Direct fluorination as a novel organophilic modification method for the preparation of Illite/polypropylene nanocomposites

This study reports the application of illite as a clay filler and direct fluorination as an organophilic modification for clays. Illite was also modified using conventional methods, with reagents such as 3-aminopropyltrimethoxysilane and hexadecyl-trimethoxysilane for comparison of the resultant illite/polypropylene (PP) composites with the fluorinated illite/PP composites. The thermal properties, flame retardancy, and mechanical properties of the resultant composites were also investigated. Fluorination of illite resulted in exfoliation and more thermally stable organophilic modification compared with the conventional silane treatment. When comparing two different silane-treated illite/PP composites with fluorinated illite/PP composites, fluorinated illite had better thermal stability and exfoliation after modification and more improved dispersion in PP matrix. This resulted in improved thermal stability, flame retardancy, and mechanical properties compared with the silane-treated illite/PP composites. The fluorinated illite/PP composite exhibited a 28% increase in thermal stability and a 50% increase in flame retardancy compared with neat PP. Fluorination of illite yielded at least 50% further improvement in the thermal stability and flame retardancy of the resulting illite/PP composites compared with the conventional silane treatments.     

Two-dimensional SnS nanosheets fabricated by a novel hydrothermal method

Two-dimensional (2D) Tin (II) sulfide (SnS) nanosheets were successfully synthesized by a novel thioglycolic acid (TGA) assisted hydrothermal method. X-ray diffraction characterization reveals that the product is well-crystallized SnS with orthorhombic structure. Transmission electron microscopy observation shows that the SnS crystals display 2D sheet-like nanomorphology. Further structure characterization by selected area electron diffraction identifies that the SnS nanosheets are single crystalline in nature. Furthermore, the mechanism and critical factors for the TGA-assisted hydrothermal synthesis of the SnS nanosheets have been preliminarily discussed.     

Effects of surface modification on the fluorescence properties of conjugated polymer/ZnO nanocomposites

We report the effects of surface modification on the fluorescence properties of conjugated polymer/zinc oxide nanocomposites. Zinc oxide nanoparticle surface was partially capped by poly(vinylpyrolidone) (PVP) during hydrolysis of zinc acetate dihydrate in methanol in ambient condition. The ZnO-capped nanoparticles were characterized by XRD and TEM. The fluorescence properties of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/ZnO nanocomposites with different mass ratios were studied by steady-state and time-resolved spectroscopy. The results indicate that the surface-modified ZnO nanoparticles are more effective to quench the emission of MEH-PPV by charge transfer process than the non-capped ZnO. The more effective charge transfer in MEH-PPV/ZnO-capped is attributed to the better dispersion of the nanoparticles in MEH-PPV matrix and THF solvent.     

Preparation of PMN–PT–BT/Ag nanocomposites by surface modification with MgO sol

Nanocomposites of 0.96(0.91Pb(Mg_1/3Nb_2/3)O₃–0.09PbTiO₃)–0.04BaTiO₃ (PBT) with Ag were prepared via synthesis of low-temperature-sinterable PBT/Ag composite powder and its surface modification with a MgO sol. Dielectric properties and modulus of rupture were investigated as a function of the amount of the MgO sol at sintering temperature in the range from 850 to 1000 °C. The MgO sol seemed to suppress the diffusion and migration of Ag during the heat treatment to give rise to the homogeneous microstructure with 300–80 nm of Ag particles in about 3.5–2.5 μm grains. The proper amount of the MgO sol seemed to be 0.5–1.0 wt.% for the PBT powder with 3.0 mol% Ag. The PBT/Ag nanocomposites showed density >99% T.D., ɛ_rt of 18,000–20,000, tan δ of 1–0.5%, specific resistivity of 10¹² Ω cm, and MOR of 125–145 MPa.     

Graphite oxide/poly(methyl methacrylate) nanocomposites prepared by a novel method utilizing macroazoinitiator

Graphite oxide (GO)/poly(methyl methacrylate) (PMMA) nanocomposites were prepared by a novel method utilizing macroazoinitiator (MAI). The MAI, which has a poly(ethylene oxide) (PEO) segment, was intercalated between the lamellae of GO to induce the inter-gallery polymerization of methyl methacrylate (MMA) and exfoliate the GO. The morphological, conductivity, thermal, mechanical and rheological properties of these nanocomposites were examined and compared with those of intercalated nanocomposites prepared by polymerization with the normal radical initiator, 2,2′-azobisisobutyronitrile. The improvement in conductivity by GO was more evident in exfoliated nanocomposites compared to that of intercalated nanocomposites. For example, a conductivity of 1.78 × 10⁻⁷ S/cm was attained in the exfoliated nanocomposite prepared with 2.5 parts GO per 100 parts MMA, which was about 50-fold higher than that of the intercalated nanocomposite. The thermal, mechanical and rheological properties also indicate that thin GO with a high aspect ratio is finely dispersed and effectively reinforced the PMMA matrix in both exfoliated and intercalated nanocomposites.     

