Carbon Nanotube Yarns Research Articles

Superior Conductive, Large Diameter CNT Composite Yarn of Insulative Polymer: Inferences of a Unidirectional Compression‐Stretching Technique

ABSTRACTLarge diameter yet highly conductive Carbon Nanotube (CNT) yarn could have prospective control on high‐tech application field spanning from electronic devices to wearable textiles; although the development of such macroscopic CNTs is extremely challenging. Especially, while fabricating CNT composite yarn with polymer, insulative nature of polymeric materials inherently propagates poor electrical conductivity to CNT yarn. To address this, we have proposed an exciting approach to fabricate large dimension, highly conductive yet flexible CNT‐Thermoplastic Polyurethane (TPU) composite yarn through unidirectional compression‐stretching process. Our technique allowed TPU molecules to be well dispersed into inner and inter‐CNT bundles facilitating well flexibility while the simultaneous functions of pressure and tension allowed more closely packed CNTs network within densified CNT yarn reducing the inherent voids and contact resistance. The consequent yarn possessed high conductivity of 1613 S/cm, attractive mechanical performance (tensile strength 1.3 GPa, Young's modulus 12 GPa, toughness 100.75 MJ/m3), exceptional anti‐abrasive ability (up to 46,350 cycles) endowing its multidirectional adaptability for smart textiles. Moreover, the desirable E‐heating performance together with excellent electrical stability allows successful exploitation of the prepared CNT yarn as stretchable heater. Such amazing integrated characteristics may allow the resultant yarn to replace traditional carbon fiber in various high‐tech arena as well.

Shielding Effectiveness of Textile Woven Fabric with Carbon Nanotubes Yarn

ABSTRACT This study explores the electromagnetic properties of flat textile products enhanced with carbon nanotube (CNT) threads used as the weft. CNT threads, fabricated via dry-spinning, were integrated into fabrics by wrapping them around steel threads to form a solenoid-like structure. To further improve electromagnetic attenuation, the CNT yarn was coated with graphene oxide and silver nanoparticles. The research assessed the impact of these modifications on the fabric’s ability to attenuate alternating electromagnetic fields across a range of frequencies. Results showed enhanced attenuation at 30 MHz and 500 MHz. CNT yarn wrapped around steel threads achieved attenuation efficiencies of 18 dB at 30 MHz and 22 dB at 500 MHz, with a notable 10 dB improvement at 30 MHz over the reference. Fabrics with CNT yarn coated with graphene oxide demonstrated similar performance to the reference fabric at 500 MHz and an 8 dB increase at 30 MHz. Similarly, CNT yarn with silver nanoparticles showed comparable performance at higher frequencies but matched the reference at 30 MHz. These results indicate significant enhancement at lower frequencies, with benefits diminishing at higher. This study underscores the potential of integrating CNTs and metal nanoparticles into textiles to improve electromagnetic shielding, especially across specific frequencies.

Dual-functional carbon nanotube yarn supercapacitor for real-time reactive oxygen species monitoring and sustainable energy supply in implantable device

Smart stents integrate embedded sensors and advanced technology, providing a real-time diagnostic feedback, particularly for detection of thrombotic events. A continuous monitoring reactive oxygen species (ROS) in blood vessels is crucial for cardiovascular disease. The provision of a continuous power supply to sensors integrated within blood vessels is challenging. This study introduces a novel device that combines a sensor and supercapacitor, functioning as a ROS sensor and enabling continuous charging and discharging within blood vessels. This device uses yarn-shaped electrodes integrated with cytochrome c and carbon nanotubes (Cyt.c/CNT). The Cyt.c/CNT electrode exhibits a high specificity to ROS with an sensitivity (49.02 μA μM−1 cm−2), as a real-time biosensor for monitoring of cellular ROS levels in living cells. In addition, it exhibited an energy storage performance of 257.95 mF cm−2 as a supercapacitor and maintained a stable performance during 10,000 repeated cycles in various biofluids. Notably, the integration of the Cyt.c/CNT electrode with an enzymatic biofuel cell enables continuous charging and discharging in a biofluid, making it a promising system for in-vivo applications. This study presents the potential of Cyt.c for ROS sensing as well as its potential as an energy storage system, showing new possibilities for implantable devices for cardiovascular diseases.

