The preparation of submicrometer-sized rings by embedding and selective etching of spherical silica particles

Silica particles were embedded in a polymer layer on a water surface in such a way that they protruded out of the top and the bottom surfaces. Etching of this layer with hydrofluoric acid vapors gradually removed the particles to yield membranes with pores that continuously widen until the particles are completely removed. Removing the polymer at intermediate stages of etching revealed that the particles are first converted into rings and sickles before they are finally completely destroyed.     

Effects of the concentrations of precursor and catalyst on the formation of monodisperse silica particles in sol–gel reaction

The monodispersed hybrid silica particles could be synthesized through the one-step sol–gel reaction with organosilane (3-mercaptopropyl trimethoxysilane, MPTMS) in aqueous solution. In this study, the effects of the concentrations of organosilane and the catalyst ((NH₄OH) on the formation of silica particles were investigated. For the first time we reported the successful one-step synthesis of monodisperse hybrid silica particles using organosilane chemicals in the previous study. In order to obtain better insight about the reaction processes, the silica particles were prepared in the presence of various concentrations of MPTMS and NH₄OH. On the basis of the experimental results, it was found that particle size increases as the concentration of organosilane increases. Also, as the concentration of catalyst increases, the diameter of these monodisperse particles decreases significantly. This research can contribute to a new broad avenue for the surface functionalization and hybrid material formation with various sizes.     

Effect of surfactants on the size and morphology of the silica particles prepared by an emulsion technique

Studies were performed on precipitation of silica in an emulsion system from aqueous solution of sodium metasilicate and hydrochloric acid. Cyclohexane formed the organic phase. Anionic, cationic and non-ionic surfactants were used as emulsifiers. Optimum composition of the emulsion and optimum parameters for the precipitation reaction were established. Effects of a dispersing medium on quality of the produced silicas were examined. The silicas were subjected to physicochemical characterization. Bulk density, water, dibutyl phthalate and paraffin oil absorbing capacities were measured. Surface charge of the obtained dispersion, particle size and shape of the formed silicas were estimated. Specific surface area (BET) was defined and the complete pore characteristics was also presented for the selected silicas. Application of Rokanol K-7 (C_16–22O(CH₂CH₂O)₇H) as an emulsifier resulted in production of almost ideally spherical silica particles of nanometric size and of a monodisperse character.     

Effect of particles size on the AC electrical behavior of iron/polystyrene composites

The AC electrical characteristics of polystyrene/Iron composites filled with iron particles of average sizes: 5, 40, 110 and 250 μm, have been investigated. The AC electrical properties were studied in frequency range (50 kHz–1 MHz), and temperature range (30–110 °C) using the impedance method. The AC-conductivity and dielectric constants were determined from the measured impedance data. It was found that the applied frequency, temperature, and iron particles size affect the electrical and dielectric properties of the composites. The AC-electrical conductivity is increasing with temperature. The dielectric constant and the dielectric loss of the composites increase with decreasing the iron particles size. The universal power-law of the electrical conductivity gives exponent with 0 < m < 1 characterizing hopping conduction. The small values of the activation energy indicate that the composite of smallest iron particle size, electrons can tunnel or hop more easily from the valence band to conduction energy band due to the reduction of interparticles separation.     

Processing and interfacial bonding strength of 2014 Al matrix composites reinforced with oxidized SiC particles

The SiC powder with a SiO₂ protective layer is used as the reinforcements for 2014 Al/SiC_p composites to suppress the reaction between the Al matrix and the SiC particle. 2014 Al/SiC_p composites were fabricated by vacuum hot pressing (VHP) and subsequent extrusion using 2014 Al powders and the SiC particles covered with a SiO₂ layer. The interfacial product was found to be Mg spinel (MgAl₂O₄) formed mainly by the chemical reactions of the SiO₂ layer covered on SiC particles with the Mg, Al in the 2014 Al alloy matrix. Also the interfacial bonding strength of the composites was investigated using push-out tests of SiC rods with the SiO₂ oxidation layer, which were processed within 2014 Al alloy.     

