Synthesis of Y-junction single-wall carbon nanotubes

Y-junction single-wall carbon nanotubes (SWNTs) are synthesized using controlled catalysts by chemical vapor deposition. Mo-doped Fe nanoparticles supported by aluminum oxide particles are used as catalysts for growing Y-junction single-wall carbon nanotubes. Distribution of Mo-doped Fe particles plays an important role in Y-junction formation. Transmission electron microscopy confirmed the formation of single-walled structures of Y-junctions with diameters of 2-5 nm. Radial breathing mode peaks in Raman spectra show that our sample has both metallic and semiconducting nanotubes, indicating the possible formation of Y-branching with different electrical properties. The different electrical properties of branch and stem can be utilized in nanoscale three terminal electronic devices. The growth mechanism of Y-junction SWNTs is proposed.     

Processing and characterization of epoxy nanocomposites reinforced by cup-stacked carbon nanotubes

The effect of the dispersion, ozone treatment and concentration of cup-stacked carbon nanotubes on mechanical, electrical and thermal properties of the epoxy/CSCNT nanocomposites were investigated. Ozone treatment of carbon fibers was found to increase the surface oxygen concentration, thereby causing the contact angle between water, epoxy resin and carbon fiber to be decreased. Thus, the tensile strength, modulus and the coefficient friction of carbon fiber reinforced epoxy resin were improved. Moreover, the dispersion of fibers in polymer was increased and the electrical resistivity was decreased with the addition of filler content. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus of the polymer was increased by the incorporation of CSCNTs. But the glass transition temperature decreased with increasing fiber loading for the ozone treated fiber composites. The ozone treatment did affect the morphology, mechanical and physical properties of the CSCNT.     

Voltammetric determination of bisoprolol fumarate in pharmaceutical formulations and urine using single-wall carbon nanotubes modified glassy carbon electrode

The electrochemistry of bisoprolol fumarate (BF) has been investigated by differential pulse voltammetry at a single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode (GCE). The prepared electrode showed an excellent electrocatalytic activity towards the oxidation of BF leading to a marked improvement in sensitivity as compared to bare glassy carbon electrode where electrochemical activity for the analyte cannot be observed. The SWNTs-modified GCE exhibited a sharp anodic peak at a potential of ∼950 mV for the oxidation of BF. Under optimum conditions linear calibration curve was obtained over the BF concentration range 0.01-0.1 mM in 0.5 M phosphate buffer solution (pH 7.2) with a correlation coefficient of 0.9789 and detection limit of 8.27 × 10⁻⁷ M. The modified electrode has been applied for the drug determination in human urine with no prior extraction and in commercial tablets. The proposed method has also been validated.     

Multi-component nanocomposites of epoxy/silsesquioxane reinforced with carbon fibers and carbon nanotubes processed by resin transfer molding

ABSTRACT

In this work, an epoxy resin modified by silsesquioxane oligomers was used to produce multi-component nanocomposites reinforced with carbon fiber (CF) and multi-walled carbon nanotubes (CNT) by resin transfer molding (RTM). The combination of sonication process with the incorporation of silsesquioxane domains (i.e. increasing the degree of crosslinking of the epoxy matrix), improved the mechanical strength of the hybrid matrix and hybrid/CF/CNT nanocomposites. The multi-component nanocomposites produced by RTM presented Young modulus of 35 ± 8 GPa, tensile strength of 303 ± 41 MPa and impact strength of 1.0 ± 0.3 kJ m^?1. The results showed a significant increase in the tensile strength and impact resistance of the epoxy matrix by the incorporation of silsesquioxanes and sonication before curing of the matrices, showing the promising potential of this multi-component nanocomposite for pipelines and other structural applications.     

Supercritical carbon dioxide-assisted silanization of multi-walled carbon nanotubes and their effect on the thermo-mechanical properties of epoxy nanocomposites

Supercritical carbon dioxide was employed as the solvent for the functionalization of multi-walled carbon nanotubes (MWCNTs) with an epoxy-capped silane. The silanization protocol was found to be a suitable green alternative to traditional routes that rely on organic solvents for grafting nearly monolayers of silane molecules onto the nanotube surfaces. The addition of silanized MWCNTs to a model epoxy markedly increased its T_g, and measurements of the network cooperativity length scale linked this change to a reduction in polymer segment mobility. Composites filled with low loading levels of both pristine and silanized MWCNTs exhibited significantly higher strain at break and toughness than the neat epoxy, and the greatest improvements were observed at low loading levels. SEM analysis of the composite fracture surfaces revealed that nanotube pullout was the primary failure mechanism in epoxy loaded with pristine MWCNTs while crack bridging predominated in composites containing silanized MWCNTs as the result of strong interfacial bonding with the matrix. The elevated T_g and toughness achieved with small additions of silanized MWCNTs promise to extend the engineering applications of the epoxy resin.     

