificity and therapeutic efficacy with this platform for the treatment of different cancers. Our findings present an effective approach for drug delivery by metabolic targeting of tumors.

Biomimetic mineralization of positively charged silica nanoparticles templated by thermoresponsive protein micelles: applications to electrostatic assembly of hierarchical and composite superstructures.

High information content building blocks offer a path toward the construction of precision materials by supporting the organization and reconfiguration of organic and inorganic components through engineered functions. Here, we combine thermoresponsiveness with biomimetic mineralization by fusing the Car9 silica-binding dodecapeptide to the C-terminus of the (VPGVG)54 elastin-like polypeptide (ELP). Using small angle X-ray scattering, we show that the short Car9 cationic block is sufficient to promote the conversion of disordered unimers into 30 nm micelles comprising about 150 proteins, 5 °C above the transition temperature of the ELP. While both species catalyze self-limiting silica precipitation, micelles template the mineralization of highly monodisperse (62 nm) nanoparticles, while unimers yield larger polydisperse species. Strikingly, and unlike traditional synthetic silica, these particles exhibit a positive surface charge, likely due to cationic Car9 sidechains projecting from their surface. Capitalizing on the high monodispersity and positive charge of the micelle-templated products, we use smaller silica and gold particles bearing a native negative charge to create a variety of superstructures via electrostatic co-assembly. This simple biomimetic route to positively charged silica eliminates the need for multiple precursors or surface modifications and enables the rapid creation of single-material and composite architectures in which components of different sizes or compositions are well dispersed and integrated.

Shear thickening inside elastic open-cell foams under dynamic compression.

We measure the response of open-cell polyurethane foams filled with a dense suspension of fumed silica particles in polyethylene glycol at compression speeds spanning several orders of magnitude. The gradual compressive stress increase of the composite material indicates the existence of shear rate gradients in the interstitial suspension caused by wide distributions in pore sizes in the disordered foam network. The energy dissipated during compression scales with an effective internal shear rate, allowing for the collapse of three data sets for different pore-size foams. When scaled by this effective shear rate, the most pronounced energy increase coincides with the effective shear rate corresponding to the onset of shear thickening in our bulk suspension. Optical measurements of the radial deformation of the foam network and of the suspension flow under compression provide additional insight into the interaction between shear thickening fluid and foam. This optical data, combined with a simple model of a spring submerged in viscous flow, illustrates the dynamic interaction of viscous drag with foam elasticity as a function of compression rate, and identifies the foam pore size distribution as a critically important model parameter. Taken together, the stress measurements, dissipated energy, and relative motion of the fluid and the foam can be rationalized by knowing the pore size distribution and the average pore size of the foam.

Styrene-butadiene-styrene-based nanocomposites as self-healable antibacterial coatings

This study presents the development of self-healing antibacterial polymeric composite coatings to minimize infection risks and ensure adaptability for large spaces by using readily available materials and scalable, efficient fabrication techniques. These coatings were prepared by incorporating 300–400 nm solid silica particles capped with a polydopamine layer of ~40 nm thickness and decorated with silver nanoparticles within a styrene-butadiene-styrene matrix. The aqueous dispersion of filler particles upon exposure to near-infrared 808 nm light exhibits a temperature increase of ~15 °C caused by the photothermal activity of polydopamine in synergy with silver nanoparticles. This photothermal activity of fillers helps to achieve the complete healing of micron-sized scratches of nanocomposite films with light intensities as low as 1.19 W/cm2 over 10 min (total energy fluence of 716 J/cm2), demonstrating promising results for real-world applications. Additionally, the coatings exhibit significant enhancement in antibacterial activity, reducing bacterial colony counts by >99.9 %. These findings underscore the potential of such coatings to reduce the risk of pathogenic infections in clinical settings while offering sustainable and eco-friendly solutions.

Nanoscale Janus particle fabrication and direct observation by super-resolution microscopy

We have developed a new and facile approach for synthesis, labeling, and characterizing amphiphilic nanoscale Janus particles. The aqueous dispersion of the Aerodisp W1226 fumed silica particles were embedded into polycarbonate (P.C.) microspheres surfaces via inverse solvent displacement method and further primary functionalization by an amine group. Subsequently, the polymer was dissolved, and a second modification was preferred to introduce a thiol group on the revealed embedded side of the particles, forming silica-based Janus/amphiphilic particles. We first characterized the Janus particles by laser scanning confocal microscopy and then with direct stochastic optical reconstruction microscopy (dSTORM) to detect the labeling distribution of the different functional groups. Super-resolution imaging results confirmed that the fabricated particles are Janus particles with different chemical properties on each hemisphere. The particles were also characterized by scanning and transmission electron microscopy for size and shape. The results showed aspherical particles with two hemispheres, confirming successful fabrication and chemical modification. Also, this work successfully demonstrated the synthesis, characterization and analysis of nanoscale Janus/amphiphilic particles nanoscale Janus particle.

