Coiled Carbon Nanotubes Research Articles

Twist-Stabilized, Coiled Carbon Nanotube Yarns with Enhanced Capacitance.

Coil-structured carbon nanotube (CNT) yarns have recently attracted considerable attention. However, structural instability due to heavy twist insertion, and inherent hydrophobicity restrict its wider application. We report a twist-stable and hydrophilic coiled CNT yarn produced by the facile electrochemical oxidation (ECO) method. The ECO-treated coiled CNT yarn is prepared by applying low potentiostatic voltages (3.0-4.5 V vs Ag/AgCl) between the coiled CNT yarn and a counter electrode immersed in an electrolyte for 10-30 s. Notably, a large volume expansion of the coiled CNT yarns prepared by electrochemical charge injection produces morphological changes, such as surface microbuckling and large reductions in the yarn bias angle and diameter, resulting in the twist-stability of the dried ECO-treated coiled CNT yarns with increased yarn density. The resulting yarns are well functionalized with oxygen-containing groups; they exhibit extrinsic hydrophilicity and significantly improved capacitance (approximately 17-fold). We quantitatively explain the origin of the capacitance improvement using theoretical simulations and experimental observations. Stretchable supercapacitors fabricated with the ECO-treated coiled CNT yarns show high capacitance (12.48 mF/cm and 172.93 mF/cm2, respectively) and great stretchability (80%). Moreover, the ECO-treated coiled CNT yarns are strong enough to be woven into a mask as wearable supercapacitors.

Conical coiled carbon nanotubes with highly controllable mechanical properties

Nanostructures composed of carbon nanotubes (CNTs) show great diversity in geometrical morphology, leading to effective augmentability in their unique properties and practical technological applications. In the present study, for the first time, highly controllable mechanical properties of three-dimensional (3D) conical coiled CNTs (CCNTs) structure, which are assembled from straight CNTs in a form of nanocone, were reported, resourcing to molecular dynamics simulations. As a result of the conical morphology, tensile mechanical behaviors of conical CCNTs are dominated by van der Waals (vdW) forces and covalent forces. Tensile stiffness and the way of phase transformation are controlled by geometrical characteristics in vdW forces’ domination section. Stretchability - that is situated in section of covalent forces’ domination - can vastly range from 250% to 23000%, depending on radius of each coil. More interestingly, originating from the hollow conical geometry, conical CCNTs can be highly compressed, as well as show different behaviors between cyclic compression and tension. This work provides new insights into mechanics of carbon nanostructures, and indicates that conical CCNTs are good potential candidates for mechanical robust nanodevices.

Modeling and Analysis of the Geometry‐Dependent Mechanical and Thermal Properties of Coiled Carbon Nanotubes

Coiled carbon nanotubes (CNTs) have attracted much attention thanks to their unique geometrical structure along with outstanding mechanical and thermal properties. However, the relationship between the geometrical parameters and mechanical and thermal properties of coiled CNTs remains largely unexplored. Herein, coiled CNTs are constructed with various geometries by phase‐field crystal (PFC) modeling and their mechanical and thermal properties are investigated by molecular dynamics (MD) simulations. It is found that the effect of geometrical parameters of coiled CNTs on the Young's modulus can be well captured by analytical formulas derived from the mechanical spring tube model. These extensive MD simulations show that the Young's modulus of coiled CNTs increases with an increase in coil pitch l and CNT radius r, but decreases with an increase in coil radius R. Furthermore, using the nonequilibrium MD (NEMD) method, it is found that the thermal conductivity of coiled CNTs decreases with an increase in coil radius R, but increases slightly with an increase of coil pitch l and CNT radius r. Valuable insights into the mechanical and thermal properties of coiled CNTs are provided and the findings here may serve as useful guidelines for the design of coiled CNTs for device applications.

