Monodisperse SiO2 Nanoparticles Research Articles

EFFICIENT PRODUCTION OF SMALL-SIZED SiO2 NANOPARTICLES AND THEIR APPLICATION IN A WATERBORNE ACRYLIC-AMINO VARNISH

In this study, we optimized the preparation of 100–160 nm monodispersed SiO2 nanoparticles and, through doping, investigated their effects on the physical properties of a water-based acrylic-amino varnish. First, using a non-fixed point feeding technique based on the half-batch sol-gel method, we enhanced the yield of small-sized monodispersed SiO2 nanoparticles. To reduce the cost of production and organic-matter pollution, we assessed certain solution parameters including tetraethyl orthosilicate (TEOS), ethanol (ETOH) and ammonia in a single-reaction system. We found that the gloss, clarity, hardness, adhesion, and other physical properties of the acrylic-amino varnish were successfully enhanced through an addition of 1.2 % SiO2 nanoparticles.

Design of Multi-Luminescent Silica-Based Nanoparticles for the Detection of Liquid Organic Compounds.

Tracer testing in reservoir formations is utilised to determine residual oil saturation as part of optimum hydrocarbon production. Here, we present a novel detection method of liquid organic compounds by monodisperse SiO2 nanoparticles (NPs) containing two luminophores, a EuIII:EDTA complex and a newly synthesised fluorophore based on the organic boron-dipyrromethene (BODIPY)-moiety. The particles exhibited stable EuIII PL emission intensity with a long lifetime in aqueous dispersion. The fluorescence of the BODIPY was also preserved in the aqueous environment. The ratiometric PL detection technique was demonstrated by using toluene and 1-octanol as model compounds of crude oil. The optimal synthesis conditions were found to give NPs with a diameter of ~100 nm, which is suitable for transport through porous oil reservoir structures. The cytotoxicity of the NPs was confirmed to be very low for human lung cell and fish cell lines. These findings demonstrate the potential of the NPs to replace the hazardous chemicals used to estimate the residual oil saturation. Moreover, the ratiometric PL detection technique is anticipated to be of benefit in other fields, such as biotechnology, medical diagnostics, and environmental monitoring, where a reliable and safe detection of a liquid organic phase is needed.

Construction of Wash-Resistant Photonic Crystal-Coated Fabrics based on Hydrogen Bonds and a Dynamically Cross-Linking Double-Network Structure.

Structural coloration as the most possible way to realize the ecofriendly dying process for textiles or fabrics has attracted significant attention in the past decades. However, photonic crystals (PCs) are a typical example of materials with structural color usually located on the surface of the fabrics or textiles, which make them not stable when rubbed, bent, or washed due to the weak interaction between the PC coatings and fabrics. Here, double networks were constructed between the PC coatings and the fabrics for the first time via a hydrogen bond by introducing tannic acid (TA) and dynamic cross-linking with 2-formylphenylboronic acid to increase the wash resistance of the structural colored fabrics. On modifying the monodispersed SiO2 nanoparticles, poly(dimethylsiloxane), and the fabrics, the interaction between the PC coatings and the fabrics increased by the formation of double networks. The structural color, wash, and rub resistance of the PC-coated fabrics were systematically studied. The obtained fabrics with the TA content at 0.030% (SiDT30) showed the best wash and rub resistance. The construction of double networks not only improved the wash and rub resistance of PCs but also retained the bright structural color of the PC coatings, facilitating the practical application of structural coloration in the textile industry.

Ligand‐Free MAPbI3Quantum Dot Solar Cells Based on Nanostructured Insulating Matrices

The stability, either chemical or thermal, and performance of colloidal quantum dot (CQD) devices are typically limited by the presence of surface‐bonded organic ligands required to stabilize the nanocrystals. In addition, optimization of charge transport implies lengthy ligand exchange processing. Herein, evidence of efficient charge transport through a network of ligand‐free perovskite quantum dots (PQDs) embedded in an insulating porous matrix made of monodisperse SiO2nanoparticles is shown. Methylammonium lead iodide (CH3NH3PbI3or MAPbI3) QDs are prepared in situ by infiltration of precursors within the matrix pores, which act both as nanoreactors for the synthetic reaction and as supporting scaffolds, hence reducing the number of synthetic and postprocessing steps usually required in CQD solar cells. Above a certain nanocrystal load, charge percolation is reached and dot‐to‐dot transport achieved without compromising quantum confinement effects. Solar cells based on MAPbI3QDs prepared in this way present a 9.3% efficiency, the highest reported for a scaffold‐supported PQD solar cell, and significantly improved stability under solar illumination with respect to their bulk counterparts. Therefore, adequately designed networks of ligand‐free PQDs can be used as both light harvesters and photocarrier conductors, in an alternative configuration to that used in previously developed QD solar cells.

