Improved dispersion and mechanical properties of hybrid nanocomposites

Dispersion of nanoparticles and its effect on the mechanical properties were investigated by fabricating nanocomposites via conventional sonication, sol–gel, and a combination of sonication and sol–gel methods. Silica nanoparticles in epoxy produced via sol–gel was procured as Nanopox F 400 to produce silica/epoxy nanocomposite whereas the conventional sonication method was followed to produce alumina/epoxy and carbon nanofibers (CNF)/epoxy nanocomposites. Then, the conventional sonication method was employed in the presence of sol–gel nanoparticles to improve the dispersion quality of conventional dry nanoparticles as well as to increase the particle loading. In the current method, the epoxy with silica nanoparticles produced by the sol–gel method was used as the starting material for sonication. In the subsequent step, particles of the second type were added to the silica/epoxy precursor via sonication. Using this method, two different types of nanoparticles were added to produce hybrid nanocomposites with higher particle loading where alumina and CNF were used as hybridizing particles. TEM micrographs revealed an improved dispersion quality of alumina nanoparticles and CNFs in the presence of very well dispersed silica nanoparticles. The improvement in dispersion was reflected in much improved mechanical properties of the nanocomposites.     

Synthesis of soluble polyimide/silica–titania core–shell nanoparticle hybrid thin films for anti-reflective coatings

In this study, researchers prepared polyimide/silica–titania core–shell nanoparticle hybrid thin films (PI/SiO₂–TiO₂) from soluble fluorine-containing polyimide, colloidal silica, and titanium butoxide. The soluble polyimide with carboxylic acid end groups (6FDA–6FpDA–4ABA–COOH) could condense with titanium butoxide to provide organic–inorganic bonding, and thus prevent macrophase separation. TGA and DSC analysis showed that the decomposition temperature of hybrid materials increased with an increase in the content of silica–titania nanoparticles within the hybrid films. FTIR spectra indicated that the imidization was complete and the cross-linking Ti–O–Ti network formed. HRTEM and HRSEM images showed that the size of the core–shell nanoparticles were 18–20 nm. The thickness of titania shell on the silica is about 2.5 nm. The n&k and UV–Vis analysis showed that the prepared hybrid films had good optical properties and a high refractive index of 1.735. Researchers applied the prepared PI/SiO₂–TiO₂ hybrid thin films to develop a three layer antireflective (AR) coating on the glass and PMMA substrate. Results showed that the reflectance of the AR coating on the glass and PMMA substrate at 550 nm was 0.356 and 0.495%, respectively. The transparency was greater than 90% for both AR coatings on the glass and PMMA substrates.     

Multi-functional hybrid coatings containing silica nanoparticles and anti-corrosive acrylate monomer for scratch and corrosion resistance

Multi-functional hybrid coatings having both anti-corrosion and scratch resistance were prepared from modified silica nanoparticles and functional acrylates. To improve the dispersion properties of silica nanoparticles in the organic/inorganic hybrid coatings, the surface of the nanoparticles was modified with γ-methacryloxypropyltrimethoxysilane. The coating solution could be prepared by mixing modified silica nanoparticles, tetrasiloxane acrylate, di-acrylate monomer containing an anti-corrosion functional group, acrylic acid, and an initiator in a solvent. The mixture was then dip-coated on iron substrates and finally polymerized by ultraviolet (UV) irradiation. Corrosion and scratch resistance of the coated iron was evaluated by electrochemical impedance spectroscopy (EIS) and a pencil hardness test, respectively. From the EIS results, the coatings with tetrasiloxane acrylate and di-acrylate did not show any decrease in impedance or phase angle, even after 50 days' exposure to 0.1 M NaCl electrolyte, whereas the conventional acrylate coatings started to fail after only 24 h. A hybrid coating containing the amine-quinone functional group exhibited excellent corrosion protection properties with 4-5H pencil hardness.     