Influence of size and volume share of WC particles on the properties of sintered metal matrix composites

Steel matrix composites are being increasingly investigated because of their wear and corrosion properties, allowing their wide application in various industrial sectors. The interaction of tungsten carbide (WC) with the steel matrix, including an analysis of its volume share and particle size, is crucial in determining the resistance to wear and corrosion of the metal matrix composite (MMC). However, there is little information in the literature about sintered MMCs based on low-alloy steels. This paper presents the results of an analysis of the influence of the volume share of WC (5?vol.% and 20?vol.%) and carbide particle size (0.7?µm and 5.0?µm) on the resistance to abrasion of a friction pair: sintered composite and bearing steel, analysed using two rotational speeds (0.02?m/s and 0.2?m/s). Moreover, the resistance to corrosion in 3.5% NaCl solution is also characterized. It is shown that both the volume share and the size of the WC particles used as reinforcement of the steel matrix have a significant impact on the densification behaviour as well as the resistance to abrasive wear and corrosion of sintered MMCs based on low-alloy steel.     

Effect of surface modification with carbon-containing groups on the size, properties, and morphology of silica particles

We report the properties of hydrated silica surface-modified with aminopropyl, 3-(2-imidazolin-1-yl)propyl, or 1H,1H,2H,2H-perfluorodecyl. The modifier groups reside on the surface of the silica nanoparticles, as shown by NMR spectroscopy. We examine the effect of the nature and concentration of the modifier on the particle size and specific surface area of silica. Thermal analysis results demonstrate that the modified materials are stable up to 430°C.     

The use of CTAB to control the size of copper nanoparticles and the concentration of alkylthiols on their surfaces

Copper nanoparticles protected by self-assembled monolayers of decanethiol have been prepared by the controlled reduction of aqueous copper salts using the modified Brust synthesis. For comparison, the nanoparticles are synthesized on different concentration of cetyltrimethylammonium bromide (CTAB). TEM, XPS, XRD, IR have been employed to investigate the structure and formation of these nanoparticles. It was found that CTAB plays a critical role in controlling stability and ease to formation 3D SAMs during synthesis.     

Effect of eutectic particles on the grain size control and the superplasticity of aluminium alloys

Aluminium alloys containing eutectic particles of the Al-Ni, Al-Mg-Si, Al-Ni-Ce and Al-Cu-Ce systems are investigated. The particles which control grain growth and stimulate grain nucleation are studied. The Zener-Smith law about dependence between grain size and particle parameters is confirmed and experimental coefficients are found. Experimental coefficients of the Zener-Smith equation obtained in this study depend on the particle size and differ from theoretical coefficients proposed by Zener and Smith. Some alloys with grain size about 3 μm demonstrate very good superplasticity indicators, namely: the strain rate sensitivity index m = 0.5-0.6 and the elongation over 400% at constant strain rate 5 × 10⁻³ s⁻¹.     

Effect of support size on the catalytic activity of metal-oxide-doped silica particles in the glycolysis of polyethylene terephthalate

Zinc oxide (ZnO) and cerium oxide (CeO2) nanoparticles were deposited on the surface of preformed silica spheres with diameters ranging from 60 to 750 nm. Ultrasonic irradiation was employed to promote the deposition of the metal oxide nanoparticles on the surface of silica. Silica-supported zinc oxide or cerium oxide was used as a catalyst in the glycolysis of polyethylene terephthalate, one of the key processes in the depolymerization of polyethylene terephthalate. The effect of the support size on the catalytic activity was studied in terms of monomer yield, and the monomer concentration was analyzed via high-performance liquid chromatography (HPLC). The morphologies and surface properties of the catalysts were characterized using a scanning electron microscope, a transmission electron microscope, and a BET surface area analyzer, while the monomer was characterized via HPLC and nuclear-magnetic-resonance spectroscopy. Both the zinc oxide and cerium oxide deposited on a smaller support showed better distribution and less aggregation. The high specific surface area of the smaller support catalysts provided a large number of active sites. The highest monomer yield was obtained with a catalyst of 60-nm silica support.     

The stacked lamellar texture on the fracture surfaces of fibre composites

A fracture surface texture, which has been variously termed as lacerations, hackles or serrations, is often observed on the matrix surface of fibre composites, most often in resin-rich regions. This texture, referred to here as a stacked lamellar texture to emphasize its plate-like nature, was studied in an E-glass/epoxy composite. Scanning electron fractographs of these materials suggest that the stacked lamellar texture arises from crack fingers due to a meniscus instability mechanism interacting with a reorienting stress field.     

