Preparation polystyrene/multiwalled carbon nanotubes nanocomposites by copolymerization of styrene and styryl-functionalized multiwalled carbon nanotubes

Styryl-functionalized multiwalled carbon nanotubes (p-MWNTs) were prepared by esterification based on the carboxylate salt of carbon nanotubes and p-chloromethylstyrene in toluene. Then in situ radical copolymerization of p-MWNTs and styrene initiated by 2,2′-azobis(isobutyronitrile) (AIBN) was applied to synthesize composites of styryl-functionalized multiwalled carbon nanotubes and polystyrene (PS) (p-MWNTs/PS). Characterizations carried out by FT-IR, ¹H NMR, UV–vis show that styryl group covalently bond to the surface of MWNTs. The results of UV showed that the solutions of p-MWNTs/PS in chloroform have the hyperchromic effect. Transmission electron microscopy (TEM) images of p-MWNTs/PS composites and scanning electron microscopy (SEM) images of fracture surface of p-MWNTs/PS composites showed the functionalized nanotubes had a better dispersion than that of the unfunctionalized MWNTs in the matrix. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) suggested that the thermal stability of p-MWNTs/PS composites improved in the presence of MWNTs.     

3D electron microscopy study of metal particles inside multiwalled carbon nanotubes

The location of palladium nanoparticles on and inside the multiwalled carbon nanotubes channel is presented for the first time using electron tomography (3D TEM). The palladium salt precursor was rapidly sucked inside the nanotube channel by means of capillarity that is favored by the hydrophilic character of the tube wall after acidic treatment at low temperature. Statistical analysis indicates that the palladium particles were well dispersed and the palladium particle size was relatively homogeneous, ranging from 3 to 4 nm regardless of their location within the nanotube, within the resolution limit of the technique for our experimental conditions, i.e., about 2 nm. Three-dimensional TEM analysis also revealed that introduction of foreign elements inside the tube channel is strongly influenced by the diameter of the tube inner channel, i.e., easy filling seems to occur with a tube channel >or=30 nm , whereas with tubes having a smaller channel (<15 nm), almost no filling by capillarity occurred leading to the deposition of the metal particles only on the outer wall of the tube.     

Fabrication and characterisation of multiwalled carbon nanotubes decorated by magnetic Ni nanoparticles

Abstract

Magnetic carbon nanotube (CNT) composites have been successfully fabricated by employing a microwave assisted method after sensitisation and activation. The phase structures and morphologies of the composites were characterised in detail by transmission electron microscope and X-ray powder diffraction. The results show that sensitisation and activation are absolutely necessary for a dense layer of magnetic nanoparticles obtained on the surface of CNTs. Magnetic measurements using a vibrating sample magnetometer demonstrate that the prepared composites are ferromagnetic.     

Field emission properties of Fe70Pt30 catalysed multiwalled carbon nanotubes

Multi-walled carbon nanotubes were grown on nanocrystalline Fe₇₀Pt₃₀ film using low-pressure chemical vapour deposition (LPCVD) method. The growth time was varied between 5?min to 30?min. SEM micrograph of this film revealed that the size of nanoparticles varied from 5?nm to 10?nm. The diameter of the carbon nanotubes varied from 20?nm to 50?nm as verified by TEM. HRTEM image confirmed that the carbon nanotubes are bamboo-shaped multiwalled carbon nanotubes (MWNTs). Field emission characteristics of MWNTs at various growth times (5?min, 15?min and 30?min) with working distances (50?µm, 100?µm and 150?µm) were also studied. The carbon nanotubes grown for 30?min with working distance 150?µm exhibited the lowest turn-on field of 2.45?V/µm. The turn-on field increases from 2.45?V/µm to 6.21?V/µm as the growth time decreases from 30?min to 5?min whereas for lower working distances (100?µm and 50?µm), the turn-on field increases from 4.74?V/µm to 6.74?V/µm and from 8.79?V/µm to 14.49?V/µm respectively. The turn-on field (E _to) and field enhancement factor (β) were studied as a function working distance (d) and growth time respectively to see the effect of these parameters on field emission properties. The field enhancement factor (β) was also studied as a function of radius of apex curvature (r) . It was found the field enhancement factor (β) decreases with the increase in radius of apex curvature (r) and growth time whereas the value of field enhancement factor (β) increases as working distance (d) increases. On the basis of the dependence of β on radius of apex curvature (r) a relationship of β?∝?r ^?1/2 is fitted.     

