Multiwalled Carbon Nanotube Yarns Research Articles

Structural criticality manifested by a polarized ionic layer on a MWCNT yarn surface under mechanical loading

The electrochemical capacitance of an energy harvester based on a multiwalled carbon-nanotube yarn is proportional to the total strain and then rapidly decreases after the strain exceeds a critical value. Rigorous characterization of the nonlinearities in the distortion of the polarized ion layer under an external load is necessary to systematically optimize the performance of energy-harvesting fibers. In this study, we conducted electrochemical experiments and all-atom molecular dynamics simulations to elucidate the dynamics of an ionic polarization layer on a nanotube surface. The in-plane compressive strain exerted under the mechanical tension of the energy harvester induced the radial buckling of the nanotubes, which in turn became the driving force behind the repulsion between adjacent polar ion layers. Therefore, electrochemical stability was guaranteed only under structural stability and the resulting elastic deformation experienced by each nanotube. The proposed mechanism reveals the available mechanical range wherein the polarized ionic layers can substantially function in chemomechanical energy conversion.

Energy Generation through Thermopower Waves using Multi-walled Carbon Nanotube Yarn

Thermopower waves (TWs) are based on a heat transfer process that occurs by combusting chemical fuels with the help of nanomaterials. As a result of this process, electrical energy is generated. Within the scope of this article, studies were carried out to increase the energy production performance of the prepared nano yarns, and catalysts were used to increase the catalytic reaction. For this, in the first step, nano yarn was prepared using multi-walled carbon nanotubes (MWCNT) and polyvinyl alcohol (PVA). The nano yarn fibers were characterized by a scanning electron microscope (SEM). In this test system, formic acid and methanol were used as liquid fuels and potassium nitrate and sucrose were used as solid fuels. In most of the experimental outputs, a minimum of 2 mV, and a maximum of 8 mV electrical energy were obtained. According to the experimental data of the study, it was observed that the used catalyst activates the thermopower-based energy system. This study is a study that will guide future studies on electrical energy-based energy production from derivatives of carbon-based nanomaterial.

In-plane thermal conductivity of multi-walled carbon nanotube yarns under mechanical loading

We present a computational and experimental study of the in-plane heat transfer behavior of a coiled multi-walled carbon nanotube (MWCNT) yarn. The surface temperature of the MWCNT yarn in contact with the high-temperature wire is measured to verify that the thermal conductivity in the radial direction (TCRD) of the coiled MWCNT yarn is high enough to be captured by a thermal imaging camera. A significant change in the TCRD is observed under mechanical strain in particular. Furthermore, the in-plane heat flow of MWCNTs is studied using molecular dynamics simulations. The results confirm that the structural deformation of interstitial spaces between MWCNTs during mechanical loading is a key factor in explaining the heat transfer paths generated by the thermal vibrations of carbon atoms. It is also confirmed that the change in TCRD is reduced owing to an increase in the radial buckling strength of the yarn comprising MWCNTs of a smaller diameter. The TCRD change is crucial in MWCNT-yarn applications such as twistron energy harvesters.

Outer diameter Curvature effects in Multi-Walled carbon nanotubes on the twistron energy harvester

We describe an experimental and computational study of increased electrical double layer capacitance (EDLC) changes and improved harvesting performances in multi-walled carbon nanotube (MWCNT) yarn-based energy harvesters using smaller-diameter MWCNTs. Twisted MWCNT yarn-based energy harvesters convert tensile mechanical energy into electrical energy by utilizing changes in the EDLC on the surface of MWCNTs. The correlation of the variance in EDLC and open circuit voltage (OCV) of the coiled MWCNT yarn was investigated under the mechanical stretch applied to the twistron energy harvester, and both OCV and capacitance increased as the MWCNT diameter decreased. We performed molecular dynamics (MD) simulations to elucidate the mechanisms of the increasing EDLC and OCV of twistron energy harvesters, which were verified by experiment. The computational results elucidate the relationship between the decrease in MWCNT diameters and the increasing number density of interstitial spaces between multi-walled MWCNTs. The decrease in the total surface area of the interstitial spaces is an important factor in the capacitance change of the twistron energy harvester under longitudinal stretching. Such novel findings are a foundation for the development of a twistron harvester with significantly improved energy harvesting performance.