Electrical and thermophysical properties of epoxy/aluminum nitride nanocomposites: Effects of nanoparticle surface modification

The traditional epoxy resin used for electrical and electronic industry has a poor thermal conductivity and no longer meets the increasingly cooling requirements of electric equipments and electronic devices. Ceramic nanoparticles with high thermal conductivity and low dielectric constant represent good candidates to improve the thermophysical properties of epoxy resin. This paper reports the effects of surface modification of AlN nanoparticles on morphology, glass transition, electrical property and thermal conductivity of the epoxy composites. Gamma-aminopropyl triethoxysilane was used as a silane coupling agent for the surface modification of the AlN nanoparticles. It was found that the surface modification of the nanoparticles not only improved the dispersion of the nanoparticles, but also showed an enhancement in electrical and thermophysical properties of the epoxy composites. The surface modification technology presented a strategy to prepare nanocomposites having high thermal conductivity simultaneously with low dielectric loss.     

Nanoporous surface fabricated on metal sheets by alloying/dealloying technique

An alloying/dealloying technique including stacking rolling was used to fabricate nanoporous architecture on Au sheet surface. Under appropriate conditions, a nanoporous surface layer with a thickness of 150-250 nm was generated. The extended immersion of the sample in the electrolyte (HNO₃) increased the ligament size of the nanoporous architecture up to 41 nm. Cross-sectional observations suggested that the nanoporous surface layer can be seamlessly bonded to the bulk substrate Au. True surface area, which was measured by an electrochemical method, decreased as ligament size increased by the extended immersion. The relationship among surface area, ligament size and volume shrinkage was investigated.     

Enhancing mechanical properties of styrene–butadiene rubber/silica nanocomposites by in situ interfacial modification with a novel rare-earth complex

In this study, a novel rare-earth complex, dithio-aminomethyl-lysine samarium (DALSm), was prepared and then was employed as activator, accelerator, cross-linker and interfacial modifier to improve the mechanical properties of SBR/silica nanocomposites. The results showed that 6 phr DALSm performed a higher vulcanization efficiency than the combination of 5 phr activator zinc oxide (ZnO), 2 phr stearic acid (SA), and 2 phr accelerator diethyl dithiocarbamate zinc (EDCZn). Meanwhile, the XPS and FTIR analysis of DALSm/silica model compounds confirmed that hydrogen bonds and coordination bonds could be formed between DALSm and silica during vulcanization process, which can effectively facilitate the homogenous dispersion of silica particles into SBR matrix and enhance the interface adhesion between rubber matrix and filler. As a consequent, the mechanical properties of SBR/DALSm/silica nanocomposites were substantially improved and much more excellent than those of the SBR/EDCZn/silica nanocomposites containing equivalent filler content. Based on the results of immobilized polymer layer, the reinforcing mechanism of DALSm in SBR/silica nanocomposites was analyzed.     

Mechanism of surface modification of a porous-coated Ti-6Al-4V implant fabricated by electrical resistance sintering

A porous-coated Ti-6Al-4V implant was fabricated by electrical resistance sintering, using 480 F capacitance and 1.5 kJ input energy. X-ray photoelectron spectroscopy (XPS) was used to study the surface characteristics of the implant material before and after sintering. There were substantial differences in the content of O and N between as-received atomized Ti-6Al-4V powders and the sintered prototype implant, which indicates that electrical resistance sintering alters the surface composition of Ti-6Al-4V. Whereas the surface of atomized Ti-6Al-4V powders was primarily TiO₂, the surface of the implant consisted of a complex of titanium oxides as well as small amounts of titanium carbide and nitride. It is proposed that the electrical resistance sintering process consists of five stages: stage I – electronic breakdown of oxide film and heat accumulation at the metal-oxide interface; stage II – physical breakdown of oxide film; stage III – neck formation and neck growth; stage IV – oxidation, nitriding, and carburizing; and stage V – heat dissipation. The fourth stage, during which the alloy repassivates, is responsible for the altered surface composition of the implant.     

Titanium dioxide/cellulose nanocomposites prepared by a controlled hydrolysis method

TiO₂/cellulose nanocomposites were prepared through the titanyl sulphate hydrolysis in acidic medium in the presence of cellulosic fibres. The influence of several reaction parameters on the morphological characteristics of the nanocomposites was investigated. There is evidence from this study that in specific experimental conditions, the cellulose fibres promote the nucleation and growth of TiO₂ particles, yielding hybrid materials containing up to 46% TiO₂. Two series of paper handsheets having distinct TiO₂ content have been prepared, one from a selected hybrid composition and the other from mixtures of commercial TiO₂ and cellulose fibres. Comparative optical studies performed on the paper handsheets revealed a much higher opacity for the synthetic sample.     

