Behavior Of Multi-walled Carbon Nanotubes Research Articles

Multiwalled Carbon Nanotube/Water Nanofluid or Helical Coiling Technique, Which of Them Is More Effective?

A set of experiments were performed to investigate the effect of two different techniques of heat transfer enhancement: nanofluidics and helical coiling. The convection heat transfer behavior of multiwalled carbon nanotube (MWCNT)/water nanofluids through helical coiled tubes with different geometries was reported. Solutions of 0.1, 0.3, and 0.5% particle weight concentration of MWCNT in distilled water were prepared using a two-step method, and the effects of a wide range of different parameters such as Reynolds and Helical numbers, geometrical parameters of the coils, and nanofluid weight fractions were studied. It was observed that by increasing the Reynolds number or weight concentration of nanofluid, the Nusselt number increases considerably. The maximum thermal performance factor at 4.24 was achieved in this study. Also, the helical coiling technique showed better performance than nanofluidics in these experiments. In addition, the empirical correlations were developed for Nusselt number and pressure drop in terms of Helical number, Prandtl number, and weight concentration fit to the experimental data within +25% and −20%.

Stiffener Insertion Based Variance in Radial Stiffness of Multi-Concentric Hollow Tubes

ABSTRACTShell theory solutions for radial buckling of multiply-concentric hollow cylinders are presented. Multi-cylindrical systems are those composed of two or more concentically mounted hollow tubes, wherein the annular space mediates inter-tube forces, attractive or repulsive depending on structural details of composites. Reflecting the multiple core-shell structures, the systems often exhibit peculiar radial buckling modes, which should be relevant to macro scale applications for deep water oil and gas transportation andmicroscale realization in lipid bilayer tubes. In this article, we focus on an illustrative example of such the multiply-tubular systems with nanometric dimension, the so-called multiwalled carbon nanotubes (MWNTs). Theoretical analysis based on a thin shell theory allows us to find anomalous radial buckling behaviors of MWNTs driven by hydrostatic pressure. The obtained buckling modes are characterized by petal-like wavy cross sections, which is what we call the radial corrugation of MWNTs. An important observation is the mechanical consequence of stiff core-tube insertion into the innermost hollow region of a given MWNT. The insertion results in a significant variance in the critical buckling pressure, above which the MWNT undergoes radial corrugation. The insertion-induced-variance in the critical pressure is due to the primary role of inter-tube interaction between adjacent constituent tubes, as explained within our theoretical model.

A novel approach to the chemical stabilization of gamma-irradiated ultrahigh molecular weight polyethylene using arc-discharge multi-walled carbon nanotubes

A complete study was made of the stabilization of gamma-irradiated ultrahigh molecular weight polyethylene (UHMWPE) using arc-discharge multi-walled carbon nanotubes (MWCNTs) as inhibitors of the oxidative process. MWCNTs were efficiently incorporated into the polymer matrix by ball milling and thermo-compression processes at concentrations up to 5 wt% and subsequently gamma irradiated at 90 kGy. Raman spectroscopy demonstrated the generation of radicals on the walls of the MWCNTs and that the G/D ratio was altered by their generation. The same spectra showed interactions between the polymer chains as a series of shifts are observed in the UHMWPE bands. The effect of the MWCNTs as inhibitors for the oxidative process of the UHMWPE was evaluated by means of Electron Spin Resonance (ESR) and Fourier Transformed Infrared Spectroscopy (FTIR). ESR detection of the radiation-induced radicals proved the radical scavenger behaviour of MWCNTs. FTIR measurements were performed to ascertain the influence of the irradiation and of the accelerated ageing protocol in the oxidation index of the polymer and the composites. The results pointed to the positive contribution of the MWCNTs in increasing the oxidative stability of the composite when compared to pure UHMWPE. A comparison is made between composites obtained using MWCNTs produced by the carbon vapour deposition and arc-discharge methods.

