CNT Type Research Articles

The effects of CNT type, alignment and dopants on piezoresistance in CNT fibres

The effects of CNT type, alignment and dopants on piezoresistance in CNT fibres

Nonsimilar convection analysis of single and multilayer carbon nanotubes based nanofluid flow over a vertical cone in a complex porous media subjected to thermal radiations and chemical reaction

The objective of this article is to present a novel model and the consequences of natural convection in magneto hydrodynamic (MHD) boundary-layer flow of carbon nanotubes (CNT’s) based nanofluid above a vertical cone immersed in a porous medium subjected to the suction/injection effects. Two distinct types of CNT’s are investigated within the base fluid known as single wall carbon nanotubes (SWCNT’s) and multiple wall carbon nanotubes (MWCNT’s). Moreover, heat and mass transport mechanisms are examined in the presence of thermal radiations and chemical reactions, respectively. Nonsimilarity transformations are operated to transmute the partial differential system (PDE’s) into dimensionless PDE’s. Numerical solution is acquired by employing local nonsimilarity (LNS) via bvp4c algorithm. Graphical results are plotted and discussed comprehensively against the variation of appealing parameters namely Biot number B10.5-35, Buoyancy ratio parameter Nr0.1-8, chemical reaction parameter Cr0.1-20, Prandtl number Pr(6.2-30), injection parameter Vo0.1-2, Magnetic field M0.2-60 and radiation parameter R(0.1-2). Moreover, the values of Sherwood number Sh, amount of concentration and temperature are examined for distinct values of dimensionless parameters and the conclusions are reported in tabular formation. It is noticed that the Sherwood number escalates with increasing B1 in both SWCNT’s-water and MWCNT’s-water nanofluids, while velocity and temperature profiles are decreasing function of Prandtl number. An excellent comparison is noticed that influence of SWCNT’s is higher than MWCNT’s for velocity, temperature and concentration portray. Finally, the present work is certified via comparison with already published article in limiting case. The novelty of the considered model lies in the fact that the nonsimilar model of the considered model has not been addressed in literature.

Effect of CNT Parameter Variations on CNTFET Amplifier Performance

In this paper we propose a procedure to study the dependence of a CNTFET amplifier performance on CNT parameters that fully identify the geometrical properties of a regular CNT. In particular these parameters are the length and structural indices (n,m) of CNT. We analyse the effects on a linear common source amplifier using a N type CNTFET with a resistive gate polarization. We polarize at a fixed drain voltage and current, gradually changing the CNT parameters. As regards the indices, we present the analysis for a zig-zag CNT. However the proposed procedure can be applied to other types of CNT. We show the effect on gain, on the 3 dB cut off frequency, F3dB, on the input and output resistances, obtaining that F3dB has a clear inverse dependence on the length and that also decreases at higher structural indices for zig-zag CNT.

Acoustic response analysis of periodic orthogonal stiffened composite sandwich structure with pyramidal truss cores

This paper presents analytical studies on the sound transmission loss behavior of functionally graded carbon nanotube reinforced composite (FG-CNTRC) truss core sandwich structure plates subjected to plane sound wave excitation, wherein three different functionally graded patterns are introduced for the carbon nanotubes through the thickness direction of structures. The effective CNTs material properties for each type are determined by the extended rule of mixture and the governing equations are based on the first order shear deformation theory. The compatibility of displacements on the interface between the plate and the stiffeners is employed to derive the governing equation of each stiffener. By using the modal expansion approach and Rayleigh integral, the sound transmission loss is described analytically. Since no existing results of sound insulation can be found for such composite material plate structure, experimental measurements of composite stiffener sandwich plate which is composed of carbon fiber reinforced composite material are subsequently carried out to validate the theoretical model, and good agreement is achieved. Based on the developed theoretical model, the influences of the volume fractions of CNT, truss core type, distribution type of CNT, stiffener spacing, and truss core height on sound transmission loss are subsequently presented.