pH sensitive multiwalled carbon nanotubes

The CNTs-based sensors have received considerable attention because of their outstanding properties, such as faster response, higher sensitivity, and lower operating temperature. And we expect that CNTs-based electrochemical sensors offer substantial improvements in the performance of pH sensing device. This letter reports experimental results that demonstrate the pH sensing capability of the multiwalled carbon nanotubes (MWCNTs) film by using the thermal chemical vapor deposition (thermal CVD). It was found that electronic properties of MWCNTs can be changed by the introduction of different pH value solutions. The absorption of the hydroxide in pH buffer solution changes conductivity of the MWCNTs. We observed in situ measurement of electrical conductivity by cycling solution range from acid to base.     

电场诱导多壁碳纳米管有序排列对多壁碳纳米管/环氧树脂复合材料性能的影响

采用交流（AC）电场诱导法制备了多壁碳纳米管（MWCNTs）均匀分散且定向有序排列的MWCNTs/环氧树脂复合材料。采用SEM、偏振拉曼光谱等研究了电场强度、MWCNTs含量、加电时间及温度（黏度）等因素对MWCNTs定向排列的影响,讨论了MWCNTs有序排列对MWCNTs/环氧树脂复合材料电学和力学性能的影响。结果表明：MWCNTs沿电场方向有序排列;MWCNTs/环氧树脂复合材料施加AC电场后的拉曼强度明显高于未施加电场的情况;当MWCNTs含量从0wt%增加到0.025wt%时,MWCNTs/环氧树脂复合材料导电率从2.3×10^-12 S/cm增加到1.3×10^-8 S/cm,增加了约4个数量级;MWCNTs含量为2.5wt%时,MWCNTs/环氧树脂复合材料拉伸强度提高了26.3%。     

Physical properties of multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWNTs), which were prepared by hydrogen arc discharge, were purified by using an infrared radiation heating system. The morphology, structure, vibrational modes and crystalline perfection of purified MWNTs were investigated by using scanning electron microscopy, high-resolution transmission electron microscopy, an X-ray diffractometer and a Raman spectrometer. Moreover, the electrical conductivity of individual purified MWNTs was measured using a two-probe method using a micro manipulator system. It turned out that the MWNTs had a high degree of graphitization, an electrical conductivity of about 1.85×10³ S cm⁻¹ along the long axis, and an enormous current density of more than 10⁷ A cm⁻².     

Preparation and structure of multiwalled carbon nanotubes

The structure of oxidized multiwalled carbon nanotubes has been studied by transmission electron microscopy and X-ray diffraction. The results demonstrate that oxidation disrupts nanotubes. Subsequent heat treatment at 300°C also changes the structure of the nanotubes, increasing their inner diameter and reducing their outer diameter.     

Thermodynamic properties of multiwalled carbon nanotubes

The experimental study of the heat capacity of multiwalled carbon nanotubes has been conducted at a constant pressure and a temperature in the range from 60 to 300 K. The derived temperature dependence of the heat capacity has been shown to differ from that of graphite. The explanation of the fact has been given in terms of the special features of phonon spectra of the above materials. Based on the experimental results and reliable literature data standard values of the basic thermodynamic functions of multiwalled carbon nanotubes (enthalpy, entropy, and Gibbs reduced energy) have been calculated.     

Ballistic conduction in multiwalled carbon nanotubes

The electrical transport in multiwalled carbon nanotubes is shown to be ballistic at room temperature with mean free paths on the order of tens of microns. The measurements are performed both in air and in the transmission electron microscope by contacting the free end of a nanotube pointing out of a fiber to a liquid metal and measuring the dependence of the nanotube resistance between the contacts. For a specific representative nanotube the resistance per unit length is found to be Rt = 31 +/- 61 omega/micron and the contact resistance with the liquid metal, Rc = 165 +/- 55 omega microns, corresponding to a mean free path l = 200 microns. Current-to-voltage characteristics are in accord with the electronic structure. The nanotubes survive high currents (up to 1 mA, i.e., current density on the order of 10(9) A/cm2). In situ electron microscopy shows that a relatively large fraction of the nanotubes do not conduct (even at high bias), consistent with the existence of semiconducting nanotubes. Discrepancies with other measurements are most likely due to damage caused to the outer layer(s) of the nanotubes during processing. The measured mean free path of clean, undamaged arc-produced multiwalled carbon nanotubes is several orders of magnitude greater than that for metals, making this perhaps the most significant property of carbon nanotubes.     

