Distribution Of Carbon Nanotubes Research Articles

Strategy for constructing electromagnetic interference shielding and flame retarding synergistic network in poly (butylene succinate) and thermoplastic polyurethane multilayered composites

Fabricating electromagnetic interference (EMI) shielding materials with excellent flame retarding properties is significant to attenuate undesirable electromagnetic waves caused by electronic devices and simultaneously improve the flame safety of the electronic components. Herein, a novel EMI shielding composite with multilayered structure was fabricated at a low particle loading via layer-multiplying coextrusion technology. Especially, within the multilayered composites, poly (butylene succinate) (PBS) filled with carbon nanotubes (CNTs) was used to construct conducting layer while thermoplastic polyurethane (TPU) filled with intumescent flame retardants (IFRs) and CNTs was used to construct synergistic flame-retarding layer. The content of CNTs and IFRs in the whole system were below 4 wt% and 20 wt%, respectively. Morphological observation demonstrated the alternating multilayered structure and the selective distribution of IFRs and CNTs. Besides, by tailoring the layer numbers, the composites showed tunable EMI shielding and flame retarding performances. With regard to EMI shielding performance, the absorption-dominated average EMI shielding effectiveness (SE) values of both 8- and 16-layer specimens exceeded 30 dB in the range of 8.2–12.4 GHz. Furthermore, superior flame retardancy with prompt self-extinguishment and anti-dripping was achieved in these specimens owning to the production of continuous and foaming carbonaceous structure among layers. Especially the 8-layer specimen, the UL-94 rating was categorized in V-0. Consequently, this work provided a promising and facile route to fabricate polymeric composites simultaneously possessing excellent EMI shielding and flame-retarding properties to fulfill the stringent requirements in practical application.

Free vibration analysis of functionally graded hybrid matrix/fiber nanocomposite conical shells using multiscale method

This study is dedicated to propose a numerical solution for free vibration analysis of nanocomposite conical shells. The First-order Shear Deformation Theory (FSDT) is used to achieve the governing equations. Then, an efficient numerical method, namely the Generalized Differential Quadrature Method (GDQM), is employed to solve the Donnell-type governing differential equations. The effects of the nanofillers aggregation are investigated throughout this research. It is considered that a single conical shell is composed of a variety of the constituent material. This type of material includes three phases: polymer matrix, macro-scale fibers and nano-scale Carbon Nano Tubes (CNTs). Two well-known approaches, namely Han and Chamis, are employed for the homogenization procedure to obtain the equivalent material properties. It is worth mentioning that the power pattern is employed for the functionally distribution of CNTs within the polymer matrix. Furthermore, the effects of different boundary conditions, geometric and material properties on the dimensionless frequency parameter of the multiscale nanocomposite conical shells are considered. Afterward, a parametric study is implemented to determine the deep influences of the volume fraction of the nanofillers throughout the inclusion on the vibrational behaviors of conical shells. It is found out that increasing the agglomeration parameter increases the frequency parameter of the conical structures. Moreover, increasing the power exponent of the volume fraction of FG-CNT material deals decrease of the frequency parameter of conical shells. Comparing the obtained results with the outputs of some well-known benchmarks proves the correctness, accuracy and high capability of the proposed formulation.

Controlled growth of crossed ultralong carbon nanotubes by gas flow

Carbon nanotubes (CNTs) work as the promising components of miniature electromechanical systems due to their excellent performances from individual to bundle scales. But it’s challenging to achieve precise patterning at nanoscale resolution with controlled position and orientation. Here, we demonstrate a fluidic strategy to interlace one-dimensional (1D) ultralong CNTs into the crossed pattern in a one-step in-situ process. Semi-circular substrates of different diameters were placed in front of the growth substrate to change the path and momentum of gas flow. Such flow perturbation caused by substrates could be markedly reflected within a micro-channel reactor, which led to formation of crossed ultralong CNTs at definite positions. Furthermore, precise control over the crossing angle as well as the diameter distribution of CNTs was achieved by varying the CNT length and diameter of semi-circular substrates. Our strategy has offered a feasible route for production of crossed ultralong CNTs and will contribute to multidimensional fluidic assembly of flexible nanomaterials.

