Aspect Ratio Of Carbon Nanotubes Research Articles

Strain‑Sensing Properties of Multi‑Walled Carbon Nanotube/Polydimethylsiloxane Composites with Different Aspect Ratio and Filler Contents.

For filler composite systems used in strain sensor applications, piezoresistive effect, strain hysteresis, and repeatability are critical factors, which have to be clearly evaluated and understood. To investigate the effects of the aspect ratio and content of a multi-walled carbon nanotube (MWCNT) on the strain sensor properties of the composite, MWCNT/Polydimethylsiloxane (PDMS) composites with varying filler contents and aspect ratios were fabricated. In order to uniformly disperse MWCNTs on the polymer matrix, we used a three-roll milling method to generate high shear force for de-bundling MWCNTs. Mechanical and electrical properties of the MWCNT composites were evaluated for each case. In addition, through the cyclic stretching test, we optimized the strain-sensing properties of the MWCNT composites by considering their piezoresistive effects and strain hysteresis.

Carbon nanohorns/nanotubes: An effective binary conductive additive in the cathode of high energy-density zinc-ion rechargeable batteries

Manganese oxide (MnO2) is proven to be an efficient cathode material in zinc-ion batteries (ZIBs). However, its poor electronic conductivity strongly limits the performance of Zn–MnO2 batteries. In order to improve performance beyond typical graphitic carbon additives, a binary conductive additive, a combination of carbon nanohorns (CNHs) and carbon nanotubes (CNTs), is added into the MnO2 electrode to establish high-speed electron-channels in the CNTs/CNHs network with an efficient “line-to-surface-to-point” microstructure. In this electrode, the high aspect-ratio CNTs create a conducting highway for the collected charges, while the CNHs provide extra surface area for electron transfer. Moreover, the specific surface area of the electrode increases due to the introduction of CNHs, which increases the Zn2+ diffusion coefficient. As a result, the corresponding battery reaches a high specific capacity (343 mAh g−1 at 0.3 A g−1), excellent rate performance (191.3 mAh g−1 at 3 A g−1) and long-life cycle. Moreover, it achieves an admirable specific energy density of 466 W h kg−1, together with a peak power density of 9.4 kW kg−1 (normalized to the weight of MnO2), the performance of which is among the best reported ZIBs. This work reveals new pathways to improve the performance of MnO2 cathodes for ZIBs.

A new modified Hamilton-Crosser and Nan models for thermal conductivity of different lengths carbon nanotubes water-based nanofluids

In order to investigate the shape effect of nanoadditives on thermal conductivity of nanofluids, different length carbon nanotubes (CNTs) are made and using a two-step method, different nanofluids are prepared. The CNTs are cut into different lengths by functionalization at different refluxing times of 1, 2 and 4 hours. To probe the effect of aspect ratio of CNTs on the obtained experimental data, modified Hamilton-Crosser and Nan models are developed. It is found that the original Hamilton-Crosser and Nan models could not predict the experimental thermal conductivities. By replacing n = 6 + xL/D instead of the shape factor of n=6 in the Hamilton- Crosser, where L and D were length and diameter of CNTs and also by replacing φ (xL/D) instead of φ (volume fraction) in the Nan model, the prediction of modified equations show very good accordance with the experimental data which means the shape of nanoadditives has high impact on nanofluids’ properties.

Nonlinear vibration of thick multi-scale composite doubly curved shells

ABSTRACT: In this paper, the large amplitude vibration of moderately thick three-phase multi-scale composite doubly curved shells is investigated. The epoxy resin is enriched by carbon nanotubes (CNTs) and the E-glass fibers are embedded in the reinforcement matrix. The effective materials properties are predicted by combination of Halpin-Tsai relation and micromechanics approach. The von Kármán geometric nonlinearities terms and first-shear deformation theory are employed to obtain the governing equations. Galerkine’s method is used to reduce the coupled governing equations to an ordinary nonlinear differential equation. The first-order analytical approximate and periodic solution is derived by homotopy perturbation method (HPM). The results include the effect of CNTs weight percentage, CNTs aspect ratio and vibration amplitude on nonlinear frequency of multi-scale composite doubly curved shells.