Self-assembly of superstructures at all scales

Summary Controllable assembly of molecular and nanoscale building blocks into uniform superstructures up to bulk dimensions remains a key challenge in the next phase of nanotechnology development. Here, we report the self-assembly of superstructures at all scales by taking advantage of the partial miscibility of water and 1-butanol to generate transient aqueous emulsion droplets that can encapsulate the target materials and introduce them into template holes. Further diffusion of water into 1-butanol depletes the emulsion droplets, assembling the building blocks into one well-defined superstructure in each hole. Superstructuring of various types and shapes of nanoparticles, biomolecules, and inorganic compounds could be achieved without the need for surfactants and chemical modifications. The versatility, scalability, low-cost, and accurate positioning are crucial advantages for the future development of advanced precision manufacturing.

Strong Lewis Acid-Base and Weak Hydrogen Bond Synergistically Enhancing Ionic Conductivity of Poly(ethylene oxide)@SiO2 Electrolytes for a High Rate Capability Li-Metal Battery.

Solid-state composite polymer electrolytes (CPEs) usually suffer from intrinsic low ionic conductivity and a solid-solid interface, badly inhibiting their widespread commercial application in all-solid-state Li-metal battery (ASSLMB) energy storage. Herein, a synergetic strategy using strong Lewis acid-base and weak hydrogen bonds was employed for self-assembly in situ construction of three-dimensional (3D) network-structured poly(ethylene oxide) (PEO) and SiO2 CPEs (PEO@SiO2). Ascribed to this synergistically rigid-flexible coupling dynamic strategy, a harmonious incorporation of monodispersed SiO2 nanoparticles into PEO could remarkably reduce crystallinity of PEO, significantly enhancing the ionic conductivity (∼1.1 × 10-4 S cm-1 at 30 °C) and dramatically facilitating solid electrolyte interface stabilization (electrochemical stability window > 4.8 V at 90 °C). Moreover, the PEO@SiO2-based ASSLMBs possess excellent rate capability over a wide temperature range (∼105 mA h g-1 under 2 C at 90 °C), high temperature cycling capacity (retaining 90 mA h g-1 after 100 cycles at 90 °C), and high specific capacity (146 mA h g-1 under 0.3 C at 90 °C). Unambiguously, these high ionic conductivity CPEs along with excellent flexibility and safety can be one of the most promising candidates for high-performance ASSLMBs, evidently revealing that this synergistically rigid-flexible coupling dynamic strategy will open up a way to exploit the novel high ionic conductivity solid-state electrolytes.

Metallosupramolecular Photonic Elastomers with Self-Healing Capability and Angle-Independent Color.

Photonic elastomers that can change colors like a chameleon have shown great promise in various applications. However, it still remains a challenge to produce artificial photonic elastomers with desired optical and mechanical properties. Here, the generation of metallosupramolecular polymer-based photonic elastomers with tunable mechanical strength, angle-independent structural color, and self-healing capability is reported. The photonic elastomers are prepared by incorporating isotropically arranged monodispersed SiO2 nanoparticles within a supramolecular elastomeric matrix based on metal coordination interaction between amino-terminated poly(dimethylsiloxane) and cerium trichloride. The photonic elastomers exhibit angle-independent structural colors, while Young's modulus and elongation at break of the as-formed photonic elastomers reach 0.24 MPa and 150%, respectively. The superior elasticity of photonic elastomers enables their chameleon-skin-like mechanochromic capability. Moreover, the photonic elastomers are capable of healing scratches or cuts to ensure sustainable optical and mechanical properties, which is crucial to their applications in wearable devices, optical coating, and visualized force sensing.