二乙烯三胺改性碳纳米管对环氧树脂纳米复合材料力学性能影响研究

采用二乙烯三胺(DETA)对碳纳米管(MWNTs)进行改性,并用X射线衍射(XRD)和傅里叶变换红外光谱(FTIR)对其进行表征。发现DETA被有效地包覆在MWNTs表面。并将改性前后的MWNTs与环氧树脂进行复合,采用浇铸成型法制备了MWNTs/环氧树脂纳米复合材料,测试其力学性能,并采用透射电镜(TEM)研究其分散性,扫描电镜(SEM)对其断口进行了分析研究。结果表明,少量的改性MWNTs可以使复合材料的力学性能提高,具有明显的增韧作用。当MWNTs的含量为0.6%时,纳米复合材料的冲击强度与纯环氧体系相比,提高幅度达400%以上,弯曲强度和弯曲模量的提高幅度均达到了100%以上。     

Iron(III) protoporphyrin IX—single-wall carbon nanotubes modified electrodes for hydrogen peroxide and nitrite detection

Iron(III) protoporphyrin IX (Fe(III)P), adsorbed either on single-walled carbon nanotubes (SWCNT) or on hydroxyl-functionalized SWCNT (SWCNT-OH), was incorporated within a Nafion matrix immobilized on the surface of a graphite electrode. From cyclic voltammetric measurements, performed under different experimental conditions (pH and potential scan rate), it was established that the Fe(III)P/Fe(II)P redox couple involves 1e⁻/1H⁺. The heterogeneous electron transfer process occurred faster when Fe(III)P was adsorbed on SWCNT-OH (11 s⁻¹) than on SWCNT (4.9 s⁻¹). Both the SWCNT-Fe(III)P- and SWCNT-OH-Fe(III)P-modified graphite electrodes exhibit electrocatalytic activity for H₂O₂ and nitrite reduction. The modified electrodes sensitivities were found varying in the following sequences: S_{SWCNT-OH-Fe(III)P} = 2.45 mA/M ≈ S_{SWCNT-Fe(III)P} = 2.95 mA/M > S_Fe(III)P = 1.34 mA/M for H₂O₂, and S_{SWCNT-Fe(III)P} = 3.54 mA/M > S_Fe(III)P = 1.44 mA/M > S_{SWCNT-OH-Fe(III)P} = 0.81 mA/M for NO₂⁻.     

Thermal conductivity of carbon nanotubes and graphene in epoxy nanofluids and nanocomposites

We employed an easy and direct method to measure the thermal conductivity of epoxy in the liquid (nanofluid) and solid (nanocomposite) states using both rodlike and platelet-like carbon-based nanostructures. Comparing the experimental results with the theoretical model, an anomalous enhancement was obtained with multiwall carbon nanotubes, probably due to their layered structure and lowest surface resistance. Puzzling results for functionalized graphene sheet nanocomposites suggest that phonon coupling of the vibrational modes of the graphene and of the polymeric matrix plays a dominant role on the thermal conductivities of the liquid and solid states.PACS: 74.25.fc; 81.05.Qk; 81.07.Pr.     

Copolyester nanocomposites based on carbon nanotubes: reinforcement effect of carbon nanotubes on viscoelastic and dielectric properties of nanocomposites

Nanocomposites based on an amorphous copolyester, poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate) and carbon nanotubes were fabricated using a simple melt processing technique. The reinforcement effect of carbon nanotubes in the copolyester was investigated experimentally using different approaches based on dynamic mechanical analysis, rheology and dielectric analysis. The nanocomposites show a mechanical reinforcement effect with significant increase in the stiffness especially in the rubbery regime with increasing nanotube content. An increase in T_g and a decrease in damping are seen, which are derived from the presence of a percolating superstructure of the filler. Rheological experiments show an increase in storage modulus up to four orders of magnitude. Viscolelastic characterization shows that the percolation threshold is at 3 wt% of nanotubes. Dielectric relaxation spectroscopy confirms the presence of this percolating structure. We conclude that the responses of both rheological and electrical properties are different, although both are related to the formation of a percolating network superstructure of the filler. Copyright © 2007 Society of Chemical Industry     

