Continuous Carbon Nanotube Research Articles

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.

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.

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.

Upcycling of waste photovoltaic silicon: Co-MOF derived coating layer enhanced lithium storage

Large amounts of silicon waste (W-Si) powders or ingots from the photovoltaic (PV) industry can be recycled as the improved raw negative electrode material in Lithium-ion batteries. Herein, Co-MOFs (ZIF-67) is produced in the form of small particles which turns into the uniform coating layer on the surface of micro-sized W-Si by solvent evaporation, and then ZIF-67 is carbonized to form nitrogen-doped carbon (NC) layer and carbon nanotubes (CNTs). Finally, W-Si/NC/Co/CNTs composites are formed. The continuous and uniform NC layer and CNTs formed by the catalyzation of Co on the surface of the silicon particles can inhibit the volume expansion of silicon during the charge and discharge process, showing the reversible discharge capacity of 1039 mAh g−1 after 100 cycles. The rate performance is also improved due to the high conductivity composite structure. This work can provide a choice for the composite of MOF and micro-silicon, and the meaning guidance for the application of silicon waste from PV industry.

Nucleation of disclinations in carbon nanotube bundle structures under twisting loads

Twisting is a simple and effective method for assembling individual carbon nanotubes (CNTs) into high-strength, tough, and continuous CNT yarns. However, the unexpectedly low stretching performance of the resulting carbon nanotube bundle (CNTB) structures is a problem that must be resolved. In this study, we investigated the impact of twisting on the structure and stretching performance of CNTBs through molecular dynamics (MD) simulations while considering the presence of disclinations within the CNTB structure. We found that disclinations nucleate in twisted CNTBs, and the longer the disclination line in CNTBs, the lower the Young's modulus. The presence of disclination lines in the twisted CNTBs may be an important reason for the decrease in the tensile properties of the CNT yarns. Although the theoretical equations in textile field can be applied to describe the mechanical properties of CNT yarns, there are significant relative errors between the equations and the MD simulation results presented herein. Therefore, we revised the equations based on the simulation results to reduce the relative error for seven-layer CNTBs to less than 10 %. This paper provides new insights into the low tensile performance of CNT yarns and offers potential guidance for the production of high-performance CNT yarns through twisting.

Characterization of multidirectional carbon-nanotube-yarn/bismaleimide laminates under tensile loading

Unidirectional, cross-ply, and quasi-isotropic composite laminates are made from continuous carbon nanotube (CNT) yarns with bismaleimide (BMI) resin. The laminates are highly graphitic and have low resin content. Elastic modulus and strength of CNT/BMI laminates and IM7/8552 carbon-epoxy laminates are measured using a scaled-down tensile test method. For CNT/BMI laminates, the variation in the measured tensile modulus is high and the laminates fail in a more gradual manner than IM7/8552 laminates. Microscopy of the failed specimens indicates that intra-yarn splitting is a common feature in all CNT/BMI laminates tested. The results of this investigation will inform the development of CNT yarn reinforced composites for structural applications.

Constructing independent CNTs conductive network to boost combustion performance of metastable intermixed composites

AbstractNovel metastable intermixed composites (MICs) constructed by carbon nanomaterials are expected to achieve high energy content and high combustion efficiency, but traditional preparation technologies always bring barely improvement in performance. Herein, novel PVDF/CuO/Al@CNTs MICs with independent continuous carbon nanotubes (CNTs) conductive networks were prepared by thoroughly utilizing the conductivity and photothermal properties of CNTs. A conductive network can be constructed at the interface of each encapsulated PVDF/CuO/Al particle with the addition of >0.5 wt% CNTs. The great increase in electrical and thermal conductivity of PVDF/CuO/Al@CNTs MICs indicates excellent energy transfer efficiency across the sample. Significant enhancement of the combustion reaction has been achieved, with the minimum ignition energy and ignition delay time of PVDF/CuO/Al@CNTs3 reduced by ~31% and ~50%, respectively. This indicates that the CNTs with unique photothermal properties can be utilized as an effective igniter. Moreover, the optimal PVDF/CuO/Al@CNTs1 MICs enhanced the pressurization rate (~300%), energy output (~55%), and combustion velocity (~200%). The mechanism of the fast combustion reaction can also be discussed by the weak interface interaction and the energy conductive of the CNTs network throughout the sample. This work provides a modern strategy for strong combustion MICs that can be generalized and applied in the field of energetic materials.Highlights An independent continuous CNTs conductive network was prepared with a small amount of CNTs. The electrical and heat conversion efficiency is greatly improved. CNTs with unique photothermal properties can be utilized as an effective igniter. The laser sensitivity is improved, and the reaction energy, pressure, and pressure rates are significantly increased. The combustion performance was significantly improved, and more intense, and the combustion speed was significantly increased.