Synthesis and characterization of phospholipid-modified multiwalled carbon nanotubes

A simple three-step strategy to functionalize multiwalled carbon nanotubes using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine phospholipids has been described. The resulting phospholipid-modified multiwalled carbon nanotubes were analyzed by TEM, AFM, NMR, IR, UV-vis and TGA techniques. The experimental results show that the use of amine-terminated phospholipids not only improves the dispersity of multiwalled carbon nanotubes in both aqueous and organic solvents greatly, but also results in the significant enhancement of biocompatibility. These findings will serve as a future biological platform for new devices ranging from biosensors to nano-detectors.     

Light-scattering and dispersion behavior of multiwalled carbon nanotubes

Elliptically polarized light-scattering measurements were performed to investigate the dispersion behavior of multiwalled carbon nanotubes (MWNT). Xylene- and pyridine-derived MWNT powders were dispersed in water and ethanol in separate optic cells and allowed to sit undisturbed over a two-week time period after probe sonication. Continuous light-scattering measurements taken between scattering angles of 10-170 deg and repeated over several days showed that the nanotubes formed fractal-like networks. The pyridine-derived MWNTs showed greater dispersion variation over time, tending to aggregate and clump much faster than the xylene-derived tubes. The water suspensions appeared much more stable than the ethanol suspensions, which transformed into nonfractal morphology after a few hours. We relate the dispersion stability to size and fringe patterns on the outer surface of the nanotubes. Measured values of fractal dimension were distinctly lower than those in previous studies of single-walled carbon nanotubes. Profiles of both diagonal and off-diagonal scattering matrix elements are presented.     

Functionalization and solubilization of thin multiwalled carbon nanotubes

The reaction of thin multiwalled carbon nanotubes with a mixture of concentrated HNO₃ and H₂SO₄ has been studied by IR absorption and x-ray photoelectron spectroscopies. The results indicate the attachment of-C(O)OH groups to nanotubes and subsequent conversion of these groups to-C(O)Cl groups via reaction with SOCl₂ and then to-C(O)NR₂ via reaction with didodecylamine. The yield of the carboxylated nanotubes is 53%, and that of the amidated nanotubes is 28%. The O:C atomic ratio in the carboxylated tubes is 1.0:9.0. The solubility of the carboxylated tubes in water is 3.13 g/l, and that of the amidated tubes in chloroform is 1.30 g/l.     

Graphite nanoplatelets/multiwalled carbon nanotubes hybrid nanostructure for electrochemical capacitor

Recently, the focus on carbon based nanostructures for various applications has been due to their novel properties such as high electrical conductivity, high mechanical strength and high surface area. In the present work, we have investigated the charge storage capacity of modified graphite nanoplatelets and hybrid structure of graphite nanoplatelets-multiwalled carbon nanotubes (MWNTs). These MWNTs can be used as spacers to reduce the possibility of restacking of graphite nanoplatelets and hence increases the surface area of the hybrid carbon nanostructure thereby high degree of metal oxide decoration is achieved over the hybrid structure. MWNTs were prepared by catalytic chemical vapor deposition technique and further purified with air oxidation and acid treatment. Graphite was treated with conc. nitric acid and sulphuric acid in the volumetric ratio of 1:3 for 3 days and these modified graphite nanoplatelets were further stirred with MWNTs in equal weight ratio to form hybrid nanostructure. Further, ruthenium oxide (RuO2) nanoparticles were decorated on this hybrid structure using chemical route followed by calcination. RuO2 decorated hybrid carbon nanostructure was characterized by using X-ray diffraction, Electron microscopy and Raman spectroscopy. The performance of the hybrid structure based nanocomposite as electrochemical capacitor electrodes was analyzed by studing its capacitive and charge-discharge behaviours using cyclic voltammetry and chronopotentiometry techniques and the results have been discussed.     