Transpiration-Inspired Fabrication of Opal Capillary with Multiple Heterostructures for Multiplex Aptamer-Based Fluorescent Assays.

In this work we report a method for the fabrication of opal capillary with multiple heterostructures for aptamer-based assays. The method is inspired by plant transpiration. During the fabrication, monodisperse SiO2 nanoparticles (NPs) self-assemble in a glass capillary, with the solvent gradually evaporating from the top end of the capillary. By a simple change of the colloid solution that wicks through the capillary, multiple heterostructures can be easily prepared inside the capillary. On the surface of the SiO2 NPs, polydopamine is coated for immobilization of aminomethyl-modified aptamers. The aptamers are used for fluorescent detection of adenosine triphosphate (ATP) and thrombin. Owing to fluorescence enhancement effect of the photonic heterstructures, the fluorescent signal for detection is amplified up to 40-fold. The limit of detection is 32 μM for ATP and 8.1 nM for thrombin. Therefore, we believe this method is promising for the fabrication of analytical capillary devices for point-of-care testing.

Patterned Photonic Nitrocellulose for Pseudopaper ELISA.

We report an enzyme-link immunosorbent assay (ELISA) based on patterned pseudopaper that is made of photonic nitrocellulose for highly sensitive fluorescence bioanalysis. The pseudopaper is fabricated using self-assembled monodisperse SiO2 nanoparticles that are patterned on a polypropylene substrate as template. The self-assembled nanoparticles have a close-packed hexagonal (opal) structure, so the resulting nitrocellulose has a complementary (inverse opal) photonic structure. Owing to the slow-photon effect of the photonic structure, fluorescence emission for ELISA is enhanced by up to 57-fold without increasing the assay time or complexity. As the detection signal is significantly amplified, a simple smartphone camera suffices to serve as the detector for rapid and on-site analysis. As a demonstration, human IgG is quantitatively analyzed with a detection limit of 3.8 fg/mL, which is lower than that of conventional ELISA and paper-based ELISA. The consumption of sample and reagent is also reduced by 33 times compared with conventional ELISA. Therefore, the pseudopaper ELISA based on patterned photonic nitrocellulose is promising for sensitive, high-throughput bioanalysis.

Facile synthesis of surfactant-free SiO2 nanoparticles via emulsion method

Silica (SiO2) nanoparticles have wide potential applications in many advanced areas. In this paper, we report an easy method for the synthesis of monodisperse SiO2 nanoparticles by a simple emulsion method. The novelty of this method lies in the synthesis of nanoparticles without the traditional use of any surfactants and toxic solvents. The phase purity of the synthesized SiO2 nanoparticles were determined by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). Morphology and nanoparticle size was determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the concentration of tetraethyl orthosilicate (TEOS), ammonia and water on the final size of the nanoparticles was observed. By precisely controlling the concentration of ammonia and water, SiO2 nanoparticles ranging between 30 and 90nmwere synthesized without the use of any surfactants. The results presented a simple, convenient and non-toxic method for the synthesis of SiO2 nanoparticles on a large-scale with precise control of the particle size.

Size regulation and prediction of the SiO2 nanoparticles prepared via Stöber process

ABSTRACTIn this study, monodispersed SiO2 nanoparticles with controllable size ranging from 20 to 100 nm have been successfully prepared by using a Stöber sol-gel process. The particle size, distribution, and morphology were examined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). In order to accurately regulate the particle size, the effects of various reaction parameters on the particle size and morphology of SiO2 nanoparticles were systematically investigated. It was found that, to some extent, the SiO2 particle size increased linearly with the increase of ammonia or water content, as well as the decrease of reaction temperature, while nearly kept constant with the increase of tetraethyl orthosilicate (TEOS). Based upon the results, an empirical formula has been developed to model/predict the particle size of the SiO2 nanoparticles over a wide range of various reaction conditions.