Structure-Mechanical Property Relationships in Carbon Nanotube Yarns

Carbon nanotube (CNT) is an innovative material with significant potential for a wide range of applications, including but not limited to the development of lightweight composite materials or superconductors. A single CNT demonstrates an exceptional degree of tensile strength. CNTs are commonly employed in a structure of yarn, wherein several CNT strands are arranged and aligned together. CNT yarns, on the other hand, have a lower tensile strength than individual CNTs due to the different parameters of the yarn. This study aimed to investigate the effect of different structural parameters on the mechanical properties of CNT yarn. Sixty CNT yarn models with different structures were simulated with the molecular dynamic (MD) simulation. The varied parameters are the chirality of the CNTs, CNTs’ inner diameter, number of walls, crosslink density, and yarn twist angle. Tensile strength results from the simulations were compared concerning the varied parameters, and their influence on the nominal tensile strength of the CNT yarn was studied. It was found that the parameters for the CNT yarn that yields a higher tensile strength are the armchair type CNT with a small diameter, a large number of walls, crosslink density higher than approximately 1%, and a low twist angle.

Radial gradient characteristics formed by the interstitial space of MWCNT yarn owing to twisting

The interstitial space of a multiwalled carbon nanotube (MWCNT) yarn is key to creating electric double-layer capacitance for harvesting energy. Despite various fabrication methods for MWCNT yarns, the formation mechanism of the interstitial space inside the yarns is poorly understood. Herein, the twisting process of a cylindrical MWCNT bundle into a yarn was simulated using the mesoscale coarse-grained particle dynamics model. A larger fraction of interstitial space was observed in the sheath region of the yarn, where large-diameter MWCNTs were mainly distributed. Small-diameter MWCNTs first swirled toward the inner core during the twisting process, causing the large-diameter MWCNTs to be sparsely distributed throughout the sheath region. The proposed methodology and its results can be applied to the geometric design of twisted MWCNT bundles to maximize the fraction of the interstitial space therein.

Physical properties of industrially produced carbon nanotube yarns for use in structural nanocomposites

Industrially-produced carbon nanotube (CNT) networks are a promising base for high-performance, continuous CNT nanocomposites, motivating widespread use in research and application development. Floating catalyst chemical vapor deposition (FCCVD) is a scalable, widely-adopted approach for synthesis of CNT networks; however, FCCVD can yield networks with organic impurities which complicate their characterization and processing. Herein, we analyze two varieties of FCCVD-synthesized commercial CNT yarn to explore the effects of densification and purification as they relate to forming infiltrated polymer composites. First, the fluid permeabilities and porosities of neat roving and chemically-stretched CNT yarns (CSYs) are estimated and compared to gas adsorption studies, which suggest high-tenacity CSYs are largely impermeable, leading to dry-core composites when polymer infiltration is attempted. Next, the presence and effects of oxygen-rich amorphous carbon impurities in the CSYs are identified and found to exist at the scale of CNT bundles, wherein the amorphous carbon behaves like a hygroscopic polymer matrix in a composite. Removal of the amorphous carbon phase in a 130%-increase in specific surface area, as quantified by BET analysis, and a statistically significant reduction in tensile properties. We discuss challenges in estimating yarn alignment and crystallinity resulting from these factors, and place our results in context of past studies analyzing intrinsic organic coatings in FCCVD-synthesized CNT networks.