Stability of electrostatically stabilized Pickering emulsion of silica particles and soy hull polysaccharides: Mechanism of pH and ionic strength.

To enhance the surface hydrophobicity and emulsification capacity of silica colloidal particles, a natural surface modification of soy hull polysaccharides (SHP) was conducted. Here, the effects of pH and ionic strength on the stability, microstructure and rheological properties of concentrated Pickering emulsions were investigated. Experimental results show emulsions gelled at pH2, with increasing pH (2-10), SiO2-SHP absolute zeta potential (from -19.6 to -44.7mV) and interfacial tension (from 15.2 to 25.09 mN/m) increased, and viscosity, viscoelasticity and storage stability decreased. Additionally, at low NaCl concentrations (<150mM), SiO2-SHP interfacial tension remained low (21.3 mN/m), promoting stable emulsions (TSI<1.5). In this case, the electrostatic interaction was slightly affected by ions, facilitating the occurrence of composite coagulation. However, as ionic concentration increased (150-300mM), interfacial tension increased (from 20.5 to 27.6 mN/m). Thus, our study presents important insights into the pH and salt ions dependent mechanism of emulsion stabilization by SiO2-SHP.

Tailored cerium phosphate/silica hybrid epoxy for enhanced corrosion protective coating

The current study focuses on finding a reliable, inexpensive and healable approach by modifying conventional silica particles to prevent steel in saline media.

One-pot sol-gel process and simultaneous formation silica particles cross-linked network (SPCN)

In this work, a simple sol-gel process method was studied for “one-pot” fabrication of silica particle cross-linked networks (SPCN). It is the first time that the co-precursors of tetraethoxysilane (TEOS) and ?-glycidoxypropyltrimethoxysilane (GPTMS) and capping agent of cetyltrimethylammonium bromide (CTAB) are formulated to achieve the complete co-polymerization of the reaction solution. The reaction solution proposed involved TEOS and GPTMS (5:1 w/w) for feasibility preparation of SPCN. The copolymerization temperature was set at 40? for 24h of aging time. The results indicated that, by means of cetyltrimethylammonium bromide as a capping agent, SPCN exhibited a well-defined three-dimensional (3D) porous network. The prepared SPCN was used for the synthesis of silica monolithic columns to show interstices distributed across the whole SPCN as well as monolithic columns. The BET surface area of the SPCN column was obtained at approximately 156 m2/g and an average pore width smaller than 26 nm.

Disordered mesoporous silica particles: an emerging platform to deliver proteins to the lungs

Pulmonary delivery and formulation of biologics are among the more complex and growing scientific topics in drug delivery. We herein developed a dry powder formulation using disordered mesoporous silica particles (MSP) as the sole excipient and lysozyme, the most abundant antimicrobial proteins in the airways, as model protein. The MSP had the optimal size for lung deposition (2.43 ± 0.13 µm). A maximum lysozyme loading capacity (0.35 mg/mg) was achieved in 150 mM PBS, which was seven times greater than that in water. After washing and freeze-drying, we obtained a dry powder consisting of spherical, non-aggregated particles, free from residual buffer, or unabsorbed lysozyme. The presence of lysozyme was confirmed by TGA and FT-IR, while N2 adsorption/desorption and SAXS analysis indicate that the protein is confined within the internal mesoporous structure. The dry powder exhibited excellent aerodynamic performance (fine particle fraction <5 µm of 70.32%). Lysozyme was released in simulated lung fluid in a sustained kinetics and maintaining high enzymatic activity (71–91%), whereas LYS-MSP were shown to degrade into aggregated nanoparticulate microstructures, reaching almost complete dissolution (93%) within 24 h. MSPs were nontoxic to in vitro lung epithelium. The study demonstrates disordered MSP as viable carriers to successfully deliver protein to the lungs, with high deposition and retained activity.