Mechanism Of Carbon Nanotubes Research Articles

MeLM, a generative pretrained language modeling framework that solves forward and inverse mechanics problems

We report a flexible multi-modal mechanics language model, MeLM, applied to solve various nonlinear forward and inverse problems, that can deal with a set of instructions, numbers and microstructure data. The framework is applied to various examples including bio-inspired hierarchical honeycomb design, carbon nanotube mechanics, and protein unfolding. In spite of the adaptable nature of the model-which allows us to easily incorporate diverse materials, scales, and mechanical features-it performs well across disparate forward and inverse tasks. Based on an autoregressive attention-model, MeLM effectively represents a large multi-particle system consisting of hundreds of millions of neurons, where the interaction potentials are discovered through graph-forming self-attention mechanisms that are then used to identify relationships from emergent structures, while taking advantage of synergies discovered in the training data. We show that the model can solve complex degenerate mechanics design problems and determine novel material architectures across a range of hierarchical levels, providing an avenue for materials discovery and analysis. To illustrate the use case for broader possibilities, we outline a human-machine interactive MechGPT model, here trained on a set of 1,103 Wikipedia articles related to mechanics, showing how the general framework can be used not only to solve forward and inverse problems but in addition, for complex language tasks like summarization, generation of new research concepts, and knowledge extraction. Looking beyond the demonstrations reported in this paper, we discuss other opportunities in applied mechanics and general considerations about the use of large language models in modeling, design, and analysis that can span a broad spectrum of material properties from mechanical, thermal, optical, to electronic.

Dynamic electrical failure of carbon nanotube ribbons

Emerging carbon nanotube (CNT)-based cutting-edge applications such as fast-response artificial muscle, fast-charging energy storage system, lightning strike protector, etc. Call for the study of dynamic electrical failure (DEF) of CNTs. In addition, the reported ampacities of CNTs were tested under different electrical signal applying conditions (e.g. the duration of testing), which led to the direct comparison of them may be virtually invalid. Here, the DEF behavior and mechanism of carbon nanotube (CNT) ribbons was studied by experiments and theoretical calculations as well. The considerable impact of electrical stress rates (ESRs) is demonstrated. Electrical failure resistance (EFR) of CNT ribbons increases with increasing ESR (from 0.5 V/s to 200 V/s), both in air and vacuum. EFR in vacuum is generally higher than that in air. This discrepancy attenuates significantly at high ESR regime due to the vacuumizing oxygen failure (VOF) mechanism (thermal oxidation is largely suppressed) in air. The DEF behavior is outlined by a theoretical model and a cube root relationship between EFR and ESR is obtained. We obtain that the way to apply electrical signal has a significant effect on the testing ampacity result and the establishment of a uniform standard of ampacity testing method is highly recommended.

Review of Recent Progress in Wastewater Treatment Using Carbon Nanotubes

Background: Clean and clear water is an essential element in our life. Finding new and innovative approaches to purify water is a critical topic in research and development. Carbon nanotubes are promising adsorbent for many stable organic compounds. The ability of wastewater treatment using carbon nanotubes was studied in this review article. Methods: Adsorption mechanism was discussed based on several research studies. Kinetics and thermodynamics of sorption were reviewed using carbon nanotubes. This review has discussed the approach of removing dyes and heavy metal ions from wastewater using nanomaterials as adsorbent. Furthermore, the paper provides several essential parameters involved in the adsorption mechanism of carbon nanotubes for wastewater applications. Results: The results of this review show that carbon nanotubes are an advantageous source of the adsorbent for wastewater applications. High thermal and chemical stability make carbon nanotubes more attractive for the wastewater treatment application. It is observed that both kinetics and equilibrium studies are essential to understand the adsorption phenomena. The adsorption rate constant is considered an important factor to study the adsorption. Conclusion: Nanomaterials in the adsorption process make the process more effortless compared to other types of adsorbents. Carbon nanotubes have several properties that help in surface modification, which make them an effective and environmentally friendly material for wastewater treatment.