Viscoelastic behavior of multiwalled carbon nanotubes into phenolic resin

Nanostructured polymer composites have opened up new perspectives for multi-functional materials. In particular, carbon nanotubes (CNTs) have the potential applications in order to improve mechanical and electrical performance in composites with aerospace application. This study focuses on the viscoelastic evaluation of phenolic resin reinforced carbon nanotubes, processed by using two techniques: aqueous-surfactant solution and three roll calender (TRC) process. According to our results a relative small amount of CNTs in a phenolic resin matrix is capable of enhancing the viscoelastic properties significantly and to modify the thermal stability. Also has been observed that when is used TRC process, the incorporation and distribution of CNT into phenolic resin is more effective when compared with aqueous solution dispersion process

Effect of dc-bias on the dielectric behavior of CNT/ABS nanocomposites

Several aspects of the dielectric behavior of multi-walled carbon nanotube (MWCNT)/acrylonitrile–butadiene–styrene (ABS) nanocomposites were studied. MWCNT/ABS nanocomposites with filler content between 2wt% and 15wt% were prepared by melt mixing and characterized by the impedance technique. The results showed that the dc and ac conductivities increase with increasing dc bias and MWCNT content. The effect of dc bias was more pronounced for nanocomposites with low MWCNT content. The bode diagram of the real impedance for nanocomposites containing 2wt% MWCNT or higher exhibited a frequency independent plateau in the low frequency region revealing that dc conduction is the dominant conduction mechanism. The critical frequency at which ac conductivity becomes frequency dependent increased with increasing dc bias and MWCNT content.

Dynamic shell buckling behavior of multi-walled carbon nanotubes embedded in an elastic medium

This paper studies the dynamic shell buckling behavior of multi-walled carbon nanotubes (MWNTs) embedded in an elastic medium under step axial load based on continuum mechanics model. It is shown that, for occurrence of dynamic shell buckling of MWNTs or MWNTs embedded in an elastic medium, the buckling stress is higher than the critical buckling stress of the corresponding static shell buckling under otherwise identical conditions. Detailed results are demonstrated for dynamic shell buckling of individual double-walled carbon nanotubes (DWNTs) or DWNTs embedded in an elastic medium. A phenomenon is shown that DWNTs or embedded DWNTs in dynamic shell buckling are prone to axisymmetric buckling rather than non-axisymmetric buckling. Numerical results also indicate that the axial buckling form shifts from the lower buckling mode to the higher buckling mode with increasing buckling stress, but the buckling mode is invariable for a certain domain of buckling stress. Further, an approximate analytic formula is presented for the buckling stress and the associated buckling wavelength for dynamic axisymmetric buckling of embedded DWNTs. The effect of radii is also examined.

Thermal Buckling Analysis of Multi-Walled Carbon Nanotubes Through a Nonlocal Shell Theory Incorporating Interatomic Potentials

Described in the current study is the thermal buckling behavior of multi-walled carbon nanotubes (WCNTs) via a nonlocal atomistic-based shell model. The model including the effects of small-scale length and the van der Waals (vdW) forces between adjacent nanotubes is established through the incorporation of the interatomic potential into the nonlocal Flügge shell theory. This model links the strain energy density induced in the continuum to Eringen's nonlocal constitutive relations. The set of coupled field equations are analytically solved for two types of temperature distribution. The present model is of a distinguishing feature which is its independence from the widely scattered values of Young's modulus and the effective wall thickness of carbon nanotubes.

Relationship between the electrochemical behavior of multiwalled carbon nanotubes (MWNTs) loaded with CuO and the photocatalytic activity of Eosin Y-MWNTs-CuO system

The photocatalytic system containing Eosin Y, multiwalled carbon nanotubes (MWNTs) and CuO (Eosin Y-MWNTs-CuO) was fabricated; meanwhile its photocatalytic activity for hydrogen evolution from triethanolamine (TEOA) aqueous solution was evaluated. Under visible light irradiation, the amount of hydrogen (H2) evolution increased greatly due to introduction of CuO in the photocatalytic system. Moreover, the electrochemical behavior of MWNTs loaded with CuO was explored using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results clearly indicate that there is a strong relationship between the electrochemical behavior of MWNTs-CuO and the photocatalytic activity of Eosin Y-MWNTs-CuO, and the high photocatalytic activity of Eosin Y-MWNTs-CuO may mainly originate from the efficient electron-transfer in the system.