Enhanced magnetic properties of aluminum oxide nanopowder reinforced with carbon nanotubes

Magnetic carbon nanotubes (CNTs)/alumina (Al2O3) nanocomposites were synthesized by the direct growth of CNTs on alumina by chemical vapor deposition (CVD) process. X-ray diffraction studies show that the crystalline structure of alumina nanoparticles remains preserved during the CVD process. Electron microscopy studies reveal the uniform distribution of CNTs within the alumina matrix. CNTs of average diameter 20 nm are spread around alumina particles of size 120 nm. The proportion of CNTs in alumina composites is determined to be approximately 10% from the thermogravimetric analysis. CNT-reinforced alumina nanocomposites demonstrate a significant improvement of the magnetic properties as compared with pristine alumina powder. The diamagnetic property of alumina nanopowder is transformed into a strongly pronounced ferromagnetic response upon the incorporation of CNTs. The saturation magnetization increased by ~ 2500%, and a pronounced coercivity of 68 Oe was observed in the nanocomposites. It is suggested that the encapsulation of cobalt inside the CNTs constrains the magnetic moments to result in higher saturation magnetization. Hence, the CNTs/Al2O3 system synthesized in this work can be employed to engineer novel ceramic composites with enhanced magnetic properties.

Buckling and free vibrations of CNT-reinforced cross-ply laminated composite plates

This article deals with the investigation of free vibration and buckling behaviors of carbon nanotube (CNT)-reinforced cross-ply laminated composite plates. The plate kinematics is assumed to follow a first-order shear deformation theory (FSDT). After the coupled equations of motion and buckling are derived, the method of discrete singular convolution (DSC) is used for the numerical solution of the problems. Both the regularized Shannon’s and Lagrange’s delta kernels are used for spatial discretizing of the resulting governing equations of buckling and vibration of CNT-reinforced laminated plates. Natural frequencies and critical buckling loads are obtained for different cases. Wherever possible, the present DSC results are verified by comparing them with the existing analytical results available in the literature. Then, a detailed parametric study is performed to examine the effects of boundary conditions, CNT distributions and volume fraction, aspect ratio, length-to-width ratio, and number of layers on the frequencies and buckling loads.

Constructing a Microcapacitor Network of Carbon Nanotubes in Polymer Blends via Crystallization-Induced Phase Separation Toward High Dielectric Constant and Low Loss.

Tailoring the distribution of nanoparticles and further constructing effective microcapacitors in polymer blends are important issues for developing high-performance polymer dielectric nanocomposites. The common method to control the selective localization of nanoparticles in an immiscible polymer blend is relatively difficult and it easily results in the accumulation of nanoparticles in one component, which usually leads to a dramatic increase of the dielectric loss in the nanocomposites. In this work, a novel strategy based on step-by-step crystallization has been proposed to tailor the refined distribution and dispersion of carbon nanotubes (CNTs) in a melt-miscible blend poly(butylene succinate)/poly(vinylidene fluoride) (PBS/PVDF) through the crystallization-induced phase separation and the engineered interfacial affinity between CNTs and polymer components to acquire high dielectric constant and low dielectric loss. The results reveal that PBS is excluded along the growth front of PVDF spherulites and locates in the margin areas of PVDF spherulites during the step-by-step crystallization process. Moreover, because of the higher interfacial interaction between CNTs and PBS, CNTs are located in the PBS-rich domain, resulting in a high concentration of CNTs in the interspherulites of PVDF. Thus, the dielectric constants of the nanocomposites are greatly improved by nearly 5-24 times compared with the nanocomposites achieved by quick cooling and, simultaneously, the dielectric loss of the nanocomposites is still maintained at a low level. This work shows that the step-by-step crystallization method can be used to fabricate the nanocomposites with a synergistic increase in the dielectric performance due to the formation of a refined microcapacitor assembly. To the best of our knowledge, this is the first report to show that the dielectric constant of the nanocomposites can be greatly enhanced just through the crystallization-optimized distribution and dispersion of CNTs in immiscible polymer blends, and it possibly gives a new technical route for the fabrication of advanced dielectric composites.

