Distribution Of Carbon Nanotubes Research Articles

Highly Sensitive and Stretchable Carbon Nanotube/Fluoroelastomer Nanocomposite with a Double‐Percolated Network for Wearable Electronics

AbstractA smart stretchable material is developed from a composite of carbon nanotube (CNT) and fluoroelastomer (FKM), which is fabricated via an internal melt‐mixer method. A unique, double‐percolated, electrically conductive network is observed with ultralow percolation thresholds of 0.45 phr and 1.40 phr CNT. This provides the CNT/FKM nanocomposites with a wide range of strain sensitivity. Thin‐film nanocomposites at the first plateau of conductivity show an ultrahigh sensitivity with a gauge factor (GF) of 1010 at 23% strain for 0.6 phr and of 6750 at 34% strain for 1 phr. At the second plateau of conductivity, 1.5 phr nanocomposite corresponds to higher levels of strain of 78% strain with ultrahigh GF of more than 4 × 104 and 2 phr nanocomposite to almost 100% strain with GF of 1.3 × 105. The CNT/FKM nanocomposites possess a high elongation at break of 430% and up to 232% strain sensitivity. The unique distribution of CNTs in the polar fluoroelastomer FKM facilitates simultaneous high sensitivity and high stretchability, and improved mechanical strength over reported polymer‐based nanocomposite stretchable sensors. The novel, stretchable CNT‐based FKM conductors have great potential for wearable electronics such as stretchable sensors, stretchable light‐emitting diodes (LEDs), and human motion monitoring.

Compression‐compression fatigue performance of aluminium matrix composite foams reinforced by carbon nanotubes

AbstractThe compression‐compression fatigue performance of carbon nanotube (CNT) reinforced aluminium matrix composite foams (AMCFs) were investigated. The ε‐N curves of AMCFs are composed of three stages (the elastic, strain hardening, and rapid accumulation stages), while the fatigue strain of AMCFs accumulates very rapidly in stage III compared with Al foams. The fatigue strength of AMCFs with CNT contents of 2.0, 2.5, and 3.0 wt% increases by 6%, 44%, and 102% than Al foams, respectively. Different from Al foams' deformation of layer‐by‐layer, the main failure modes of AMCFs are the brittle fracture and collapse of pores within significant shear deformation bands under fatigue loading. The uniform distribution of CNTs and good interfacial bonding of CNTs and Al matrix is the important factor for the improvement of fatigue properties of AMCFs.

Study of self-organized structure in carbon nanotube forest by fractal dimension and lacunarity analysis

In this work, a fractal analysis of a morphology of carbon nanotube (CNT) forest was conducted. A self-similarity between the formation of catalyst nanoparticles, low and high-density CNT forest growth, and Raman mapping was investigated, for a catalyst thickness of 0.8, 1.0, and 1.2 nm. To explain reasons behind fluctuations of the CNT forest structure, a fractal dimension (Df) and lacunarity (Λ) were calculated, using a box-counting method. During the fractality analysis of catalyst particles, the highest Df was obtained for the 0.8-nm-thick film (Df = 1.91), while the lowest one was noted for the Fe catalyst thickness of 1.2 nm (Df = 1.72). The progressive increase of the catalyst thickness affected the dewetting, Ostwald ripening and diffusion processes, affecting the catalyst size distribution and arrangement. The same thickness variation led to a similar decreasing trend of Df changes, which was observed in the planar and linear analysis of the distribution of CNTs and in the IG/ID ratio distribution in Raman mapping, confirming the complexity and the self-organizing properties of CNT forest. The self-similarity and scaling of properties of self-organized CNT forest structure were proved by the analysis of fractal dimension and lacunarity analysis and revealed different stages of the catalyst annealing.