Mechanisms of Carbon Nanotubes and Graphene Growth: Kinetics versus Thermodynamics

Thermodynamics must be favorable for the growth of carbon nanotubes (CNTs) and graphene to take place, but a kinetic study is required to find the operating mechanism. In fact, thermodynamics indicates whether a reaction is possible; however, the route prevailing is not necessarily the most thermodynamically favorable, but the fastest one. Detailed kinetic studies state that there are three alternative routes operating under different temperature and pressure rates. The modes and rates of diffusion of carbon (C) atoms and noble metals have been known since the 1930s, but proof of C bulk diffusion operating in CNT growth came from detailed kinetic studies performed in the early 1970s, when reversible versus irreversible C formation was discussed with examples. The reason for interstitial C bulk diffusion in transition metals is evidenced based on the values of covalent radius. The reason for operating under steady-state conditions (linearity of the weight versus time) when searching for the operating mechanism is discussed herein. The steady-state C formation process operates sometimes with two different solid phases at each side of the catalyst particle (e.g., Ni and Ni3C), with thicknesses proportional to 1/D of the respective C bulk diffusivities when the carbon bulk diffusion step is the rate-determining one.

One step synthesis and characterization of high aspect ratio network-like carbon nanotubes containing calcium aluminate cement composite powders

The poor water dispersion and oxidation resistance of carbon has restricted the widely industrial application of carbon containing castables. High aspect ratio network-like carbon nanotubes containing calcium aluminate cement composite powders were synthesized by carbon-bed sintering method using calcium acrylate and activated alumina as raw materials, and nickel nitrate as catalyst. Meanwhile the effects of catalyst content on the structure and morphology of carbon nanotubes were also studied. The synthesized products were characterized by X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The results indicated that the phase compositions of composite powders were similar to that of commercial Secar71. The length of carbon nanotubes was ca. 25 μm, and the diameter of carbon nanotubes was 55 nm. The aspect ratio of carbon nanotubes is ca. 450. The formation process and mechanism of carbon nanotubes was studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The growth temperature of carbon nanotubes was 700 °C, and the growth of carbon nanotubes agrees with vapour–solid (V–S) model. In addition, the thickness of floating layer, floating ratio and oxidation ratios of the synthesized product were lower than those of the same carbon containing Secar71 cement (S71CB) composite powders, implying that the water dispersion and oxidation resistance of carbon nanotubes were improved because the high aspect ratio network-like carbon nanotubes were not easily separated from calcium aluminate cement and the carbon nanotubes were encased in calcium aluminate cement.

The electrocatalytic characterization and mechanism of carbon nanotubes with different numbers of walls for the VO2+/VO2+ redox couple

Carbon nanotubes (CNTs) have been applied as catalysts in the VO2+/VO2+ redox, whereas the mechanism of CNTs for the redox reaction is still unclear. In this work, the mechanism of the VO2+/VO2+ redox is investigated by comparing the electrocatalytic performance of CNTs with different distributions. For different CNTs, the peak current density of the VO2+/VO2+ redox increases with increasing content of oxygen-functional groups on the surface of CNTs, especially the carboxyl group which is proved as active sites for the redox reaction. Moreover, the reversibility of the VO2+/VO2+ redox decreases with increasing defects of CNTs, as the defects affect the charge transfer of the catalytic reaction. Nevertheless, when a multi-walled CNT sample is oxidized to achieve a high content of oxygen functional groups and defects, the peak current density of the redox reaction increases from 38.5 mA mg-1 to 45.4 mA mg-1 whilst the peak potential separation (ΔEp) also increases from 0.176 V to 0.209 V. Overall, a balance between the oxygen functional groups and the defects of CNTs affects the peak current and the reversibility for the VO2+/VO2+ redox.

Nanomedicine: A New Approach for Treatment Neuropsychiatric Diseases

Nervous system diseases, such as Alzheimer's disease, stroke, and Parkinson's disease, are spreading around the world. These diseases involve complicatedly pathological processes, and so far, there are no effective medicines for therapy. Another type of psychiatric disorder is induced by drugs. The synthetic drugs, represented by methamphetamine, are becoming widely abuse. At present, the cure of methamphetamine dependence is mainly symptomatic treatment, but the recurrence rate is very high. As the common brain impairments in neuropsychiatric disease, it is necessary to summary novel strategies effectively restored brain function. In recent years, carbon nanotubes have attracted the attention due to their unique properties in the field of translational medicine. Recently, new advances reported that carbon nanotubes as a nanomedicine to treat various neuropsychiatric disorders. The purpose of this review is to introduce the therapeutic approaches and mechanisms of carbon nanotubes on neuropsychiatric disorders.