Impact of ultrasonication on carbon nanotube demixing and damage in polymer nanocomposites

AbstractWhile ultrasonication is universally employed for dispersion and distribution of carbon nanotubes (CNTs) in a solvent or polymer solution, the current work focuses on the underlying mechanisms of CNT demixing and CNT damage that can occur during processing. Here, multi‐walled CNTs were dispersed in a polycaprolactone polymer matrix using an established solution processing technique. Electrical, rheological, and mechanical characterization results suggest that once nanocomposite property enhancements reach an optimal level, further sonication leads to a decrease in the corresponding properties due to a combination of CNT damage and demixing mechanisms. Evidence of CNT damage from transmission electron microscopy, poor CNT distribution from optical image analysis and shear‐induced crystallization results, and reagglomeration observed from ultraviolet–visible results, taken together, suggest that mechanisms of demixing and damage of the CNTs coexist for excessive sonication times.

On the dynamics of axially functionally graded CNT strengthened deformable beams

In this study, by functionally grading carbon nanotube (CNT) fibres through the axial direction of deformable beams, a new model for strengthening such structures is formulated. The strengthened deformable beam is additionally supported by a varying elastic foundation which is modelled via the Winkler–Pasternak elastic foundation. CNT distribution in the longitudinal direction is modelled using a power-law function presenting general forms of variation from linear to parabolic models. Equations of motion are determined using Hamilton’s principle and are solved by employing the generalised differential quadrature approach method. A comprehensive parametric investigation is presented in order to indicate the influence of having CNT fibres distributed functionally through the length. It is shown that grading CNT fibres axially have a significant effect in varying the natural frequency parameter. Moreover, the influence of having Winkler–Pasternak elastic bed on the free vibration of such structures is discussed considering different types of foundation stiffness variation through the length. A comprehensive comparison study is presented to verify the current methodology and formulation by using previous literature for foundation modelling and FE modelling for linearly varying CNT’s longitudinal distribution, which for all the cases, a good agreement between the results is observed.

Buckling analyses of carbon nanotube reinforced functionally graded composite cylindrical panels

This paper investigates the buckling analyses of carbon nanotube (CNT) reinforced composite cylindrical panels via a geometrically nonlinear finite element model with large rotations based on the first-order shear deformation (FOSD) hypothesis. Fully geometrically nonlinear strain-displacement relations and large rotation of shells are considered in the model. First, the proposed model is validated by a frequency analysis of a simply supported CNT reinforced composite cylindrical panel from an existing reference. Then, the model is applied to simulate the behaviors of carbon nanotube reinforced functionally graded (CNT-FG) composite cylindrical panels. The effects of curvature ratio, different buckling behaviors and four representative forms of CNT distributions are studied for their material performance comparatively.

Effect of Carbon Nanotubes (CNT) Functionalization and Maleic Anhydride-Grafted Poly(trimethylene terephthalate) (PTT-g-MA) on the Preparation of Antistatic Packages of PTT/CNT Nanocomposites

Electronic devices require the use of antistatic packing to prevent electrostatic discharge during their storage or transport. Poly (trimethylene terephthalate) (PTT) is a polyester with excellent properties and can be a good candidate for this application. To make this insulating polymer an extrinsic conductor, carbon nanotubes (CNT) can be added to reduce the electrical resistivity of the nanocomposites. In order to facilitate the CNT distribution on polymeric matrix, it was proposed a chemical functionalization using nitric acid for the creation of functional groups on its surface. Moreover, the PTT matrix was modified with a compatibilizer agent based on maleic anhydride grafted PTT (PTT-g-MA), to improve interfacial adhesion between the nanofiller and matrix. In this work, nanocomposites based on PTT/PTT-g-MA/CNT were prepared by extrusion process, with 0.5 wt% and 1.0 wt% of CNT and functionalized CNT. CNT was characterized by stability dispersion in water, Raman spectroscopy, FTIR and XPS analysis, which prove the success of functionalization. The nanocomposites were evaluated by thermal analysis, tensile tests, electrical conductivity, and morphological analysis. The CNT functionalization and the addition of PTT-g-MA increased the dispersion and distribution of CNT in the PTT matrix. The electrical properties show that this material can be used as an antistatic packaging.