Mussel inspired preparation of functional silica nanocomposites for environmental adsorption applications

Surface modification of nanomaterials with polymers is an effective route to render new functions and improve the performance of the final nanocomposites. Here, a facile method was developed to fabricate polyacrylic acid (PAA)-grafted monodisperse SiO2 nanoparticles (SiO2-PDA-PAA) through a combination of mussel inspired chemistry and Michael addition reaction. To obtain the products, the SiO2 nanoparticles were first coated with polydopamine (PDA) through self-polymerization of dopamine under rather mild conditions. The PDA thin films can then be further conjugated with amino-terminated PAA, which was synthesized by chain transfer free radical polymerization using cysteamine hydrochloride as a chain transfer agent and acrylic acid as a monomer. The SiO2-PDA-PAA nanocomposites were characterized via transmission electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and X-ray photoelectron spectroscopy. The effects of contact time, solution pH, temperature and methylene blue (MB) concentration on the removal of MB were investigated. The results demonstrated that SiO2-PDA-PAA showed significant improvement in adsorption efficiency towards MB. The kinetics and isotherm studies showed that pseudo-second-order and Langmuir isotherm models were well fitted the experimental data. The values of thermodynamics parameters such as entropy change (ΔS0), enthalpy change (ΔH0) and Gibbs free energy (ΔG0) were calculated based on the Van’t Hoff equation. The negative values of thermodynamic parameters indicated that the adsorption of MB was a feasible, spontaneous and exothermic process. In summary, we developed a facile method to fabricate SiO2-based polymer nanocomposites, which showed obviously enhanced adsorption capability towards MB.

Tribological Behaviors of Carbon Fiber Reinforced Epoxy Composites Under PAO Lubrication Conditions

In order to avoid occurrence of severe seizure of motion components exposed to mixed and boundary lubrication, e.g., in engine and transmission systems, to replace metal–metal friction pairs by polymer–metal pairs provides a potential solution. In the present work, the tribological behaviors of short carbon fiber (SCF)-reinforced epoxy (EP) composites when lubricated with polyalphaolefin base oil were investigated. It was identified that the running-in tendency and friction coefficient of the composites show a close dependence on the lubrication regimes. SCF improves greatly the wear resistance of EP although they increase slightly the friction coefficient. It was demonstrated that further addition of monodispersed SiO2 nanoparticles into the EP composite filled with SCF and graphite leads to higher wear resistance. The reinforcement of SCF and the formation of a high-performance tribofilm on the surface of steel counterpart play an important role on the tribological properties of EP-based materials.

Patterned Photonic Nitrocellulose for Pseudo-Paper Microfluidics.

We report a pseudo-paper microfluidic chip based on patterned photonic nitrocellulose. The photonic nitrocellulose is fabricated using self-assembled monodisperse SiO2 nanoparticles as template. The SiO2 nanoparticles form a photonic crystal having a close-packed hexagonal structure in the microchannels, so the resulting nitrocellulose has a complementary inverse-opal structure. After lamination, a hollow channel is obtained that is partially filled with the photonic nitrocellulose. Owing to the highly ordered photonic structure of the pseudo-paper chip, the flow profile of aqueous solution wicking through the channel is more uniform than conventional paper microfluidic chip. It is also found that the wicking rate of aqueous solution can be easily manipulated by changing the diameter of the self-assembled monodisperse SiO2 nanoparticles, which determines the pore size of the photonic nitrocellulose. The fluorescent enhancement property of the photonic nitrocellulose is used to increase the fluorescent intensity for multiplex detection of two cancer biomarkers. Label-free detection of human immunoglobin G based on the structure color of the photonic nitrocellulose is also demonstrated.

Core–shell SiO2@RGO hybrids for epoxy composites with low percolation threshold and enhanced thermo-mechanical properties