Recent advances in understanding the reinforcing ability and mechanism of carbon nanotubes in ceramic matrix composites

Since the discovery of carbon nanotubes (CNTs), commonly referred to as ultimate reinforcement, the main purpose for fabricating CNT–ceramic matrix composites has been mainly to improve the fracture toughness and strength of the ceramic matrix materials. However, there have been many studies reporting marginal improvements or even the degradation of mechanical properties. On the other hand, those studies claiming noticeable toughening measured using indentation, which is an indirect/unreliable characterization method, have not demonstrated the responsible mechanisms applicable to the nanoscale, flexible CNTs; instead, those studies proposed those classical methods applicable to microscale fiber/whisker reinforced ceramics without showing any convincing evidence of load transfer to the CNTs. Therefore, the ability of CNTs to directly improve the macroscopic mechanical properties of structural ceramics has been strongly questioned and debated in the last ten years. In order to properly discuss the reinforcing ability (and possible mechanisms) of CNTs in a ceramic host material, there are three fundamental questions to our knowledge at both the nanoscale and macroscale levels that need to be addressed: (1) does the intrinsic load-bearing ability of CNTs change when embedded in a ceramic host matrix?; (2) when there is an intimate atomic-level interface without any chemical reaction with the matrix, could one expect any load transfer to the CNTs along with effective load bearing by them during crack propagation?; and (3) considering their nanometer-scale dimensions, flexibility and radial softness, are the CNTs able to improve the mechanical properties of the host ceramic matrix at the macroscale when individually, intimately and uniformly dispersed? If so, how? Also, what is the effect of CNT concentration in such a defect-free composite system? Here, we briefly review the recent studies addressing the above fundamental questions. In particular, we discuss the new reinforcing mechanism at the nanoscale responsible for unprecedented, simultaneous mechanical improvements and highlight the scalable processing method enabling the fabrication of defect-free CNT-concentered ceramics and CNT-graded composites with unprecedented properties. Finally, possible future directions will be briefly presented.

Experimental Study of Damage Mechanism of Carbon Nanotube as Nanocomponent of Electronic Devices Under High Current Density

The damage mechanisms of carbon nanotubes are considered to be the oxidation by Joule heating and migration of carbon atoms by high-density electron flows. In this study, a high current density testing system was designed and applied to multiwalled carbon nanotubes (MWCNTs) collected at the gap between thin-film electrodes. Local evaporation of carbon atoms occurred on the cathode side of the MWCNTs under relatively low current density conditions, and the center area of the MWCNTs under high current density conditions. The damaged morphology could be explained by considering both Joule heating and electromigration behavior of MWCNTs.

Theoretic optimisation of microfluidic and magnetic self‐assembly of carbon nanotubes

In this reported work, a magnetic and fluidic analysis has been performed to theoretically analyse the self-assembly mechanism of carbon nanotubes (CNTs) and to characterise the assembling environments for the high-density integration of individual CNTs. In previous work by the present author, the residual iron (Fe) catalyst at one end of a CNT was magnetically captured and the captured CNT was aligned along the flow direction by fluid drag force, leading to precise individual integration of CNTs between electrodes. To advance the previous work and technique, theoretic characterisations were executed to optimise the assembling conditions which increased the number of attached CNTs with a high density of integration. For calculating the fluidic force applied to the individual CNT, the slender-body theory was adopted by modelling the CNT as a slender object. Moreover, magnetic simulation was performed to calculate the magnetic force applied to the residual Fe catalysis at one end of the CNT. These simulation results were combined and used to determine the critical height where the fluidic force was equal to the magnetic force. On the basis of these analyses, the array of CNT-assembled electrodes was implemented with a 2 m interval, whereas only a single CNT-assembled electrode was achieved in the previous work. A result of the present work, enables dense integration of the CNT circuit as a highly functional nanodevice.