Interfacial modification of carbon fiber by carbon nanotube gas-phase dispersion

The interfacial bonding between carbon fiber(CF) and matrix is one of the important technical difficulties during the development of CF. In the paper, a physical modification method of rapidly spraying CF surface by carbon nanotubes(CNTs) gas-phase dispersion was adopted to strengthen the interfacial bonding between CF and matrix. SEM was used to observe the structure of fiber surface and the distribution of CNTs. And the mechanical and thermoelectric properties of the formed CF composite specimens were measured. The results showed that interlaminar shear strength, tensile strength and compression strength of the CF composite fibers increased by 12.07%, 8.73% and 13.83%, and CF composites treated with CNTs had higher thermal diffusivity and lower resistivity than before. It has good application significance for modification and reinforcement of CF and CF composites.

Vibration and stability of initially stressed functionally graded carbon nanotube-reinforced hybrid composite plates in thermal environments

The vibration and stability of hybrid functionally graded (FG) composite plates subject to an arbitrary initially stress in thermal environments is investigated. The plate is reinforced by single walled carbon nanotubes (CNTs). Various profiles of CNTs distributions and volume fractions of hybrid nanocomposite plates are considered. Based on the perturbation method, the governing equations for the hybrid nanocomposite plate considering the effects of non-uniform initial stresses are established. The effects of the CNTs volume fraction, CNTs distribution type, layer thickness ratio, temperature and initial stress on the buckling loads and natural frequencies of hybrid nanocomposite plates are studied in detail.

Buckling of carbon nanotube (CNT)-reinforced composite skew plates by the discrete singular convolution method

A geometric transformation method based on discrete singular convolution (DSC) is firstly applied to solve the buckling problem of a functionally graded carbon nanotube (FG-CNT)-reinforced composite skew plate. The straight-sided quadrilateral plate geometry is mapped into a square domain in the computational space using a four-node DSC transformation method. Hence, the related governing equations of plate buckling and boundary conditions of the problem are transformed from the physical domain into a square computational domain by using the geometric transformation-based singular convolution. The discretization process is achieved via the DSC method together with numerical differential and two different regularized kernels such as regularized Shannon’s delta and Lagrange-delta sequence kernels. The accuracy of the present DSC results is first verified, and then, a detailed parametric study is presented to show the impacts of CNT volume fraction, CNT distribution pattern, geometry of the skew plate and skew angle on the axial and biaxial buckling responses of FG-CNTR composite skew plates with different boundary conditions. Some new results related to critical buckling of an FG-CNT-reinforced composite skew plate are also presented, which can serve as benchmark solutions for future investigations.

Enhancing Strength and Toughness of Hierarchical Composites through Optimization of Position and Orientation of Nanotubes: A Computational Study

Hierarchical composites that combine microscopic fibers and carbon nanotubes (CNTs) offer opportunities to further improve mechanical properties. Motivated by the experimental evidence that the spatial distribution of CNTs has a significant effect on the strength and toughness of these composites, we developed a novel modelling tool to help us explore mechanisms of strengthening and toughening in an efficient way. The spatial position and orientation of CNTs are chosen as design variables and their optimization is performed on the example of a unidirectional fiber-reinforced composite (FRC) subjected to transverse tensile loading. The model relies on the use of genetic algorithm and finite element method. Our modelling results show that the CNT network with an optimized morphology suppresses stress concentrations in the matrix near the fibers. The optimized morphology is shown to activate a new strengthening and toughening mechanism—diffusion of damage at micro-scale. It allows substantial increase in the consumption of the strain energy by matrix cracking, delocalization of damage, and with it, improvement of the strength and toughness. When the network morphology of 1.0 wt% of CNTs is optimized, the strength and toughness are increased by 49% and 65%, respectively, compared to the pristine FRC. The same amount of homogenously distributed CNTs in the composite leads to only 2% of the strength increase accompanied by a 13% decrease in toughness. The work emphasizes the importance of optimizing spatial position and orientation of CNTs for the strength and toughness improvements of composites.