Modeling the Electromagnetic Scattering Characteristics of Carbon Nanotube Composites Characterized by 3-D Tomographic Transmission Electron Microscopy

In all prior electromagnetic modeling studies of carbon nanotube (CNT) composites, the exact three-dimensional (3D) shape and spatial distribution of the CNTs in the composite were unknown. Therefore, simplifying assumptions had to be made regarding the CNT distributions. The effect of such assumptions on the electromagnetic response of CNT composites has not been quantified. Recent advances in electron-tomography and image analysis have allowed the generation of 3D maps of multi-walled carbon nanotube (MWCNT) distributions with sub-nanometer resolution. In this work, the electromagnetic responses of experimentally mapped 3D structures of aligned-CNT polymer nanocomposites were calculated using both full-wave electromagnetic solvers and dilute-limit Effective Medium Approximations (EMA). Our results show that the electromagnetic response calculated using the full-wave solver exhibits additional resonances that are absent in the response calculated using the dilute-limit EMA. This difference is due to the strong electromagnetic coupling between adjacent MWCNTs, within five CNT radii, of each other. Using the mapped 3D MWCNTs, we also studied the anisotropy in the electromagnetic response of the composites and showed that it increases with the MWCNT volume fraction. The full-wave analysis presented in this work provides a more accurate understanding of the electromagnetic reflection and anisotropy of CNT composites.

Vibration analysis of sandwich sector plate with porous core and functionally graded wavy carbon nanotube-reinforced layers

This paper deals with free vibration of FG sandwich annular sector plates on Pasternak elastic foundation with different boundary conditions, based on the three-dimensional theory of elasticity. The plates with simply supported radial edges and arbitrary boundary conditions on their circular edges are considered. The influence of carbon nanotubes (CNTs) waviness, aspect ratio, internal pores and graphene platelets (GPLs) on the vibrational behavior of functionally graded nanocomposite sandwich plates is investigated in this research work. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness of upper and bottom layers of the sandwich sectorial plates and their mechanical properties are estimated by an extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The core of structure is porous and the internal pores and graphene platelets (GPLs) are distributed in the matrix of core either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. A semi-analytic approach composed of 2D-Generalized Differential Quadrature Method (2D-GDQM) and series solution is adopted to solve the equations of motion. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Some new results for the natural frequencies of the plate are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. The new results can be used as benchmark solutions for future researches.

Vibration behavior of functionally graded sandwich beam with porous core and nanocomposite layers

This paper presents the influence of carbon nanotubes (CNTs) waviness, aspect ratio, internal pores and graphene platelets (GPLs) on the vibrational behavior of functionally graded nanocomposite sandwich beams resting on two-parameter elastic foundations. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness of upper and bottom layers of the sandwich beam and their mechanical properties are estimated by an extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes\' effective aspect ratio as the filler content increases. The core of structure is porous and the internal pores and graphene platelets (GPLs) are distributed in the matrix of core either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. The equations of motion are derived based on Timoshenko beam theory and employing Hamilton\'s principle. The problem is modeled using a semi-analytical approach composed of generalized differential quadrature method (GDQM) and series solution adopted to solve the equations of motion. Detailed parametric studies are carried out to investigate carbon nanotubes (CNTs) waviness, CNT aspect ratio, porosity coefficient, porosity distribution, graphene platelets (GPLs) distribution, Winkler foundation modulus, shear elastic foundation modulus and geometrical conditions on the vibrational behavior of the sandwich structure.

Probing Heteroatomic Dopant-Activity Synergy over Co3O4/Doped Carbon Nanotube Electrocatalysts for Oxygen Reduction Reaction.