Computational study on bonding of carbon nanotubes onto metallic substrates

Mechanism of carbon nanotube bonding onto the metal substrate is investigated using molecular dynamics in this study. Different temperatures and types of the metal atoms to the carbon nanotube surface are considered. It is shown that there is close relationship between surface melting and contact length of the bonding. The melting firstly occurs on the surface of the metal and the contact length increases with the melting propagating from the open surface to the interior of the metal as the temperature rising. In addition, the wetting property of the metal atoms plays an important role during the bonding of the carbon nanotube onto the metal. The carbon nanotube will be easily welded onto the metal with excellent wetting property. The results indicate that the bonding process of the carbon nanotube onto the metal can be controlled by two ways. First, concentrating energy on the metal surface to enhance the surface melting. Second, selecting the metal with excellent wetting property or effective method is utilized to enhance the wetting property of the metal atoms to the carbon nanotube surface.

On the van der Waals interaction of carbon nanotubes as electromechanical nanothermometers

Electromechanical carbon nanothermometers are devices that work based on the interactions and relative motions of double-walled carbon nanotubes (DWCNTs). In this paper, the mechanics of carbon nanotubes (CNTs) constituting two well-known configurations for nanothermometer, namely shuttle configuration and telescope configuration are fully investigated. Lennard-Jones (LJ) potential function along with the continuum approximation is employed to investigate van derWaals (vdW) interactions between the interacting entities. Accordingly, semi-analytical expressions in terms of single integrals are obtained for vdW interactions. Acceptance condition and suction energy are studied for the shuttle configuration. In addition, a universal potential energy is presented for the shuttle configuration consisting of two finite CNTs. Also, for the telescope configuration, extensive studies are performed on the distributions of potential energy and interaction force for various radii and lengths of CNTs. It is found that these geometrical parameters have a considerable effect on the potential energy.

Role of Electric Field on Sensing Mechanism of Carbon Nanotube Based Ammonia Gas Sensor

Multi-walled carbon nanotubes (MWCNTs) grown on SiO2/Si substrate, were investigated as resistive sensors for Ammonia (NH3 gas detection upto 100 ppm concentration in the presence of dry carrier gas N2. Sensitivity and recovery time are serious problem in case of NH3 sensing and these are related to the interaction mechanism between NH3 molecules and CNTs surface and the defect level of CNT. It was found that the chemisorption of NH3 molecules on the side-wall defect sites of CNTs enhances the sensitivity along with a poor recovery. We have demonstrated by an effective approach to get improved sensitivity and fast recovery. Best sensor performance and desorption of NH3 were done by tuning the DC excitation electric field applied across the sensor electrodes. Such stimulation process provides sufficient energy to the electrons to jump through defective sites due to Poole-Frenkel effect resulting in the desorption of gas.

Field Emission Model of CNT Based Ionization Gas Sensor

A new model to study the gas detection mechanism of carbon nanotube (CNT) based ionization gas sensor has been developed. The model incorporates the effect of electron field emission due to the presence of CNT. The model is then embedded in the standard Particle-In-Cell / Monte-Carlo-Collision (PIC-MCC) codes. This enhanced PIC-MCC codes serve as a tool to optimize CNT based ionization gas sensor. The functionality of the new model is validated by running simulations of DC discharges in argon and comparing the results with published experimental and simulated works. From the simulation, one order of magnitude decrease in the breakdown voltages and three orders of magnitude faster response time was observed.

Oscillatory characteristics of carbon nanotubes inside carbon nanotube bundles

This article presents a comprehensive study on the mechanics of carbon nanotubes (CNTs) oscillating in CNT bundles. Using the continuum approximation along with Lennard-Jones (LJ) potential function, new semi-analytical expressions in terms of double integrals are presented to evaluate van der Waals (vdW) potential energy and interaction force upon which the equation of motion is directly solved. The obtained potential expression enables one to arrive at a new semi-analytical formula for the exact evaluation of oscillation frequency. Also, an algebraic frequency formula is extracted on the basis of the simplifying assumption of constant vdW force. Based on the present expressions, a thorough study on various aspects of operating frequencies under different system parameters is given, which permits fresh insight into the problem. The strong dependence of oscillation frequency on system parameters, such as the extrusion distance and initial velocity of the core as initial conditions for the motion is indicated. Interestingly, a specific initial velocity is found at which the oscillation frequency is independent of the core length. In addition, a relation between this specific initial velocity and the escape velocity is disclosed.

