Characterization Of Carbon Nanotubes Research Articles

Thermal transport characteristics of supported carbon nanotube: Molecular dynamics simulation and theoretical analysis

With the rapid development of carbon nanotube (CNT)-based devices, thermal transport characteristics of CNT supported on substrate is to be urgently explored. Herein, we systematically study the thermal transport properties of supported single-wall CNT including length, temperature and substrate coupling strength dependence of thermal conductivity using molecular dynamics (MD) simulation. Interestingly, a theoretical model is proposed to describe the length dependent thermal conductivity of supported SWCNT, which matches well with our MD results. Moreover, the phenomenon of non-monotonic change of thermal conductivity with the variation of coupling coefficient is first discovered in supported CNT. The underlying mechanism is revealed by spectral energy density (SED), phonon transport and stress distribution analysis. Our study provides valuable insights towards the thermal dissipation performance of CNT-based electronic and photonic devices.

Interphase thickness and electrical conductivity of polymer carbon nanotube (CNT) nanocomposites assuming the interfacial conductivity between polymer matrix and nanoparticles

The interphase thickness in polymer carbon nanotube (CNT) nanocomposites (PCNT) is expressed by CNT characteristics and interfacial conductivity between CNT and polymer matrix. Also, the effective length and concentration of CNT are defined supposing interfacial conductivity to suggest the percolation threshold and the fraction of networked CNT. Furthermore, a simple model is developed to predict the conductivity of PCNT assuming tunneling effect, interphase region and interfacial conductivity. The influences of all parameters on the interphase thickness, percolation threshold, the fraction of networked CNT and the conductivity of PCNT are studied. In addition, some experimental results are provided to compare the predictions of developed model to the experimental measurements. The high levels of CNT radius, CNT length, CNT conductivity, interfacial conductivity and conductivity transferring can produce a thick interphase, but the waviness cannot change it. Moreover, the developed model can properly calculate the conductivity of studied samples. A desirable conductivity is obtained by thin and long CNT, medium CNT conductivity, poor waviness, high interfacial conductivity and good conductivity transferring, because they provide high effective CNT concentration and low percolation threshold in nanocomposites.

Production and Applications of Carbon Nanotube Buckypapers

The present work aimed to prepare and characterize carbon nanotube (CNT) buckypapers (BPs) and to provide a perspective on possible applications in the optical device industry and power generation through triboelectric nanogenerators. The CNTs were dispersed in aqueous solution with the aid of a dispersing agent and then vacuum filtered. The prepared buckypaper has low average optical reflectance and shows an improvement in electrical conductivity and power generation when silver nanowires were added. This material includes new horizons and future applications for carbon nanotube buckypapers,including aerospace applications.

Mechanical and electrical enhancement of super-aligned carbon nanotube film by organic and inorganic doping

Inspired by the chemical and physical doping methods on traditional composites, bismaleimide (BMI) resin and graphene oxide (GO) are selected for doping modification of carbon nanotube (CNT) film in this paper. Based on the diverse enhancement effects of CNT film, the mechanisms and characteristics of resin crosslink and inorganic doping are compared. Due to the crosslinking network of resin, BMI is more beneficial for cooperative deformation and mechanical enhancement, while GO doping shows more advantages in improving electrical performance because of the numerous functional groups on the surface, and good intrinsic properties. With the appropriate doping method and optimized process conditions, the tensile property and electrical conductivity of CNT film can be improved by over 150% and 200% (e.g., tensile strength and modulus of 2990 MPa and 149 GPa, and electrical conductivity of 38 700 S m−1).

Tensile characteristics of carbene-functionalized CNTs subjected to physisorption of polymer chains: a molecular dynamics study.

Tensile properties such as Young's modulus and ultimate tensile force are important properties in understanding the characteristics of nanocomposites. Besides, the importance of functionalization methods in modification of the unique mechanical and elastic properties of carbon nanotubes (CNTs) is being widely recognized. In this paper, the tensile properties of CNTs functionalized with carbene under physisorption of polymer chains, i.e., aramid and polyketone chains, are investigated by using a series of molecular dynamics (MD) simulations. The results illustrated that Young's modulus of carbene-functionalized CNTs (cfCNTs) decreases by rising the weight percentage of carbene. By contrast, Young's modulus of cfCNTs under physisorption of polymer chains (cfCNTs/polymers) increases as the carbene weight rises. In a particular carbene weight, Young's modulus of cfCNTs/polymers decreases by increasing the chains of non-covalent functional groups. Moreover, it is shown that similar to Young's modulus, ultimate tensile force of cfCNTs reduces by increasing the weight percentage of carbene whereas the ultimate tensile force of cfCNTs/polymers has an increasing trend with raising the carbene weight.