Understanding and predicting how heteroatomic dopants of carbon nanotubes (CNTs)-based catalysts alter their catalytic performance at nanoscale is essential to design superior electrocatalysts for oxygen reduction reaction (ORR). This report describes findings of an investigation of the heteroatomic dopant-activity relationship for Co3O4/doped CNTs catalysts with different heteroatoms including N, O, and P atoms in ORR. By using an array of techniques to probe the structure and elementary valence of the catalysts, the incorporation of the Co3O4 nanoparticles can introduce defects into the doped CNTs, especially the N-CNTs, which should contribute to the generation of active sites. The Co3O4/N-CNTs are shown to exhibit both the highest ORR activity and stability compared with Co3O4/O-CNTs, Co3O4/P-CNTs, and Co3O4/CNTs, manifesting the synergistic correlation of Co3O4 nanoparticles, heteroatoms, and CNTs. This kind of synergy is assessed by density functional theory calculations based on the electronic properties and molecular orbitals. It is found that N, O, or P atoms can tune the charge distribution of CNTs by decreasing the lowest unoccupied molecular orbital-highest occupied molecular orbital energy gap, thus activating the adjacent C atoms. And the addition of Co3O4 will further redistribute the charge of CNTs from CNTs to Co3O4 toward enhanced ORR activity. Moreover, the Co3O4/N-CNTs catalyst exhibits a maximum structural stability due to the strong electronic interaction between Co2+ ions and N atoms, which is believed to result in its high ORR stability. Analysis of the results, along with a combined theoretical and experimental study, has provided implications for the design of catalysts with controlled activity and stability for ORR.

Free Vibration Analysis of Laminated Functionally Graded Carbon Nanotube-Reinforced Composite Doubly Curved Shallow Shell Panels Using a New Four-Variable Refined Theory

In this paper, a new four-variable refined shell theory is developed for free vibration analysis of multi-layered functionally graded carbon nanotube-reinforced composite (FG-CNTRC) doubly curved shallow shell panels. The theory has only four unknowns and satisfies zero stress conditions at the free surfaces without correction factor. Five different types of carbon nanotube (CNTs) distribution through the thickness of each FG-CNT layer are considered. Governing equations of simply supported doubly curved FG-CNTRC panels are derived from Hamilton’s principle. The resultant eigenvalue system is solved to obtain the frequencies and mode shapes of the anti-symmetric cross-ply laminated panels by using the Navier solution. The numerical results in the comparison examples have proved the accuracy and efficiency of the developed model. Detailed parametric studies have been carried out to reveal the influences of CNTs volume fraction, CNTs distribution, CNTs orientation, dimension ratios and curvature on the free vibration responses of the doubly curved laminated FG-CNTRC panels.

Nonlinear Vibration of Carbon Nanotube Reinforced Composite Truncated Conical Shells in Thermal Environment

This paper is concerned with the nonlinear vibration and dynamic response of carbon nanotube (CNT) reinforced composite truncated conical shells resting on elastic foundations in a thermal environment. The material properties of shells are assumed to be temperature-dependent and graded in the thickness direction according to various linear functions. The nonlinear equations of motion are expressed in the form of two-component deflection function and solved by the analytical method. Detailed studies for the influences of various types of distribution and volume fractions of CNTs, geometrical parameters, Winkler and Pasternak elastic foundations on the dynamic response and nonlinear vibration of CNT polymer composite truncated conical shells are examined and the comparison study is carried out to verify the accuracy and efficiency of the proposed method.

Influence of Unsizing and Carbon Nanotube Grafting of Carbon Fibre on Fibre Matrix Interfacial Shear Strength of Carbon Fibre and Polyamide 6

Carbon Fibre Reinforced Thermoplastics (CFRTP) are expected to be applied to the automotive industry instead of CFRP which require curing time, due to the expected short production cycle time of CFRTP, which is using thermoplastic as a matrix. We reported that the grafting of carbon nanotubes (CNTs) on the carbon fibre improves the fibre matrix interfacial shear strength. In our process to graft CNTs on carbon fibre, chemical vapour deposition (CVD) method was used and Ni, which was used as the catalyst, was electrically plated onto carbon fibres. Since commercially available carbon fibre was sized, which may affect the plating behaviour of Ni, the effects of sizing agents on CNT deposition have to be clarified. In this study, Ni for catalytic metal was plated by electrolytic plating using a watt bath on spread PAN-based carbon fibre and unsized carbon fibre, and the influence of the sizing agent to the distribution of Ni was evaluated. The morphological observation of carbon fibre and single fibre pull-out test were conducted to clarify the influence of sizing agent on the CNT deposition and the interfacial shear strength between the CNT grafted carbon fibre and Polyamide 6 (PA6). Uniform distribution of small sized Ni particles can be obtained on unsized carbon fibre and uniform Ni particles results in uniform CNT distribution. The CNT grafted unsized carbon fibre showed higher interfacial shear strength with PA6 than that of sized carbon fibre.