On The Free Vibration of Doubly Clamped Single-Walled Coiled Carbon Nanotubes: A Novel Size Dependent Continuum Model

In this paper, the size dependent vibration behavior of doubly clamped single-walled coiled carbon nanotubes (CCNTs) is investigated using nonlocal helical beam model. This model is based on Washizu’s beam theory so that all displacement components of CCNT in the equations of motion are defined at the centroidal principal axis and transverse shear deformations are considered. After deriving the nonlocal free vibration equations, they are solved by the generalized differential quadrature method (GDQM). Then, the natural frequencies and corresponding mode shapes are determined for the clamped-clamped boundary conditions (BCs). After that, a parametric study on the effect of different parameters, including the helix cylinder to the tube diameters ratio , the number of pitches, the helix pitch angle, and the nonlocal parameter on the natural frequencies is conducted. It is worth noting that the results of the proposed method would be useful in the practical applications of CCNTs such as using in nanoelectromechanical systems.

The past, the present and the future of nanotechnologies

Abstract Artists from the time of Mesopotamia or Egypt and in the Middle Ages astonished us with various coloured Stained-glass windows, prepared with the help of metal nanoparticles. The paper will deal with zeolites, nanoparticles and carbon nanotubes. The latter will be developed more extensively, because we have founded the Nanocyl company, selling carbon nanotubes and it has become the best European company. One carbon nanotube is 100,000 times thinner than a human hair, it is very light – twice as light as aluminium –, its mechanical resistance is much higher than that of steel and it conducts electricity better than metal conductors. The use of carbon nanotubes is very important in nanotechnology. For example, with the help of coiled carbon nanotubes, the weight of a single nanoparticle can be measured, it is equal to one femtogram (10−15 gram). Carbon nanotubes are used in car spray painting to cancel the build-up of static electricity. With the help of carbon nanotubes, it is possible to decrease the velocity of flame propagation, when they are included in composite materials. Carbon nanotubes are also very good as sensors for toxic gases. Their uses will take up the most part of this paper. The future of nanotechnology will be illustrated by nanomachines, by the lift between the Earth and the Moon, and by graphene (one single sheet of graphite). The use of carbon nanotubes will be evoked in waste water cleaning, in the production of drinking water from seawater.

Optimizing Structural and Mechanical Properties of Coiled Carbon Nanotubes with NSGA-II and Reactive Molecular Dynamics Simulation

Coiled Carbon Nanotubes (CCNTs) are increasingly set to become a vital factor in the new generation of nanodevices and energy-absorbing materials due to their outstanding properties. In the following work, the multi-objective optimization of CCNTs is applied regarding their mechanical performances. Apart from finding the best trade-off between conflicting mechanical properties (e.g. yield stress and yield strain), the optimization enables us to find the astonishing CCNTs concerning their stretchability. To the best of our knowledge, these structures have not been recognized before, both experimentally and computationally. Several highly accurate analytical equations are derived by insights from the findings of multi-objective optimization and fitting a theoretical model to the results of Molecular Dynamics (MD) simulations. The structures resulted from optimizations are highly resilient because of two distinct deformation mechanisms depending on the dimensions of CCNTs. For small CCNTs, extraordinary extensibility is mainly contributed by buckling and nanohinge-like deformation with maintaining the inner coil diameter, whereas for large CCNTs this is accomplished by the creation of a straight CNT-like structure in the inner-edge of the CCNT with a helical graphene ribbon twisted around it. These findings would shed light on the design of CCNT based mechanical nanodevices.