Active Material‐Free Continuous Carbon Nanotube Fibers with Unprecedented Enhancement of Physicochemical Properties for Fiber‐Type Solid‐State Supercapacitors

AbstractFiber‐type solid‐state supercapacitors (FSSCs) are gaining traction as wearable energy storage devices, given their adaptability akin to traditional fibers. Carbon nanotube fibers (CNTFs) generated via a liquid crystalline (LC) wet‐spinning process demonstrate outstanding electrical conductivity, mechanical strength, and flexibility. However, their intrinsic “defect‐free” sp2 carbon surface restricts immediate FSSC application, limited by lower specific surface area and scant pseudocapacitive sites. This study develops LC‐spun CNTFs with inherent electrochemical activity, eliminating the need for post‐processing or additional active materials, a requirement typically essential in most previous research. This advancement arises from the wet‐spinning of functionalized CNTs from a LC solution with an exceptionally high concentration of 160 mg mL−1, facilitated by the manipulation of the LC phase transition range. The resultant CNTFs exhibit a refined internal structure, yielding an electrical conductivity of 1.9 MS m−1 and a mechanical strength of 0.93 GPa. Simultaneously, they demonstrate inherent electrical energy storage capabilities with a specific capacitance of 139.4 F g−1 and a volumetric capacitance of 192.4 F cm−3 at 0.5 A g−1. This innovation signifies a step forward in the potential for mass production without the burden of additional materials and steps.

Gamma-ray irradiation to achieve high tensile performance of unidirectional CNT yarn laminates

Continuous carbon nanotube (CNT) yarn fabricated from a floating catalyst chemical vapor deposition (FCCVD) method is treated under gamma-ray irradiation to enhance the mechanical properties of the CNT yarn and its unidirectional composite laminates. Gammy-ray doses varying from 50 kGy to 1200 kGy are used to irradiate CNT yarns and their microstructures, tensile properties and surface characterizations are studied. The graphitic structure change is not clear from the transmission electron microscopy, however, the specific tensile strength and modulus of yarn vary slightly within 10 % as the dose increased. This modulus trend coincides with mesoscopic distinct element modeling (mDEM) simulation results. Surface characterization shows additional oxygen functional groups and smaller contact angles after irradiation. Interestingly, the specific tensile properties of composite laminates also increase relative to the yarns, and the unidirectional laminate from CNT yarn treated with the optimal dose of 700 kGy achieves specific strength and modulus as high as 1.89 GPa/gcm−3 and 258 GPa/gcm−3, respectively, which are 30.9 % and 37 % increases compared to the control laminate. The results indicate that radiation-induced crosslinking among the CNTs and the formation of surface-active sites leads to enhanced load transfer in the yarns and promote CNT/resin interfacial bonding.

Toward Self-Powered Sensing and Thermal Energy Harvesting in High-Performance Composites via Self-Folded Carbon Nanotube Honeycomb Structures.

The development of high-performance self-powered sensors in advanced composites addresses the increasing demands of various fields such as aerospace, wearable electronics, healthcare devices, and the Internet-of-Things. Among different energy sources, the thermoelectric (TE) effect which converts ambient temperature gradients to electric energy is of particular interest. However, challenges remain on how to increase the power output as well as how to harvest thermal energy at the out-of-plane direction in high-performance fiber-reinforced composite laminates, greatly limiting the pace of advance in this evolving field. Herein, we utilize a temperature-induced self-folding process together with continuous carbon nanotube veils to overcome these two challenges simultaneously, achieving a high TE output (21 mV and 812 nW at a temperature difference of 17 °C only) in structural composites with the capability to harvest the thermal energy from out-of-plane direction. Real-time self-powered deformation and damage sensing is achieved in fabricated composite laminates based on a thermal gradient of 17 °C only, without the need of any external power supply, opening up new areas of autonomous self-powered sensing in high-performance applications based on TE materials.

Scalable High Tensile Modulus Composite Laminates Using Continuous Carbon Nanotube Yarns for Aerospace Applications.