Behavior of multiwalled carbon nanotubes functionalized with sulfo groups in aqueous salt solutions

The functionalization of multiwalled carbon nanotubes (MWCNTs) with sulfanilic acid through the diazotization reaction, which yielded the covalent bonding of sulfo groups to the nanotube surfaces, was performed. Stable aqueous nanotube dispersions were obtained. The sizes of functionalized nanotubes in aqueous salt and salt-free solutions and their hydrodynamic characteristics were measured by dynamic light scattering. The data were compared with the data of scanning electron microscopy.

Impact of diameter on carbon nanotube transport in sand

Carbon nanotubes are the subject of intense research due to their unique properties: light weight, significant strength, excellent conductivity, and outstanding chemical resistance. This has led to their application in a wide variety of industries (e.g., in composite materials). As a result of their potential impact to humans and ecosystems, there is increasing interest in understanding the factors that control the transport of carbon nanotubes in the environment, and of particular interest to this study, their transport in porous media. In this work, the transport behavior of multiwall carbon nanotubes (MWCNTs) is investigated in sand packed column experiments. To determine the importance of MWCNT diameter, experiments were conducted using four commercially available MWCNTs. Results suggest that smaller MWCNTs are less mobile than their larger counterparts, likely due to the increase in Brownian motion leading to more MWCNT collisions with the porous media with decreasing MWCNT size. A numerical model was used to simulate observed MWCNT transport behavior and facilitate comparison with published studies. These results suggest that careful characterization of MWCNT characteristics (i.e., dimensions and initial MWCNT mass in suspension) is essential to adequately interpret observed results. Results from this study suggest that MWCNTs may be mobile under conditions expected in subsurface aquifers.

Nanoindentation studies on MWCNT/aluminum alloy 6061 nanocomposites

The nanomechanical behavior of Multiwalled Carbon Nanotubes (MWCNT)/aluminum alloy 6061 (AA6061) nanocomposites was studied for varying volume fractions of MWCNTs by nanoindentation. Nanoindentation testing on the matrix portion with dispersed MWCNTs indicated an increase in Young's modulus by 21% and 22% and an increase in the nanohardness by 43% and 54% by the addition of 1wt% and 2wt% copper coated MWCNTs respectively. The microhardness and nanohardness of the nanocomposites were measured and compared. A comparison was made between the experimental values and various theoretical models to correlate Young's modulus of the nanocomposite.

Synthesis and Photoluminescent Behavior of Multi-Walled Carbon Nanotubes and Samarium Nanocomposites

Synthesis and Photoluminescent Behavior of Multi-Walled Carbon Nanotubes and Samarium Nanocomposites

Thermal Degradation Behavior and Kinetic Analysis of Ultra High Molecular Weight Polyethylene Based Multi-Walled Carbon Nanotube Nanocomposites Prepared Via in-situ Polymerization

Thermal degradation behavior of multi-wall carbon nanotubes (MWCNTs)/ultra high molecular weight polyethylene (UHMWPE) nanocomposites, with different nanotubes contents (0.5, 1.5 and 3.5 wt%) prepared via in-situ polymerization technique have been investigated using thermal gravimetric analysis (TGA). TGA spectra revealed that these nanocomposites had enhanced thermal stability and no significant mass loss (<0.4 wt%) occurred up to 350°C. Thermal degradation of these UHMWPE/MWCNT nanocomposites was investigated in terms of parameters such as the onset temperature of degradation (T10), the decomposition temperature at 50% wt loss (T50), the degradation temperature of maximum rate of the weight loss (Tm), and the residual yields (WR) from TGA. The degradation activation energies (E) of virgin UHMWPE and its nanocomposites were estimated using the Friedman, the Ozawa, Flynn, and Wall (OFW), and the Kissinger's methods. Results indicated that the degradation activation energy for the virgin UHMWPE was 281.3 kJ/mol. The activation energy increased with increasing nanotube loading up to 1.5 wt% indicating that MWCNTs had a stabilizing effect on the degradation of the matrix. However, loadings of 3.5 wt% of nanotube or more could slightly decrease the activation energy. The decrease in the activation energy for degradation of nanocomposites with higher MWCNT concentrations might be attributed to the catalytic effects of nanotubes and polymerization catalyst residues. The “model fitting” method indicated a mechanism of n th-order auto-catalysis from the form of the conversion curves for UHMWPE/MWCNTs nanocomposites prepared via in-situ polymerization.