Self-Powered Carbon Nanotube Yarn for Acceleration Sensor Application

Accelerometers are indispensable for detecting accelerating forces in automotive electronic systems. Although several accelerometers have been developed, they are still unstable for vehicle dynamics' applications in the low-frequency range (0-20 Hz). Here, we report a novel type of accelerometer based on a coiled carbon nanotube (CNT) yarn as a self-powered and low-frequency range-covered acceleration sensor. The proposed sensor is designed in a compact fiber-like structure for practical applications. Open-circuit voltage (OCV) signals are consistently generated during the stretch-and-release process of the coiled CNT yarn by the applied sinusoidal accelerations, and the OCV changes increase linearly with increasing acceleration from 4.84 to 48.37 m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Our accelerometer exhibits excellent dynamic sensing performance in the low-frequency range compared with commercial accelerometers. In an application as a CNT yarn device configured with a mass load, the OCV change is linearly proportional to the applied acceleration. When our accelerometer is attached to a seatbelt in a vehicle, it generates OCV changes from the movement of the body mass underlying a certain acceleration change. Given its excellent sensing performance, the CNT yarn acceleration sensor could further be developed for practical applications, such as seatbelts and car seats with fabric and textile.

Computational Studies on Mechanical Properties of Carbon-based Nanostructures Reinforced Nanocomposites

Computational methods can play a significant role in characterization of the carbon-based nanocomposites by providing simulation results. In this paper, we prepared a brief review of the mechanical properties of carbon nanotubes (CNTs), Graphene, and coiled carbon nanotube (CCNTs) reinforced nanocomposites. Varies simulation studies in mechanical properties of nanocomposites including representative volume element (RVE) approaches using the finite element, multiscale simulation and molecular dynamics studied is mentioned. All the simulation results show a significant role of interphase properties, interphase thickness, elastic properties of nanostructure, various loading conditions and orientation of the nanostructure on mechanical behavior of nanostructure reinforced nanocomposite. Some researchers employed various approaches for comparing simulation results of the effective elastic properties of nanostructures reinforced nanocomposite. Although it is a huge challenge for scientists to make a connection between MD simulations and continuum mechanics, in some researches scientists tried to couple MD and continuum mechanics for more precise results in nanocomposites.

Prediction of mechanical and thermal properties of polymer nanocomposites reinforced by coiled carbon nanotubes for possible application as impact absorbent

This paper presents three-dimensional finite element modeling of nanocomposite materials made from polyethylene polymer reinforced by coiled carbon nanotubes. A method of Python scripting was used to generate representative volume elements in order to determine the mechanical behavior in elastic and plastic zones as well as effective thermal conductivity using the finite element software. The properties of the nanocomposites are investigated by considering the interphase zone between carbon nanofillers and matrix. The effects of different volume fractions, geometrical parameters, and orientations of the nanofillers on the elastic and thermal characteristics of the nanocomposites are studied considering both cohesive interaction and perfect bonding between the fillers and matrix. Moreover, the effects of applying strain on the effective thermal conductivity of the representative volume elements are analyzed. The results reveal that both stress–strain curves and thermal conductivity coefficients of the nanocomposites are following similar trends vs. the changes of the volume fractions as well as the geometries and orientations of the coiled carbon nanotubes. Analysis of the tensile toughness of all samples reveals that it is affected by both stress and the number of fillers in the representative volume element. In addition, thermal-displacement analysis shows that thermal conductivity coefficient decreases by increasing the applied strain on the representative volume element, while the intensity of decrease of the nanocomposite thermal conductivity depends on the volume fraction and interaction of the nanofillers and interphase zone. Finally, crashworthiness analysis of the nanocomposite material proves that they are appropriate candidates for absorbing energy under impact loadings in comparison to metals.

Self-Powered Coiled Carbon-Nanotube Yarn Sensor for Gastric Electronics.

