Assembly Of Carbon Nanotubes Research Articles

Hybrid Plasma-Liquid Treatment of Carbon Nanotubes for Application in Direct Absorption Solar Thermal Collectors

Covalent functionalization of carbon nanotubes (CNTs) with oxygen-based or nitrogen-based functional groups is one of the most popular techniques to modify the surface energy and inherent properties of the CNTs.1 This functionalization generates interest for a broad range of applications including mechanically superior advanced composites,2 more sensitive gas sensors,3 enhanced energy storage materials4 or ultra-conductive fibers.5 As an alternative to the harsh chemicals used by traditional chemical functionalization, plasma-based surface treatments can be used with great efficacy and reduced reaction times, providing an array of application-specific benefits.Awareness of the environmental pollution caused by fossil fuels and the ever-increasing demand for energy has driven research focussed on zero-carbon renewable energy sources. Conscious of this, direct absorption solar thermal collectors are gaining prominence, both for domestic heating and steam generation. CNTs have been investigated as an additive to take advantage of the near blackbody absorption and high thermal conductivity to improve system efficiency. Critical to the success of the additive nanoparticles is the stability in the fluid, however, due to their high surface energy CNTs tend to agglomerate which can limit the efficacy of their integration into real-world products.In this work, macroscopic ribbon-like assemblies of carbon nanotubes are functionalized by plasma-induced non-equilibrium electrochemistry (PiNE) implemented through a simple direct current-based plasma-liquid system. This system utilizes the plasma-generated species in an electrolyte of 10 %vol ethanol in water, with or without a nitrogen precursor, for the oxygen and/or nitrogen functionalization of the carbon nanotube assembly. For this treatment, a ribbon-like piece of CNT was used as the anode and a helium plasma discharge triggered by applying 10 mA and 1 - 1.6 kV to act as the cathode. The plasma-generated species are then expected to migrate towards the CNTs and functionalize the sidewalls.The oxygen content is shown to be increased by between 70 % and 300 % when the treatment solution of 10 %vol ethanol is used in the ribbon electrode configuration. When ethylenediamine is added as a nitrogen precursor, the atomic concentration of nitrogen reaches 23 %, with amine groups, pyrrolic groups and graphitic nitrogen observed in the x-ray photoelectron spectra. This nitrogen content is unmatched in quantity when compared to either a simple soaking procedure or an electrolysis process with a platinum foil replacing the plasma as the counter-electrode. This demonstrates that the plasma either directly or indirectly, through plasma-generated species, facilitates and enhances the availability of nitrogen from the ethylenediamine precursor. The potential plasma-induced chemical pathways which lead to the functionalization of the CNTs are also investigated and discussed.In the application of a direct absorption solar collector system, it is found that the covalent functionalization provided by the plasma-liquid system enhances the stability of the CNT-ethylene glycol nanofluid, with the oxygen-functionalized samples producing the most stable nanofluids. This is explained through the lower value for contact angle measurements, suggesting greater hydrophobicity of the CNTs.References(1) Mallakpour, S.; Soltanian, S. Surface Functionalization of Carbon Nanotubes: Fabrication and Applications. RSC Adv. 2016, 6 (111), 109916–109935. https://doi.org/10.1039/c6ra24522f.(2) Williams, J.; Broughton, W.; Koukoulas, T.; Rahatekar, S. S. Plasma Treatment as a Method for Functionalising and Improving Dispersion of Carbon Nanotubes in Epoxy Resins. J. Mater. Sci. 2013, 48 (3), 1005–1013. https://doi.org/10.1007/s10853-012-6830-3.(3) Ham, S. W.; Hong, H. P.; Kim, J. H.; Min, S. J.; Min, N. K. Effect of Oxygen Plasma Treatment on Carbon Nanotube-Based Sensors. J. Nanosci. Nanotechnol. 2014, 14 (11), 8476–8481. https://doi.org/10.1166/jnn.2014.10007.(4) Hulicova-Jurcakova, D.; Seredych, M.; Lu, G. Q.; Bandosz, T. J. Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on Its Electrochemical Performance in Supercapacitors. Adv. Funct. Mater. 2009, 19 (3), 438–447. https://doi.org/10.1002/adfm.200801236.(5) Li, L.; Liu, E.; Shen, H.; Yang, Y.; Huang, Z.; Xiang, X.; Tian, Y. Charge Storage Performance of Doped Carbons Prepared from Polyaniline for Supercapacitors. J. Solid State Electrochem. 2011, 15 (1), 175–182. https://doi.org/10.1007/s10008-010-1087-8. Figure 1

Study of the prostate-specific antigen–aptamer stability in the PSA–aptamer-single wall carbon nanotube assembly by docking and molecular dynamics simulation