Flexible and air-stable n-type oleylamine/carbon nanotube hybrid yarns for high-performance wearable thermoelectric generators

Wearable thermoelectric generators (TEGs), envisioned to harness the temperature gradient (ΔT) between the human body and the environment into electricity, hold great promise for powering wearable electronics. However, their practical application has been hampered by the scarcity of flexible n-type thermoelectric (TE) materials boasting both high performance and long-term air stability. Here, we introduce a significant advancement by developing an n-type TE material through immersing carbon nanotube yarn (CNTY) into an oleylamine (OAm)/ethanol solution, followed by drying under atmospheric conditions. The resulting OAm/CNTY exhibits a Seebeck coefficient of -80.48 μV K-1, an electrical conductivity of 1353.18 S cm-1 and a power factor of 876.25 μW m-1 K-2, all while exhibiting exceptional mechanical flexibility. Notably, this hybrid yarn maintains stable n-type behavior even after enduring exposure to air for over 370 days, surpassing previous n-type TE materials based on CNT fibers and CNTY. Leveraging this advancement, we construct a prototype wearable TEG by alternately embroidering pristine p-type CNTY and n-type OAm/CNTY into a polyester spacer fabric, electrically connecting them in series using conductive silver paint. The resulting wearable TEG, featuring with 150 p-n couples, yields an output voltage of 705.94 mV and a maximum output power of 44.34 μW at a ΔT of 40 K. This groundbreaking work opens new avenues for the development of high-performance, air-stable, and flexible n-type TE material, ushering in a new era for wearable TEGs.

Advanced doping method for highly conductive CNT fibers with enhanced thermal stability

Abstract Due to the inherent limitations of metals, such as their poor performance at high temperatures caused by thermo-oxidation and expansion, carbon nanotube yarns (CNTFs) have emerged as promising alternatives because of their high electrical conductivity and thermal stability. Doping of CNTFs has been widely studied because it significantly increases electrical conductivity through a simple process. Despite these advantages, doped CNTFs are not suitable for extreme environments, especially high temperatures. This is due to the weak interaction between dopants and CNTFs, along with the low thermal stability of the dopants themselves, leading to dopant decomposition and oxidation at high temperatures. Herein, we present doped CNTFs that are covalently functionalized with a nitrogen compound composed of imide and nitro groups, which are renowned for good thermal stability. The electron-withdrawing effect of this nitrogen compound polarizes the CNTFs to a positive charge, inducing p-type doping effects and enhancing electrical conductivity from 2989 to 4008 S cm−1. The strong covalent bonding between the nitrogen compound and CNTFs, along with the thermal stability of the dopants, ensures that the electrical conductivity of our doped CNTFs is maintained even after annealing at 300 °C for 12 h. Our proposed doped CNTFs offer a guideline for expanding the practical applications of doped CNTFs to a wider range of high-temperature environments.

Reversible Electrochemical Swelling of Straight Carbon Nanotube Yarns for High-Performance Linear Actuation.

Coiled artificial muscle yarns outperform their straight counterparts in contractile strokes. However, challenges persist in the fabrication complexity and the susceptibility of the coiled yarns to becoming stuck by surrounding objects during contraction and recovery. Additionally, torsional stability remains a concern. In this study, it is reported that straight carbon nanotube (CNT) yarns when driven by a low-voltage electrochemical approach, can achieve a contractile stroke that surpasses even NiTi shape memory alloy fibers. The key lies in the suitable match between a yarn consisting of randomly aligned CNTs and the reversible and substantial electrochemical swelling induced by solvated ions. Wrinkled structures are formed on the surface of the CNT yarn to adapt to the swelling process. This not only assures torsional stability but also enhances the surface area for improved electrode-electrolyte interaction during electrochemical actuation. Remarkably, the CNT artificial muscle yarn generates a contractile stroke of 8.8% and an isometric stress of 7.5 MPa under 2.5 V actuation voltages, demonstrating its potential for applications requiring low energy consumption while maintaining high operational efficiency. This study highlights the crucial impact of CNT orientation on the effectiveness of electrochemically-driven artificial muscles, signaling new possibilities in smart material and biomechanical system development.