碳纳米管增强天然橡胶复合材料的制备与性能研究

碳纳米管以其特殊的结构与优异的性能成为橡胶的理想填料。本文分别采用四种不同牌号(分别为Flotube7000 9000 9011 9400)的碳纳米管为实验原料,制备了碳纳米管/天然橡胶复合材料,并对其性能进行了研究探讨。结果发现,碳纳米管的加入能显著提高复合材料的力学性能和热导率,具有一维取向排列且长径比较大的Flotube7000(以下简称7000)对力学性能的提高程度最大,Flotube7000以及经过酸处理的表面具有-OH、–COOH官能团的Flotube9011(以下简称9011)对导热性能提高程度最为明显。     

Processing and properties of syntactic foams reinforced with carbon nanotubes

This article presents synthesis and mechanical characterization of carbon nanotube (CNT)‐reinforced syntactic foams. Following a dispersion approach (comprising ultrasonic, calendering, and vacuum centrifugal mixing), single‐ and multi‐walled functionalized CNTs (FCNTs) were incorporated into two foam composites containing various commercially available microballoon grades (S38HS, S60HS, and H50 from 3M). The FCNT‐reinforced composites were tested for compressive strength and apparent shear strength before and after hot/wet conditioning. The results showed that the FCNT‐reinforced composites' mechanical properties depended on the vacuum pressure used during processing. Compared with pristine and commercially available syntactic foam (EC‐3500 from 3M), the FCNT‐reinforced composites processed at high vacuum (0.2 kPa) showed significant increase in compressive strength and apparent shear strength before and after hot/wet conditioning. Dynamic mechanical analysis showed an increase of about 22°C in glass transition temperature for composites processed at high vacuum with 0.5 wt % FCNT and 45 wt % S38HS–5 wt % S60HS microballoons. Thermogravimetric analysis indicated water absorption and lower decomposition temperature for the FCNT‐reinforced composite mixed at atmospheric pressure, whereas no significant change was observed for the compound processed at high vacuum. Fracture analysis showed matrix failure for the composite processed at high vacuum and microballoon crushing for the composite mixed at atmospheric pressure. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of dispersion states of carbon nanotubes on physical properties of epoxy nanocomposites

Effects of different dispersion states of carbon nanotubes (CNTs) on rheological, mechanical, electrical, and thermal properties of the epoxy nanocomposites were studied. The dispersion states were altered depending upon whether a solvent was employed or not. To characterize dispersion of the CNTs, field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) were used. It was found that the nanocomposites containing poorly dispersed CNTs exhibited higher storage modulus, loss modulus, and complex viscosity than ones with well dispersed CNTs. It means that the poorly dispersed CNTs/epoxy composites have, from a rheological point of view, a more solid-like behavior. Tensile strength and elongation at break of the nanocomposites with different dispersion of CNTs were measured. Both of the well and the poorly dispersed CNTs composites showed a percolation threshold of electrical conductivity at less than 0.5 wt.% CNTs loading and the former had higher electrical and thermal conductivities than the latter. Effects of the CNTs content on the physical properties were also examined experimentally. As loading of the CNTs increased, improved results were obtained. From the morphological observation by FESEM and TEM, it was found that when the solvent was not used in the CNTs dispersion process, aggregates of pristine CNTs remained in the nanocomposites.     

Preparation,structure and properties of thermoplastic olefin nanocomposites containing functionalized carbon nanotubes

The morphology and properties of multiwalled carbon nanotube modified polypropylene (PP)/ethylene–octene copolymer blends were studied. Polypropylene chains are covalently grafted onto the surface of carbon nanotubes (CNTs) in order to improve their interaction with the polymer matrix. It is observed that functionalization of CNTs improves their dispersion and increases the interfacial bonding between CNTs and polymer matrix. The functionalized CNTs are selectively distributed in the continuous polypropylene phase. The size of the dispersed elastomer phase decreases after the addition of CNTs. Functionalized CNTs act as a nucleating agent and increase the crystallinity of the polypropylene. More importantly, an important increase in impact strength, stiffness and toughness can be achieved through introducing functionalized CNTs. Copyright © 2011 Society of Chemical Industry     

碳纳米管炭黑天然橡胶复合材料的制备与性能研究

碳纳米管以其特殊的结构与优异的性能成为橡胶补强的理想填料。本文中我们采用两种不同牌号的碳纳米管(分别为Flotube 7000、9011)与炭黑N660作为实验原料,制备了碳纳米管/炭黑/天然橡胶复合材料,并对其性能进行了探讨。结果发现：碳纳米管的加入能明显提高复合材料的定伸应力,具有一维取向排列且长径比较大的Flotube 7000(以下简称7000)对力学性能的提高程度最大。且我们将碳纳米管7000、9011分别与炭黑N660并用,对于提高复合材料的导热性能并没有如我们预期的一样存在所谓的“叠加关系”甚至是“协同效应”,而是对于提高复合材料导热有着一定的“负协同效应”。     