An approach is established for fabricating high-strength and high-stiffness composite laminates with continuous carbon nanotube (CNT) yarns for scaled-up mechanical tests and potential aerospace structure applications. Continuous CNT yarns with up to 80% degree of nanotube alignment and a unique self-assembled graphitic CNT packing result in their specific tensile strengths of 1.77 ± 0.07 N/tex and an apparent specific modulus of 92.6 ± 3.2 N/tex. Unidirectional CNT yarn reinforced composite laminates with a CNT concentration of greater than 80 wt % and minimal microscale voids are fabricated using filament winding and aerospace-grade resin matrices. A specific tensile strength of up to 1.71 GPa/(g cm-3) and specific modulus of 256 GPa/(g cm-3) are realized; the specific modulus exceeds current state-of-the-art unidirectional carbon fiber composite laminates. The specific modulus of the laminates is 2.76 times greater than the specific modulus of the constituent CNT yarns, a phenomenon not observed in carbon fiber reinforced composites. The results demonstrate an effective approach for fabricating high-strength CNT yarns into composites for applications that require specific tensile modulus properties that are significantly beyond state-of-the-art carbon fiber composites and potentially open an unexplored performance region in the Ashby chart for composite material applications.

Two-step method to realize continuous multi-wall carbon nanotube grafted on the fibers to improve the interface of carbon fibers/epoxy resin composites based on the Diels-Alder reaction

A new simple and continuous method was developed for chemically grafting multi-wall carbon nanotubes (MWCNTs) onto the surface of carbon fibers (CF) to improve the interlaminar properties of composites. In this method, maleimide-grafted waterborne polyurethane emulsion and furan functionalized MWCNTs were prepared. Then, based on the Diels-Alder reaction under mild reaction conditions (60 °C), CF/MWCNTs multi-scale reinforcements (MSCF) were successfully prepared through a two-step method of MWPU sizing and MWCNTs ultrasonic grafting, which overcame the complex process flow, greatly shortened the preparation time and avoided damage to fibers. The successful grafting of MWCNTs was proved by the results of SEM and HRTEM. After grafting MWCNTs, the interface between the matrix and fibers was enhanced. The interlaminar shear strength (ILSS) and flexural strength of MSCF/epoxy reinforced composites were promoted to 64.54 MPa and 981.95 MPa, which was prominently increased by 52.84% and 32.32%, respectively. In addition, this process could match the current production of carbon fibers for commercialization, but further research was expected to control the grafting amount of MWCNTs and their impact on performance.

Fiber-reinforced liquid crystalline elastomer composite actuators with multi-stimulus response properties and multi-directional morphing capabilities

Liquid crystalline elastomers (LCEs) are promising materials for soft actuations. LCE composites (LCECs), via the inclusion of fillers into LCEs, bring diverse functionalities and stimuli-responsive capabilities. It is still a challenge to improve the mechanical properties of LCEC and ensure that the material can perform reversible transformations. Here we present a cost-effective LCEC design and fabrication method by dispersing continuous carbon fibers and carbon nanotubes into LCEs, forming a new type of LCEC actuator. We found that through adjusting the angle (such as 45° and 90°) between the carbon fiber and the stretching axis of LCEC matrix, complex deformable geometries can be easily achieved including bending and twisting structures with enhanced storage modulus (400.9 MPa at 25 °C). Furthermore, the LCEC actuators could be driven by various stimuli including heat (120 °C), light (800 mW cm−2), and electricity (2.0 V). As a result, our new LCEC actuator outperforms other LCE actuators by having the largest number of morphing geometries and stimulus-responsive modes. Our LCEC design and manufacturing strategy represents a promising general methodology that can be easily extended to other continuous fibers (such as glass fiber, aramid fiber, etc.) filled LCECs, bringing even rich shape-changing capabilities that are needed for soft robots and beyond.

Highly Electrical Conductive PEDOT:PSS/SWCNT Flexible Thermoelectric Films Fabricated by a High-Velocity Non-solvent Turbulent Secondary Doping Approach.