The strong peristaltic contraction of the stomach facilitates mixing and emptying of ingested food, which occurs rhythmically at approximately 3 cycles/min (cpm) in humans. Generally, most patients with gastroparesis show gastric electrical dysrhythmia that is disrupted electrical signals controlling gastric contractions. For treatment of gastric electrical dysrhythmia, in vivo electrical impulses to the stomach via an implanted gastric stimulator have been known to restore these gastric deformations. Nevertheless, improved sensors to monitor gastric contractions are still needed in current gastric stimulators. Recently, we have developed a new technology converting mechanical motion to electrical energy by using stretch-induced capacitance changes of a coiled carbon-nanotube (CNT) yarn. For its potential use as a gastric deformation sensor, the performance of a coiled CNT yarn was evaluated in several biological fluids. For a sinusoidal stretch to 30%, the peak-to-peak open-circuit voltage (OCV) was consistently generated at frequencies below 0.1 Hz. This sinusoidal variation in OCV augmented as the strain increased from 10 to 30%. In an in vitro artificial gastric system, the OCV was approximately linearly proportional to the balloon volume, which can monitor periodic deformations of the balloon at 2, 3, and 4 cpm as shown for human gastric deformations. Moreover, stretchy coiled yarns generate the peak electrical voltage and power when deformed. The present study shows that a self-powered CNT yarn sensor can not only monitor the changes in frequency and amplitude of volumetric change but also generate electrical power by periodic deformations of the balloon. Therefore, it seems possible to automatically deliver accurate electrical impulses according to real-time evaluation of a patient's gastric deformation based on information on the frequency, amplitude, and rate of the OCV from CNT yarn.

High Yielding Fabrication of Magnetically Responsive Coiled Single-Walled Carbon Nanotube under Flow

The curvature in coiled single-walled carbon nanotubes (SWCNTs) rings impacts on their properties relative to straight CNTs, but the availability of such rings is limited. This has been addressed i...

Numerical homogenization of coiled carbon nanotube reinforced shape memory polymer nanocomposites

Shape memory polymers (SMPs) are a group of smart materials that, by applying an external stimulation such as the temperature, retrieve their permanent shape from a temporary one. SMP nanocomposites have been developed to improve the mechanical, thermal, electrical, and magnetic properties of SMPs for potential applications in e.g. medical equipment, sensors, actuators, and drug delivery systems. In this research, SMP is reinforced with Coiled carbon nanotubes (CCNT) due to its geometric properties which let material tolerate higher strains and improve thermomechanical properties of SMP. In this paper, the effect of addition of CCNT on thermomechanical response of SMP under large deformations is numerically investigated. Employing a thermo-visco-hyperelastic constitutive model for SMP, a cubic representative volume element is realized using Monte Carlo algorithm. The effect of inclusion’s geometry (e.g. spring length or aspect ratio, pitch or number of coils of CCNT), volume fraction, as well as their distribution on the thermomechanical properties of SMP/CCNT composite in two stress- and shape recovery processes in different heating rates and pre-strains is studied using Finite Element technique. Results reveal that increasing the volume fraction up to 0.6%, leads to a 15% rise in the effective stress in the nanocomposite. Increasing the spring length of the CCNT, the strain recovery of the nanocomposite increases about 8%. It is shown that when the mechanical loading is parallel to the CCNTs orientation, the stress is about 25% larger than when the loading is perpendicular to the unidirectional CCNTs. But for the strain recovery, the orientation does not play an important role in the strain recovery.

Insight into Geometry-Controlled Mechanical Properties of Spiral Carbon-Based Nanostructures

The spiral structures of carbon-based materials such as coiled carbon nanotube (CCNT) and graphene helicoid have attracted great attention for use in electrical and mechanical nanodevices. There are a couple of main reasons for this attitude such as striking properties and behavioral diversity with regard to the ever-increasing need for miniaturization of devices. In this research, using atomistic simulations, the effects of geometric parameters (e.g., cross-sectional shape, pitch angle, inner diameter, and outer diameter) on the mechanical properties of CCNT are studied. Interestingly, the results show that the mechanical properties (e.g., Young’s modulus, stretchability, etc.) have a heavy reliance on CCNTs’ geometric parameters. The stretching of the CCNT increases with the raising inner radius. Geometric changes affect the various stages that the CCNTs encounter during tensile and compression tests. The different mechanical behavior of various types of CCNTs leads to their diverse applications. Thus, ...

Carbon nanotube and graphene fiber artificial muscles.

