The sol-gel preparation of ZnO/silica core-shell composites and hollow silica structure

Three kinds of different ZnO colloid particles (flowerlike particles, nanoribbons and microspheres) and one kind of ZnO film have been coated with silica via a simple sol-gel method in the Stöber system and ZnO/silica core-shell microparticles or films have been obtained. The thickness of silica shell can be controlled by adjusting the concentration of TEOS added into the system. If the ZnO core is etched off by HCl, corresponding, hollow silica particles or film will be generated.     

Preparation of acetylcellulose/silica composites by sol-gel method and their mechanical properties

Acetylcellulose (AC)/silica composites were prepared by sol-gel method in an attempt to realize materials with Young's moduli and bending strengths similar to those of cortical bones. Si(OCH₃)₄ (TMOS)-AC-H₂O-HNO₃-tetrahydrofuran-CH₃OC₂H₄OH solutions were allowed to be gelled, where AC/TMOS mole ratios were defined for AC monomers, and the gels were dried at 30–70^∘C to obtain composites. The composites prepared from solutions of mole ratios of AC/TMOS = 0.5 and 1.0 were composed of micrometer-sized particles rich in silica surrounded by the matrix rich in AC. The composites from solutions of AC/TMOS = 2.0, on the other hand, the interface between the particles and the matrix was much less distinct. All the composite samples showed good machinability, which could be cut into 5 mm × 2 mm × 4.4 mm rectangular specimens by an electric saw without cracking or fracture. The specimens were subjected to three-point bending test, where the degree of plastic deformation and the fracture strain increased, and Young's modulus and bending strength decreased with increasing AC/TMOS ratio in the starting solutions. When the gels were dried at higher temperatures, Young's modulus and strength increased. Young's modulus and bending strength could be varied in the range of 1.8–3.9 GPa and 48–100 MPa, respectively, by varying the AC/TMOS ratio in solutions and the drying temperature.     

Carbon nanotube/polycarbonate composites as multifunctional strain sensors

In this study we demonstrate that multiwalled carbon nanotube fillers can impart a strain sensing functionality to a composite. The nanocomposite is fabricated by dispersing 5% weight of multiwalled nanotube fillers into a polycarbonate matrix. When subjected to linear and sinusoidal dynamic strain inputs, the instantaneous change in the electrical resistance (deltaR/R0) of the nanocomposite responds in a manner similar to a strain gage. The sensitivity of the nanocomposite sensor was measured to be approximately 3.5 times that of a typical strain gage. This sensitivity of the nanocomposite's electrical properties to mechanical stress implies that in addition to enhancing mechanical properties (strength, stiffness, structural damping, etc.), these multifunctional materials show the potential to provide real-time structural health monitoring and self-diagnostic functionalities.     

碳纳米管复合铌酸钠钾压电陶瓷的制备和研究

采用传统固相反应法制备了铌酸钠钾(KNN)粉体,在该粉体中添加碳纳米管(CNT)后,制备成CNT-KNN复合材料,研究了该复合材料的介电和压电性能。实验发现CNT的添加没有改变KNN压电陶瓷的晶体结构。少量的CNT添加(0.02‰(质量分数))提高了压电性能,过多的CNT(0.02‰(质量分数))会导致压电性能降低。同时发现,CNT的添加降低了样品的介电常数,介电性能明显依赖于密度关系。     

Carbon nanotube composites synthesized by ion-assisted pulsed laser deposition

We have synthesized thin CN_x films on Si (100) substrate at high temperatures (600 and 700°C) by nitrogen ion-assisted pulsed laser deposition (PLD). The bonding characteristics and microstructure determinations have been accomplished using X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), respectively. The radial distribution function (RDF) analysis of the electron diffraction patterns was performed to determine the short range atomic order in these films. The results reveal the presence of carbon predominantly in the trigonally-coordinated state with small fractions of nitrogen (upto 20 at.%) bonded to carbon. The electron diffraction and the high resolution images in cross-section view reveal that there is a textured growth of nanotube or graphite-like ribbons. The plan-view specimens show high resolution images with bended layers similar to that of onion or nanotube like features. The kinetics of the ions assisting the growth is assumed to be important to grow the basal planes (00l) of graphite perpendicular to the substrate. The large anisotropic surface energies in two perpendicular directions in graphite suggest that ions can create nonequilibrium conditions to alter the growth mode of graphitic planes. The importance of ion-assisted PLD to grow novel nanotube or fullerenelike structure in the form of thin film composites for electron field emission devices is emphasized.     