In-situ continuous growth of carbon nanotubes on the surface of carbon fibres

An efficient method for growing carbon nanotubes (CNTs) on the surface of continuously moving carbon fibres has been developed by a unique open-ended chemical vapor deposition (CVD) furnace. Scanning electron microscopy (SEM) is used to observe the morphological characteristics of CNTs grown on carbon fibre surfaces, and high-resolution transmission electron microscopy (HRTEM) is used to study the microstructure of CNTs. The results show that the CNTs achieve uniform and orderly growth. In the process of CNTs growth, the cross-linking of adjacent graphite crystallites is formed and the damage of the catalyst nanoparticles to the fibres is repaired, so the tensile strength is increased compared to the carbon fibres undergoing reduction. CNTs-grown carbon fibres can be used to fabricate the flexible supercapacitor electrodes to improve electrochemical capacitance and promote electrochemical stability.

Improvement of mechanical properties in epoxy adhesive joints of Al alloy via carbon nanotubes from flame

Carbon nanotubes (CNTs) from the flame were used as interface enhancers for epoxy-bonded Al alloy joints. The structure characteristics of CNTs were investigated in detail by the combination of scanning electron microscopy (SEM), transmission electron microscope (TEM), and Raman spectroscopy. The effects of CNTs incorporation on the lap shear strength (LSS) of bonded joints were investigated in comparison with those of the CNTs-uncontained bonded joints. The CNTs-incorporated LSS was enhanced evidently, the maximum LSS value reached 20.1 MPa. The dependence of micromorphology of failure of the bonded joints was analyzed systematically based on the images from the SEM. The strengthening mechanism was also illuminated according to the fracture morphology of the bonded joints and evidently improved static contact angle of the surface of the Al alloy plates.

Mechanical properties of carbon-nanotube-reinforced cementitious materials: database and statistical analysis

This paper aims to provide guidelines for selecting the correct type of carbon nanotube (CNT) to improve the mechanical properties of cementitious materials. Previous researchers have discussed the effect of CNT characteristics on their dispersion quality. However, the effect of these characteristics on the mechanical properties of CNT-reinforced cementitious materials is not fully understood. To clarify this, the study reported in this paper was conducted in two phases. In the first phase, a database was established from the literature to study the influences of three different parameters associated with CNTs (length, diameter and concentration based on the weight percent of cement powder (c-wt%)) on compressive and flexural strengths. The analyses revealed that short and small-diameter CNTs could be beneficial for increasing compressive strength. Conversely, relatively long and large-diameter CNTs were more effective in increasing flexural strength. In general, an average CNT length of 10–20 μm and an average diameter of 20–32·5 nm resulted in the highest overall mechanical performance. The optimal upper limit concentrations for flexural and compressive strengths were found to be 0·15 and 0·20 c-wt%, respectively. In the second phase of this study, the statistical analyses were experimentally verified using the CNT optimum length, two diameters and three levels of concentrations.

Physical aspects of Darcy-Forchheimer bidirectional flow in carbon nanotubes (SWCNTs and MWCNTs)

PurposeThis paper aims to examine the three-dimensional (3D) flow of carbon nanotubes (CNTs) due to bidirectional nonlinearly stretching surface by considering porous medium. Characteristics of both single-walled CNTs and multi-walled CNTs are discussed by considering Xue model. Darcy–Forchheimer model is used for flow saturating porous medium.Design/methodology/approachOptimal homotopy analysis method is used for the development of series solutions.FindingsThe authors deal with 3D Darcy–Forchheimer flow of CNTs over a nonlinearly stretching surface. Heat transport mechanism is discussed in the presence of Xue model. The homogeneous and heterogeneous effects are also accounted. The mathematical modeling is computed using boundary-layer approximations.Originality/valueNo such work has been done yet in the literature.