Inhaled multi-walled carbon nanotubes differently modulate global gene and protein expression in rat lungs

Inhalation of multi-walled carbon nanotubes (MWCNTs) induces lung inflammation. Depending on industrial applications, CNTs with different physicochemical characteristics are produced and workers can potentially be exposed. This raises concerns about the long-term health effects of these nanomaterials. Because of the wide variety of MWCNTs, it is essential to study the toxicological effects of CNTs of various shapes and to better understand the impact physical and chemical properties have on their toxicity. In this study, rats were exposed by nose-only to two pristine MWCNTs with different morphologies: the long and thick NM-401 or the short and thin NM-403. After four weeks of inhalation, animals were euthanized at four different times during the recovery period: three days (short-term), 30 and 90 days (intermediate-term) and 180 days (long-term). Analyses of the transcriptome in the whole lung and the proteome in the bronchoalveolar lavage fluid of exposed animals were performed to understand the MWCNT underlying mechanisms of toxicity. Following inhalation of NM-401, we observed a dose-dependent increase in the number of differentially expressed genes and proteins, whereas there is no clear difference between the two concentrations of NM-403. After NM-403 inhalation, the number of differentially expressed genes and proteins varied less between the four post-exposure times compared to NM-401, which supports the postulation of a persistent effect of this type of CNT. Our toxicogenomics approaches give insights into the different toxicological profile following MWCNT exposure.

Organic thermoelectric thin films with large p-type and n-type power factor

P- and n-type thermoelectric (TE) materials were prepared by using a layer-by-layer method. Assembled nanocomposites displayed high TE properties. For the p-type nanocomposites, polyaniline (PANi)/graphene-poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/PANi/carbon nanotubes (CNT)-PEDOT:PSS quadlayers (QL) were assembled by immersing a substrate alternately to aqueous solutions of these charged materials. Various concentrations of three types of CNT (single-walled, double-walled (DWNT), and multi-walled) and two different surface areas of graphene (300 and 750 m2 g−1) were investigated. The best QL films, assembled with graphene and DWNT, exhibit a power factor (PF = S2 σ) of 3050 µW m−1 K−2 at room temperature, which is among the highest values for a fully organic material. In an effort to improve TE properties in n-type organic thin films, hydrazine is introduced to the films in which DWNT, stabilized by polyethylenimine (PEI), is alternately deposited with graphene, stabilized by polyvinylpyrrolidone (PVP). After doping these films for 5 min with hydrazine, electrical conductivity and Seebeck coefficient significantly increase. An 80 DWNT-PEI/graphene-PVP bilayer film achieves a PF as high as 380 µW m−1 K−2 at room temperature, exhibiting a twofold improvement relative to that of un-doped films. In light of the growing interest in organic thermoelectric nanocomposites, this study provides an effective means to achieve high performance that will allow these unique materials to replace inorganic semiconductors in some applications.

Electronic transport of CNT-encapsulated carbyne

Using density functional theory in combination with Green’s functional formalism we study the effect of CNT-encapsulation on the electronic transport properties of 1D carbon allotrope – carbyne. Structural changes are obtained in carbyne for smaller size of CNT, resulting in strong reduction of the electronic transport. The current in this hybrid system increases with increasing the size of the CNT due to reduced electrostatic potential variations and it becomes larger than the sum of the currents obtained for pristine carbyne and CNT. With further increasing the CNT size, the current in the system decreases and saturates to the sum of the currents obtained for the isolated samples. The obtained results are independent of the encapsulation method (i.e., full or partial encapsulation) and the CNT type (armchair and zig-zag). These findings can be of practical importance for deployment of such hybrid systems in nanotechnology development.

Polymeric Nanofiber-Carbon Nanotube Composite Mats as Fast-Equilibrium Passive Samplers for Polar Organic Contaminants.