Effect of solution chemistry on multi-walled carbon nanotube deposition and mobilization in clean porous media

There are increasing concerns over the environmental impact and health risks of carbon nanotubes (CNTs) because they may be released into soil and groundwater systems. The present work systematically investigated the transport, deposition, and mobilization behaviors of multi-walled carbon nanotubes (MWNTs) in saturated columns packed with acid-cleaned glass beads and quartz sand of two different grain sizes. Combined effects of pH (5.6 and 10) and ionic strength (IS: DI water, 1mM, and 10mM) on the fate and transport of the MWNTs in the columns were examined. MWNTs were relatively mobile in all the tested conditions with DI water as the experimental solution. Their deposition in the saturated porous media, however, was very sensitive to solution chemistry, particularly IS. Slight increase in solution IS (1mM) caused strong deposition of MWNTs in both quartz sand (>44%) and glass beads (>39%). Mobilization experimental results indicated that most of the MWNT attachment (>73%) to the porous media was irreversible and reduction in solution IS only caused a small portion of re-entrainment (<27%) of deposited MWNT for all the tested conditions. This indicates that more MWNTs are trapped in the primary minimum, although the deposition of MWNTs in saturated porous media occurs in both primary and secondary minimum. It is suggested that, under unfavorable conditions, weak associated MWNTs in the secondary minimum may be transferred into the primary minimum due to the effect of hydrodynamic force and/or local favorable sites associated with surface heterogeneity.

A glance on the effects of temperature on axisymmetric dynamic behavior of multiwall carbon nanotubes

In this paper the effects of temperature on the radial breathing modes (RBMs) and radial wave propagation in multiwall carbon nanotubes (MWCNTs) are investigated using a continuum model of multiple elastic isotropic shells. The van der Waals forces between tubes are simulated as a nonlinear function of interlayer spacing of MWCNTs. The governing equations are solved using a finite element method. A wide range of innermost radius-to-thickness ratio of MWCNTs is considered to enhance the investigation. The presented solution is verified by comparing the results with those reported in the literature. The effects of temperature on the van der Waals interaction coefficient between layers of MWCNTs are examined. It is found that the variation of the van der Waals interaction coefficient at high temperature is sensible. Subsequently, variations of RBM frequencies and radial wave propagation in MWCNTs with temperatures up to 1 600 K are illustrated. It is shown that the thick MWCNTs are more sensible to temperature than the thin ones.

Transmission-Line Model for Multiwall Carbon Nanotubes With Intershell Tunneling

The electromagnetic behavior of multiwall carbon nanotubes (MWCNTs), in the frequency range where only intraband transitions are allowed, depends on the combinations of different aspects: the number of effective conducting channels of each shell, the electron tunneling between adjacent shells, and the electromagnetic interaction between shells and the environment. This paper proposes a general transmission-line (TL) model for describing the propagation of electric signals along MWCNTs at microwave through terahertz frequencies that takes into account all these aspects. The dependence of the number of conducting channels of the single shell on the shell chirality and radius is described in the framework of the quasi-classical transport theory. The description of the intershell tunneling effects on the longitudinal transport of the π-electrons is carried on the basis of the density matrix formalism and Liouville's equation. The electromagnetic coupling between the shells and ground plane is described in the frame of the classical TL theory. The intershell tunneling qualitatively changes the form of the TL equations through the tunneling inductance and capacitance operators, which have to be added, respectively, in series to the (kinetic and magnetic) inductance matrix and in parallel to the (quantum and electrical) capacitance matrix. For carbon nanotube (CNT) lengths greater than 500 nm, the norm of the tunneling inductance operator is greater than 60% of the norm of the total inductance in the frequency range from gigahertz to terahertz. The tunneling inductance is responsible for a considerable coupling between the shells and gives rise to strong spatial dispersion. The model has been used to analyze the eigenmodes of a double-wall CNT above a ground plane. The intershell tunneling gives arise to strong anomalous dispersion in antisymmetrical modes.