Reduced graphene oxide (RGO)-encapsulated SiO2 hybrids (SiO2@RGO) were fabricated from the thermal reduction of electrostatically assembled SiO2@GO hybrids. Then, epoxy composites, filled with SiO2, SiO2@GO and SiO2@RGO hybrids, were prepared by a solvent-free curing process, and their thermal, dielectric and thermo-mechanical properties were investigated and compared. In the SiO2@RGO/epoxy composites, the mono-dispersed SiO2 nanoparticles are firmly embedded in the thin layer of RGO nanosheets, forming unique core–shell nanostructures that effectively prevent the aggregation of RGO nanosheets in the polymer matrix, construct conductive pathways at the particle–polymer interface and afford the epoxy composites with outstanding thermo-mechanical properties. The dielectric properties of the SiO2@RGO/epoxy composites exhibit a typical percolation transition near 0.174 vol% for RGO (20 wt% of SiO2@RGO hybrids), where the dielectric constant could reach 77.23 at 1 kHz, which is 22 times that of the neat epoxy resin. Upon further increase of the loading content, the gradual contact of the filler particles leads to the formation of interfacial continuous conductive networks, and both the thermal conductivity and dielectric constant of the composites show a dramatic increase. With a filler loading of 40 wt% SiO2@RGO (0.373 vol% for RGO), a thermal conductivity of 0.452 W m−1 K−1 is obtained, which is two times larger than that of neat epoxy. In addition, SiO2@RGO/epoxy composites reveal significantly decreased coefficient of thermal expansion (CTE) and increased glass transition temperature (Tg). We believe this special core–shell SiO2@RGO structure, with its inner mechanically enhanced inorganic particles and outer interfacial conductive phase, could make full use of the enhancement effect of different components and thus endow the polymer composites with outstanding properties overall.

Turning on Lanthanide Luminescence via Nanoencapsulation

Encapsulation of macrocyclic europium(III) chelates by discrete, monodisperse SiO2 nanoparticles (NPs) has been carried out, and the resulting significant enhancement of metal-derived luminescence has been studied to rationalize this dramatic effect. The tetraiminodiphenolate motif chosen for this study is easily synthesized and incorporated into the NP matrix under ambient conditions. The free complex exhibits primarily weak ligand-derived emission at room temperature, typical for these compounds, and displays intense metal-centered luminescence from the europium only when cooled to 77 K. Upon encapsulation by the NPs, however, europium-derived luminescence is visibly "turned on" at room temperature, yielding strong emission peaks characteristic of europium(III) with a corresponding enhancement factor of 6 × 10(6). The similar ligand singlet and triplet excited-state energies determined for the free complex (20820 and 17670 cm(-1), respectively) versus the encapsulated complex (20620 and 17730 cm(-1)) indicate that encapsulation does not affect the energy levels of the ligand appreciably. Instead, a detailed analysis of the metal-centered emission and ligand singlet and triplet emission bands for the free and encapsulated complexes reveals that the enhanced metal emission is due to the rigid environment afforded by the silica NP matrix affecting vibrationally mediated energy transfer. Further, the metal-centered emission lifetimes in methanol versus deuterated methanol indicate a decrease in the number of coordinated solvent molecules upon encapsulation, changing from an average of 3.3 to 2.1 bound methanol molecules and reducing the known quenching effect on europium-centered luminescence due to nearby OH vibrations.

Role of monodispersed nanoparticles on the tribological behavior of conventional epoxy composites filled with carbon fibers and graphite lubricants

The present work focuses on the role of monodispersed SiO2-nanoparticles, with an average diameter of 20nm (as introduced via a sol–gel process), on the tribological behavior of conventional epoxy (EP) composites, i.e. EP filled with short carbon fibers and graphite flakes. Moreover, the contribution of these nanoparticles was directly compared to that of sub-micron (TiO2/ZnS) particles (300nm in diameter). In particular, the tribological performance of the composites when sliding either against a rough stainless steel (Ra=0.30μm) surface or an initially mirror polished counterface (Ra=0.01μm) was compared. The monodispersed nanoparticles lead to a significant reduction in the friction and wear rate, and they contribute significantly better to the tribological performance than the sub-micron particles. When sliding took place against the rough surface, the nanoparticles resulted in an extremely thin transfer film, which was created from the initial roughness while its grooves were filled up completely. A rough counterface seems to be an essential precondition for the starting of material transfer. With the polished counterface, significant material transfer starts only after the countertface is scratched. This is true especially for the conventional composite and the hybrid composite reinforced with sub-micron particles. Whereas, the addition of nanoparticles promotes the formation of a homogeneous transfer film before the counterbody is severely scratched.

Sol-Gel Synthesis of Monodispersed SiO2 Nanoparticles in the Presence of Organic Amines

Preparation of monodispersed SiO2 nanoparticles of varied size by hydrolysis of tetramethoxysilane and polycondensation of the hydrolysis products was studied as influenced by the basicity and nucleophilicity of organic amines.