Effect of reinforcement of carbon nanotubes on air plasma sprayed conventional Al2O3-3%TiO2 ceramic coatings

Abstract The characterization of carbon nanotubes (CNT) doped plasma sprayed ceramic coatings were carried out by varying the percentage of CNT as 2 wt%, 4 wt%, and 6 wt%. The coatings were deposited using conventional Alumina-3 wt% Titania powders mixed with CNT using Air Plasma Spraying (APS) process. The adhesion strength of this ceramic coating is increased due to the addition of CNTs. This phenomenon is due to CNT bonding across the powder splats on the coatings which results in the refinement of coating features. On the other hand distinct factors impacting adhesion of coatings were found to be absence of CNT in bond coat and uneven distribution of CNT in top coat. The surface roughness also plays a vital role in characterization of coatings. It was also found that the surface roughness of the coatings increased with increasing percentage of CNT due to the pores available in conventional powders were filled with carbon nanotubes. The overall effect of adding CNTs to the Alumina-Titania coating system improves both mechanical and microstructural properties.

Thermal transfer, interfacial, and mechanical properties of carbon fiber/polycarbonate-CNT composites using infrared thermography

Electrical resistance (ER) and thermogram measurements were used to evaluate thermal transfer, interfacial and mechanical properties of carbon fiber reinforced thermoplastic polycarbonate composites. Carbon nanotubes (CNTs) were fairly uniformly dispersed in polycarbonates using a solvent dispersion method. The CNTs were then further dispersed with an additional time using a twin screw extruder. The effect of CNT on the mechanical properties of polycarbonate was evaluated using a thin film tensile test. For thermogram to evaluate the transferring temperature the composite was placed on a hotplate and copper wires were inserted in the composite at uniform thickness intervals. Due to the different inherent thermal conductivity of CNT, ER was measured to detect thermal changes in the carbon fiber/CNT-polycarbonate composites. The comparison of interlaminar shear strength (ILSS) was to investigate effects of CNT on mechanical and interfacial properties. The uniform distribution of CNTs affected all of these properties in carbon fiber-reinforced thermoplastic composite. Furthermore, heat transfer and heat release become more rapid with the addition of CNT than the without case.

Vibration of functionally graded carbon nanotube reinforced quadrilateral plates using geometric transformation discrete singular convolution method

SummaryFree vibration characteristics of thick skew plates reinforced by functionally graded carbon nanotubes (CNTs) reinforced composite are presented. Discrete singular convolution (DSC) method is used for the numerical solution of vibration problems via geometric mapping technique. Using the geometric transformation via a four‐node element, the straight‐sided quadrilateral physical domain is mapped into a square domain in the computational space. Then the method of discrete singular convolution with some singular kernels such as Regularized Shannon's delta (RSD) and Lagrange's delta kernels (LDK) have been used for spatial discretizing of the resulting governing equation of motion. Calculated results have been presented in order to show the effects of volume fraction of CNT, skew angles, CNT distribution types, plate aspect ratio and length‐to‐thickness ratio on the frequency of CNT reinforced skew plate. The current results are compared with the related results available in the literature and obtained by different methods. It is shown that reasonable accurate results are obtained for free vibration of nanocomposite plates with less computational effort for higher modes. Several test examples for different plate have been selected to demonstrate the convergence properties, accuracy, and simplicity in numerical implementation of DSC procedures. This approach has verified the accuracy and applicability of DSC method to the class of problem considered in this study. Furthermore, in the numerical examples in the scope of the study, the results obtained with DSC method using a coarser grid are more accurate than the values obtained by finite elements and differential quadrature (DQ) methods. It is also revealed that the method of discrete singular convolution is a promising and potential approach for computational mechanics of nonrectangular plates with nanocomposite reinforced.

