Aspect Ratio Of Carbon Nanotubes Research Articles

Effect of aspect ratio of multi-wall carbon nanotubes on the dispersion in ethylene-α-octene block copolymer and the properties of the Nanocomposites

Effects of aspect ratio of multi-wall carbon nanotubes (MWCNTs) on the dispersion of MWCNTs in ethylene-α-octene block copolymer (OBC) and the properties of OBC/MWCNTs nanocomposites were studied, and two series of MWCNTs with different aspect ratios based on the same length and the same diameter were considered. Scanning electron microscope (SEM) and transmission electron microscope (TEM) results show that small and large agglomerates induced by intra- and inter-entanglement of MWCNTs are present for MWCNTs with high aspect ratio having smaller diameter and larger length, respectively. Rheological, electrical and tensile properties of OBC/MWCNTs nanocomposites are related to the aspect ratio and dispersion of MWCNTs. The formation of agglomerates, especially large agglomerates, influence the network perfection, weakening the contribution of MWCNTs to the rheology and electrical properties. The inter-entanglement shows less negative effect on the enhancement for the modulus and strength of OBC nanocomposites, and intra-entanglement of MWCNTs shows discounted enhancing properties. The aspect ratios of MWCNTs related to not only the length but also the diameter play the dominant role on the dispersion in polymers and the properties of polymer nanocomposites.

Electro-thermo-mechanical responses of laminated smart nanocomposite moderately thick plates containing carbon nanotube – A multi-scale modeling

Bending analysis of laminated carbon nanotube (CNT) piezo-nanocomposite moderately thick rectangular plates is presented by a multi-scale approach. Firstly, a unit cell based micromechanical model is developed to obtain the electro-thermo-mechanical behavior of material to transfer to the structure scale. The nanocomposite representative volume element consists of three phases, including CNT, piezoelectric Polyvinylidene Fluoride (PVDF) matrix and an interphase representing the CNT/PVDF van-der Waals interaction. The matrix is also polarized through the plate thickness. The macro-scale analysis of plate is performed based on the first order shear deformation theory via implementing the finite element method. Good agreements are reported for the presented results compared with the available results in literature and other modeling strategies at both the micro and macro levels. Also, the results of the mesh sensitivity analysis at both the micro and macro scales guarantee the model accuracy and low-computational cost. The effects of the nano-scale parameters, including the CNT content, aspect ratio, packing and the interphase characteristics are examined on the response of smart plates with different dimensions, supports and loadings. The results reveal that the effects of the CNT aspect ratio and the interphase thickness on the plate response are more pronounced at high values of the plate width-to-thickness ratio.

Insights into the Surface Science, Storage Mechanism and Electrochemical Phase Evolution of MoS2/CNT Hybrid Electrodes for Supercapacitive Application

Lately, layered MoS2 is found to be one of the most researched pseudocapacitive electrode material for Li+ and Na+ ion batteries because of its unique layered structure for initial ion intercalation and de‐intercalation and high conversion chemistry. As far as supercapacitors are considered, the charge storage in nanostructured MoS2 takes place via electric double layer formation, intercalation and de-intercalation pseudocapacitance and redox pseudocapacitance. Recently, a vast majority of studies on layered MoS2, have been focused on designing hierarchical deformed structures instead of regularly ordered crystallites which may accommodate intercalation stress upto some extent while retaining the original structure. In this study, we have synthesized large aspect ratio carbon nanotubes with a high specific surface area and an appropriate superstructure forming a thin layer of molybdenum disulfide nanoflakes hierarchically dispersed on the surface of the CNTs. This novel technique of preparing MoS2@CNT superstructure using a combination of chemical and physical deposition techniques proved to be very efficient in structurally engineering the microstructure of electrode material. Moreover, sputtering as a fabrication technique, provided an opportunity to precisely grow hierarchical structured MoS2 nanoflakes uniformly throughout the matrix, easily scalable and controllable at lengths down to nanometer ranges irrespective of superhydrophobic nature of CVD grown CNTs. The designed hybrid nanostructure form an open porous network with shorter ionic as well as electron diffusion lengths and provides larger number of intercalation sites. The super capacitive measurements of the MoS2@CNT electrode revealed capacity of 337 mF/cm2 at the sweep rate of 5 mV/s. The storage mechanism involves both electrostatic ionic adsorption as well as Na+ intercalation into the MoS2@CNT matrix. The electrochemical performance of the hybrid is far more superior due to the contribution from both faradaic and non-faradaic processes. Also, the cyclic retention have been immensely improved as compared to bare CNT and MoS2 and has shown a retention of 97.6% after 3500 cycles. Further, to elucidate the charge storage mechanism Trasatti’s and Dunn’s analysis are performed which suggest that pseudocapacitive phenomenon is dominantly responsible for superior charge storage in the hybrid. The electrodes subjected to 10, 50, 1000, 2000 and 3500 charging discharging cycles at 100mV/s were then analyzed using X-ray photoelectron spectrophotometer to understand the change in surface science of the material and reason behind cyclic fading. The phase transformation of electrode suggests that the binding energies of MoS2 shits towards shifts towards lower energies after cycling. This shift indicates partial transition of 2H→1T MoS2 phase due to the transverse gliding of S plane upon the intercalation of electrolytic ions. Additionally, we observed the formation of thin MoO3 oxide layer on the surface of electrode which may be due to the presence of dangling bonds generated by ionic intercalation. Thus, this thin insulating layer may be the reason of capacitive fading after 3500 cycles of constant charging and discharging. The all solid state supercapacitor built using symmetric MoS2@CNT electrodes was found to have high areal and volumetric capacitance of 131 mF/cm2 and 2.9 F/cm3 respectively, with high cyclic stability of 97.6% after 2500 cycles. Figure 1