Versatile fabrication of carbon nanotube yarn composites by in-situ interfacial polymerization of polyetherimide

Manufacturing of high-performance carbon nanotube (CNT)-based polymer composites has long been complicated by the difficulty of infiltrating the nanoporous network presented by continuous CNT materials; this can yield composites with heterogeneities that drastically worsen their mechanical properties. We show the synthesis of CNT-polyetherimide (PEI) composite yarns via in-situ interfacial polymerization (ISIP), which side-steps slow, viscous polymer transport by infiltrating and reacting monomer species in-situ via a rapid and scalable process. We demonstrate the ISIP technique on two distinct, industrially-produced CNT yarns, and identify processing parameters that achieve conformal polymer coatings, yielding statistically-significant increases to linear density-specific tensile properties. Using ISIP on pre-densified yarns results in composites with specific stiffness and tenacity of 142 N/tex and 2.2 N/tex, respectively. When ISIP is applied to lightly-processed, porous CNT yarn, the specific stiffness and tenacity reach up to 66 N/tex and 0.7 N/tex. The role of interfacial effects, particularly from amorphous carbon, on the composite properties is also explored. Finally, we demonstrate a prototype roll-to-roll ISIP apparatus which can process arbitrary lengths of yarn for continuous composite production.

Biscrolled hierarchical hybrid structure of PEDOT:PSS/CNTs-NMP yarn based solid state linear supercapacitor for wearable e-textile

The environmental friendly flexible solid state linear supercapacitor (FSLSc) based on the hierarchical hybrid yarn with core-shell type structure of poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) and hydrophilic carbon nanotubes (CNTs) sheet, fabricated using novel biscrolling technique is proposed. The hierarchical hybrid yarn structure of the electrode establishes the improved electrochemical interface of PEDOT:PSS with the both the hydrophilic CNTs and an aqueous PVA/H3PO4 gel electrolyte. The exterior surface of the yarn electrode rich in PEDOT:PSS which interact with ions from electrolyte and stores charges faradaically while the core region with dense CNTs yarn contributes with its multifunctional capabilities such as EDLC type capacitor, current collector and mechanical support. The observed two-fold decrease in ESR value (∼49Ω) and two-fold increase in capacitance (∼112.76 F/g) for hybrid yarn electrode with N-methyl-2-pyrrolidone (NMP) treated hydrophilic CNTs compared to the one with pristine CNTs, confirms the improved interface of PEDOT:PSS formed with hydrophilic CNTs and aqueous electrolyte. The FSLSc devices with NMP treated CNTs hybrid yarn electrodes exhibited excellent electrochemical performance in terms of the maximum power and energy density of 980 W/kg and 3.799 Wh/kg, respectively. The FSLSc displayed remarkable cycling performance upto 5000 cycles of charge-discharge and a robust bending stability after 1000 bending cycles, making it promising for practical application of the next-generation flexible solid state electrochemical energy storage in e-textiles.

Strain sensing of structural composites by integrated piezoresistive CNT yarn sensors

This work presents the development of piezoresistive strain sensors for the next-generation airframe parts. The sensors consist of polyetherketoneketone (PEKK) coated thermoplastic filaments with a continuous carbon nano-tube (CNT) yarn reinforcement fully integrated into the structural thermoplastic CFRP laminates. PEKK coating improves the piezoresistive behaviour of CNT yarns by increasing internal stress transfer. When consolidated in a laminate, the CNT sensors have a gauge factor of 10.5 and 12 for 0.2 % tensile and compressive deformations, respectively. The CNT sensors were calibrated and compared with commercial strain gauges at the coupon level and demonstrated high sensitivity in three- and four-point bend tests.

Harvesting continuous rotational mechanical energy using coiled sheath-core carbon nanotube yarn

Twisted and coiled carbon nanotube (CNT) yarns utilize the capacitance change induced by mechanical deformation to convert mechanical energy into electrical energy without requiring a bias voltage. Improved techniques are needed for improving the energy generation of a single yarn. Here we report a sheath-core CNT yarn harvester (SCCH) using a twisted CNT sheath and a polymer fiber core, which increases the energy conversion efficiency to 6.1 %, up from 1.7 % for the neat coiled yarn. The SCCH generated a 2.2 times peak power density (233 W kg−1) than neat CNT yarn when cyclic stretched at 15 Hz. Additionally, the twistron was coated with gel electrolytes to create a sensor capable of monitoring human motion. The twistron was further employed to harness continuous rotational energy in diverse environments where fluid flow is present, facilitating the operation of temperature or humidity-sensing electronic devices.