Aspect ratio effect of multi-walled carbon nanotubes and carbon fibers on high-performance cement mortar matrices

Formulation of high-performance cement mortar matrices reinforced with varying aspect ratios of carbon nanotubes and carbon fibers have been devised. Investigations on comparative effect of varying aspect ratios of carbon nanotubes and carbon fibers, with varying loads at two different water to cement ratios (w/c) of 0.45 and 0.50 in cement mortar matrices, were studied for the fracture response of the composites in crack initiation and propagation phases. The experiments concluded that an optimum addition of carbon nanotubes results in substantial improvements in terms of fracture properties. However, in case of carbon fibers, optimum increase in flexural strength was attained for carbon fibers having 12 mm length with 0.45 w/c, with the inclusion percentage of 0.15 by weight of cement indicating the increase in flexural strength up to 62.47%, followed by carbon fibers of 6 mm length at 0.45 w/c with the increase of 41.02%. Research also provides novelty for selection of optimum formulations among different aspect ratios. The field emission scanning electron microscopy evidenced a uniform level of tubes/fibers dispersion, the effective reinforcing effect by the tubes/fibers on the host matrix by providing the fracture mechanics phenomena of crack initiation, crack suppression, crack bridging and fiber–matrix debonding.

Physical, mechanical and thermal properties of high frequency microwave treated plantain (Musa Paradisiaca) fibre/MWCNT hybrid epoxy nanocomposites

Natural fibre reinforced polymer composite has many industrial applications especially in automobile. However low mechanical and thermal property has limited its application. In this study, natural fibre reinforced hybrid nanocomposite was manufactured by the incorporation of high frequency microwave treated Plantain (Musa paradisiaca) fibre and multiwalled carbon nanotubes (MWCNT) using a single epoxy resin matrix. The consequence of harmonized existence of MWCNT at different loading (0.5−2wt.%) on the physical, mechanical and thermal Properties of the hybrid nanocomposite was examined, using the ultrasonic technique for dispersion of nanoparticles and hand lay-up and compression moulding process for composite production. The experimental results demonstrate that the mechanical properties strength improve up to 52%, while up to 30% improvement was recorded for micro-hardness and impact strength, caused by increment in MWCNT content. Scanning electron microscope (SEM) analysis reveals good mechanical dovetailing of hybrid fibres with polymer matrix. Thermal conductivity has shown significant improvement up to 43% as MWCNT contents increases. These enhancements are primarily ascribed to the high aspect ratio, high modulus, strength and good dispersal of carbon nanotubes (CNT) in the hybrid nanocomposites.

Free convection with MWCNT/water nanofluid having varying aspect ratio of MWCNT nanoparticle in thermally undulated enclosures

The Aspect ratio of carbon nanotubes (CNTs) in cavities of different geometrical aspect ratio is one of the critical parameters of the design in thermal engineering. The present work documented a numerical simulation of 2D, steady and laminar free convection in rectangular cavities with different aspect ratios filled with water-based nanofluid. The nanoparticle considers in the present work is MWCNT with varying average diameter and length consequently varying aspect ratio. The Navier–Stokes and energy equations are solved numerically, coupling Thang et al. [43] model for calculating the effective thermal conductivity and Brenner and Condiff [44] model for determining the effective dynamic viscosity. The results are presented in the form of streamlines, isotherms, vertical velocity and Nusselt numbers. The novelty of the present study is to find the effect of MWCNT nanoparticle aspect ratio on fluid flow and heat transfer. Maximum of about 65% increment in average Nusselt number is observed at maximum aspect ratio (length/diameter) of 6 × 104 for any temperature undulation and cavity aspect ratio. Maximum MWCNT aspect ratio (or minimum diameter) is proposed for better heat transfer. A range of Rayleigh number is observed for better heat transfer for different temperature undulation value at the left wall.

Analysis of critical interfacial shear strength between polymer matrix and carbon nanotubes and its impact on the tensile strength of nanocomposites

This paper focuses on the critical interfacial shear strength (τc) and interfacial shear strength (τ) between polymer matrix and carbon nanotubes (CNT) in nanocomposites, which divide the interphase region to two zones: τ < τc near the polymer matrix and τ > τc beside the CNT. “τc” is defined by CNT properties and a model is developed to consider the roles of “τ” and “τc” in the tensile strength of nanocomposites. Numerous experimental data for various samples and the parametric examines are applied to approve the developed approach. The high aspect ratio of CNT (thin and long CNT) produces a low “τc”, but the CNT strength directly influences the “τc”. The suitable agreement between experimental data and calculations for all samples and the proper roles of all parameters in the tensile strength of nanocomposites confirm the developed model. Low “τc” and high “τ” cause a high nanocomposite strength, but the strength of nanocomposites largely increases when τ > 5 τc.