High strain rate compression of epoxy based nanocomposites

This work aimed to investigate the strain-rate effect (0.001–3000 s⁻¹) on compressive properties of the highly cross-linked epoxy and the epoxy sample filled with 10 wt% sol-gel-formed silica nanoparticles. As the strain rate increased, the compressive modulus and transition strength of both samples went up distinctly, the strain at break and ultimate strength decreased more or less, while the strain energy at fracture nearly did not change. Adding the sol-gel-formed silica nanoparticles can improve effectively the compressive modulus, transition strength as well as strain energy at fracture of the epoxy polymer owing to their homogeneous dispersion in epoxy matrix.     

自组装法制备中空二氧化硅纳米粒子减反射薄膜

以正硅酸乙酯(TEOS)为壳层材料, 聚丙烯酸(PAA)为核材料, 以传统的Stöber水解法为基础制备得到结构规整的中空二氧化硅纳米粒子, 并采用自组装法制备单层减反射薄膜和宽波段双层减反射薄膜。主要研究中空二氧化硅纳米粒子的结构调控方法; 自组装次数和中空二氧化硅纳米粒子分散液的pH值对减反射薄膜透光率的影响规律, 以及具有渐变折射率的双层减反射薄膜的制备。研究结果表明: 通过调节PAA和TEOS的用量可精确调控中空二氧化硅纳米粒子的粒径和空腔体积分率, 进而可精确调控减反射薄膜的厚度和折射率; 通过酸洗工艺, 将自组装次数由10次减少为2次, 简化了涂膜的工艺条件, 在最佳工艺条件下所制备的单层减反射薄膜在350~800 nm波长范围内可显著提高玻璃的透光率, 在最佳波长(λ=520 nm)处将玻璃的透光率由91.6%提高至98.1%; 双层减反射薄膜可在更宽的波段范围内提高基材的透光率, 在400~1500 nm波长范围内将玻璃的透光率提高了5%以上。     

Strength of unidirectional glass/epoxy composite with silica nanoparticle-enhanced matrix

A technique was developed to improve the strength of unidirectional composites by enhancing the matrix properties through nanoparticles infusion. A commercially available standard DGEBA epoxy with silica nanoparticles (Nanopox F 400) was used as the matrix to make fiber composites. The silica nanoparticles in Nanopox were grown in situ via a sol–gel process resulting in a concentration of 40 wt% which was later diluted to 15 wt% particle loading. TEM images showed very uniform dispersion of silica nanoparticles with a size distribution of about 20 nm. Compression test revealed a substantial improvement (40%) in elastic modulus of the modified epoxy. A modified vacuum assisted resin transfer molding process was used to fabricate unidirectional E-glass fiber reinforced silica/epoxy nanocomposites. Inclusion of silica nanoparticles dramatically increased the longitudinal compressive strength and moderately increased the longitudinal and transverse tensile strengths. A microbuckling model was used to verify the compression testing results.     

Palladium supported on functionalized mesoporous silica as an efficient catalyst for Heck reaction

Pd nanoparticles supported in functionalized mesoporous silica were prepared. Mesoporous silica support was modified with [3-(2-aminoethyl aminopropyl)] trimethoxysilane. Palladium ions were grafted onto the functionalized mesoporous silica and reduced with hydrazine hydrate to obtain the Pd nanoparticles supported on functionalized mesoporous silica. The Pd loading in the nanocomposite of Pd supported on the functionalized mesoporous silica is 4.30 wt%. CO chemisorption analysis on the nanocomposite shows a Pd dispersion as high as 35% and a Pd surface area of 156 m²/g. The surface area, pore size, and pore volume decrease slightly with the incorporation of the Pd nanoparticles into the functionalized mesoporous silica. Pd supported on the functionalized mesoporous silica with controlled molar ratio of amino groups to palladium exhibits an excellent catalytic activity and low Pd leaching for the Heck carbon-carbon coupling reaction. The catalyst can be reused for at least six recycles in air with only a minor loss of activity.     