Unveiling Ion Dynamics in the Electric‐Double Layer Under Piezoionic Actuation of Chemo‐Mechanical Energy Harvesters

AbstractUnderstanding the ion dynamics within the electric double layer (EDL) is crucial for maximizing the potential of chemo‐mechanical energy harvesters. This study elucidates the electrochemical response of EDL to the compressive mechanical stimulation of carbon nanotube (CNT) yarns from the perspective of ion adsorption. The results revealed that H3O+ contributed to the ionic capacitance of the EDL by forming a polarized layer with Cl− on the outer Helmholtz plane. The unique molecular shape, compatible with spx hybridized orbitals of CNTs also enhance surface adsorption properties. In contrast, Cl− provides a strong electrostatic potential to the electrode, which has electronic structures incompatible with the spx hybridized orbitals of CNTs. The differing dynamic behaviors of these two ions jointly induce delamination of the cationic and anionic layers, as well as unipolarization of the EDL under mechanical compression of the microstructure. The ion dynamics revealed by multiscale simulations satisfactorily explain the experimentally observed high ion capacitance and energy conversion process of the HCl‐based EDL.

Integration of carbon nanotube yarns into glass‐fiber reinforced composites for electrical self‐sensing of damage under cyclic bending and impact loading

Integration of carbon nanotube yarns into glass‐fiber reinforced composites for electrical self‐sensing of damage under cyclic bending and impact loading

Enhancing Carbon Nanotube Yarns via Infiltration Filling with Polyacrylonitrile in Supercritical Carbon Dioxide.

Carbon nanotube (CNT) fibers are renowned for their exceptional axial tensile strength and modulus. However, in yarn form, they frequently encounter transverse loading in practical applications, which exposes their suboptimal mechanical attributes rooted in inadequate inter-tube interactions and yarn surface defects. Efforts to mitigate micro-slippage among CNTs have encompassed gap-filling methodologies with varied materials, yet the outcomes have fallen short of expectations. This work aimed to enhance the mechanical properties of CNT yarns via infiltration with polyacrylonitrile (PAN) under supercritical carbon dioxide (sc-CO2) conditions. PAN was strategically chosen for its capability to undergo pre-oxidation and subsequent carbonization, leading to robust graphitic reinforcement. Leveraging sc-CO2's swelling and high permeability properties, the infiltration process effectively plugged interstitial spaces, elevating the yarn's tensile strength to 277.50 MPa and Young's modulus to 5094.05 MPa. Additional enhancements were realized after pre-oxidation, conferring a dense, reinforced shell structure that augmented tensile strength by 96.93% and Young's modulus by 298.80%. Scanning electron microscopy (SEM) analyses revealed a homogeneous PAN distribution within the yarn matrix, corroborated by X-ray photoelectron spectroscopy (XPS) evidence of C-N bonding, indicative of a successfully interlaced network. Consequently, this investigation introduces a novel strategy to tackle micro-slippage in CNT yarns, thereby achieving substantial improvements in their mechanical resilience.

Hygrothermal effect and statistical analysis of the interfacial performance of nano and microscale polymer composites