Homogeneous chitosan/carbonate apatite/citric acid nanocomposites prepared through a novel in situ precipitation method

Homogeneous nanocomposites composed of carbonate apatite and chitosan in the presence of citric acid were synthesized by a novel in situ precipitation method. The morphological and componential properties of composites were investigated. The carbonate apatite particulates, in sizes of about 50–100 nm, were distributed within the network chitosan hydrogel homogeneously, moreover, inorganic particles could be controlled by the size of networks of organic matrix which was mediated with crosslink degree of chitosan. Through highly magnified TEM observation, it can be shown that inorganic particles were composed of more fine sub-particles whose diameters were between 2 and 5 nm in size without regular crystallographic orientation. The concept of multiple-order template mediation was brought forward for the first time. A novel hierarchical porous nanocomposite scaffold was also prepared by multilevel freeze-drying technique and its mechanical performance had obvious increase compared with neat chitosan. These results provided an efficient approach toward new biomimetic tissue scaffold for the biomedical applications with enhanced intensity/bioactivity and controlled resorption rates.     

Effect of fiber surface modification on the mechanical and water absorption characteristics of sisal/polyester composites fabricated by resin transfer molding

Sisal fibers were subjected to various chemical and physical modifications such as mercerization, heating at 100 °C, permanganate treatment, benzoylation and silanization to improve the interfacial bonding with matrix. Composites were prepared by these fibers as reinforcement, using resin transfer molding (RTM). The mechanical properties such as tensile, flexural and impact strength were examined. Mercerized fiber-reinforced composites showed 36% of increase in tensile strength and 53% in Young’s modulus while the permanganate treated fiber-reinforced composites performed 25% increase in flexural strength. However, in the case of impact strength, the treatment has been found to cause a reduction. The water absorption study of these composites at different temperature revealed that it is less for the treated fiber-reinforced composites at all temperatures compared to the untreated one. SEM studies have been used to complement the results emanated from the evaluation of mechanical properties.     

A new method for surface modification of TiO2/Al2O3 nanocomposites with enhanced anti-friction properties

In this paper, the TiO₂/Al₂O₃ composite nanoparticles were prepared by a hydrothermal method and in situ modified with acrylic acid. It was found that the mean particle size of modified TiO₂/Al₂O₃ composite nanoparticles was about 80 nm with a uniform distribution by the particle size analysis. The modified TiO₂/Al₂O₃ composite nanoparticles can disperse in lubricating oil homogenously for several weeks. The dispersion stabilization of modified TiO₂/Al₂O₃ composite nanoparticles in lubricating oil was significantly improved in comparison with the as-prepared nanoparticles, which was due to the introduction of grafted polymers by surface modification. The formation of covalent bands was identified by Fourier transform infrared spectrum. Under an optimized concentration of 0.1 wt%, the averaged friction coefficient was reduced by 14.75%, when the modified TiO₂/Al₂O₃ composite nanoparticles were used as lubricating oil additivities.     

Unsaturated polyester/bentonite nanocomposites: Influence of clay modification on final performance

In this work, unsaturated polyester/bentonite nanocomposites were obtained and characterized. The bentonite used was unmodified and with different chemical treatments. The effects of these different chemical modifications (cation exchange reactions with quaternary ammonium and phosphonium salts) of this clay as well as the effect of clay content on the thermal, barrier (water absorption), mechanical (flexural) and dynamic-mechanical properties of unsaturated polyester matrix were analyzed. The results clearly show that the chemical modifications of the clay cause a desired effect on its final properties improving the performance of the nanocomposites. The enhancements could be directly related to the dispersion of the clay inside the matrix, as shown by transmission electron microscopy.     