Mechanical Characterization of Concrete Reinforced with Different Types of Carbon Nanotubes

The main purpose of this study is to characterize the mechanical properties of concrete reinforced with carbon nanotubes (CNT). For this, an extensive experimental program was carried out involving the production and characterization of concrete mixes with five types of CNT, in terms of flexural, splitting tensile and compressive strength, ultrasonic pulse velocity, elastic modulus and fracture toughness. The dispersion ability of CNT in a wide range of pH aqueous suspensions was evaluated prior to their incorporation in concrete. It was found that 0.05–0.1% of CNT were effective to improve all tested properties, increasing the compressive, flexural and splitting tensile strength, as well as the fracture energy and elastic modulus up to 23%, 18%, 27%, 42% and 15%, respectively. The CNT showed great potential to improve the crack resistance and the fracture toughness of concrete, especially in the pre-peak performance of concrete. In relative to other types of CNT, concrete containing higher dosages of lower aspect ratio CNT had the highest improvement of mechanical strength. This is explained by the lower structural damage and higher dispersion capacity of this type of CNT in high pH environments. Nevertheless, higher aspect ratio CNT showed better contribution for the fracture energy, due to their more efficient bridging effect.

Agglomeration and aspect ratio effects on the long-term creep of carbon nanotubes/fiber/polymer composite cylindrical shells

The present study is an attempt to trace the influences of agglomeration, uniform dispersion, and aspect ratio of carbon nanotubes on long-term creep strain and stress in carbon nanotubes/fiber/polymer composite cylindrical shells. The thin-walled cylindrical vessel is subjected to an internal pressure. For this purpose, the effect of the carbon nanotubes agglomeration and aspect ratio on the elastic properties of carbon nanotube-reinforced composites were investigated, by means of the Halpin–Tsai and Eshelby–Mori–Tanaka approaches. Classical-laminated plate theory and stress–strain relations were used to derive the governing equations for radial and circumferential creep strain. The Schapery single integral nonlinear viscoelasticity model was used for modeling the behavior of materials reliably. The present results indicated that the higher aspect ratio and uniform dispersion decreased creep strain, but agglomeration increased creep strain.

A percolation network model to predict the electrical property of flexible CNT/PDMS composite films fabricated by spin coating technique

Carbon nanotubes (CNTs) based flexible films have great potential on the flexible electronics due to their relatively uniform electrical properties in the film and ease of fabrication technology. In this work, CNT/polydimethylsiloxane (PDMS) composite films with various film thickness was fabricated successfully. By introducing a percolation network model, this work reveals theoretically that the observed rapidly drops of conductivity in thin films mainly depends on the change of CNT network morphology during spin coating. Junctions formed by structural distorted tubes are also observed at the cross section of film samples. By considering both CNT re-orientation and CNT structural distortion into percolation network model, the simulation results are in good agreement with the experimental data. Furthermore, a comprehensive numerical investigation reveals the relationship between film conductivity and some core parameters including CNT loadings, CNT intrinsic conductivity and CNT aspect ratio.