Directional enhancement of refractive index and tunable wettability of polymeric coatings due to preferential dispersion of colloidal TiO2 nanorods towards their surface

We demonstrate the fabrication of nanocomposite coatings, of organic-capped colloidal TiO₂ nanorods dispersed into a poly(methyl methacrylate) matrix, with rising value of refractive index from the bottom to the top layers, and UV-induced surface wettability alteration, in a reversible manner. This behaviour is attributable to preferential dispersion of the TiO₂ nanoparticles towards the superficial layers of the coatings. Above a critical TiO₂ loading, the nanorods at the surface form aggregates deteriorating the optical and the surface properties of the nanocomposites. The optimal conditions for nanocomposite films preparation in terms of optimized nanorods dispersion, optical clarity, and surface smoothness are determined.     

On the surface roughness and hydrophobicity of dual-size double-layer silica nanoparticles

An array of double-layer silica nanoparticles with two different length scales was introduced onto the glass substrates for investigating the effect of surface morphology on wettability. Silica nanoparticles of 7, 12, 20, and 40 nm in diameters were individually functionalized using 3-aminopropyltriethoxysilane or 3-glycidoxypropyltrimethoxysilane. Silica nanoparticles functionalized with the complementary amine and epoxy groups were deposited alternately on glass surfaces to obtain durable and covalently bound dual-size double-layer silica nanoparticle coatings. Order of the deposition of nanoparticles for the fabrication of dual-size double-layer coatings was found to be the most determinant factor on surface roughness and hence the wettability. Deposition of the bigger nanoparticles on top of smaller ones resulted in rougher surfaces and consequently higher hydrophobicity. Based upon these findings, it is now possible to fine-tune surface roughness and subsequent wettability by controlling the size ratio of dual-size double-layer silica nanoparticles.     

Large-scale assembly of colloidal nanoparticles and fabrication of periodic subwavelength structures

This paper reports a simple and scalable spin-coating technique for assembling 70?nm silica nanoparticles into non-close-packed colloidal crystals over a large area. The thickness of the shear-aligned colloidal crystals can be controlled from hundreds of layers to a single monolayer by adjusting the spin-coating conditions. We further demonstrate that the spin-coated colloidal monolayers can be used as structural templates to pattern sub-100?nm pillar arrays directly on silicon substrates. The resulting subwavelength-structured pillar arrays exhibit excellent broadband antireflective and superhydrophobic properties, which are promising for developing self-cleaning antireflection coatings for crystalline silicon solar cells. This bottom-up approach enables large-scale production of periodic nanostructures with resolution beyond the optical diffraction limit that have important technological applications ranging from high-density data storage and optoelectronics to biological sensing and subwavelength optics.     

High-performance, single-layer antireflective optical coatings comprising mesoporous silica nanoparticles

Mesoporous silica nanoparticles are used to fabricate antireflectance coatings on glass substrates. The combination of mesoporous silica nanoparticles in conjunction with a suitable binder material allows mechanically robust single layer coatings with a reflectance <0.1% to be produced by simple wet processing techniques. Further advantages of these films is that their structure results in broadband antireflective properties with a reflection minimum that can tuned between 400 nm and 1900 nm. The ratio of binder material to mesoporous nanoparticles allows control of the refractive index. In this report, we discuss how control of the structural properties of the coatings allows optimization of the optical properties.     