Solid-liquid-solid growth mechanism of single-wall carbon nanotubes

Reasons are presented which suggest that the liquefaction of the catalytic particles is a decisive condition for formation of single wall carbon nanotubes (SWNTs) by physical synthesis techniques. It is argued that the SWNT growth mechanism is a kind of solid-liquid-solid graphitization of amorphous carbon or other imperfect carbon forms catalyzed by molten supersaturated carbon-metal nanoparticles. The assumption of low temperature melting of these nanoparticles in contact with amorphous carbon followed by its precipitation in the form of SWNTs allows to explain qualitatively the experimentally observed SWNT growth rates and temperature dependence of the SWNT yield. Guidelines for increasing SWNT yield are proposed.     

Improved impact strength of epoxy by the addition of functionalized multiwalled carbon nanotubes and reactive diluent

Multiwalled carbon nanotubes (MWCNTs), both oxidized and amine functionalized (triethylenetetramine—TETA), have been used to improve the mechanical properties of nanocomposites based on epoxy resin. The TGA and XPS analysis allowed the evaluation of the degree of chemical modification on MWCNTs. Nanocomposites were manufactured by a three‐roll milling process with 0.1, 0.5, and 1.0 wt % of MWCNT–COOH and MWCNT–COTETA. A series of nanocomposites with 5.0 wt % of reactive diluent was also prepared. Tensile and impact tests were conducted to evaluate the effects of the nanofillers and diluent on the mechanical properties of the nanocomposites. The results showed higher gains (258% increase) in the impact strength for nanocomposites manufactured with aminated MWCNTs. Optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to investigate the overall filler distribution, the dispersion of individual nanotubes, and the interface adhesion on the nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42587.     

Effect of single-walled carbon nanotubes on thermal and electrical properties of silicon nitride processed using spark plasma sintering

Si₃N₄ nanocomposites reinforced with 1-, 2-, and 6-vol% single-walled carbon nanotubes (SWNTs) were processed using spark plasma sintering (SPS) in order to control the thermal and electrical properties of the ceramic. Only 2-vol% SWNTs additions were used to decrease the room temperature thermal conductivity by 62% over the monolith and 6-vol% SWNTs was used to transform the insulating ceramic into a metallic electrical conductor (92 S m⁻¹). We found that densification of the nanocomposites was inhibited with increasing SWNT concentration however, the phase transformation from α- to β-Si₃N₄ was not. After SPS, we found evidence of SWNT survival in addition to sintering induced defects detected by monitoring SWNT peak intensity ratios using Raman spectroscopy. Our results show that SWNTs can be used to effectively increase electrical conductivity and lower thermal conductivity of Si₃N₄ due to electrical transport enhancement and thermal scattering of phonons by SWNTs using SPS.     

Synthesis and characterization of multi-walled carbon nanotubes reinforced polyamide 6 via in situ polymerization

Polyamide 6 (PA6)/carbon nanotubes (PA6/CNTs) composites have been prepared by in situ polymerization of ε-caprolactam in the presence of pristine and carboxylated multi-walled carbon nanotubes (MWNT and MWNTCOOH). Viscosity measurements show that adding 0.5 wt% of carbon nanotubes (CNTs) does not affect the molecular weight of PA6. Compared with pure PA6, the yield strength of PA6/CNTs composites loaded with 0.5 wt% CNTs is almost unchanged, and the tensile strength is increased slightly. Dynamic mechanical analysis (DMA) demonstrates that both the storage modulus (E′) and glass transition temperature (T_g) of the PA6/CNTs composites increase, particularly for PA6/MWNTCOOH, indicating there is some chemical bonding between PA6 and MWNTCOOH. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultra small-angle X-ray scattering (USAXS) show that MWNT and MWNTCOOH are well dispersed in PA6 matrix. Comparison of the USAXS data with a stiff-rod model and wormlike rod model reveals that the CNTs are quite flexible, regardless the degree of chemical modification. Due to the flexibility of CNTs, mechanical properties of the PA6/CNTs composites are marginally enhanced.     

多壁碳纳米管/环氧树脂纳米复合材料的固化动力学研究

采用熔融混合法向低粘度的环氧树脂中添加适量的多壁碳纳米管,制备新型纳米复合材料,并采用傅里叶变换红外光谱仪(FT-IR)测试转化率,采用差示扫描量热法(DSC)研究多壁碳纳米管/环氧树脂复合体系的固化动力学,并对纳米复合材料的力学性能进行研究。结果表明:多壁碳纳米管加入环氧树脂复合体系后,对固化反应有催化作用,固化反应速率增大,转化率提高,而复合体系的力学性能却有所下降,玻璃化转变温度变化不大。