Simulation of tensile modulus of polymer carbon nanotubes nanocomposites in the case of incomplete interfacial bonding between polymer matrix and carbon nanotubes by critical interfacial parameters

In this paper, we correlate the minimum length of carbon nanotubes (CNTs) vital for operative stress transferring between polymer matrix and nanoparticles (Lc) to the critical interfacial shear modulus between polymer and CNTs (Gc) and the interfacial shear modulus (Gi) in the case of imperfect interfacial adhesion between polymer and carbon nanotubes (CNTs). Both “Gc” and “Gi” define the effective aspect ratio and volume fraction of CNTs in nanocomposites. Moreover, the developed Hui-Shia model investigates the roles of “Lc”, “Gc” and “Gi” in the tensile modulus of nanocomposites. The impacts of various parameters on the “Lc” and effective terms are highlighted. Furthermore, the experimental results of modulus for several samples and the influences of all parameters on the modulus evaluate the developed model. The accurate agreement between experimental and theoretical results as well as the correct roles of all parameters in the modulus supports the current approach. There is a direct relationship between the modulus of nanocomposites and “Lc”. Low “Gc” and high “Gi” as well as thin and long CNTs positively control the “Lc” and effective terms producing a high modulus for nanocomposites.

A finite element study on the CNT size effect on the nonlinear response of polymer nanocomposites

The effect of carbon nanotube (CNT) aspect ratio on the elastic–viscoplastic response of polymer nanocomposites with and without interphase region is studied using the finite element method. Also, the interfacial debonding between the constituents of the nanocomposite is considered in the simulation. To characterize both the polymer and the interphase zone, an elastic–viscoplastic constitutive relation is used. The CNT is modeled as an isotropic elastic material. A phenomenological cohesive relation that allows for separation is employed to model the interface between the polymer and the CNT phases. The effects of CNT aspect ratio, interface strength and interphase thickness on the nanocomposite stress–strain behavior are analyzed. It is observed that the polymer nanocomposite stress carrying capacity significantly decreases with increasing CNT aspect ratio in the presence of both interphase zone and debonding. The results indicate that in the presence of the interphase and debonding, with increasing the aspect ratio, the main concern is dominated by debonding at the interface between the CNT and interphase, while the plasticity of matrix is the chief concern at low CNT aspect ratio. Furthermore, it is found that in the absence of interphase, the strength of nanocomposite is improved with increasing CNT aspect ratio.

Synergetic Impact of Carbon Nanotube and/or Graphene Reinforcement on the Mechanical Performance of Glass Fiber/Epoxy Composite

The exceptional and distinctive properties of the allotropes of carbonaceous nanomaterials like carbon nanotubes and graphene have attracted many researchers and engineers to enhance the performance of fibrous polymeric composites. This article extrapolates the synergetic impact of carbon nanotube (CNT) and multi-layered graphene (MLG) reinforcement onto the mechanical performance of glass fiber/epoxy composites. Magnetic stirring and ultra-sonication process have been carried out under optimized parameters for incorporation of CNT-MLG into the epoxy polymer. Incorporation of 0.1wt% of carbon nanotube to the glass fiber/epoxy composites enhances a flexural strength of 10% and addition of 0.1 wt. % of multi layered graphene to the glass fiber/ epoxy composites enhances a flexural strength of 6% when differentiated with neat GE. Embodiment of 0.1 wt. % CNT and MLG to the glass fiber/epoxy composites in three different ratios like 1:1, 1:2 and 2:1 showcases a 13%, 12.25% and 14.7% enhancement in the flexural strength respectively with respect to the neat glass fiber/epoxy composites when tested at room temperature. Among them, the ratio 2:1(CNT: MLG) contributes higher strength due to the combined action of high aspect ratio of CNT and higher specific surface area of multi-layered graphene thus, facilitating efficient stress transfer from matrix to the reinforcements. Thermal characterizations have been carried out using differential scanning calorimetry (DSC). The fractography of the samples is examined through the scanning electron microscope.

Microfluidic Synthesis of Carbon Nanotube-Networked Solid-Shelled Bubbles.