Highly dense and uniformly dispersed platinum nanoparticles on poly(acrylic acid) modified multi-walled carbon nanotubes for methanol oxidation

Poly(acrylic acid) modified multi-walled carbon nanotubes (PAA-MWNTs) were synthesized through in situ radical polymerization in acetone and the PAA-MWNTs were used as supporting material for platinum nanoparticles. Platinum nanoparticles were deposited on the surface of PAA-MWNTs with high loading and high dispersion through ethylene glycol reduction. The size of Pt nanoparticles on PAA-MWNTs can be tuned by the water content in the reaction system and the loading amount can be adjusted by the mass ratio of H₂PtCl₆ to PAA-MWNTs. The electrocatalytic properties of the Pt/PAA-MWNTs catalyst were evaluated by methanol oxidation. The results of cyclic voltammetry show that the Pt/PAA-MWNTs composite possesses high electrocatalytic activity, good long-term stability and storage property, which can be attributed to the small particle size and high dispersion of Pt nanoparticles as well as the nature of MWNTs.     

Low-energy bead-milling dispersions of rod-type titania nanoparticles and their optical properties

The low-energy dispersion of nanomaterials in the bead-milling process is examined. The effect of milling parameters including bead size, rotation speed, and milling time on the dispersibility of fragile rod-type titanium dioxide nanoparticles is investigated. From experimental data obtained for the morphological, optical, and crystalline properties of dispersed nanoparticles, an unbroken primary particle dispersion in colloidal suspension was obtained only by conducting the bead-milling process using the optimum milling parameters. Deviation from the optimum conditions (i.e., higher rotation speed and larger bead size) causes re-agglomeration phenomena, produces smaller and ellipsoidal particles, and worsens crystallinity and physicochemical properties, especially the refractive index, of the dispersed nanoparticles. We also found that decreases in refractive index induced by the milling process are related to collisions forming broken particles and the amorphous phase on the surface of the particles. In addition, the present low-energy dispersion method is prospective for industrial applications, confirming almost no impurity (from breakage of the beads) was apparent in the final product.     

Biopolymer composites of wheat gluten with silica and alumina

Two composite systems were explored to assess the effect of particle dispersion on the properties of filled wheat gluten composites. Nanosilica particles and micro-alumina particles were combined with several silane coupling agents by various methods to perform a broad brush survey of chemical and physical interactions. Thermo-gravimetric analysis (TGA) was used to assess surface coverage on coated particles. Electron microscopy (scanning and transmission) techniques were used to assess particle dispersion and surface interactions. Producing the silica particles in the wheat gluten matrix led to better physical properties, as measured by 3-point bending, than producing the silica particles first, and then mixing them into the wheat gluten. Similarly, coating the alumina particles with silane coupling agents in the wheat gluten matrix led to better mechanical properties than first coating the alumina with silane and then mixing the coated particles into the wheat gluten.     

Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium semitectum

Development of environmental friendly procedures for the synthesis of metal nanoparticles through biological processes is evolving into an important branch of nanobiotechnology. In this paper, we report on the use of fungus “Fusarium semitectum” for the extracellular synthesis of silver nanoparticles from silver nitrate solution (i.e. through the reduction of Ag⁺ to Ag⁰). Highly stable and crystalline silver nanoparticles are produced in solution by treating the filtrate of the fungus F. semitectum with the aqueous silver nitrate solution. The formations of nanoparticles are understood from the UV-vis and X-ray diffraction studies. Transmission electron microscopy of the silver particles indicated that they ranged in size from 10 to 60 nm and are mostly spherical in shape. Interestingly the colloidal suspensions of silver nanoparticles are stable for many weeks. Possible medicinal applications of these silver nanoparticles are envisaged.     

Comparative studies between synthetic routes of SiO2@Au composite nanoparticles

We studied two different methods for the deposition of Au nanoparticles (Au NPs) onto the functionalized silica microspheres. One method was to mix the two kinds of particles together and react at room temperature overnight. The other one was to reduce hydrochloroauric acid to Au NPs with sodium citrate in the presence of the functionalized silica microspheres (one for the naked silica microspheres, the other for the Au-attached silica microspheres). We investigated the morphologies of SiO₂@Au composite nanoparticles synthesized by these two methods, and found that the latter achieved a denser Au coverage on silica microspheres. Furthermore, we studied the effect of the pH values in a wide range, respectively, for the two methods. A possible mechanism was put forward to interpret the formation of SiO₂@Au composite nanoparticles and the effects of the synthetic routes and pH values on the morphologies and optical properties.     