To improve the performance of polymeric electrospun nanofiber mats (ENMs) for equilibrium passive sampling applications in water, we integrated two types of multiwalled carbon nanotubes (CNTs; with and without surface carboxyl groups) into polyacrylonitrile (PAN) and polystyrene (PS) ENMs. For 11 polar and moderately hydrophobic compounds (-0.07 ≤ logKOW ≤ 3.13), 90% of equilibrium uptake was achieved in under 0.8 days (t90% values) in nonmixed ENM-CNT systems. Sorption capacity of ENM-CNTs was between 2- and 50-fold greater than pure polymer ENMs, with equilibrium partition coefficients (KENM-W values) ranging from 1.4 to 3.1 log units (L/kg) depending on polymer type (hydrophilic PAN or hydrophobic PS), CNT loading (i.e., values increased with weight percent (wt %) of CNTs), and CNT type (i.e., greater uptake with carboxylated CNTs composites). During field deployment at Muddy Creek in North Liberty, Iowa, optimal ENM-CNTs (PAN with 20 wt % carboxylated CNTs) yielded atrazine concentrations in surface water with a 40% difference relative to analysis of a same-day grab sample. We also observed a mean percent difference of 30 (±20)% when comparing ENM-CNT sampler results to grab sample data collected within 1 week of deployment. With their rapid, high capacity uptake and small material footprint, ENM-CNT equilibrium passive samplers represent a promising alternative to complement traditional integrative passive samplers while offering convenience over large volume grab sampling.

Atomistic investigation of mechanical behavior for CNT reinforced nanocrystalline aluminum under biaxial tensile loading

In this paper, the mechanical behavior of nanocrystalline aluminum and carbon nanotube reinforced NC Al composites have been examined by using molecular dynamics simulations under biaxial tensile loading. Armchair type of (5,5) CNT, (15,15) CNT, (30,30) CNT and three different temperatures (10 K, 300 K and 681 K) have been considered to perform tensile test at a strain rate of 109 s−1. CNT reinforced NC Al composites have exhibited diminished in ultimate tensile strengths and fracture strains compared to NC Al without CNT specimen, corresponding to simulated temperatures. On the other hand, only (15,15) CNT incorporated NC Al specimen exhibited higher fracture strain in contrast to NC Al specimen at room temperature in which load bearing capacity of composite has been enriched through CNT. The thermal fluctuations have increased with increase in temperature and which leads to reduce in mechanical properties. Dislocation density analysis and Centrosymmetry parameter analysis have been carried out to evaluate the structure evolution of the composites at different strains during biaxial tensile loading. The deformation behavior of NC Al and CNT reinforced NC Al composites have been analysed at various temperatures with respect to three different CNT diameters.

Oxidized SWCNT and MWCNT as co-catalysts of polymeric carbon nitride for photocatalytic hydrogen evolution

Polymeric carbon nitride (PCN) has been found as a promising photocatalyst for hydrogen evolution from water splitting. However, disadvantages limit its commercial applications. Therefore, modification of PCN in order to increase the hydrogen evolution rate and stability of the photocatalyst are extensively studied. In this contribution, we compare the influence of oxidation and the number of walls in carbon nanotubes (SWCNT and MWCNT) on the photocatalytic performance of PCN. It was found that oxidation of both types of CNT enhanced a photocurrent response, interfacial charge transfer and separation properties leading to the enhanced hydrogen evolution rate. Interestingly, MWCNT were found to enhance the charge transfer and separation properties more significantly. However, this material affected inferior co-catalytic behavior. We suggest it was related to the lower number of reactive electrons migrating to the surface reaction sites because of transferring to the inner tubes. SWCNT influence ~12-fold increase in H2 evolution rate, while MWCNT influenced ~8-fold enhancement in comparison to pristine PCN.