In situ characterization of structural changes and the fraction of aligned carbon nanotube networks produced by stretching

The mechanism of carbon nanotube (CNT) alignment during stretching was examined by the in situ characterization of carbon nanotube networks (CNTNs) under tensile strains using X-ray and Raman scattering techniques. A method of quantifying the inhomogeneous alignment of macroscopic CNTNs is explored based on bulk property measurements of their electrical anisotropy and X-ray diffraction diagrams. The results show that the process of stretch-induced alignment of CNTNs included straightening the waviness of the long nanotube ropes, as well as the self-assembling and denser packing of the nanotubes. For samples at a strain of 40%, the fraction of aligned nanotubes was as high as 0.85. The aligned fraction of CNTs serves as an important parameter for the quality control of the alignment process and numerical simulations of structure–property relationships of CNTNs and their composites.

Experimental Investigation of Adhesive Behavior in Carbon Nanotube Based Gecko Tape

To elucidate the adhesion mechanism of carbon nanotubes (CNTs) designed to mimic natural contact surfaces in the gecko, their contact behavior was investigated using a scanning electron microscope (SEM) equipped with manipulation stages. The normal adhesion of CNTs increases in direct relation with a preload, which is true also for gecko setae. The CNT shear strength increases concomitantly with increasing CNT length, indicating that the length is an important factor enabling conformation to the surface roughness and enabling generation of a strong contact by side contact. Results revealed the CNT configuration and surface physics as important factors for synthetic gecko adhesion.

On the Unzipping Mechanisms of Carbon Nanotubes: Insights from Reactive Molecular Dynamics Simulations

ABSTRACTUnzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for the controlled and large-scale production of graphene nanoribbons (GNR). These structures are considered of great importance for the development of nanoelectronics because of its dimensions and intrinsic nonzero band gap value. Despite many years of investigations some details on the dynamics of the CNT fracture/unzipping processes remain unclear. In this work we have investigated some of these process through molecular dynamics simulations using reactive force fields (ReaxFF), as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. We considered multi-walled CNTs of different dimensions and chiralities and under induced mechanical stretching. Our preliminary results show that the unzipping mechanisms are highly dependent on CNT chirality. Well-defined and distinct fracture patterns were observed for the different chiralities. Armchair CNTs favor the creation of GNRs with well-defined armchair edges, while zigzag and chiral ones produce GNRs with less defined and defective edges.

탄소나노튜브로 보강된 탄소섬유복합재의 제조공정과 층간전단강도

Carbon nanotubes (CNTs) have been widely investigated as reinforcements of CNT/polymer nanocomposites to enhance mechanical and electrical properties of polymer matrices since their discovery in the early 90`s. Furthermore, the number of studies about incorporating CNTs into carbon fiber reinforced plastics (CFRP) to reinforce their polymer matrices is increasing recently. In this study, single-walled carbon nanotubes (SWNT) were dispersed in epoxy with 0.2 wt.% and 0.5 wt.%. Then, the SWNT/epoxy mixtures were processed to carbon fiber composites by a vacuum assisted resin transfer molding (VARTM) and a wet lay up method. The processed composite samples were tested for the interlaminar shear strength (ILSS). The relationship between the interlaminar shear strengths and processing, and the reinforcement mechanism of carbon nanotubes were investigated. CNT/epoxy nanocomposite specimens showed the increased tensile properties. However, the ILSS of carbon fiber composites was not enhanced by reinforcing the matrix with CNTs because of processing issues caused by increased viscosity of the matrix due to addition of CNTs particularly for a VARTM method.

Effect Mechanisms of Carbon Nanotubes on the Supercritical Foaming Behaviors and Mechanical Performance of Carbon Foam

Carbon nanotubes(CNTs) were dispersed uniformly into mesophase pitch(MP) by the co-dispersion of ultrasonic and magnetic force stirring.Effects of CNTs on the supercritical foaming behaviors and mechanical performance of carbon foams were investigated.The results indicate that cell nuclei will form firstly at the CNT/MP interface in the supercritical foaming process,and then diffuse,aggregate,expanse and foam.CNTs can improve the homogenicity of pore structure due to the uniform dispersed CNT/MP interface.When MP is mixed with 3.5wt% CNTs,the compressive strength of graphitized foam increases from 3.2MPa to 4.7 MPa.In the graphitization proc-ess,the heat-stress different of carbon will decrease due to the high thermal conductivity of CNTs,leading to the decrease of the amount of microcracks.Meanwhile,the one-dimensional structure of CNTs reinforces the mechani-cal strength of pore walls and ligaments.