Thermo-mechanical properties of polysulfone based nanocomposites with well dispersed silica nanoparticles

The effect of the filler on the thermo-mechanical properties of polysulfone filled nanocomposites was studied considering different loads of silica nanoparticles (0, 1, 2, 5 and 10 wt%). Thermal characterization showed that: (i) the degradation temperature slightly increases with the content of particles; (ii) glass transition temperature is not affected by the presence of the particles, suggesting a weak interaction between the matrix and the particles. Although thermogravimetric analysis indicate there may be certain favorable interactions between the polymer and the filler, they must not be so important as to reduce chain mobility nearby the surface of the particles. Mechanical properties (modulus of rupture, hardness, indentation modulus, etc.) remain almost constant up to relatively high contents of nanoparticles (5 wt%). A significant increase was only observed for the sample with 10% of nanoparticles suggesting that, in this system, interconnection between particles must exist to efficiently modify the polysulfone properties.     

Particulate structures produced by electrosprays of colloidal silica suspensions in both negative and positive zeta potentials

Interaction between surface charge (zeta potential) of colloidal silica nanoparticles and the charge-induced droplets suspended in the gas phase by electrospray is investigated for the first time based on the particle physical (morphology, size, and size distribution) and optical properties. Colloidal silica nanoparticles having negative and positive zeta potential were subjected to electrospray in both negative and positive mode, and deposited on a substrate (silicon wafer). Visual observation of the substrate with particle deposition shows various white shades, corresponding to the changes in optical properties, as supported by the ultraviolet-visible–near-infrared spectroscopy. Microscopic analysis revealed the strong correlation between the colloid surface charge and charging mode (positive or negative) of the sprayed droplets to the particle morphology and size. The findings of the present study demonstrate the capability of the electrospray method to tune the physical and optical properties of colloidal silica nanoparticles with different surface charges.     

Influence of Silicification on the Structural and Biological Properties of Buffer‐Mediated Collagen Hydrogels

A buffer‐mediated gelation route for collagen hydrogels that allows the formation of homogeneous composite and hybrid materials with various silica sources (i.e., colloidal silica and soluble silicates) at high concentration (up to 25 × 10^?3 M ) is described. Most significant improvement in rheological properties and proliferation of primary adult human dermal fibroblasts was obtained for the silicate‐based hybrid materials. A similar trend was observed in composite materials incorporating 14 nm SiO₂ nanoparticles, although to a much lesser extent, whereas larger colloids (80 and 390 nm) did not significantly impact mechanical stability and cell behavior. Modification of 80 nm particles surface with amine groups weakens the collagen‐mineral interface, resulting in the decrease of material stability and leading to particle aggregation during the course of cell proliferation experiments.     

Fabrication of nanocomposite particles with superparamagnetic and luminescent functionalities

A new kind of superparamagnetic luminescent nanocomposite particles has been synthesized using a modified Stöber method combined with an electrostatic assembly process. Fe₃O₄ superparamagnetic nanoparticles were coated with uniform silica shell, and then 3-aminopropyltrimethoxysilane was used to terminate the silica surface with amino groups. Finally, negatively charged CdSe quantum dots (QDs) were assembled onto the surface of the amino-terminated SiO₂/Fe₃O₄ nanoparticles through electrostatic interactions. X-ray diffraction (XRD), transmission electron microscopy (TEM), microelectrophoresis, UV-vis absorption and emission spectroscopy and magnetometry were applied to characterize the nanocomposite particles. Dense CdSe QDs were immobilized on the silica surface. The thickness of silica shell was about 35 nm and the particle size of the final products was about 100 nm. The particles exhibited favorable superparamagnetic and photoluminescent properties.