Modeling the mechanical properties of cementitious materials containing CNTs

This paper proposes analytical equations to predict the mechanical properties (flexural strength and flexural modulus of elasticity) of cementitious materials reinforced with Carbon Nanotubes (CNTs). Twenty-six mix proportions and literature data are used to develop rational models to consider the influence of important parameters and their interactions on the mechanical properties. The controlled experimental parameters include CNT aspect ratio, concentration, ultrasonication procedure (e.g., energy, amplitude, and superplasticizer-to-CNTs (SP/CNTs) ratio), water-to-cement (w/c) ratio, sand-to-cement (s/c) ratio, and testing age. The proposed model is based on three steps of considering CNT dispersion, matrix contents, and hydration age of cement. The proposed model can capture the interactions between the experimental parameters for predicting the mechanical properties with reasonable accuracy. Also, there are several options to achieve comparable improvements in the mechanical properties with various combinations of the experimental parameters using the proposed equations.

Nonlinear aeroelastic stability analysis of three-phase nano-composite plates

The main aim of this study is to investigate the geometrical nonlinear flutter of three-phase nano-composite plates reinforced with carbon nano-tubes (CNTs). The effective material properties are obtained using Halpin-Tsai relation and rule of mixture. The classical plate theory and von Karman geometrical nonlinearities assumptions are employed to obtain the governing equation of the system. The homotopy perturbation method (HPM) is utilized to conduct a numerical investigation to study the aeroelastic behavior of multiscale composite plates. The effects of different parameters such as CNTs weight percentage, aspect ratio, and elastic modulus ratio on flutter pressure of nano-composite plates are considered.Communicated by S. Velinsky.

A new form of a Halpin–Tsai micromechanical model for characterizing the mechanical properties of carbon nanotube-reinforced polymer nanocomposites

In the present work, a new form of a Halpin–Tsai (H–T) micromechanical model is proposed to characterize the elastic modulus and tensile strength of carbon nanotube (CNT)-reinforced polymer nanocomposites. To this end, three critical factors, including random dispersion, non-straight shape and agglomerated state of the CNTs are appropriately incorporated into the H–T model. A comparison of the model predictions with some experiments on the CNT/polymer nanocomposites serves to verify the applicability of the proposed approach. It is found that the present predictions are in good agreement with the available experimental data. The results clearly reveal that for a more accurate prediction of the mechanical properties of the CNT/polymer nanocomposites, considering the random orientation, waviness and agglomeration of CNTs into the polymer matrix is critically essential. Also, some parametric studies are carried out to show the effects of volume fraction, non-straight shape, aspect ratio, mechanical characteristics and non-uniform dispersion of CNTs as well as matrix properties on the elastic modulus and tensile strength of CNT/polymer nanocomposites. The results reveal that it is necessary to eliminate the agglomeration and use the straight CNTs if the full potential of CNT reinforcement is to be realized.

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.

Prediction of electrical conductivity of carbon fiber-carbon nanotube-reinforced polymer hybrid composites

A two-step analytical electrical conductivity method is adopted to calculate the effective electrical conductivity of the carbon fiber (CF)-carbon nanotube (CNT)-polymer hybrid composite. First, CNTs are dispersed into the non-conducting polymer matrix and the electrical conductivity of the CNT-polymer composite is obtained. Then, CFs are randomly distributed in the CNT-polymer composite and the effective electrical conductivity of CF-CNT-polymer hybrid composite is estimated. The effect of critical parameters, including the volume fraction, alignment, agglomerated state and aspect ratio of the CNTs and the potential barrier height of the polymer on the hybrid composite electrical conductivity is evaluated. Also, the influence of the content and aspect ratio of CFs on the electric conductive behavior of the polymer hybrid composites is investigated. The results show that the polymer hybrid composite with larger aspect ratio and off alignment of CNTs presents a higher electrical conductivity.

Conducting Super-Hydrophobic Thin Film for Electric Heating Applications.

Frost presents a serious problem for the human environment, resulting in such phenomena as downed power lines, damaged crops and stalled aircraft. In addition, frost and ice accumulation significantly decrease the performance of ships, wind turbines, and HVAC systems with high failure risk. Super-hydrophobic (SH) surface can be an appropriate solution for frost problems, due to its anti-icing properties that can prevent ice nucleation on the surface. In addition, in the case of conducting SH surface using carbon nanotubes (CNTs) as a filler, it can form an excellent heating unit, owing to the resistive heating effect. The purpose of this study is to produce a large-area conducting SH film that can prevent ice nucleus and remove ice formation rapidly. High aspect ratio carbon nanotubes (CNTs) as a conducting filler and adhesive polymer resin as a binder were used to form coating layer. In addition, silica particles (~7 nm) were used to stabilize nano-size roughness of the SH surface. Wet and dry etching processes were used on the substrate to improve wettability and to produce organic functional groups. To evaluate the de-icing effect, the fabricated SH surface was rapidly heated to 150 °C by applying voltage.