Bending, buckling and free vibration of nonlocal FG-carbon nanotube-reinforced composite nanobeams: exact solutions

This paper investigates the bending, buckling and free vibration behaviors of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) nanobeams by considering small-scale effect. The governing equations of motion of a Timoshenko beam under a general loading are derived utilizing the nonlocal elasticity theory. The equations governing bending and stretching behavior of CNTRC nanobeams are uncoupled to a fifth-order ordinary differential equation with respect to the rotation of cross-section for the static cases of bending and buckling. This uncoupling makes it possible to develop exact solutions for transverse deflection and buckling load of CNTRC nanobeams. Using differential operator method, the decoupled sixth-order differential equations in terms of the kinematic variables are obtained for vibration analysis. By setting the coefficients matrix in the corresponding system of homogenous algebraic equations to zero, an algebraic frequency equation is derived. Finally, based on the presented closed-form solutions, parametric studies are carried out to assess the effects of CNT distribution, nonlocal parameter and type of boundary conditions on the deflection, buckling and natural frequency of CNTRC nanobeams. Findings show that nonlocal effect on the mechanical behavior of nanobeams is strongly dependent on boundary conditions and loadings. It is seen that cantilever nanobeams become harder by taking into account nonlocal effect, contrary to clamped and simply supported nanobeams. In addition, the influence of CNT distribution on the mechanical behavior of cantilever beams is more significant than that of simply supported and clamped beams.

Influence of defect-induced deformations on electron transport in carbon nanotubes

We theoretically investigate the influence of defect-induced long-range deformations in carbon nanotubes on their electronic transport properties. To this end we perform numerical ab-initio calculations using a density-functional-based tight-binding model for various tubes with vacancies. The geometry optimization leads to a change of the atomic positions. There is a strong reconstruction of the atoms near the defect (called ‘distortion’) and there is an additional long-range deformation. The impact of both structural features on the conductance is systematically investigated. We compare short and long CNTs of different kinds with and without long-range deformation. We find for the very thin (9, 0)-CNT that the long-range deformation additionally affects the transmission spectrum and the conductance compared to the short-range lattice distortion. The conductance of the larger (11, 0)-or the (14, 0)-CNT is overall less affected implying that the influence of the long-range deformation decreases with increasing tube diameter. Furthermore, the effect can be either positive or negative depending on the CNT type and the defect type. Our results indicate that the long-range deformation must be included in order to reliably describe the electronic structure of defective, small-diameter zigzag tubes.

Aerosolization and characterization of carbon nanotube and nanofiber materials: Relationship between aerosol properties and bulk density

Potential inhalation of fibrous carbon nanomaterials depends on the manufacturing/handling process and their tendency for air dispersion. Because of the large variety of carbon nanotube and nanofiber (CNT and CNF) products, with varying physical and chemical properties, characterization of these materials and their associated exposure risks is challenging. In this study, we aerosolized different types of CNT and CNF materials using an acoustic generator (AG) and characterized their aerodynamic and physical properties. The generation characteristics of the AG for the different CNT and CNF materials were investigated by measuring aerosol number concentrations and its decay properties with time. Airborne particle properties such as mobility and aerodynamic diameters were measured using mobility and aerodynamic particle sizers. The bulk and effective densities of the powder and aerosol were obtained by measuring the mass and volume of the bulk material and aerosol particles, where effective density was calculated by a tandem mobility-mass technique. The relationship between the aerosol properties (i.e., particle size, concentration, and dustiness) and bulk density of the material was also investigated to understand the potential for dispersion in air. The results showed that the aerosol concentration decay for each nanomaterial has a unique time constant, and that the rate of decay is positively correlated with the bulk density of the powder: the lower the bulk density, the slower the concentration decay. The aerodynamic diameter increased with increasing bulk density, while the mobility diameter showed the opposite trend. In general, bulk density is smaller than the particle effective density, and the effective density tends to approach the bulk density as particle size increases. Also, the bulk density of the fibrous nanomaterials tested in this study showed a reasonable correlation with dustiness data obtained from both our measurements and the literature, which was relatively weak for non-fibrous powders. This study indicates that more loosely agglomerated CNT powders, with lower bulk densities, would be more readily dispersed, and the dispersed particles remain airborne for longer periods. Depending on particle size, such materials can pose higher exposure risks due to their ease of dispersion and longer residence times.