Fabrication and mechanical properties of well-dispersed multiwalled carbon nanotubes/epoxy composites

Multiwalled carbon nanotubes (MWCNTs)/epoxy nanocomposites were fabricated by using ultrasonication and the cast molding method. In this process, MWCNTs modified by mixed acids were well dispersed and highly loaded in an epoxy matrix. The effects of MWCNTs addition and surface modification on the mechanical performances and fracture morphologies of composites were investigated. It was found that the tensile strength improved with the increase of MWCNTs addition, and when the content of MWCNTs loading reached 8 wt.%, the tensile strength reached the highest value of 69.7 MPa. In addition, the fracture strain also enhanced distinctly, implying that MWCNTs loading not only elevated the tensile strength of the epoxy matrix, but also increased the fracture toughness. Nevertheless, the elastic modulus reduced with the increase of MWCNTs loading. The reasons for the mechanical property changes are discussed.     

Tough semiconductor polycarbonate/multiwalled carbon nanotubes nanocomposites by rubber modification

Tough polycarbonate (PC)/multiwalled carbon nanotube (MWCNT) nanocomposites (NCs) modified by a maleated styrene/ethylene–butylene/styrene (mSEBS) rubber were obtained in the melt state using a highly dispersed PC/MWCNT master-batch. An electrical percolation threshold (p_c) occurred at only 0.5% MWCNT showing a power law critical exponent of 2.60, which is characteristic of a three-dimensional percolated structure. The presence of MWCNT decreased the rubber particle size due to an increase in matrix viscosity. In addition to high electrical conductivity, the elastic modulus of the NCs was similar to that of the PC, as a result of the combined presence of 0.5% MWCNT and 4% mSEBS; the mSEBS was also able to provide (i) considerable impact strength, (ii) clear ductile behavior and (iii) increased resistance against crack propagation.     

Variation of radial elasticity in multiwalled carbon nanotubes

Correlations between the local diameter and local radial elastic modulus in multiwalled carbon nanotubes (MWNTs) were investigated via ultrasonic force microscopy. Spatial cross-correlation analysis showed that local radial modulus variations were inversely correlated with local diameter gradients ("bamboo" structures) in MWNTs grown via chemical vapor deposition (CVD). In contrast, uniform MWNTs grown via arc discharge exhibited no such correlation, indicating that reductions of elastic modulus previously reported for CVD-grown MWNTs originated from increased defect density associated with local increases in diameter.     

Broadband electrical characterization of multiwalled carbon nanotubes and contacts

The electrical response of an individual multiwalled carbon nanotube (MWNT) and its contacts, welded to a coplanar waveguide (CPW), was measured up to 24 GHz using a technique that removes environment effects. This is the first time MWNT contact effects have been systematically isolated from the CPW. Each contact response was quite different and also showed a pronounced sensitivity to ambient light. Adding more contact material clearly changed the high-frequency electrical response and the sensitivity to light.     

Electrodeposition of nickel nanoparticles onto multiwalled carbon nanotubes

The process of nickel nanoparticle nucleation and growth during galvanochemical deposition on the surface of multiwalled carbon nanotubes has been studied. The dependences of the morphology, size, and spacing of nickel nanoparticles on the deposition time at a current density of 5 and 0.5 A/dm² are determined.     

A facile procedure to shorten multiwalled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) with > 95% purity were synthesized over a Fe-Co/CaCO3 catalyst using chemical vapour deposition (CVD). Both the CNT yield and the outer diameters increased with time on line in the presence of acetylene. More significantly, the tubes were reduced in length and became stub-like with time. TEM analysis revealed that the CNTs commenced shortening after 2 h of reaction time. Reagent residues (e.g., Ca, CaO, OH/COOH groups and Fe-Co oxides) were found not to influence the CNT bond breaking reaction. CNT growth over Fe-Co supported on silica or CaCO3-Ca3(PO4)2 gave similar results. Further, MWCNTs produced by a floating catalyst method, carbon helices produced from Fe-Co-In/A2O3, and N doped CNTs also revealed tube shortening as a function of reaction time under a flow of acetylene. It is thus apparent that MWCNTs can readily be shortened by the facile procedure of depositing carbon from excess C2H2 on the outer walls of CNTs.