Carbon nanotubes (CNTs) have attracted considerable attention because of their high electrical conductivity and outstanding mechanical properties. As such, there have been numerous attempts to form CNTs into diverse structures for use in a wide range of applications. However, the intrinsic high aspect ratios of CNTs and resulting deformability have prevented the fabrication of sophisticated CNT-based structures, especially for three-dimensional (3D) cellular architectures. To challenge this limitation, we present a novel method to fabricate a 3D CNT cellular network from the assembly of microfluidically synthesized CNT-shelled microbubbles. We successfully generated stable spherical CNT-shelled bubbles with excellent size and shape uniformity by precisely controlling bubble dimensions by varying microfluidic variables. We also developed a fundamental understanding of the bubble stability, which allowed us to suppress shrinkage-induced deformation. The synthesized CNT-shelled bubbles were assembled into a 3D close-packed structure, followed by treatment with thermal reduction to induce interfacial bonding and transformation into a closed cellular network structure. Overall, this work provides a new strategy of assembling 1D nanomaterials as the building blocks for well-regulated 3D closed cellular architectures with improved structural or physical properties.

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.

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.

Unique approach to debundle carbon nanotubes in polymer matrix using carbon dots for enhanced properties

Excellent dispersion of nanofillers like carbon nanotubes (CNTS) in an aqueous medium of rubber latex through covalent interactions is required to achieve extraordinary reinforcement at very low filler concentration. Herein, aqueous dispersible carbon dots (CDOTS) have been used as dispersion aid to debundle CNTS in carboxylated acrylonitrile butadiene rubber (XNBR) latex. The amine groups of CDOTS have been covalently conjugated with the acid groups of CNTS and XNBR latex through amide bond formation that leads to enhanced interactions between XNBR and CNTS through CDOTS. In addition, CDOTS weaken the strong intertubular van der Waals attraction between the CNTS which results in the efficient dispersion of high aspect ratio CNTS in the XNBR matrix and thereby significantly improves the overall properties. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) studies establish the success of covalent conjugation of CDOTS with CNTS and XNBR latex. The mechanical, dynamic mechanical, thermal stability and thermal conductivity properties of the XNBR-CDOTS-CNTS hybrid nanocomposites are prominently higher when compared to neat XNBR, XNBR-CNTS nanocomposites and XNBR-CDOTS nanocomposites. From transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies it has been ascertained that the CDOTS act as an interconnector between CNTS that prevents agglomeration of CNTS in the XNBR matrix.

The Effect of the Preparation Method and the Dispersion and Aspect Ratio of CNTs on the Mechanical and Electrical Properties of Bio-Based Polyamide-4,10/CNT Nanocomposites.

Bio-based polymeric nanocomposites (NCs) with enhanced electrical conductivity and rigidity were obtained by adding multi-walled carbon nanotubes (CNTs) to a commercial bio-based polyamide 4,10 (PA410). Two different types of commercial CNTs (Cheap Tubes and Nanocyl NC7000TM) and two different preparation methods (using CNTs in powder form and a PA6-based masterbatch, respectively) were used to obtain melt-mixed PA410/CNT NCs. The effect of the preparation method as well as the degree of dispersion and aspect ratio of the CNTs on the electrical and mechanical properties of the processed NCs was studied. Superior electrical and mechanical behavior was observed in the Nanocyl CNTs-based NCs due to the enhanced dispersion and higher aspect ratio of the nanotubes. A much more significant reduction in aspect ratio was observed in the Cheap Tubes CNTs than in the Nanocyl CNTs. This was attributed to the fact that the shear stress applied during melt processing reduced the length of the CNTs to similar lengths in all cases, which pointed to the diameter of the CNTs as the key factor determing the properties of the NCs. The PA6 in the ternary PA410/PA6/CNT system led to improved Young’s modulus values because the reinforcing effect of CNTs was greater in PA6 than in PA410.

Evaluation of the effect of adding carbon nanotubes on the effective mechanical properties of ceramic particulate aluminum matrix composites

In this study, a high-performance hybrid aluminum matrix composite (HAMC) reinforced with ceramic particles and carbon nanotubes (CNTs) is analyzed. A novel multi-step micromechanical approach, based on the Mori-Tanaka model and the generalized method of cell, is proposed in order to predict the effective elastic modulus and Poisson's ratio of the HAMCs. The influences of volume fraction, aspect ratio, waviness shape, alignment and agglomeration of CNTs, and ceramic particle volume fraction on the mechanical properties of CNT/ceramic particle-reinforced HAMCs are explored. Moreover, the role of aluminum carbide (Al4C3) which may be formed at the CNT/matrix interface in the mechanical behavior is micromechanically investigated. It is found that adding a small amount of CNTs into the microscale ceramic particle-reinforced aluminum matrix composites (AMCs) can significantly improve the effective mechanical properties of the resultant HAMCs. As compared to HAMCs, which contain the randomly dispersed CNTs, the alignment of CNTs into the HAMCs leads to a higher level of mechanical properties. However, the waviness and agglomeration of CNTs can decrease the HAMC elastic modulus. According to the obtained results, the CNT/matrix interfacial interaction may have significant effects on the effective properties of the particulate hybrid metal-based composites. The elastic properties estimated by the micromechanical model are compared to those measured by the experimental method. The outcomes of this research suggest that these hybrid metal-based composites, containing CNTs, have significant potential in diverse engineering applications as compared to the conventional metal-based composites.