Li-Functionalized Carbon Nanotubes for Hydrogen Storage: Importance of Size Effects

We investigated Li-doped carbon nanotubes (CNTs) as a promising hydrogen storage media. In this computational model, we considered isolated lithium atom adsorbed on a CNT wall as an adsorption site for hydrogen. We focused on the influence of size effects on the structural and energetic characteristics of CNT(n,n)@Li+kH2 complexes where n = 5, 7, 9; k = 1, ..., 6; Nc = 4, 5, 6 (Nc is translation length of CNT, expressed in terms of a number of CNT unit cells). We proved that modeled CNT length substantially influences internal sorption of Li and hydrogen on the narrow tube (5,5), which subsequently alters the adsorption energies of H2 molecules and causes the deformation of the carbon framework. Moreover, the size effects are not pronounced in the case of external sorption for all considered CNT translation lengths and diameters. We have not observed any noticeable qualitative difference between internal and external hydrogen sorption in the nanotube wider than CNT(5,5). In the case of external adsorption on all considered nanotubes, doping with Li increases hydrogen adsorption energies of up to four H2 molecules by 100 meV in comparison with pure CNTs. And the local density approximation estimations (∼250 meV/H2) of adsorption energy on Li-decorated CNTs exceed the lowest requirement proposed by the U.S. Department of Energy (200 meV/H2). In the case of internal sorption on Li-functionalized tubes, the generalized gradient approximation also gives hydrogen adsorption energies in the desired range of 200–600 meV/H2. However, steric hindrances could prevent sufficient hydrogen uptakes (less than 2 wt % inside CNT(5,5)). We believe that our findings on the size effects are important for estimation of CNT’s hydrogen storage properties.

A coupled longitudinal-transverse nonlinear NSGT model for CNTs incorporating internal energy loss

The aim of the present study is to comprehensively analyse scale effects on the mechanical characteristics of carbon nanotubes (CNTs) with viscoelastic properties. A scale-dependent coupled longitudinal-transverse nonlinear formulation is presented for this aim. The roles of both the longitudinal and transverse motions as well as the viscosity effect due to the internal loss of the total energy are taken into account. The influence of large deformations due to the geometric nonlinearity is also taken into account. The nonlocal strain gradient theory (NSGT) is applied so as to describe scale effects on the mechanical characteristics of viscoelastic CNTs. Compared to the classical nonlocal theory, the NSGT better estimates scale effects since it is able to describe both the stiffness-hardening and -softening behaviours. The Kelvin-Voigt approach is used to capture the influence of the internal energy loss. Application of the NSGT together with the Hamilton principle yields the energy potential, the external work and the coupled longitudinal-transverse equations of the CNT. To determine an accurate numerical solution, the Galerkin scheme of discretisation and a continuation approach are finally utilised. The role of different parameters of the nanosystem in the nonlinear coupled mechanics of viscoelastic CNTs is discussed.

Dispersion and reinforcement efficiency of carbon nanotubes in cementitious composites

Cement pastes reinforced with various concentrations of functionalised and unfunctionalised carbon nanotubes (CNTs) with different aspect ratios were studied in terms of their dispersion and reinforcement efficiency. Mechanical strength was correlated with geometrical characteristics of CNTs, as well as the microstructure of reinforced pastes. Optimal CNTs of 0·05–0·1 wt% were found effective in increasing the flexural and compressive strength of reinforced pastes up to 36% and 27%, respectively. Efficiently dispersed CNTs were effective in bridging microcracks up to around 1 μm width. The CNTs did not significantly affect the phase composition of cement pastes but accelerated the hydration process. Based on a proposed equation, strength improvement was correlated with CNT aspect ratio and volume concentration. This equation establishes guidelines for maximised strength development based on geometrical and compositional parameters; it can be used for more rational design of CNT-reinforced cement materials, covering different compositions, as well as types and amounts of CNTs.

P- and n-type thermoelectric cement composites with CVD grown p- and n-doped carbon nanotubes: Demonstration of a structural thermoelectric generator

The thermoelectric (TE) behavior and microstructure of p- and n-doped multi-walled carbon nanotube (CNT) filled cement nanocomposites over 3, 7, 14 and 28 days age are reported for the first time. Pristine CNTs with inherent p-type semiconductor characteristics (p-CNT) and n-type Nitrogen-doped CNTs (n-CNT) were incorporated by shear mixing in a cement matrix at 1% by weight of cement and 0.5 water to cement ratio (w/c). CNTs were dispersed initially by ultrasonication using a surfactant and mixed further with the cement powder. Raman, high resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), electric and thermoelectric measurements were employed to characterize the p-CNT and n-CNT, as well as the corresponding cement/CNT nanocomposites. The Seebeck coefficient (S) and electrical conductivity (σ) of nanocomposites for 3, 7, 14 and 28 days of sample's age were examined. All the measurements were performed on as received samples after mould casting at each specific age (samples denoted as before drying) and after drying at 80 °C overnight in order to elucidate the significant effect of moisture. The cement/p-CNT nanocomposite exhibited n-type TE behavior before drying due to the water content and the anions stemming from the cementitious matrix. A p-type behavior was observed after drying and elimination of water, due to the inherent p-type characteristics of CNTs. This is realised by plausible electron withdrawing and p-doping mechanism that adsorbed and/ or chemisorbed oxygen species facilitate to the CNT backbone. The 14 days cement/n-CNT exhibited the highest performance in terms of σ and power factor (PF) reaching 1.44 µWm−1K−2 before drying, and 7.64 × 10−3 µW m−1K−2 after drying. The cement/CNT nanocomposites with p- and n-type TE characteristics allowed the construction of a thermoelectric generator (TEG) for plausible large-scale thermal energy harvesting via cement-based structural thermoelectric generators (TEGs).