Microstructure and mechanical properties of CNT/Ag nanocomposites fabricated by spark plasma sintering

Carbon nanotube/silver (CNT/Ag) nanocomposites include CNT volume fraction up to 10?vol.% were prepared by chemical reduction in solution followed by spark plasma sintering. Multiwalled CNTs underwent surface modifications by acid treatments, the Fourier transform infrared spectroscopy data indicated several functional groups loaded on the CNT surface by acid functionalisation. The acid-treated CNTs were sensitised and activated. Silver was deposited on the surface of the activated CNTs by chemical reduction of alkaline silver nitrate solution at room temperature. The microstructures of the prepared CNT/Ag nanocomposite powders were investigated by high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy and X-ray powder diffraction analysis. The results indicated that the produced CNT/Ag nanocomposite powders have coated type morphology. The produced CNT/Ag nanocomposite powders were sintered by spark plasma sintering. It was observed from the microstructure investigations of the sintered materials by HRSEM that the CNTs were distributed in the silver matrix with good homogeneity. The hardness and the tensile properties of the produced CNT/Ag nanocomposites were measured. By increasing the volume fraction of CNTs in the silver matrix, the hardness values increased but the elongation values of the prepared CNT/Ag nanocomposites decreased. In addition, the tensile strength was increased by increasing the CNTs volume fraction up to 7.5?vol.%, but the sample composed of 10?vol.% CNT/Ag was fractured before yielding.     

Mechanical properties of NBR/clay nanocomposites by using a novel testing system

NBR/clay nanocomposites are prepared by two different filler types: clay microparticles and clay nanoparticles. The morphology properties of all specimens are explored by XRD and SEM. The mechanical properties are characterized by means of a novel video-controlled method under uniaxial tension. Apart a limited increase in tensile stress at small strains, the ultimate stress at rupture of nanocomposites is much higher than microcomposites. The most dramatic phenomenon is the development of volume strain while the materials are stretched. The nucleation of voids is much more active in composites containing the filler with higher specific surface when the cavitation occurs at the poor interface between the clay platelets and the rubber matrix. In turn, the existence of very diffuse voids hinders the propagation of cracks and retards the rupture process. DMA results reveal that the interfacial action of NBR molecules with layered silicates increases with the degree of intercalation.     

Carbon monoxide detector fabricated on the basis of a tin oxide novel doping method

Toxic gas detection is a common issue of interest in domestic as well as industrial environments. There are, in fact, accurate methods to measure gas concentrations (Fourier transform infrared, gas chromatographs, or mass spectrometers) but they are too expensive and require skilled operators. Therefore, these complex detection systems are not useful for many applications, such as hazardous gas level detection in domestic appliances. In this paper, investigations lead to the fabrication of a micromachined tin oxide device for carbon monoxide detection in domestic environments. Relevant parameters that influence gas detection are analyzed and thus the device fabrication process defined by means of microtechnologies. Throughout the material optimization for CO detection, three different additive adding methods by dc sputtering PVD technique are studied and compared for two additives: Pt and Pd.     

无压熔渗制备SiCp/Al复合材料的界面改性研究进展

研究表明,SiCp/Al间界面润湿性的好坏是采用无压熔渗法制备高体积分数SiCp/Al复合材料的最关键因素,也是影响复合材料性能的主要因素.本文从界面反应和界面润湿性角度出发,综述了近几年来国内外关于SiCp/Al复合材料的界面研究情况.     

Silica surface modification reactions with aluminum and boron alkyls and (alkyl) chlorides: reactivities and surface nanostructures

The functionalization of nanoporous and nanoparticulate silica surfaces requires a molecular level understanding of the chemistry and structures which result from surface reactions. Various types of reactive groups on silica can participate, giving rise to different nanostructures. It is necessary to devise methods to alter the reactive nature of silica surfaces to control the nanoscale chemical structure. Various silica pretreatments are utilized to alter the silica surface prior to reaction with AlEt3, AlEtxCl(3-x), BEt3, BCl3, and TiCl4. Reactivities of these surface reactive reagents are compared. Aluminum compounds preferentially react with loss of alkane rather than HCl, in a thermodynamically controlled reaction as determined by ab initio computational methods. Consideration of the structures resulting from reaction of the boron and aluminum compounds above with silica surface diols has been taken into account. Particular attention has been paid to the possibility of forming a cyclic 4-membered ring structure. While this is unlikely to form from reactions with MCl3, such structures may be possible when reacting silicas with MMe3.     

Effect of silane modification on CNTs/silica composites fabricated by a non-firing process to enhance interfacial property and dispersibility

Carbon nanotube/ceramic composites have been in the spotlight thanks to their excellent properties. Sintering is the vital part of ceramics fabrication in terms of reliability, however sintering the carbon nanotube (CNT) based ceramic composites is a challenging task. In this study, interfacial bonding of silane functionalized CNT with silica ceramic is investigated by a non-firing sintering process. CNTs are first treated by a mixed acid with the aid of a silane 3-aminopropyl triethoxysilane (APTES), which improves the chemical bonding and dispersibility of CNT in ceramic bodies. The extent of APTES chemical functionalization and mechanical property of CNT/silica ceramic composites are characterized using Raman spectrometer, FT-IR analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and three-point bending strength measurement. Results show that composites are successfully prepared without sintering with stable CNT-silica interface, superior dispersibility, and good mechanical properties.