Comparative study of the rheological behavior of multiwalled carbon nanotubes and nanofiber composites prepared by the dilution of a masterbatch of polypropylene

AbstractIn this investigation, the characteristics and the rheological properties of two different nanocomposite systems were investigated. These systems consisted of a dispersion of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) in a polypropylene (PP) matrix. The mixing process was carried out by melt compounding with a twin‐screw corotating extruder with different reinforcement amounts (0.2–20 wt %) from concentrated masterbatches (20 wt %) of PP/CNT and PP/CNF. The results show a remarkable increase in the viscosity for both blends as the reinforcement amount was increased. It was important to evaluate the rheological behavior to understand the effect of the nanocarbon particles on the internal structures and their processing properties of the obtained composites. CNFs were a more viable reinforcement from a processability point of view because the obtained viscosities of the PP/CNF blends were more manageable. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Dynamic buckling behavior of multi-walled carbon nanotubes subjected to step axial loading

This paper studies the dynamic buckling behavior of multi-walled carbon nanotubes (MWNTs) subjected to step axial loading. A buckling condition is derived, and numerical results are presented for MWNTs under fixed boundary conditions. It is shown that the critical buckling load of MWNTs is of multi-branches and decreases as the time elongates. The associated buckling modes for different layers of MWNTs can be either in-phase or out of phase, which is related to the branch that the critical buckling load belongs to. For MWNTs with the same innermost tube radius, the critical buckling load is decreased when increasing the layers.

Oxidation behavior of multiwall carbon nanotubes with different diameters and morphology

Multiwall carbon nanotubes (MWNT) with three medium diameters (20–22, 9–13, and 6–8nm) and different morphology were chemically oxidized using concentrated nitric acid, mixture of nitric and sulfuric acids (“mélange” solution) and mixture of sulfuric acid and hydrogen peroxide (“piranha” solution). Influence of MWNT type and structure as well as type of oxidizer on the surface composition and structure of nanotubes after oxidation was investigated. Acid–base titration, X-ray photoelectron spectroscopy and thermal gravimetric analysis were used for quantitative and qualitative investigation of surface group composition of initial and oxidized nanotubes. Amount of oxygen-containing groups on the surface of oxidized MWNT depends on the type of initial MWNT. It was found that ratio of different oxygen containing groups is less dependent on the type of oxidizer. Electrophysical properties of initial and oxidized nanotubes were investigated in temperature range 4–293K and main types of electrical conductivity were determined. It was shown that oxidation results in decrease in electrical conductivity of all samples with simultaneous change in the conductivity mechanism. Dispersive behavior of initial and oxidized nanotubes in different commonly used solvents was investigated. It was shown that oxidation leads to the improvement of sedimentation stability of MWNT in polar solvents.

Unexpected behaviour of multi-walled carbon nanotubes during “in situ” polymerization process: When carbon nanotubes act as initiators and control agents for radical polymerization

Raw multi-walled carbon nanotubes (MWCNTs) were used, without an initiation agent, to initiate and self-control polymerization of poly(acrylic acid) and poly(methyl methacrylate) copolymers. To enhance the livingness of the radical polymerization, a stable nitroxide can be added to strongly reduce the rate energy of the macromolecular chains growth and their dispersion. During the auto-initiation and self-control processes of the radical polymerization, the grafting of the copolymers onto the MWCNTs surface has been observed and characterized by transmission electronic microscopy (TEM). In particular, the grafting can be achieved thanks to an “in situ” radical polymerization that can simultaneously lead to the grafting of the MWCNTs and improve the dispersion. This work represents a real insight and breakthrough because in one step, MWCNTs acting as chemical motors are grafted and the growth of copolymer chains is well controlled.