Multiscale reinforcement and interfacial strengthening on epoxy-based composites by silica nanoparticle-multiwalled carbon nanotube complex

The multiscale reinforcement and interfacial strengthening on epoxy-based composites by nanoscale complex composed of zero-dimensional silica nanoparticles (SiO₂) and one-dimensional multiwalled carbon nanotubes (MWCNTs) was examined. The SiO₂–MWCNT complex was successfully prepared by multi-step functionalization, which was characterized with FTIR, XPS and TEM. Mechanical properties of epoxy (EP) composites were significantly enhanced by SiO₂–MWCNTs rather than other functionalized MWCNTs, due to synergy reinforcing effect of MWCNTs and SiO₂ as well as enlarged interfacial areas by SiO₂. The chemically bonded nanoscale interfacial area between glass fiber and matrix was generated and bridged by SiO₂–MWCNTs, making glass fiber like a branched reinforcement, resulting in strong interfacial adhesion and effective stress transfer. Mechanical properties of SiO₂–MWCNT/EP composites and GF/SiO₂–MWCNT/EP composites were even higher than those predicted by Halpin–Tsai model and rule of mixtures, resulting from strengthened interfacial adhesion in the composites, high chemical reactivity of SiO₂–MWCNTs and additional reinforcing effect of SiO₂.     

Investigation of directional effects on the electrical conductivity and piezoresistivity of carbon nanotube/polypropylene composites obtained by extrusion

The electrical conductivity and piezoresistivity of multiwall carbon nanotube (MWCNT)/polypropylene (PP) composites obtained by extrusion are investigated, with particular attention to the possible directional effects generated during the extrusion process. This is accomplished by investigating the electrical and electromechanical responses of the nanocomposites at three MWCNT weight concentrations (3, 4 and 5 wt%) in three directions, viz. the extrusion direction, transverse to extrusion (in-plane) and through thickness. Higher electrical conductivity in the extrusion direction was more evident for the lowest MWCNT content. However, the piezoresistive sensitivity was similar in all directions. Films with 4 wt% showed the highest piezoresistive sensitivity, reaching gage factors of?~?4.5 for strains between 0 and 0.8%, and?~?10.2 for strains between 1 and 3%. After an initial drop in the electrical resistance, concomitant with stress relaxation, the changes in electrical resistance showed large reproducibility. Digital image correlation conducted during cyclic piezoresistive testing at 0.8% strain indicates small accumulation of local plasticity as the number of cycles increases, especially in zones near the electrodes. These irreversible changes in the material are expected to trigger the permanent changes in the electrical resistance measured.

Graphical abstract

     

Preparation and properties of poly (p-phenylene sulfide)/multiwall carbon nanotube composites obtained by melt compounding

In this paper, electrical and mechanical properties of Poly (p-phenylene sulfide) (PPS)/multi-wall carbon nanotubes (MWNTs) nanocomposites were reported. The composites were obtained just by simply melt mixing PPS with raw MWNTs without any pre-treatment. The dispersion of MWNTs and interfacial interaction were investigated through SEM &TEM and Raman spectra. The rheological test and crystallization behavior were also investigated to study the effects of MWNTs concentration on the structure and chain mobility of the prepared composites. Though raw MWNTs without any pre-treatment were used, a good dispersion and interaction between PPS and MWNTs have been evidenced, resulting in a great improvement of electrical properties and mechanical properties of the composites. Raman spectra showed a remarkable decrease of G band intensity and a shift of D bond, demonstrating a strong filler–matrix interaction, which was considered as due to π–π stacking between PPS and MWNTs. The storage modulus (G′) versus frequency curve presented a plateau above the percolation threshold of about 2–3 wt% with the formation of an interconnected nanotube structure, indicative of ‘pseudo-solid-like’ behavior. Meanwhile, a conductive percolation threshold of 5 wt% was achieved and the conductivity of nanocomposites increased sharply by several orders of magnitude. The difference between electrical and rheological percolation threshold, and the effect of critical percolation on the chain mobility, especially on crystallization behavior of PPS, were discussed. In summary, our work provides a simple and fast way to prepare PPS/MWNTs nanocomposites with good dispersion and improved properties.     