Slippage-inhibiting effect of interfacial cross-linking of nanotubes by defluorination on the mechanical properties of free-standing multi-walled carbon nanotube yarns: Comparison with individual multi-walled carbon nanotubes

Carbon nanotube yarns (CNTYs) spun only by twisting have a low mechanical strength due to the slippage of individual CNTs. This hinders the practical applications of CNTYs. Here, we studied the slippage-inhibiting effect of the interfacial cross-linking of the nanotubes by defluorination on the mechanical properties of free-standing MWCNTYs and compared with the fracture tensile strength of the individual defluorinated MWCNTs. The mechanical properties of defluorinated MWCNTYs increased with increasing annealing temperature, and MWCNTYs defluorinated at 800 °C under a pressure of 76 Pa (p-deF800-MWCNTYs) exhibited an average specific fracture strength of 0.69 N/tex and an average specific fracture stiffness of 103.2 N/tex, with high flexibility. As the fracture tensile strength of individual defluorinated MWCNTs was low, the high strength of the p-deF800-MWCNTYs was attributed to the cross-linking of the active carbon atoms in the outer nanotubes with those of the adjacent nanotubes through sp2C and sp3C bonds, which led to the transfer of load to the yarns. Thus, the results of our study highlight the importance of good balance between the defects of CNTs and cross-linking between CNTs.

Study on the mechanical and electrical properties of twisted CNT yarns fabricated from CNTs with various diameters

The mechanical and electrical properties of multiwalled carbon nanotube (MWCNT) yarns with a wide variety of MWCNT diameters were studied to understand the relationship between the microscopic structures of MWCNTs and the load/charge transport properties of macroscopic MWCNT assemblies. The MWCNT diameters were varied from 14.6 nm to 41.6 nm by varying the amount of catalyst loaded in the synthesis by the chloride-mediated chemical vapor deposition method. We found a drastic change in the tensile behavior of twisted yarns from nonlinear deformation to elastic manner associated with the increases in the tensile strength, Young’s modulus, and electrical conductivity of the twisted MWCNT yarns for smaller-diameter MWCNTs. These improvements are due to the increase in the surface area of MWCNTs in the yarn structure. We also carried out microscopic direct tensile tests on the MWCNTs in a scanning electron microscope to investigate the tensile properties of the individual MWCNTs. The in situ experiments revealed that the obtained high value of the Young’s modulus of the yarn originated from that of the individual MWCNTs.

Biomolecule based fiber supercapacitor for implantable device

With the growing demand for electronic medical devices for healthcare applications, we studied an implantable supercapacitor that can operate in an implantable electronic device. Here, we report a flexible implantable fiber supercapacitor for an in vivo energy storage device. The fiber supercapacitor has a high flexibility and a high potential to be applied in an implant device because the fiber can be implanted in the blood vessel and the wound can be stitched with the fiber-like suture. The fiber electrodes were fabricated in a biscrolling process that trapped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/ferritin nanoclusters within multiwalled carbon nanotube (MWNT) sheets that provide mechanical strength and electrical conductivity. In addition, the supercapacitor is biocompatible because the MWNT sheets are coated with biocompatible materials such as PEDOT:PSS and ferritin. The areal capacitance of the PEDOT:PSS/ferritin/MWNT fiber supercapacitor was 32.9 mF/cm2 in a phosphate buffered saline solution, and the areal energy density was 0.82 μWh/cm2; these values are 52 times higher than that of the guest-free MWNT yarn. The supercapacitor operated well in a mouse and exhibited excellent biocompatibility; the capacitance was maintained above 90% in the mouse after eight days.

Magnetic torsional actuation of carbon nanotube yarn artificial muscle.

Magnetically driven torsional actuation of a multiwalled carbon nanotube (MWNT) yarn was realized by first biscrolling NdFeB magnetic particles into helical yarn corridors to make a magnetic MWNT yarn. The actuating device comprised a pristineMWNT yarn that was connected to the magnetic MWNT yarn, with a paddle attached between these yarns. The application of a magnetic field reversibly drove torsional actuation of up to 80° within ∼0.67 seconds. This magnetic actuator was remotely powered, and its actuation stroke was the same when the muscle array was at 20 °C and at −100 °C.