A Unified View on Nanoscale Packing, Connectivity, and Conductivity of CNT Networks

AbstractThe design of functional structures from primary building blocks requires a thorough understanding of how size, shape, and particle–particle interactions steer the assembly process. Specifically, for electrically conductive networks build from carbon nanotubes (CNTs) combining macroscopic characterization and simulations shows that the achievable conductivity is mainly governed by CNT aspect ratio, length dispersity and attractive interactions. However, a direct link between the actual 3D network topology that leads to the observed electrical conductivity has not been established yet due to a lack in nanoscale experimental approaches. Here it is shown experimentally for randomly packed (jammed) CNT networks that the CNT aspect ratio determines, as theoretically predicted, the contact number per CNT which in turn scales linearly with the resulting electrical conductivity of the CNT network. Furthermore, nanoscale packing density, contact areas, contact distribution in random and nonrandom configurations, and least resistance pathways are quantified. The results illustrate how complex nanoscale networks can be imaged and quantified in 3D to understand and model their functional properties in a bottom‐up fashion.

Effects of adding CNTs on the thermo-mechanical characteristics of hybrid titanium nanocomposites

Feasibility of using carbon nanotubes (CNTs) for improving the thermo-mechanical properties of titanium (Ti) matrix composites (TMCs) is studied by means of a multi-stage micromechanical approach. The hybrid Ti matrix nanocomposite (HTMNC) system consists of Ti-6Al-4 V alloy reinforced by unidirectional SiC fibers and randomly dispersed CNTs. An efficient micromechanics procedure is proposed to investigate the CNT aggregation encountered frequently in real engineering situations. The effects of the SiC fiber volume fraction, off-axis angle, aspect ratio and arrangement type as well as the CNT volume fraction, waviness, aspect ratio and non-uniform dispersion are examined on the HTMNC effective properties. Owing to their high Young's modulus and low coefficient of thermal expansion (CTE), the CNT use into the conventional TMCs is revealed to be effective at improving the resulting HTMNC thermo-mechanical properties. Also, the HTMNC elastic moduli and CTEs tend to further improvement by the use of straight CNTs. However, it is demonstrated that the CNT aggregation has a deterioration effect on the effective properties. Generally, the model predictions agree well with the experimental measurements. The results could be actually useful to guide design of general metal matrix composites containing CNTs with superior thermo-mechanical properties.

Thermal expansion properties of the polycaprolactam nanocomposites reinforced with single-walled carbon nanotubes

Abstract The effect of carbon nanotube loading and aspect ratio on the thermal expansion properties of polymer nanocomposites was investigated in terms of the material properties, configuration, and phase geometry of each individual component. The objective of this research is to provide methods for fabricating carbon nanotube reinforced polymer nanocomposites with very low coefficients of thermal expansion. The thermal expansion properties of polycaprolactam nanocomposites prepared with different levels of thermal histories were investigated to gain a better understanding of the morphology-property relationships. The effects of carbon nanotube loading and aspect ratio on the thermal expansion behavior of the polymer nanocomposites were evaluated. The results indicated that the loading and aspect ratio of carbon nanotubes have a significant effect on the thermal expansion properties of the polymer nanocomposite, and high aspect ratios and loading of the filler are preferred. The issue of carbon nanotube dispersion is critical to efficient reduction in thermal expansion properties. Additionally, it is desirable to achieve a high degree of alignment of carbon nanotubes in the matrix along the desired direction for fabricating polymer nanocomposites with very low coefficient of linear thermal expansion in this direction. Furthermore, flow-induced alignment of carbon nanotubes in the matrix along the direction of flow leads to reduced thermal expansion properties of the polymer nanocomposite. Finally, there is an excellent linear correlation between the relative Young's modulus and the relative thermal expansion of the nanocomposite and the matrix.