Use of Raman spectroscopy to identify carbon nanotube contamination at an analytical balance workstation

ABSTRACTCarbon nanotubes (CNTs) are cylindrical molecules of carbon with diverse commercial applications. CNTs are also lightweight, easily airborne, and have been shown to be released during various phases of production and use. Therefore, as global CNT production increases, so do concerns that CNTs could pose a safety threat to those who are exposed to them. This makes it imperative to fully understand CNT release scenarios to make accurate risk assessments and to implement effective control measures. However, the current suite of direct-reading and off-line instrumentation used to monitor the release of CNTs in workplaces lack high chemical specificity, which complicates risk assessments when the sampling and/or measurements are performed at a single site where multiple CNT types are handled in the presence of naturally occurring background particles, or dust. Herein, we demonstrate the utility of Raman spectroscopy to unequivocally identify whether particulate matter collected from a multi-user analytical balance workstation comprised CNTs, as well as, whether the contamination included CNTs that were synthesized by a Ni/Y-catalyzed electric-arc method or a Co/Mo-catalyzed chemical vapor deposition method. Identifying the exact CNT type generated a more accurate risk assessment by knowing the metallic impurities involved, and it also led to the identification of the users who handled these CNTs, a review of their handling techniques, and an improved protocol for safely weighing CNTs.

Vibrational analysis of functionally graded carbon nanotube-reinforced composite spherical shells resting on elastic foundation using the variational differential quadrature method

Abstract In this paper, the free vibration characteristics of embedded functionally graded carbon nanotube-reinforced composite (FG-CNTRC) spherical shells are studied based on a numerical approach. The elastic foundation is considered to be Pasternak-type. Moreover, the extended rule of mixture is used so as to obtain the material properties of FG-CNTRC. The shell is also modeled according to the first-order shear deformation shell theory. The energy functional of the structure is obtained first. Using differential operators, the discretized form of the energy functional is derived. By means of the variational differential quadrature (VDQ) method, the reduced forms of mass and stiffness matrices are then obtained. Selected numerical results are given to investigate the effects of different parameters such as elastic foundation coefficients, boundary conditions, CNT volume fraction, thickness-to-radius ratio and type of distribution of CNT on the vibrations of FG-CNTRC spherical shells.

Effect of filtration in functionalized and non-functionalized CNTs and surface modification of fibers as an effective alternative approach

Abstract Fabrication of multiscale composites by the addition of CNT in epoxy matrices as previous step to the impregnation process leads to several manufacturing difficulties associated to filtration effects and viscosity increments. These effects have been analyzed finding a relation between the type of CNT and the dispersion degree with the change in the rheological behavior and the heterogeneity of the mechanical properties. This heterogeneity is associated to filtration effects of the nanoreinforcement. Modification of the carbon fibers by a nanoreinforced sizing has been presented as an alternative, obtaining homogeneous composites and avoiding the filtration effects. These multiscale composites have higher electrical and interlaminar mechanical properties.

Dynamic Analysis of Cylindrically Layered Structures Reinforced by Carbon Nanotube Using MLPG Method

This paper deals with the dynamic analysis of stress field in cylindrically layeredstructures reinforced by carbon nanotube (CLSRCN) subjected to mechanical shock loading.Application of meshless local integral equations based on meshless local Petrov-Galerkin(MLPG) method is developed for dynamic stress analysis in this article. Analysis is carriedout in frequency domain by applying the Laplace transformation on governing equations andthen the stresses are transferred to time domain, using Talbot inversion Laplace techniques.The mechanical properties of the nanocomposite are mathematically simulated using fourtypes of carbon nanotube distributions in radial volume fraction forms. The propagation ofstresses is indicated through radial direction for various grading patterns at different timeinstants. The effects of various grading patterns on stresses are specifically investigated.Numerical examples, presented in the accompanying section 4 of this paper, show thatvariation of *CN V has no significant effect on the amplitude of radial stresses. Examplesillustrate that stress distributions in cylindrical layer structures made of a CNT type  aremore sensitive rather than other grading pattern types of CNTs. Results derived in thisanalysis are compared with FEM and previous published work and a good agreement isobserved between them.