Coiled nanotube yarn generates electricity

A new material could help harvest the energy from ocean waves or even human movement. The material, a carbon nanotube yarn, generates electricity when stretched or twisted. An international team, led by Seon Jeong Kim of Hanyang University and Ray H. Baughman of the University of Texas, Dallas, made the materials by twisting multiwalled carbon nanotube yarns until they became tightly coiled. Stretching decreases the ability of the yarn to store electrical charge, which increases its voltage, leading to an electrical current (Science 2017, DOI: 10.1126/science.aam8771). The scientists also coated the yarns with a gel electrolyte and then interwove the fibers with fabric in a shirt, allowing the researchers to monitor a person’s breathing from the current generated as the person’s chest expanded and contracted. According to Baughman, the team’s “twistrons” generate more than 100 times as much power as similar electricity-generating materials that can be woven into fabric. The

Probe Sensor Using Nanostructured Multi-Walled Carbon Nanotube Yarn for Selective and Sensitive Detection of Dopamine.

The demands for electrochemical sensor materials with high strength and durability in physiological conditions continue to grow and novel approaches are being enabled by the advent of new electromaterials and novel fabrication technologies. Herein, we demonstrate a probe-style electrochemical sensor using highly flexible and conductive multi-walled carbon nanotubes (MWNT) yarns. The MWNT yarn-based sensors can be fabricated onto micro Pt-wire with a controlled diameter varying from 100 to 300 µm, and then further modified with Nafion via a dip-coating approach. The fabricated micro-sized sensors were characterized by electron microscopy, Raman, FTIR, electrical, and electrochemical measurements. For the first time, the MWNT/Nafion yarn-based probe sensors have been assembled and assessed for high-performance dopamine sensing, showing a significant improvement in both sensitivity and selectivity in dopamine detection in presence of ascorbic acid and uric acid. It offers the potential to be further developed as implantable probe sensors.

Field Emission from Lateral Multiwalled Carbon Nanotube Yarn Emitters

A field emission from a lateral emitter made by a multiwalled carbon nanotube (MWCNT) yarn was investigated. The lateral emitter showed an excellent field emission performance with a low turn-on electric field of 1.13 V/um at an emission current of 1 uA, high emission current of 0.2 mA at an applied voltage of 700 V, and long-time emission stability for over 20 h without any significant current decay under an initial emission current of about 0.10 mA. The lateral emitter also demonstrated a uniform line emission pattern. It is suggested that the field emission occurs from the outmost MWCNTs which are protruding out from the yarn surface.

Probe Sensor Using Nano-Structured Multi Walled Carbon Nanotube Yarn for Direct Selective and Sensitive Dopamine Detection

Dopamine (DA) is an important neurotransmitter in the central nervous system. Insufficient or excessive level of DA related to Schizophrenia and Parkinson diseases[ 1 ]. Therefore, early detection of DA represents a hot topic in biosensing field. Recently, electrochemical bio-sensor (ECB) based on carbon material has received a great attention as an inexpensive and simple analytical method with remarkable detection sensitivity for neurochemicals detection[ 1 ]. Therefore, ECB’s fabrication and structure have attracted researcher’s efforts to obtain higher sensitivity and highly selectivity simultaneously. Traditional film-based ECB have shown some disadvantages such as large sizes, random structure, time consuming for film fabrication and low efficient[ 2 ]. As a result, a new biosensor based on nano carbon material designed in a probe style has been considered as an excellent candidate for sensing stimulation as they have aligned and packed structure which provides a bridge for electrons transfer and that enhances electrical conductivity, also, fibres can be fabricated in small sizes which gives the ability to be implanted with low tissue damages, in addition, simplicity of handling and ability to be grafted with different materials[ 3 ]. The aim of this study is to develop hybrid multi wall carbon nanotube yarn due to fascinating properties for CNTs (i.e. high surface area, fast electron kinetics transfer, reduced electrode fouling, wide electrochemical potential window, bio-compatibility, grafting ability, and increased sensitivity and selectivity (high efficient)). In a typical bio-sensing system, DA has been used with ascorbic acid (AA) and uric acid (UA) (as coexistence compounds[ 4 ]) for investigating both sensitivity and selectivity of the prepared CNT yarn viacyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. CV and DPV results have demonstrated selective and sensitive detection of DA in a sea of AA and UA with the potential to be a promising probe bio-sensor for real-time measurement.