Electrosensing tool for nonsteroidal drug flufenamic acid at multiwalled carbon nanotubes modified graphite electrode

The sensitivity, high aspect ratio, electrocatalytic and enhancing properties of multi-walled carbon nanotubes (MWCNTs) were well utilized to fabricate the present sensor based on graphite electrode. The modified sensor used to determine flufenamic acid (FFA), a non-steroidal anti-inflammatory drug. The sensitivityand selectivity of sensor towards FFA, were enriched at MWCNTs modified electrode compared to the bare one. The influence of pH, amount of modifier, preconcentration time, sweep rate and concentration on the signal enhancement of FFA were studied. FFA is electrochemically active in all the pHs studied, but in pH 4.2 an accentuated peak was observed. From the acquired data, mixed adsorption diffusioncontrolled process and two protons, two electrons involvement was witnessed. The currents obtained from square wave voltammetric (SWV) measurements were linearly associated with FFA concentration. The concentration of FFA was found linear in the concentration range of about 0.1 µM to 0.8 µMwith alimit of detection (LOD) value of 2.2 nM. Contrasted with prior reports, the present result is very impressive on account of modifiers utilized and expedient because of its affectability, selectivity,and LOD value. In addition, the modified electrode processes some unique characteristics, such as appropriate charge transfer rate, enduring stability, exceptional reproducibility and antifouling effects. The practical usefulness of the modified sensor was evaluated by the analysis of FFA in spiked human urine samples.

Modification of Specialty Rubbers by Carbon Nanomaterials

In the elements of aviation structures of large size and low rigidity rubber thermal protective coatings are used, which do not collapse when the structure is deformed. The use of rubber for supersonic aircraft and spacecraft is limited due to high requirements for heat and frost resistance of materials, as well as to their stability under the conditions of radiation and in a vacuum. Therefore, the development of new rubber with improved characteristics is an urgent problem. Multiwall carbon nanotubes are among the most anisotropic materials known and have extremely high values of Young's modulus. Carbon nanotube aspect ratio of length to diameter is more than 103; this distinguishes it from other nanoparticles. New composites with carbon nanotubes (CNTs) as additives were studied intensively during the last decade. Composites are characterized by extremely high specific strength properties, electrical and thermal conductivity. The effect of multiwalled carbon nanotubes on the performance characteristics of rubbers based on nitrile-butadiene was studied with various methods of their preliminary treatment and introduction into the composition of rubbers. It was shown that the introduction of 0.5-1.0 wt. % сarbon nanotubes into elastomers of different chemical structures leads to an increase in their physic mechanical characteristics, wear resistance and aging resistance, which significantly increases the service life of such products.

Effects of the aspect ratio of multi-walled carbon nanotubes on the structure and properties of regenerated collagen fibers

Collagen is a natural one-dimensional nanomaterial. Multi-walled carbon nanotubes (MWNTs) have been previously shown to interact with biomolecules and to have promising applications in reinforced biopolymers for tissue engineering and regenerative medicine. In this work, collagen/MWNT composite fibers are prepared using dry-jet wet-spinning technology. Three types of MWNTs with aspect ratios of 40, 150, and 4000 are used to investigate the effects of the MWNT aspect ratio on the properties of the composite fibers. There results show that there are strong molecular interactions between the MWNTs and collagen molecules. The mechanical properties and thermal stability of the composite fibers are significantly improved compared to those of the collagen fibers. The diameter and aspect ratio of the MWNTs are the main factors affecting the self-assembled structure of the collagen molecules, the alignment of the microfibrils, and the mechanical and thermal performance of the composite fibers.

Influence of carbon nanotubes on steel–concrete bond strength

In this study, the bond strength between steel and concrete reinforced with multi-walled carbon nanotubes (CNTs) is analysed. To this end, pull-out tests were carried out for concretes with incorporation of 0.05–0.1% of different types of functionalized and unfunctionalized CNTs with distinct aspect ratios and dispersion techniques. The results showed that CNTs can improve both compressive strength and steel–concrete bond up to 21% and 14% respectively, as compared to plain concrete. The highest compressive strength was found in concrete with higher amounts of lower aspect ratio CNTs, while the best steel–concrete bond performance was attained for concrete with lower amounts of higher aspect ratio CNTs. CNTs were effective to retain the crack propagation, increasing the bonding stiffness and reducing the deformation of concrete consoles between steel ribs. CNTs of higher aspect ratio could better contribute with their microcrack bridging effect. Microscopic analysis confirmed the adequate dispersion and microcrack bridging provided by CNTs, delaying the macrocrack propagation within the aggregate–paste and steel–concrete interfacial transition zones.

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.