Electrical properties of multiwalled carbon nanotube reinforced fused silica composites

Multiwalled carbon nanotube (MWCNT)-fused silica composite powders were synthesized by solgel method and dense bulk composites were successfully fabricated via hot-pressing. This composite was characterized by XRD, HRTEM, and FESEM. MWCNTs in the hot-pressed composites are in their integrity observed by HRTEM. The electrical properties of MWCNT-fused silica composites were measured and analyzed. The electrical resistivity was found to decrease with the increase in the amount of the MWCNT loading in the composite. When the volume percentage of the MWCNTs increased to 5 vol%, the electrical resistivity of the composite is 24.99 omega cm, which is a decrease of twelve orders of value over that of pure fused silica matrix. The electrical resistivity further decreases to 1.742 omega. cm as the concentration of the MWCNTs increased to 10 vol%. The dielectric properties of the composites were also measured at the frequency ranging from 12.4 to 17.8 GHz (Ku band) at room temperature. The experimental results reveal that the dielectric properties are extremely sensitive to the volume percentage of the MWCNTs, and the permittivities, especially the imaginary permittivities, increase dramatically with the increase in the concentration of the MWCNTs. The improvement of dielectric properties in high frequency region mainly originates from the greatly increasing electrical properties of the composite.     

Polyazomethine/carbon nanotube composites

Composites were synthesized by “in-situ” polymerization of polyazomethine, a liquid crystal polymer (LCP), in presence of multi-walled carbon nanotubes (MWNTs) previously dispersed in one of the employed monomers. Fiber processing was carried out by extrusion from the composites containing 1 and 10 wt.% of MWNTs at the mesophase temperature. We have observed that the typical highly oriented internal fibrillar structure can be significantly disrupted by increasing the nanotube content in the composite fibers. Evidences of MWNT alignment were found in the studied LCP/MWNT composites.     

Effect of doping levels on the pore structure of carbon nanotube/silica xerogel composites

This letter reports the effect of CNT doping levels on the pore structure of carbon nanotube (CNT)/silica xerogel composites, which would greatly influence the composite's physical behaviors and their applications in the field of optics. The composites were prepared by sol-gel technique and carried out pore structure analysis. The results show that there are mainly two grades of pores, centering at 8 and 15 nm respectively, that existed in the structure. The relative ratio of the two-grade pores, also BET surface area and pore volume of the composites, change with the different CNT doping levels. The reason may be that the addition of CNTs can act as inhomogeneous crystalline sources, seduce the silica xerogel network to grow around them and therefore change the gel formation process of silica granules.     

Multifunctional composites by high-pressure spray processes

A series of spraying processes designed to generate powders and composites using supercritical fluids have been proposed in the past 15 years. In this review, thermo- and fluid-dynamic aspects and engineering principles are discussed and advantages of such technologies are demonstrated. These new techniques display convincing advantages, producing competitive high-quality products with tailor-made properties. Initial industrial applications have been achieved in the production of food products and fine-chemicals.     

Sugarcane bagasse cellulose/HDPE composites obtained by extrusion

Natural fibers used in this study were both pre-treated and modified residues from sugarcane bagasse. Polymer of high density polyethylene (HDPE) was employed as matrix in to composites, which were produced by mixing high density polyethylene with cellulose (10%) and Cell/ZrO₂·nH₂O (10%), using an extruder and hydraulic press. Tensile tests showed that the Cell/ZrO₂·nH₂O (10%)/HDPE composites present better tensile strength than cellulose (10%)/HDPE composites. Cellulose agglomerations were responsible for poor adhesion between fiber and matrix in cellulose (10%)/HDPE composites. HDPE/natural fibers composites showed also lower tensile strength in comparison to the polymer. The increase in Young’s modulus is associated to fibers reinforcement. SEM analysis showed that the cellulose fibers insertion in the matrix caused an increase of defects, which were reduced when modified cellulose fibers were used.     