Exploring the formation of focal adhesions on patterned surfaces using super-resolution imaging

The formation of focal adhesions on various sizes of fibronectin patterns, ranging from 200 μm to 250 nm, was systematically investigated by total internal reflection fluorescence microscopy and super-resolution imaging. It was found that cells adhered to and spread on these micro/nanopatterns, forming focal adhesions. On a micrometer scale the shape of the focal adhesions was elongated. However, on the nanometer scale, the shape of focal adhesions became dotlike. To further explore the distribution of focal adhesion proteins formed on surfaces, a localization-based super-resolution imaging technique was employed in order to determine the position and density of vinculin proteins. A characteristic distance of 50 nm was found between vinculin molecules in the focal adhesions, which did not depend on the size of the fibronectin nanopatterns. This distance was found to be crucial for the formation of focal adhesions. In addition, the density of vinculin at the focal adhesions formed on the nanopatterns increased as the pattern size decreased. The density of the protein was found to be 425 ± 247, 584 ± 302, and 703 ± 305 proteins μm(-2) on the 600, 400, and 250 nm fibronectin patterns respectively. Whereas 226 ± 77 proteins μm(-2) was measured for the matured focal adhesions on homogeneous fibronectin coated substrates. The increase in vinculin density implies that an increase in mechanical load was applied to the focal adhesions formed on the smaller nanopatterns.     

Experimental and computational study of the effect of the system size on rough surfaces formed by sedimenting particles in quasi-two-dimensions

The roughness exponent of surfaces obtained by dispersing silica spheres through a viscous fluid in a quasi-two-dimensional cell is examined using experimental and computational methods. The cell consists of two glass plates separated by a gap which is comparable in size to the diameter of the beads. We have studied the effect of changing the gap between the plates to a limit of about twice the diameter of the beads. If a conventional scaling analysis is performed, the roughness exponent is found to be robust against changes in the gap between the plates. The surfaces formed have two roughness exponents in two length scales, which have a crossover length of about 1 cm.; however, the computational results do not show the same crossover behavior. The single exponent obtained from the simulations stays between the two roughness exponents obtained in the experiments.     

Effects of surface treatments and size of fly ash particles on the compressive properties of epoxy based particulate composites

Particulate reinforcements for polymers are selected with dual objective of improving composite properties and save on the total cost of the system. In the present study fly ash, an industrial waste with good properties is used as filler in epoxy and the compressive properties of such composites are studied. Particle surfaces are treated chemically using a silane-coupling agent to improve the compatibility with the matrix. The compressive properties of these are compared with those made of untreated fly ash particulates. Furthermore properties of fly ash composites with two different average particle sizes are first compared between themselves and then with those made using the as-received bimodal nature of particle size distribution. Microscopic observations of compression tested samples revealed a better adherence of the particles with the matrix in case of treated particles and regards the size effect the composites with lower average particle size showed improved strength at higher filler contents. Experimental values of strengths and modulii are compared with some of the theoretical models for composite properties.     

生物陶瓷及其复合材料表面诱导类骨磷灰石层形成的研究

钙磷生物材料表面类骨磷灰石层的形成对其植入体内诱导新骨生成起非常重要的作用.本实验采用2倍模拟体液(2×SBF)为介质,通过仿生浸泡的方法研究了羟基磷灰石(HA)陶瓷及其复合材料羟基磷灰石/聚乳酸(HA/PLA)、羟基磷灰石/聚己內脂(HA/PCL)、羟基磷灰石/丝素(HA/SF)和羟基磷灰石/壳聚糖(HA/CS)表面诱导类骨磷灰石层形成的差异.实验结果表明,HA陶瓷及其复合材料在2×SBF溶液中仿生浸泡7d后,各样品表面均有一层厚度不同的类骨磷灰石层生成.并且该类骨磷灰石层的结晶度较低,晶粒较细(15～30nm),与人体自然骨无机物的结构非常类似.其中,在这4种复合材料中,HA/CS和HA/SF复合材料中因丝素蛋白和壳聚糖富含多种功能基团,能有效促进类骨磷灰石晶体的形核和生长,因而诱导类骨磷灰石生成的能力最强,显示其良好的生物活性.     

Effect of submicron size SiC particles on microstructure and mechanical properties of AZ31B magnesium matrix composites

The magnesium matrix composites reinforced with three volume fractions (3, 5 and 10 vol.%) of submicron-SiC particles (∼0.5 μm) were fabricated by semisolid stirring assisted ultrasonic vibration method. With increasing the volume fraction of the submicron SiC particles (SiCp), the grain size of matrix in the SiCp/AZ31B composites was gradually decreased. Most of the submicron SiC particles exhibited homogeneous distribution in the SiCp/AZ31B composites. The ultimate tensile strength and yield strength of the 10 vol.% SiCp/AZ31B composites were simultaneously improved. The study of interface between the submicron SiCp and the matrix in the SiCp/AZ31B composite suggested that submicron SiCp bonded well with the matrix without interfacial activity.