Materials based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can be potentially employed as flexible thermoelectric generators (TEGs) to capture waste heat and generate electrical energy. Among various methods, secondary doping is an effective way to modulate its thermoelectric (TE) performance. Different from conventional measures such as dropping, soaking, and steam fumigation, strong shear is integrated with the doping process and termed high-velocity non-solvent turbulent secondary doping (HNTD). We systematically investigate the transformation of PEDOT:PSS during this procedure and the formation mechanism of its highly conductive pathway. It is illustrated that PEDOT:PSS experiences PSS swelling, the phase separation of PEDOT from PSS, the removal of isolated PSS, and the evolution of PEDOT to a linear conformation. These evolutions contribute to the substantial elevation of electrical conductivity (σ). Furthermore, by employing continuous single-walled carbon nanotube (SWCNT) networks as structural units, highly conductive flexible PEDOT:PSS/SWCNT TE thin films could be prepared without sacrificing the Seebeck coefficient (S). Additionally, the effect of HNTD and direct addition method on TE properties of composite films is also compared. Finally, the PEDOT:PSS composite film with 40 wt % SWCNTs by the HNTD method exhibits the maximized power factor (PF) of 501.31 ± 19.23 μW m-1 K-2 with σ of 4717.8 ± 41.51 S cm-1 and S of 32.6 ± 0.13 μV K-1 at room temperature. It is worth mentioning that the σ value 4717.8 ± 41.51 S cm-1 is the highest among the composites based on commercial carbon fillers and organic semiconductors. Finally, a 6-leg TEGs prototype is assembled and illustrates an output power of 4.416 μW under a temperature difference (ΔT) of 58 K. It is thought that such a strategy may provide some guidelines for manufacturing PEDOT:PSS-based functional materials.

In situ N-doped carbon nanotubes modified NiS2 hierarchical hollow microspheres for boosting sodium storage performance

Engineering novel electrode materials with distinctive architectures has a significant influence on tuning the structural/electrochemical properties for boosting the sodium storage performance. Herein, starting from metal-organic framework (MOF), we report an in situ catalytic method with chemical transformation strategy to fabricate NiS2 hierarchical hollow microspheres (HMs) with continuous N-doped carbon nanotubes (NCNTs) networks (NiS2@NCNTs HMs). Benefitting from the hierarchical hollow structure and three-dimensional (3D) NCNTs networks as well as the robust structural stability, the prepared NiS2@NCNTs HMs indicates excellent Na+ storage performance. More specifically, the composite shows a high reversible capacity of 626.6 mA h g−1 at 0.2 A g−1 for Na+ storage and retains 333.3 mA h g−1 at 5.0 A g−1, remarkably higher than those of the previously reported NiS2-based anode materials. In particular, it maintains a stable reversible capacity of 343.0 mA h g−1 even at 3.0 A g−1 over 3000 cycles. The in situ catalytic NCNTs on MOF precursors strategy for hierarchical structural composites can be extended to other novel electrodes for high performance energy storage devices.

Purification of dense carbon nanotube networks by subcritical hydrothermal processing

Carbon nanotube (CNT)-reinforced composites are promising materials for high-performance, lightweight structures; however, homogeneous infiltration of CNTs by a matrix material is necessary to achieve desired mechanical properties. Critical to overcoming this challenge at scale is purification of CNT materials produced by floating-catalyst chemical vapor deposition. Here, we present a hydrothermal processing technique for purification of CNT yarns, wherein as-received material is exposed to superheated, subcritical water in a hydrothermal reactor. This process selectively removes amorphous carbon and acid impurities while preserving the yarn structure. We find this technique to be consistent and tunable, with processing time directly correlating to linear density reduction up to a saturation limit. Using commercially-available yarns, we find that after 4 h of treatment at 200 °C, the weight loss of the yarn under inert atmosphere is reduced from 12% to 5%, the atomic percentage of oxygen at the surface by 42%, and the I D /I G by 30%. In addition, the yarn specific strength (1.3 N/tex) is preserved, while the specific Young's modulus is significantly increased by 20% (79 to 95 N/tex). At longer treatment times, we obtain greater purity and higher specific Young's modulus, but at a substantial reduction in tensile strength, which we hypothesize results from eliminating amorphous carbon toughening CNT bundles. The reported method could be scaled to continuous processing in tandem with post-purification treatments, and appears broadly applicable to different continuous CNT networks.

One-step floating conversion of biomass into highly graphitized and continuous carbon nanotube yarns

The rapid growth of the demand for carbon nanotubes (CNTs) has greatly promoted their large-scale synthesis and development. However, the continuous production of CNT fibers by floating catalyst chemical vapor deposition (FCCVD) requires a large amount of non-renewable carbon sources. Here, the continuous production of highly graphitized CNT yarns from biomass tannic acid (TA) is reported. The chelation of TA and catalyst promotes the rapid cracking of biomass into carbon source gas, and the pyrolysis cracking produces the reducing gas, which solves the problems of the continuous production of CNT yarns using biomass. Through simple twisting, the mechanical strength of CNT yarn can reach 886 ± 46 MPa, and the electrical conductivity and graphitization (IG/ID) can reach 2 × 105 S m−1 and 6.3, respectively. This work presents a promising solution for the continuous preparation of CNT yarns based on green raw material.