New mesoporous silica/carbon composites by in situ transformation of silica template in carbon/silica nanocomposite

Hard template-based fabrication of mesoporous carbon unavoidably goes through the removal process of the template to generate template-free carbon replica, including troublesome disposal of template waste often accompanied by toxic etchant, which not only increases the fabrication cost of materials but also raises serious environmental concerns. As a novel strategy to overcome such problem, a direct in situ synthesis approach using silica waste in carbon/silica nanocomposite as a silica source and cetyltrimethylammonium bromide as a porogen under basic condition is reported in this study for the generation of a new composite composed of mesoporous MCM-41 silica and hollow carbon capsule. The resultant MCM-41/carbon capsule composite offers a 3-D interconnected multimodal pore system, which discloses a wide pore range of ordered uniform mesopores (ca 2.3?nm) resulting from MCM-41 silica and disordered uniform mesopores (ca 3.8?nm) and macropores (ca 300?nm) from hollow mesoporous carbon, respectively. The composite has a high specific surface area (ca 909?m²/g) and large pore volume (ca 0.73?cm³/g). The in situ transformation approach of silica waste into valuable mesoporous silica is considered as a promising scalable route for efficient new multi-functional composites useful for a wide range of applications such as adsorption of volatile organic compounds and radioactive wastes produced in a nuclear facility.     

Polyindole/ carboxylated-multiwall carbon nanotube composites produced by in-situ and interfacial polymerization

Composites of polyindole (PIn), a conducting polymer, with carboxylated-multiwalled carbon nanotubes (c-MWCNT/PIn) were synthesized; the synthesis was done using (i) two miscible solvents (in-situ method) and (ii) two immiscible solvents (interfacial method). A tubular composite, with a uniform coating of the polymer over c-MWCNTs, was observed in the case of interfacial synthesis. However, the in-situ synthesis of c-MWCNT/PIn composites exhibited a densely packed spherical morphology, with c-MWCNT incorporated within the polymer spheres. The spherical morphology was probably obtained due to fast polymerization kinetics and the formation of micelles in case of in-situ polymerization, whereas tubular morphology was obtained in case of interfacial polymerization due to the sufficient time provided for the growth of polymer chains over the c-MWCNT surfaces. Nanoscale electrical properties of composites, in a metal/(c-MWCNT/PIn) configuration, were studied using current sensing atomic force microscopy. Interfacial c-MWCNT/PIn composite, on Al metal substrate, exhibited a typical rectifying diode behavior. This composite had manifested enormous potential for electronic applications and fabrication of nanoscale organic devices.     

Carbon fibre composites based on polyimide/silica ceramers: aspects of structure-properties relationship

Polyimide/silica ceramers, based on the products of the hydrolysis of tetraethoxysilane (TEOS) and a commercial poly(amic acid) solution, were used to fabricate unidirectional carbon fibre composites, which were subsequently evaluated with respect to thermal and mechanical properties. There is evidence to suggest that the silica component of these ceramers is present as dispersed discrete particles at low silica concentration (i.e. 7 wt%) and as fine interconnected domains trapped within the polyimide matrix at higher silica content (i.e. 14 wt%). The dimensions of the silica domains were in the region of 7–20 nm. Carbon fibre composites produced from ceramer solutions (CF/ceramers) were found to exhibit lower thermal expansion and a greater retention of flexural and interlaminar shear properties at elevated temperature than the corresponding polyimide-matrix composites (CF/polyimide). The properties of CF/ceramers were generally better for systems containing the higher amount of silica and were improved further by lowering the pH value of the precursor ceramer solution. This is believed to have resulted from the enhanced fluidity of the ceramer gel within the pre-impregnated fibres, giving rise to a higher packing density of the fibres and a more homogeneous distribution of fibres. CF/ceramers were also found to exhibit a better thermal oxidative stability at 350°C than the corresponding CF/polyimide, although a substantial amount of porosity developed in the case of ceramers with the higher silica content.     

纳米碳管/聚合物功能复合材料

纳米碳管(Carbonnanotubes,CNT)具有π π共轭电子结构,可与结构相似的聚合物(Polymer)通过范德华力结合形成复合材料。导电聚合物(Electricallyconductingpolymer,ECP)包覆多壁纳米碳管(Multi walledcarbonnanotubes,MWNT)后,可用于诸如超级电容器等电子器件。共轭发光聚合物修饰纳米碳管形成的CNT polymer复合材料,具有很强的发光性能,有望用于电子接收器和光电器件。通过连结氨基聚合物,可使多壁纳米碳管溶解和功能化,从而将纳米碳管引入生物学系统中。研究结果表明,CNT polymer复合物有许多潜在的应用,有待进一步发展。