Three dimensional Darcy-Forchheimer radiated flow of single and multiwall carbon nanotubes over a rotating stretchable disk with convective heat generation and absorption

Several important characteristics of CNTs (carbon nanotubes) like excellent electrical conductivities, extraordinary thermal conductivities, good mechanical and chemical stability and extremely light mass make CNTs a model material which is utilized in various electro-chemical mechanisms. Keeping the said significance of carbon nanotubes in notice our main aim in this analysis is to establish the import relation of Darcy Forchheimer in three dimensional (3D) flows of classical fluid (water) based CNTs in presence of slip velocity due to rotating stretchable disk. Analysis of nanoparticles like single and multi-walled (SWCNTs, MWCNTs) carbon nanotubes are developed and equated. Present investigation further comprises non-linear thermal radiation, heat generation/absorption as well as convective thermal boundary condition aspects. The pertinent non-linear ordinary differential equations after utilizing the appropriate variables are calculated. HAM (Homotopy Analysis Method) technique is utilized for the analysis of velocities and thermal distribution. Various graphs have been plotted in order to examine that by what means the velocities and thermal field are altered by different model quantities. The main features of flow like the CFReα, CGReα (skin friction), Nu(Reα)−1/2 (heat transfer rate) have been intended numerically and graphically.

Thermal conductivity and diffusion behaviour of lauric acid confined in carbon nanotubes as heat storage materials

ABSTRACTThe thermal conductivity and diffusion behaviour of lauric acid (LA) confined in single-walled carbon nanotube (CNT) with the filling ratio of 80% are investigated by molecular dynamics (MD) simulations. It is found that the concentric multilayer LA tubes are clearly observed under the interaction of CNT and LA and the hydrogen bonds (HB) among LA molecules in a confined environment. Due to the phonon scattering in low-frequency and the high-thermal conductivity characteristics of CNT, the axial thermal conductivity of CNT/LA is 49–57% lower than that of empty CNT and 115–188 times higher than that of crystal LA at the temperature range of 280 and 360 K. The confined LA molecules move as a whole cluster due to the long-lasting HB action and travel much faster than the bulk.

Effect of the Plasma Functionalization of Carbon Nanotubes on the Formation of a Carbon Nanotube–Nickel Oxide Composite Electrode Material

The unique properties of carbon nanotubes (CNTs) make these systems promising for the production of composite electrode materials based on a combination of CNTs and transition metal oxides. The effect the parameters of the functionalization of vertically aligned CNT arrays in mixed argon–oxygen high-frequency plasma have on the structural characteristics of CNTs is studied by Raman spectroscopy. The effect the duration of treatment at higher partial argon consumption and low total gas consumption of the working mixture has on the distribution of nickel oxide over a CNT array deposited via SILAR is determined. Results from scanning electron microscopy show that lengthening the duration of functionalization from 30 to 1200 s allows the depth of coating a CNT surface with a nickel oxide layer to be increased from 300 nm to 2.5 μm. Composite structures produced in this work can be used as electrodes of supercapacitors.

Engineering the Surface and Mechanical Properties of Water Desalination Membranes Using Ultralong Carbon Nanotubes.