Actuator materials capable of producing a rotational or tensile motion are rare and, yet, rotary systems are extensively utilized in mechanical systems like electric motors, pumps, turbines and compressors. Rotating elements of such machines can be rather complex and, therefore, difficult to miniaturize. Rotating action at the microscale, or even nanoscale, would benefit from the direct generation of torsion from an actuator material. Herein we discuss the advantages of using carbon nanotube (CNT) yarns and/or graphene (G) fibers as novel artificial muscles that have the ability to be driven by the electrochemical charging of helically wound multiwall carbon nanotubes or graphene fibers as well as elements in the ambient environment such as moisture to generate such rotational action. The torsional strain, torque, speed and lifetime have been evaluated under various electrochemical conditions to provide insight into the actuation mechanism and performance. Here the most recent advances in artificial muscles based on sheath-run artificial muscles (SRAMs) are reviewed. Finally, the rotating motion of the CNT yarn actuator and the humidity-responsive twisted graphene fibers have been coupled to a mixer for use in a prototype microfluidic system, moisture management and a humidity switch respectively.

FREE-VIBRATION ANALYSIS OF HELICALLY COILED CARBON NANOTUBES CONSIDERING NONLOCAL EFFECT USING CURVED-BEAM ELEMENTS

In this paper a numerical method is proposed to study the free vibration of helically coiled carbon nanotubes considering the nonlocal effects. In this method, the governing equations are obtained using the spatial curved-beam theory based on Washizu's static model. In the equations of motion all displacement functions are defined at the centroid axis and the effects of rotary inertia and transverse shear deformation are included. Moreover, nonlocal theory of elasticity is used in 3D curved-beam modeling. Therefore, six coupled equations including stresses and their second derivatives are obtained which should be combined with six coupled partial differential equations of motion of the system. Finite element method is used to solve the resulting equations, numerically. Curved elements with three nodes and six degrees of freedom per node are used in this method. In order to verify the developed MATLAB code, the results obtained from the proposed method by neglecting nonlocal effects are compared with those of ANSYS simulation. Besides, the effects of different boundary conditions and various parameters including helix radius, pitch, number of turns, and nonlocal parameter are studied.

3D flower-like binary nickel cobalt oxide decorated coiled carbon nanotubes directly grown on nickel nanocones and binder-free hydrothermal carbons for advanced asymmetric supercapacitors

The development of high performance supercapacitors with high energy densities without sacrificing power densities has always been at the leading edge of the emerging field of renewable energy. Herein, the design and fabrication of innovative high performance binder-free electrodes consisting of coiled carbon nanotubes (CNTs) and biomass-derived hydrothermal carbon spheres (HTCSs) as, respectively, positive and negative electrodes is reported. High performance asymmetric supercapacitors (ASCs) were developed using novel 3D core/shell-like binary Ni-Co oxide (NCO) decorated coiled CNTs directly grown on Ni nano-cone arrays (NCAs) and HTCSs directly deposited on NCAs. Novel 3D structures of NCAs were synthesized via a facile and scalable cathodic electrodeposition route and coiled CNTs were directly grown on them by catalytic chemical vapour deposition (CVD) followed by a facile hydrothermal method to integrally decorate the coiled CNTs/NCAs by 3D flower-like NCO. A one-pot hydrothermal method is also used to direct the synthesis of biomass-derived HTCSs on NCAs to fabricate a novel binder-free negative electrode. The ASC based on NCO@coiled CNTs/NCAs//HTCSs/NCAs not only exhibits superior energy density (72.5 W h kg-1) at a reasonable power density of 1.4 kW kg-1, but also represents remarkable cycling durability (retaining almost over 85% of its initial capacitance after 5000 charge-discharge cycles). The fabricated ASC, therefore, seems to be a potent candidate for practical applications in future high performance energy storage systems.