ABSTRACT Hygrothermal exposure significantly impacts polymer composite (PMC) performance, affecting various industries. This study evaluated the short-term hygrothermal effects on PMCs by examining interfacial shear strength (IFSS), water uptake, glass transition temperature (Tg), and morphology. Data-driven techniques minimized experimental time while analyzing multiple factors. Specimens were immersed in water at 25°C and 70°C for 3, 7, and 14 days. The IFSS between carbon nanotube yarns and carbon fiber with epoxy (EPON™ 862) was measured before and after exposure. Statistical analysis indicated that fiber type significantly influenced IFSS, while time had a marginal effect and temperature had no impact. The IFSS decreased by 4.14% for CF/epoxy and 14.9% for CNT/epoxy. Water uptake analysis revealed weight gains of 0.465% and 1.566% for epoxy after 14 days at 25°C and 70°C, respectively. Morphological studies showed moisture penetration between 7 and 14 days. Thermomechanical analysis (TMA) indicated that pristine epoxy expanded by 0.318% of its original height. After 14 days, the Tg of epoxy decreased by 6.4% at 25°C and 9.7% at 70°C. Dynamic mechanical analysis (DMA) on dried epoxy samples showed similar Tg but varied tan delta curves due to plasticization. Short-term hygrothermal evaluation revealed degradation in interface quality and viscoelastic properties.

Lamellar structure of high-strength direct-spun CNT yarns: Implications for interface failure

A previously unreported nanoscale lamella structure in a direct spun high strength carbon nanotube (CNT) yarn was identified and characterized. The thickness of the lamellae is in the order of 100 nm. The lamella structure is present in the entire cross-section. It is hypothesized that the lamella structure originates from a single thin sheet (felt) during the manufacturing process, between steps of CNT aerogel and CNT roving. The existence of this lamella structure has direct implications on the yarn-resin interface behavior of derived composites and, subsequently, the mechanical performance of CNT yarn composites. Peridynamic simulations of four distinct yarn pullout experiments captured the observed failure behavior influenced by microstructure.

Improvement of apparent IFSS and specific modulus of CNT yarns

Due to the high strength of carbon nanotubes (CNTs) significant effort has been devoted to incorporating them into fibers and composites. To maximize their potential in these areas, there must be strong interactions between the CNT structures and the matrix of the composite. For CNT yarn, progress in this area has been limited. In this work, we present a method for modifying CNT yarn which improves the apparent interfacial shear strength (IFSS) by up to 45 %, as measured by single yarn pullout testing. An ammonium peroxide mixture (APM) treatment method is used to modify the yarn, and this is followed by treatment with commercial sizing agents. A tensioned heat treatment method is also employed to limit the effect of APM treatment on strength and modulus. This method increased the specific modulus of CNT yarns by as much as 16 %. The combined heat and chemical treatments yield increases as high as 43 % in IFSS and 6 % in specific tensile modulus while tempering the decreases in specific tensile strength. The yarn is characterized by SEM, EDS and Raman spectroscopy to show surface carbon being removed from the yarn, seemingly without damaging the CNT structures in the yarn. The main mechanism for IFSS increase appears to be removal of non-graphitic material from the yarn and slight oxidation of the yarn surface. The increase seen in IFSS has the potential to improve the performance of CNT yarn/polymer matrix composites for aerospace applications.

Monitoring of static and vibration responses of laminated composite materials using integrated carbon nanotube fibers

Carbon nanotube fibers or yarns (CNTYs) are lightweight, stiff, strong, electrically, and thermally conductive fiber-like materials that exhibit a piezoresistive response and could be integrated in glass-fiber/epoxy laminated composite materials to measure strain and to detect damage. Aiming at extending the scope of previous studies, this work is about the piezoresistive response of CNTY sensors integrated in composite laminates of industrial interest, accounting for interactions between the CNTY and the typical heterogeneous, anisotropic surrounding media, including the effects induced by the curing process of the composite matrix. This study reports experimental results on the mechanical response of laminated composite materials under quasi-static and vibration loading monitored using integrated CNTY sensors. A combination of CNTY sensor configurations and experimental setups were used to monitor the deformation and strains among the various layers of the laminated composites. As the laminated composites were mechanically loaded under quasi-static four-point bending, the CNTY sensors captured instantaneously the deformation as demonstrated by the change in their electrical resistance. Also, as the laminated composites were subjected to sinusoidal loading at specific frequencies, the integrated CNTY sensors were able to capture the loading cycles exactly including durations and peaks. Integrated sensing using CNTYs may offer a highly adaptive, practical, and sensitive structural monitoring method for a variety of applications.