In this work, novel polysulphone (PS) porous membranes for water desalination, incorporated with commercial and produced carbon nanotubes (CNT), were fabricated and analyzed. It was demonstrated that changing the main characteristics of CNT (e.g., loading in the dope solutions, aspect ratio, and functionality) significantly affected the membrane properties and performance including porosity, water flux, and mechanical and surface properties. The water flux of the fabricated membranes increased considerably (up to 20 times) along with the increase in CNT loading. Conversely, yield stress and Young’s modulus of the membranes dropped with the increase in the CNT loading mainly due to porosity increase. It was shown that the elongation at fracture for PS/0.25 wt. % CNT membrane was much higher than for pristine PS membrane due to enhanced compatibility of commercial CNTs with PS matrix. More pronounced effect on membrane’s mechanical properties was observed due to compatibility of CNTs with PS matrix when compared to other factors (i.e., changes in the CNT aspect ratio). The water contact angle for PS membranes incorporated with commercial CNT sharply decreased from 73° to 53° (membrane hydrophilization) for membranes with 0.1 and 1.0 wt. % of CNTs, while for the same loading of produced CNTs the water contact angles for the membrane samples increased from 66° to 72°. The obtained results show that complex interplay of various factors such as: loading of CNT in the dope solutions, aspect ratio, and functionality of CNT. These features can be used to engineer membranes with desired properties and performance.

Porous SnO2–CuxO nanocomposite thin film on carbon nanotubes as electrodes for high performance supercapacitors

Metal oxides are promising materials for supercapacitors due to their high theoretical capacitance. However, their poor electrical conductivity is a major challenge. Hybridization with conductive nanostructured carbon-based materials such as carbon nanotubes (CNTs) has been proposed to improve the conductivity and increase the surface area. In this work, CNTs are used as a template for synthesizing porous thin films of SnO2–CuO–Cu2O (SnO2–CuxO) via an electroless deposition technique. Tin, with its high wettability and electrical conductivity, acts as an intermediate layer between copper and the CNTs and provides a strong interaction between them. We also observed that by controlling the interfacial characteristics of CNTs and varying the composition of the electroless bath, the SnO2–CuxO thin film morphology can be easily manipulated. Electrochemical characterizations show that CNT/SnO2–CuxO nanocomposite possesses pseudocapacitive behavior that reaches a specific capacitance of 662 F g−1 and the retention is 94% after 5000 cycles, which outperforms any known copper and tin-based supercapacitors in the literature. This excellent performance is mainly attributed to high specific surface area, small particle size, the synergistic effect of Sn, and conductivity improvement by using CNTs. The combination of CNTs and metal oxides holds promise for supercapacitors with improved performance.

Physically consistent nonlocal kernels for predicting vibrational characteristics of single walled carbon nanotubes

In the present work, at first, the drawbacks of the continuum mechanics (CM) based method in predicting the vibrational and wave dispersion characteristics of carbon nanotubes (CNTs) are illustrated and discussed. For this purpose, the response of the Euler-Bernoulli and Timoshenko beam theories together with the differential form of the Eringen’s nonlocal elasticity theory under different boundary conditions are examined. The same problems are simulated via molecular dynamics (MD) approach. By considering the results of MD simulation as the benchmark solutions, it is shown that the optimum value of the length scale parameter of the nonlocal elasticity theory of Eringen depends on the nanotube boundary conditions, aspect ratio and vibrational mode number of the CNTs. To overcome these drawbacks, a kernel with unique length scale variable is introduced by combing different Gaussian kernels and specifying two related new scale variables. These newly defined scale parameters resolve former problem in shifting between different scales. Accordingly, an improved nonlocal constitutive relation is suggested. It is shown that the proposed model can accurately predict the vibrational and flexural vibrational dispersion relation (FVDR) characteristics of CNTs even when using Euler-Bernoulli theory (EBT).

Study on understanding functional characteristics of multi-wall CNT modified asphalt binder

ABSTRACT This study evaluates important functional characteristics such as dispersion, aging resistivity potential, temperature susceptibility, and high temperature storage stability of Carbon Nano Tube (CNT) modified asphalt binders. CNT content was varied as 0%, 0.4%, 0.75%, 1.5% and 2.25% by weight of control binder (AC-10). Scanning Electron Microscopic (SEM) images was captured to get direct observation of CNT dispersion. Viscosity was further measured to understand the workability and dispersion characteristics. Further, viscosity temperature susceptibility parameters (A and VTS), activation energy and Penetration Index (PI) values were estimated to evaluate temperature susceptibility. SEM images and viscosity data showed that CNT content up to 1.5% may be recommended without potential problem of entanglement/clustering. Similarly, analysis of softening point, complex modulus and phase angle data showed positive effect of CNT on aging resistivity potential. Such improvement in functional characteristics can be attributed to high specific surface area (190 m2/gm), higher aspect ratio (length/diameter = 645) and excellent mechanical properties of CNT. Likewise, high temperature storage stability was evaluated using softening point and Multiple Stress Creep Recovery (MSCR) tests. Though softening point test method showed sufficiently stable nature of CNT under high temperature storage condition, settling of CNT (unstable nature) was observed from MSCR testing approach.