In English

This review analyses the authors’ recent and related works on electrokinetic properties and colloidal stability of aqueous suspension of multiwalled carbon nanotubes (CNTs) in the presence of surfactants and nanoparticles. Selected adsorptive properties of carbon nanotubes are also considered. The applicability of classical theories of electrophoresis for description of electrophoretic mobility of carbon nanotubes is discussed. Examples on the ζ-potential of CNTs in aqueous suspensions as a function of pH and concentration of electrolytes (KCl, CaCl 2 and AlCl 3 ) are given. Additions of cetyltrimethylammonium bromide (CTAB) cationic surfactant below the critical micelle formation concentration (CMC) values give a reduction and then an overcharging the CNT surface because of accumulation of the surfactant ions in the Stern layer. At concentrations above CMC the substantial drop in ζ is observed. It is due to the shift of the shear plane toward solution as a result of formation of hemi-micelles on the surface. An increase in the mass ratio of artificial mineral Laponite (Lap) in suspension (X) from 0 to 0.4 results in a monotonic decrease of the ζ-potential of CNT + Lap hybrids with reaching its plateau value ≈ –32 mV at X ≥ 0.4 that corresponds to the ζ of “pure” Lap platelets. This evidences the high surface coverage of nanotubes surface with Lap at X ≥ 0.4. The major methods to improve the dispersibility of carbon nanotubes, their colloidal stability and adsorptive properties are briefly discussed, namely: stabilization in mixtures of water and organic solvents; functionalization by chemical treatment; stabilization by additives of surfactants or polymers and hybridization by addition of supplementary stabilizing nanoparticles. CNTs can be significantly debundled in “good” solvents, such as 1-cyclohexyl-2-pyrrolidone, N,N-dimethylformamide, or N-methyl-2-pyrrolidone. It is demonstrated that the dispersibility of CNTs is a complex function of the type of surfactant, its concentration and the surfactant/CNTs ratio. The optimum concentration of CTAB to achieve homogeneous aqueous dispersion of carbon nanotubes was identified to be near the CMC. Additions of CTAB significantly modify the size distribution of CNTs and a sharp transition from small primary aggregates to large secondary aggregates at concentrations above CMC is observed. At optimal concentration of Lap the nanotube particles get well stabilized, and a stepwise increase of sedimentation stability is observed. We have shown also that CNT + Lap hybrids can be effectively used for removal of methylene blue dye from aqueous systems. The kinetics and mechanisms of adsorption are elucidated.

An Effective Strategy to Achieve Ultralow Electrical Percolation Threshold with CNTs Anchoring at the Interface of PVDF/PS Bi‐Continuous Structures to Form an Interfacial Conductive Layer

AbstractConductive composites based on polymers and conductive nanofillers are widely studied as a promising material. The rational design of 3D conductive networks in composites is crucial to improve their electrical conductivity and reduce the dosage of nanofillers. Herein, poly(vinylidene fluoride) (PVDF) and polystyrene (PS) bi‐continuous structures with modified carbon nanotubes (CNTs) tailored to anchor at the interface are designed to achieve an ultralow electrical percolation threshold because of the formation of a thin interfacial conductive layer. In this work, the modification of CNTs with poly(methyl methacrylate) (PMMA), which contributes to the improvement of the compatibility between PVDF and CNTs, is effective to control the distribution of CNTs in composites. It promotes the migration of CNTs from the PS phase to the interface of PVDF and PS. Consequently, the interfacial conductive layer is formed at a low CNT content, and the electrical percolation threshold of PVDF/PS/CNTs‐PMMA nanocomposites is only 0.07 vol%, having a great decrease of about 50% compared with that of PVDF/PS/CNTs nanocomposites. Thus, it is demonstrated that the distribution of CNTs can be tailored to anchor at the interface by proper chemical modification to form an interfacial conductive layer and a decrease of percolation threshold can also be achieved.