Non-polynomial framework for static analysis of functionally graded carbon nano-tube reinforced plates

The reinforcement in the form of carbon nano-tubes (CNTs) enhances the bending response of the structures. The bending characteristics are altered due to functionally graded distributions of CNTs. The bending behaviour of functionally graded CNTs reinforced plates is carried out in the present work. The carbon nano-tubes are supposed to be distributed uniformly and graded functionally. The reinforced plates are modelled for the first time in the framework of inverse hyperbolic shear deformation theory. The governing equations of the plate are obtained using the principle of virtual work under the assumptions of linear kinematics and generalised Hooke’s law. These governing equations are solved in the closed form using Navier solution for specific boundary conditions i.e. simply supported. The static response of these plates are obtained under the effect of sinusoidal load, uniform load, hydrostatic load, and central point load. The computed results are compared with some of the existing results for a few cases to ensure the validity. Further, the effects of parameters such as CNT volume fraction, orientation of reinforcement, span-thickness ratio, loading conditions, etc. on the static response characteristics are examined in details and various conclusions are observed.

Analytical solution for buckling analysis of micro sandwich hollow circular plate

In this paper, the buckling of micro sandwich hollow circular plate is investigated with the consideration of the porous core and piezoelectric layer reinforced by functionally graded (FG)carbon nano-tube. For modeling the displacement field of sandwich hollow circular plate, the high-order shear deformation theory (HSDT) of plate and modified couple stress theory (MCST) are used. The governing differential equations of the system can be derived using the principle of minimum potential energy and Maxwell\'s equation that for solving these equations, the Ritz method is employed. The results of this research indicate the influence of various parameters such as porous coefficients, small length scale parameter, distribution of carbon nano-tube in piezoelectric layers and temperature on critical buckling load. The purpose of this research is to show the effect of physical parameters on the critical buckling load of micro sandwich plate and then optimize these parameters to design structures with the best efficiency. The results of this research can be used for optimization of micro-structures and manufacturing different structure in aircraft and aerospace.

A new numerical approach for low velocity impact response of multiscale-reinforced nanocomposite plates

In this paper, the low velocity impact analysis of carbon nanotube (CNT)/carbon fiber (CF)-reinforced hybrid nanocomposite plates is presented using variational differential quadrature (VDQ) method due to its numerical essence and the framework of implementation. The hybrid nanocomposite plate deformation is formulated based on classical plate theory and the contact force between the plate and projectile is estimated using Hertzian contact law. Also, a new micromechanics approach is presented to calculate the effective mechanical properties of the CNT/CF polymer hybrid nanocomposites. Five important factors including, random orientation and random distribution of CNTs, CNT/polymer interphase region, waviness and transversely isotropic behavior of CNT are incorporated in the micromechanical analysis. The accuracy of the present approach is verified with the available open literature results showing a clear agreement. The effects of various factors such as volume fraction and non-straight shape of CNT, CNT/polymer interphase region, CF volume fraction, random and regular arrangement of CFs, plate geometrical parameters and impactor velocity on the low velocity impact behavior of the CNT/CF-reinforced hybrid nanocomposite plates are studied.