Design of a carbon-nanotube yarn field emitter for micro-focus X-ray generation

The field-emission (F-E) characteristics of multi-walled carbon-nanotube (MWCNT) yarn and its contribution to X-ray generation have been investigated in the current work. A dry spinning method was used to fabricateMWCNT yarn from superMWCNTs that had been fabricated by using microwave plasma-enhanced chemical vapor deposition (MW-PECVD). The F-E behavior of the MWCNT yarn followed the Fowler-Nordheim model. Compared to a MWCNT, the MWCNT yarn displayed a significant F-E capability in both the diode and the triode X-ray generation structures. The low-voltage F-E of the MWCNT yarn can be attributed to the field-enhancing effect of the yarn due to its shape and to the contribution of the high-aspect-ratio nanotubes that protrude from the sides of the yarn. The effect of filters on the development of X-ray images has also been demonstrated. The amount of exposure of the samples to X-rays was also manipulated. Results of this study indicate that the MWCNT yarn may be a good candidate for use in low-voltage F-E applications for X-ray imaging.

Temperature-Responsive Tensile Actuator Based on Multi-walled Carbon Nanotube Yarn.

Many temperature indicators or sensors show color changes for materials used in food and medical fields. However, they are not helpful for a color-blind person or children who lack judgment. In this paper, we introduce simply fabricated and more useful low-temperature indicator (~30 °C) for devices that actuates using paraffin-infiltrated multi-walled carbon nanotube (MWCNT) coiled yarn. The density difference of MWCNT yarn provides large strain (~330 %) when heat causes the melted polymer to move. Furthermore, the MWCNT yarn decreases the melting point of paraffin. These properties allow control of the actuating temperature. In addition, mechanical strength was enhanced by MWCNT than previously reported temperature-responsive actuators based on shape memory polymers. This simply fabricated temperature indicator can be applied in latching devices for medical and biological fields.Electronic supplementary materialThe online version of this article (doi:10.1007/s40820-016-0084-6) contains supplementary material, which is available to authorized users.

Highly Conductive Carbon Nanotube‐Graphene Hybrid Yarn

An efficient procedure for the fabrication of highly conductive carbon nanotube/graphene hybrid yarns has been developed. To start, arrays of vertically aligned multi‐walled carbon nanotubes (MWNT) are converted into indefinitely long MWNT sheets by drawing. Graphene flakes are then deposited onto the MWNT sheets by electrospinning to form a composite structure that is transformed into yarn filaments by twisting. The process is scalable for yarn fabrication on an industrial scale. Prepared materials are characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It is found that the electrical conductivity of the composite MWNT‐graphene yarns is over 900 S/cm. This value is 400% and 1250% higher than electrical conductivity of pristine MWNT yarns or graphene paper, respectively. The increase in conductivity is asssociated with the increase of the density of states near the Fermi level by a factor of 100 and a decrease in the hopping distance by an order of magnitude induced by grapene flakes. It is found also that the MWNT‐graphene yarn has a strong electrochemical response with specific capacitance in excess of 111 Fg−1. This value is 425% higher than the capacitance of pristine MWNT yarn. Such substantial improvements of key properties of the hybrid material can be associated with the synergy of MWNT and graphene layers in the yarn structure. Prepared hybrid yarns can benefit such applications as high‐performance supercapacitors, batteries, high current capable cables, and artificial muscles.

Primary liver cells cultured on carbon nanotube substrates for liver tissue engineering and drug discovery applications.

Here, we explore the use of two- and three-dimensional scaffolds of multiwalled-carbon nanotubes (MWNTs) for hepatocyte cell culture. Our objective is to study the use of these scaffolds in liver tissue engineering and drug discovery. In our experiments, primary rat hepatocytes, the parenchymal (main functional) cell type in the liver, were cultured on aligned nanogrooved MWNT sheets, MWNT yarns, or standard 2-dimensional culture conditions as a control. We find comparable cell viability between all three culture conditions but enhanced production of the hepatocyte-specific marker albumin for cells cultured on MWNTs. The basal activity of two clinically relevant cytochrome P450 enzymes, CYP1A2 and CYP3A4, are similar on all substrates, but we find enhanced induction of CYP1A2 for cells on the MWNT sheets. Our data thus supports the use of these substrates for applications including tissue engineering and enhancing liver-specific functions, as well as in in vitro model systems with enhanced predictive capability in drug discovery and development.