Thermal and thermomechanical buckling of shear deformable FG-CNTRC cylindrical shells and toroidal shell segments with tangentially restrained edges

This paper presents a simple and effective analytical approach to investigate buckling behavior of carbon nanotube-reinforced composite (CNTRC) cylindrical shells and toroidal shell segments surrounded by elastic media and subjected to elevated temperature, lateral pressure and thermomechanical load. The properties of constituents are assumed to be temperature-dependent, and effective properties of CNTRC are estimated according to extended rule of mixture. Carbon nanotubes (CNTs) are reinforced into matrix material such in a way that their volume fraction is varied in the thickness direction according to functional rules. Formulations are established within the framework of first-order shear deformation theory taking surrounding elastic media and tangential elasticity of edges into consideration. The solutions of deflection and stress function are assumed to satisfy simply supported boundary conditions, and Galerkin method is used to derive expressions of buckling loads. In thermal buckling analysis, an iteration algorithm is employed to evaluate critical temperatures. The effects of CNT volume fraction and distribution patterns, degree of in-plane edge constraints, geometrical parameters, preexisting loads and surrounding elastic foundations on the critical loads of nanocomposite shells are analyzed through a variety of numerical examples.

Enhancement of image contrast for carbon nanotube and polymer composite film in scanning electron microscope.

Image contrast between carbon nanotubes (CNTs) and polytetrafluoroethylene (PTFE) in a CNT/PTFE composite film, which is difficult to obtain by conventional backscattered electron (BSE) imaging, was optimized to better elucidate the distribution of CNT in the film. Ultra-low landing energy condition (0.3keV in this study) was used to prevent specimen damage due to electron beam irradiation. Signal acceptance maps, which represent the distributions of energy and take-off angle, were calculated to evaluate the features of the signal detection system used in this study. SEM images of this composite film were taken under several sets of conditions and analyzed using these acceptance maps. CNT and PTFE in the composite film can be clearly distinguished with material and topographic contrasts using the BSE signal under optimized energy and take-off angle ranges, even at ultra-low landing energy conditions.

Vibration characteristics of matrix cracked pretwisted hybrid composite blades containing CNTRC layers

Stiffness degradation due to matrix cracks is the main initial form of damage in composite laminates. Moreover, the vibration characteristics may change due to the degradation of blade stiffness caused by the introduction of matrix cracks. This paper presents a solution method for studying the static free vibration behaviors of pretwisted hybrid composite blade containing carbon nanotube reinforced composite (CNTRC) layers as well as matrix cracked fiber reinforced composite (FRC) layers. Two types of structure, namely Structure-I and Structure-II, are investigated. The CNTRC layers in Structure-I are considered with carbon nanotubes (CNTs) arranged in uniformly distributions, while Structure-II arranged in functionally graded distributions. The degraded stiffness of cracked layers is modeled via the self-consistent model (SCM) micromechanical framework. A shell model for pretwisted blade is proposed based on the theroy of differential geometry. To consider the effect of the transverse shear deformation and rotary inertia on the vibration behaviors, the first order shear deformation theory (FSDT) is adopted in describing the kinematics of blade. The improved moving least-squares Ritz (IMLS-Ritz) method is engaged to discretize the partial differential equations over the computational domain. Comparison studies indicate that the proposed predictive model can furnish very accurate results for pretwisted blades. Parametric studies on the effect of CNT distribution configuration, matrix crack density, aspect ratio, width-to-thickness ratio, twisted angle, as well as ply-angle on the vibration characteristics are revealed.

Shear buckling analysis of functionally graded (FG) carbon nanotube reinforced skew plates with different boundary conditions

In this paper, a four-nodded straight-sided geometric element is proposed for shear buckling problem of functionally graded material (FGM) composite and carbon nanotube (CNT) reinforced composite skew plate. By using the transformation rule, quadrilateral plate field is mapped into a square domain in the computational space using discrete singular convolution (DSC) method. Related governing equations of skew plate buckling and boundary conditions of the problem are transformed from the physical domain into a square computational domain by using the geometric transformation based singular convolution. The discretization process is achieved via the DSC method together with numerical differential and two-different regularized kernel such as regularized Shannon's delta (RSD) and Lagrange delta sequence (LDS) kernels. The accuracy of the present DSC results is first verified via exiting results in literature. Then, some parametric studies have been presented to show the effects of CNT volume fraction, CNT distribution pattern, geometry of skew plate and skew angle on the shear buckling responses of FG-CNTR composite skew plates with different boundary conditions. Some new results related to critical buckling of FGM and CNT reinforced composite skew plate have been presented which can serve as benchmark solutions for future investigations.