Evaluating the effect of addition of nanodiamond on the synergistic effect of graphene-carbon nanotube hybrid on the mechanical properties of epoxy based composites

Addition of carbon nanotubes (CNT) to Graphene (Gr) is seen to have synergistic effect as reinforcement to polymer matrix. This is possible as CNTs inhibit stacking of Gr sheets, thus providing larger surface area nanophase to get bonded with polymer matrix and providing mechanical support through load sharing and crack growth inhibition. However, tube like morphology and high aspect ratio of CNT often lead to entanglement, which restricts their effect in exfoliating Gr. The aim of the present study is to investigate the potential of ND in improving the synergistic effect of Gr-CNT hybrid as a reinforcement to epoxy matrix. This study utilizes the power of ultrasonication technique, which is very simple and scalable, for dispersing and incorporating nanofillers into epoxy matrix. Addition of ND to Gr-CNT epoxy composite improved the tensile strength from ~46% with 0.5 wt% (75Gr:25ND) to ~51% with 0.8 wt% (25Gr:25CNT:50ND) as compared to neat epoxy. While the fracture toughness improved from ~140% with 0.5 wt% (25Gr:75CNT) to 165% with 0.8 wt% (25Gr:50CNT:25ND). Fractured surfaces of composites revealed improved dispersion and strong interfacial interaction with addition of ND to Gr-CNT hybrid. NDs attaches to the surface of Gr inhibit the stacking of Gr sheets by restricting π-π stabilization. NDs also help in bridging the ends of CNTs together into long chains, thereby increasing the aspect ratio of the fiber like reinforcement. This increases the total available surface area of CNTs and Gr, to interact with epoxy matrix, improves the overall efficiency of Gr-CNT hybrid as a reinforcement, resulting into improvement in mechanical properties of the composite structure.

Effect of Carbon Nanotube Diameter and Stiffness on Their Phase Behavior in Crowded Solutions.

The unique carbon nanotube (CNT) properties are mainly determined by their geometry, e.g., their aspect ratio, diameter, and number of walls. So far, chlorosulfonic acid is the only practical true solvent for carbon nanotubes, forming thermodynamically stable molecular solutions. Above a critical concentration the system forms an ordered, nematic liquid-crystalline phase. That phase behavior is the basis for liquid-phase processing and the optimal translation of the carbon nanotube molecular properties to the macroscopic scale. The final material properties depend on the phase behavior of the "dope" from which it is prepared, which depends on the CNT parameters themselves. Earlier work determined that CNT aspect ratio controls the phase behavior, in accordance with classical rigid-rod theories. Here we use cryogenic transmission electron microscopy and Raman spectroscopy to understand the relation between the geometry of the CNTs, the chemical interaction with chlorosulfonic acid, and the phase behavior of crowded solutions. We show that the CNT diameter and number of walls also play an independent role in the phase transition and phase morphology of the system because of their effect on the CNT bending stiffness.

Reliability-based robust design optimization of polymer nanocomposites to enhance percolated electrical conductivity considering correlated input variables using multivariate distributions

In this study, reliability-based robust design optimization (RBRDO) for polymer nanocomposites (PNCs) design is conducted to secure the reliability of design conditions concerning the electrical percolation threshold and carbon nanotube (CNT) aspect ratio as well as the robustness for electrical conductivity. CNT diameter and length are known as following the lognormal and Weibull distributions respectively. To reflect the different probability distributions of CNT geometry parameters and correlations between these random input variables, Nataf transformation is employed. By performing several case studies with the first-order reliability method (FORM)-based RBRDO approaches, the objective function exhibited a noteworthy change according to the correlation coefficients and the reliability and robustness for PNCs were satisfied concurrently. Furthermore, the highlight of this work is to provide a generic framework for practical PNC design and multi-objective optimization to enhance electrical performance efficiently.