Hopes Beyond PET Recycling: Environmentally Clean and Engineeringly Applicable

Disposal of plastics in the environment has become a core of anxiety in developing countries, while in the developed countries the focus has additionally been placed on design and manufacture of emerging products from plastic wastes—a somewhat vague yet promising horizon. Central to environmental concerns are poly(ethylene terephthalate) (PET) wastes, mainly from post-consumer bottles. Because of a considerable drop in molecular weight in the course of recycling, recycled PETs are not suitable for engineering uses. An efficient yet reasonably green synthesis route is employed here to convert PET wastes into polyurethane, and then carbon nanotubes (CNTs) was added at different levels to obtain nanocomposites with high mechanical properties. The effects of isocyanate (NCO)/hydroxyl (OH) molar ratio and CNTs content on the morphology, physical and mechanical properties were discussed. Chemical/physical crosslink density was calculated from initial slope of stress–strain curves, Mooney–Rivlin plots, strain-hardening modulus, rubbery-plateau storage modulus and swelling data. High tensile strength (300 MPa) and breaking elongation (160%) of polyurethane/CNTs nanocomposites born from PET wastes seemed promising. Microscopic analyses by AFM, SEM, and TEM gave useful information about distribution of CNTs in polyurethane. Lastly, structural changes were correlated to mechanical properties improvement.

Enhanced Electrical Properties of Fly Ash Geopolymer Composites with Carbon Nanotubes

Carbon nanotubes (CNTs) are used for the application in concrete especially due to their excellent physical properties. In this study, CNTs were used as a conductive admixture to prepare composites with enhanced electrical properties that might be potentially used in smart concretes or structures. We assessed the changes in selected electrical properties of fly ash geopolymer mortars (conductivity, resistance, capacitance) depending on the concentration of CNTs that ranged from 0.05 to 0.20%. The most convenient CNTs concentration was discussed considering both the electrical and mechanical properties (compressive and flexural strength). Mercury intrusion porosimetry and scanning electron microscopy were used to observe the distribution of CNTs and porosity of the mortars.

Surface modification of ramie fibers with silanized CNTs through a simple spray-coating method

Preliminary studies performed have indicated that carbon nanotube (CNT) coating is an effective method to enhance the bonding between a natural fiber and a resin matrix. However, the reported coating process is complex, and the improvement of the bonding strength is limited owing to obvious CNT aggregation. This paper reports a simple spray-coating method with uniform distribution of CNTs coated on ramie fiber surfaces. The dispersion of CNTs in a suspension for spray-coating was found to play a key role in CNTs distribution on the fiber surface. Silylated CNTs can be stably and uniformly suspended in a water and alcohol solution with a polyvinylpyrrolidone dispersant. The suspension was sprayed onto ramie fabric by using a hand-spraying pot, and CNTs were distributed on the fiber surface uniformly, as indicated by scanning electron microscopy results. The agglomeration of CNTs on the fiber surface became increasingly evident with an increase in the number of spray layers (from one to six). The effects of CNT coating on the flexural properties of the related composite and bonding properties were studied. The CNT-coated ramie fiber reinforced epoxy plate was prepared by a vacuum assistant resin transfer molding method. The CNT coating increased the flexural strength and modulus of the composite by 38.4% and 36.8%, respectively. A microdebonding test showed that the CNT coating increased the interfacial shear strength between a single ramie fiber and the epoxy resin by 25.7%, which is believed to result from stronger mechanical interlocking and chemical bonding.

A Type of Novel Nonlinear Distributions for Improving Significantly the Stiffness of Carbon Nanotube-Reinforced Composite Beams

So far, the carbon nanotube (CNT) distributions have been still limited in the linear forms, which may lead to the limitations in maximizing the strength and potential of carbon nanotube reinforced composite (CNTRC) structures. This study, hence proposes a type of novel CNTs distribution for improving the stiffness of CNTRC beams. The distributions are in the nonlinear forms and ensure the same total CNT volume fraction along the thickness of structures. For demonstrating, the effectiveness of the proposed CNT distributions, the static, free vibration and buckling analyses of functionally graded carbon nanotube (FG-CNT) reinforced composite beams using the new CNT distributions are conducted and one-dimensional NURSB basis functions based on the third-order shear deformation theory (TSDT) are utilized to describe the exact geometry and to approximate the unknown solution in finite element model of the beam. The numerical investigations of the geometric and material parameters reveal that the new nonlinear CNT distributions can help increase the normalized frequency, buckling load and the nondimensional central deflection to the maxima of 8%, 16% and 16% respectively, in some conditions of geometric parameters.