Thermal annealing effects on multi-walled carbon nanotube yarns probed by Raman spectroscopy

The realized mechanical properties of CNT macrostructures such as webs and yarns remain significantly lower than those of the individual CNTs. Structural changes induced by thermal annealing under inert atmosphere were assessed using Raman spectroscopy. Annealing above 1000°C resulted in a marked decrease in the D/G ratio which can be attributed to an increase in the crystallite size or the distance between defects. The band component parameters obtained by spectral deconvolution reveal that the D band peak maximum shifts to slightly higher energy with increased annealing temperature. In contrast, the energy of the G band did not change. The full widths at half height (FWHH) of the D and G bands are seen to decrease with increasing annealing temperature. The tensile properties of the yarns have been investigated and it was found that the yarn tenacity did not improve with these structural changes. The effect of impurities in the annealing system such as oxygen, adsorbed water or organic surface contamination was also investigated.

Preparation and characterization of hybrid conducting polymer–carbon nanotube yarn

Hybrid polypyrrole (PPy)-multi walled carbon nanotube (MWNT) yarns were obtained by chemical and electrochemical polymerization of pyrrole on the surface and within the porous interior of twisted MWNT yarns. The material was characterized by scanning electron microscopy, electrochemical, mechanical and electrical measurements. It was found that the hybrid PPy-MWNT yarns possessed significantly higher mechanical strength (over 740 MPa) and Young's modulus (over 54 GPa) than the pristine MWNT yarn. The hybrid yarns also exhibited substantially higher electrical conductivity (over 235 S cm(-1)) and their specific capacitance was found to be in excess of 60 F g(-1). Measurements of temperature dependence of electrical conductivity revealed semiconducting behaviour, with a large increase of band gap near 100 K. The collected low temperature data are in good agreement with a three-dimensional variable range hopping model (3D-VRH). The improved durability of the yarns is important for electrical applications. The composite yarns can be produced in commercial quantities and used for applications where the electrical conductivity and good mechanical properties are of primary importance.

Detection of hydrogen using multi-walled carbon-nanotube yarns coated with nanocrystalline Pd and Pd/Pt layered structures

Robust and flexible chemiresistors fabricated from multi-walled carbon nanotube yarns decorated with nanocrystalline Pd (Pd-MWCNTs) were used to detect hydrogen from 20parts per million (ppm) and above in nitrogen at room temperature. With the chemiresistors fabricated by introducing a layer of Pt on Pd (Pt–Pd-MWCNTs), the lower limit of detection (LLD) was found to extend down to 5ppm. It is shown that the observed response to hydrogen is a resultant of two mechanisms, namely, the formation of the hydrides of Pd and nanoscopic gap closing which leads to opposing changes in resistance in the composite yarns. A deviation from the Sievert’s law is observed at concentrations above 100ppm and is attributed to the presence of these competing mechanisms. In air, the LLD was found to be 2000ppm for the Pd-MWCNT chemiresistor and 400ppm for the Pt–Pd-MWCNT chemiresistor. The Pt–Pd-MWCNT chemiresistor showed excellent response and recovery characteristics in air. For Pd-MWCNT chemiresistor, the nanoscopic gap-closing mechanism became prominent at concentrations below ∼1000ppm and allowed the detection of hydrogen down to 200ppm in air using negative changes in resistance.

Thermal and electrical conductivity of array-spun multi-walled carbon nanotube yarns

The electrical resistivity of CNT yarns of diameters 10–34 μm, spun from multi-walled carbon nanotube arrays, have been determined from 2 to 300 K in magnetic fields up to 9 T. The magnetoresistance is large and negative at low temperatures. The thermal conductivity also has been determined, by parallel thermal conductance, from 5 to 300 K. The room-temperature thermal conductivity of the 10 μm yarn is (60 ± 20) W m −1 K −1, the highest measured result for a CNT yarn to date. The thermal and electrical conductivities both decrease with increasing yarn diameter, which is attributed to structural differences that vary with the yarn diameter.