A molecular dynamics study on the mechanical properties of defective CNT/epoxy nanocomposites using static and dynamic deformation approaches

Abstract In this paper, the mechanical behavior of epoxy polymer nanocomposite with continuous single-walled carbon nanotubes (SWCNT) with and without vacancy defects has been investigated based on two approaches of deformation, molecular mechanics (static) and molecular dynamics. In this regard, molecular simulation has been performed on the basis of the compass force field. In order to validate the research steps, the results obtained for pure epoxy polymer were compared with similar molecular dynamic simulations, which confirmed the simulation process. The research process proposed a method for controlling the symmetry of the system during equilibration with an asymmetric barostat. The Souza-Martins barostat was also used to apply loading and deformation control over a constant strain rate range. The results showed that in both deformation approaches (with and without calculating the contribution of kinetic energy), the presence of defects improved the transverse tensile and shear moduli, while the longitudinal tensile modulus decreased. Also, the improvement and decrease of the longitudinal tensile modulus and longitudinal shear modulus of the nanocomposite in comparison with the net polymer have been observed in both approaches, respectively. As a general result, it was observed that the contribution of kinetic energy has a major effect on the mechanical properties of pristine and defective nanocomposites.

Nickel Catalyst with Atomically-Thin Meshed Coating Fabricated with ALD for Improved Durability in Dry Reforming of Methane

Recent advances in natural gas recovery and applications have drawn much attention to the dry reforming of methane (DRM) with carbon dioxide (CO2). While nickel (Ni) nanoparticles are attractive catalysts for DRM reactions in terms of activity and cost, its practical application is plagued by the quick deactivation in the catalytic environment. In this talk, atomically thin meshed-like Co coating catalytic structure is designed and fabricated to decorate Ni nanoparticles via atomic layer deposition. The coating structure improve the catalytic activity and effectively eliminates carbon deposition for the DRM reaction. Optimized catalytic performance is achieved by fine tuning the density of Co coating on nickel particles. The meshed coating structures partition the Ni surface to prevent continuous carbon nanotubes network formation. The Co component helps stabilizing the metallic phase of Ni in the DRM reaction. The Co-Ni interfaces created are beneficial for reducing carbon intermediates CHx formation and accelerate carbon removal. The amount of carbon formation can be reduced to 2.9%, which is a significant improvement (reduction over 2 to 6 times) compared with a series of state-of-the-art research reports (8%-23%) on Ni-based catalysts in the severe coking temperature range (around 650 ºC). The Co coating layer provides physical confinement and also improves the thermal stability of Ni nanoparticles from sintering and agglomeration up to 850 ºC. The strategies of selective ALD have demonstrated unique advantages to design and fabricate the catalysts in atomic scale and provided insights to understand the structure–activity relationship in a more direct way.

Integrated, Highly Flexible, and Tailorable Thermoelectric Type Temperature Detectors Based on a Continuous Carbon Nanotube Fiber.

As possible alternatives to traditional thermoelectric (TE) materials, carbon nanomaterials and their hybrid materials have great potential in the future application of flexible and lightweight temperature detection. In this work, an integrated, highly flexible, and tailorable TE temperature detector with high performance has been fabricated based on a continuous single-walled carbon nanotube (SWCNT) fiber. The detector consists of more than one pairs of thermocouples composed of p-type SWCNT fiber and n-type SWCNT hybrid fiber in situ doped by polyethylenimine. Due to the node contact mechanism of the detection, the sensitivity of the detector can be improved with the increase of the number of p-n thermocouples, independent of the length of the thermocouple. The temperature detection process of the detector has been studied in detail. In particular, the integrated and flexible detector can be divided into several sub-detectors easily by cutting, illustrating the prospect of large-scale preparation of this kind of novel temperature detectors. Its high flexibility ensures the detector to maintain excellent detection performance after 15000 bending circles. Furthermore, the as-designed TE type temperature detector demonstrates a great application promise for real-time temperature detection and temperature change sensing even in complex surface and harsh environment.