Low temperature graphitization of interphase polyacrylonitrile (PAN)

Ordered polyacrylonitrile (PAN) interphase structures were formed in solution-cast PAN/carbon nanotube (CNT) composite films by enhancing polymer crystallization conditions and processing parameters for five types of CNTs. All film samples were heat-treated using similar stabilization and carbonization (up to 1100°C) processes. Both the precursor and carbonized materials were characterized by electron microscopy and X-ray spectroscopy. Highly ordered graphitic structure was formed predominantly in the carbonized materials at 1100°C (i.e., ∼1500°C lower than the temperature used in a commercial graphitization process). The ordering of the graphite structure formed at 1100°C was further improved by heat treatment up to 2100°C. Multiple characterization results indicate that the early onset of PAN conversion to graphite is directly related to the polymer interphase formation as well as the CNT type. Based on the stabilization and carbonization parameters used in this study, PAN/single-wall carbon nanotube (SWNT) samples showed more prevalent graphite formation at 1100°C. This work demonstrates the influence of CNT type regarding interfacial confinement toward this low-temperature polymer-to-graphite conversion process.

Interactions of microorganisms with polymer nanocomposite surfaces containing oxidized carbon nanotubes.

In many environmental scenarios, the fate and impact of polymer nanocomposites (PNCs) that contain carbon nanotubes (CNT/PNCs) will be influenced by their interactions with microorganisms, with implications for antimicrobial properties and the long-term persistence of PNCs. Using oxidized single-wall (O-SWCNTs) and multi-wall CNTs (O-MWCNTs), we explored the influence that CNT loading (mass fraction≤0.1%-10%) and type have on the initial interactions of Pseudomonas aeruginosa with O-CNT/poly(vinyl alcohol) (PVOH) nanocomposites containing well-dispersed O-CNTs. LIVE/DEAD staining revealed that, despite oxidation, the inclusion of O-SWCNTs or O-MWCNTs caused PNC surfaces to exhibit antimicrobial properties. The fraction of living cells deposited on both O-SWCNT and O-MWCNT/PNC surfaces decreased exponentially with increasing CNT loading, with O-SWCNTs being approximately three times more cytotoxic on a % w/w basis. Although not every contact event between attached microorganisms and CNTs led to cell death, the cytotoxicity of the CNT/PNC surfaces scaled with the total contact area that existed between the microorganisms and CNTs. However, because the antimicrobial properties of CNT/PNC surfaces require direct CNT-microbe contact, dead cells were able to shield living cells from the cytotoxic effects of CNTs, allowing biofilm formation to occur on CNT/PNCs exposed to Pseudomonas aeruginosa for longer time periods.

The effect of CNT functionalization on electrical and relaxation phenomena in MWCNT/chitosan composites

The effect of the type of CNT (functionalized and non-functionalized) on the dielectric relaxation phenomena and conductivity of MWCNT/chitosan (MWCNT/CS) was investigated. Composites were prepared by the solvent cast method by homogeneously dispersing CNT into a CS matrix. FTIR analysis suggests the formation of hydrogen bonding in functionalized-MWCNT/CS whereas the CS remains unaffected in non-functionalized films. In the low conductivity region, the α-relaxation process associated with a glass transition in CS is affected by the MWCNT; the Vogel temperature increases due to a decrease of the water content. The σ-relaxation exhibits a typical Arrhenius-type temperature dependence that is independent on the moisture content. Strong interfacial interactions of functionalized-MWCNT with the CS matrix are responsible for high values of the contact resistance Rc between individual CNT. Conversely, non-functionalized MWCNTs exhibit a typical 3D percolation threshold at ca. 4 wt %.