Enhanced supercapacitor performance with binder-free helically coiled carbon nanotube electrodes

Despite their low specific surface area (<500 m2 g−1) relative to that of activated carbon (1500–2000 m2 g−1), carbon nanotubes are attractive as effective electrode materials for supercapacitors. Electrodes comprised of arrays of helically coiled carbon nanotubes (HCNTs) and multi-wall carbon nanotubes (MWCNTs) were prepared and evaluated as novel electrode materials for electric double layer capacitors (EDLCs). While both types of electrodes exhibited a linear dependence on array height and a diffusion limited behavior below the 1 V s−1 scan rate, the electrodes comprised of HCNT arrays exhibited better performance. Freestanding HCNT and MWCNT buckypapers were also prepared and used as electrodes, and the former showed a higher energy density relative to the latter with no loss in its power density and capacity fade. Collectively, this study concludes that HCNTs are well suited as binder-free electrodes that can be augmented with electroactive polymers for improved EDLC performance.

Nanotube and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) composite film for the electrode applications in organic thin-film transistor and dye-sensitized solar cells

In this study, composite films made of coiled carbon nanotubes (CCNTs) and poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) were fabricated with different composition ratios. The variations in film properties (including surface morphology, work function, and electrical conductivity) in accordance with the amount of CCNT dosing were investigated. Subsequently, through HCl-methanol treatment, we achieved a significant enhancement in electrical conductivity with little damage to the CCNT features. The characteristics of CCNT/PEDOT:PSS composite film are generally comparable to those of PEDOT:PSS film, and some of them, such as catalytic activity and work function, are significantly higher. On the basis of these versatile features, the CCNT/PEDOT:PSS composite films exhibit excellent performance as source/drain electrode in organic thin-film transistors and as catalytic counter electrode in dye-sensitized solar cells.

Nanotube-chirality-controlled tensile characteristics in coiled carbon metastructures

Helically coiled metastructures made from carbon nanotubes (CNTs) are a promising material for nanoelectromechanical systems due to the helical morphology and fantastic properties of CNTs. Mechanical properties of coiled CNT-metastructures are subtly tailored by changing the geometrical parameters; however, the role of CNT-chirality on their mechanical performances remains unknown. Here, using atomistic simulations, stretching characteristics of helical coiled CNTs (HCCNTs) having six different CNT-chirality are contrasted. High initial stiffness of HCCNTs comes from stretching of intercoil van der Waals (vdW) forces while low initial stiffness is explained by sliding action between coils. HCCNTs show distinct characteristic sawtooth patterns in the stretching stress-strain curves, originating from vdW-induced phase transformations, buckling instability and nanohinge-like plasticity. The sawtooth behavior resulting from phase transformations is described by a theoretical model. HCCNTs are highly resilient, and exhibit excellent stretchability because of two distinct deformation mechanisms depending on the CNT-chirality. For HCCNTs composed of armchair and zigzag CNT-segments, extraordinary extensibility is mainly contributed by well-distributed nanohinge-like plastic deformation, whereas for those consisting of other chiral ones this is accomplished by superelasticity and nanohinge-like fracture mechanisms. The findings shed new light in mechanical design of coiled-CNTs for practical applications in nanodevices in coupling to their other properties.

High toughness of bio-inspired multistrand coiled carbon nanotube yarn

By impressive mechanical properties, strong and lightweight carbon nanotube yarns and fibers have been reported. Among the mechanical properties of yarn, toughness is considered an important mechanical property for the protection of damage caused by external force. Here, by bio-mimicking the human muscle structure, dramatically increased toughness of carbon nanotube yarn is reported. The bio-inspired tough carbon nanotube (CNT) yarn, which is simultaneously increased in strength and elongation, is made by poly(vinyl) alcohol (PVA) infiltration and coiled multi-strand structure. This bio-inspired tough yarn provides a high-energy absorption (357.2 J/g), which is higher than spider dragline silk (165 J/g), Kevlar (78 J/g), and previous spinnable carbon nanotube yarns. Also, not only demonstrates high tough performance in various conditions such as water and temperature but also shows an ease in shape change by using water. This sewable, wearable, and shape controllable tough yarn has a potential for various applications such as bulletproof material, wearable device, stretchable electrode, aerospace industry, and artificial muscle.