ABSTRACT Prostate-specific antigen (PSA) is used to detect prostate cancer. RNA aptamers against this protein have been reported previously. In this work, the stability and interaction mechanism of aptamer with PSA and single-wall carbon nanotube (SWCNT) was studied by computational techniques. Molecular dynamics simulations were used to investigate the interaction of aptamer segments with the surfaces of SWCNT and prostate-specific antigen (PSA) protein in an aqueous solution by two steps. Firstly, the interaction of aptamer and SWCNT was studied by the molecular dynamic simulation method. Our results showed that an aptamer segment can attach to the surface of SWCNT with its helix axis perpendicularly. Our analysis shows that the π–π stacking interactions play an important role in the binding of the aptamer to carbon rings. Secondly, we analysed the interaction of PSA protein with aptamer in the aptamer–SWCNT assemble. We found that the 3D structure of aptamer in the presence of PSA protein and SWCNT was stable. Finally, this study provides evidence about the stability of aptamer as a sensor on the surface of SWCNT (as a fixed surface) for PSA protein as a ligand. This finding can help to improve new biosensors for detecting cancer protein markers.

Engineering of Microcage Carbon Nanotube Architectures with Decoupled Multimodal Porosity and Amplified Catalytic Performance.

New approaches for the engineering of the 3D microstructure, pore modality, and chemical functionality of hierarchically porous nanocarbon assemblies are key to develop the next generation of functional aerogel and membrane materials. Here, interfacially driven assembly of carbon nanotubes (CNT) is exploited to fabricate structurally directed aerogels with highly controlled internal architectures, composed of pseudo-monolayer, CNT microcages. CNT Pickering emulsions enable engineering at fundamentally different length scales, whereby the microporosity, mesoporosity, and macroporosity are decoupled and individually controlled through CNT type, CNT number density, and process energy, respectively. In addition, metal nanocatalysts (Cu, Pd, and Ru) are embedded within the architectures through an elegant sublimation and shock-decomposition approach; introducing the first approach that enables through-volume functionalization of intricate, pre-designed aerogels without microstructural degradation. Catalytic structure-function relationships are explored in a pharma-important amidation reaction; providing insights on how the engineered frameworks enhance catalyst activity. A sophisticated array of advanced tomographic, spectroscopic, and microscopic techniques reveal an intricate 3D assembly of CNT building-blocks and their influence on the functional properties of the enhanced nanocatalysts. These advances set a basis to modulate structure and chemistry of functional aerogel materials independently in a controlled fashion for a variety of applications, including energy conversion and storage, smart electronics, and (electro)catalysis.

Effect of layer-by-layer assembled carbon nanotube coatings on dropwise condensation heat transfer associated with non-condensable gas effect

The purpose of this study is to investigate the effect of layer-by-layer (LbL) assembled carbon nanotube (CNT) coatings on dropwise condensation heat transfer under steam–air mixture conditions. To promote dropwise condensation, an additional hydrophobic coating was added to the LbL-assembled CNT coatings, which resulted in a 16% enhanced condensation heat transfer coefficient (HTC) compared to that of the bare surface under saturated steam conditions. Despite the existence of the nanostructures on the CNT-layered surface, the larger droplet size was observed from the high-speed images than that of the bare surface due to flooding condensation phenomenon. Considering that the HTC was enhanced without smaller droplet size, it is evident that this enhancement was mainly attributed to the reduced constriction resistance driven by the high thermal conductivity of the CNT layers. A new HTC model for dropwise condensation incorporating constriction resistance was developed to better predict the measured condensation HTC. Although the enhancement of the condensation HTC on the LbL-assembled CNT coatings was diminished with the air mass fraction, this work reports a new perspective to enhance the dropwise condensation heat transfer performance by controlling the constriction resistance using a highly thermally conductive coating.

Photocurrent in carbon nanotube bundle: Graded Seebeck coefficient phenomenon

Polarized photovoltage of a suspended aligned carbon nanotube (CNT) bundle under uniform optical irradiation is discovered without additional structural modification or bias voltage. Such a phenomenon is very surprising considering the metallic behavior of the overall bundle and zero temperature difference between ends. The photovoltage characteristic time is found similar to the thermal response time under step Joule heating and implies a relation to the thermal behavior of the CNT bundle. A similar thermoelectric voltage is also observed during step Joule heating. Localized laser heating and scanning along the axial direction of the bundle uncovers a linear spatial variation of the local Seebeck coefficient. The Seebeck coefficient linearly decreases from root to tip of the CNT bundle with a rate of a few - µV∙K−1·mm−1. Deep investigation in both the microscopic and macroscopic structures of the CNT bundle reveals that the local alignment of CNT assemblies rather than the minor defects in individual CNTs brings about this linear distribution of Seebeck coefficient in space. The finding presents a new way for direct photon-to-electric energy conversion via Seebeck coefficient grading in CNT structures.

Hydrogen Uptake and Release in Carbon Nanotube Electrocatalysts

The recent technique of molecular beam-thermal desorption spectrometry was used here for monitoring hydrogen uptake and release from carbon nanotube networks, after electrochemical hydrogen uptake. This way, an accurate determination of the hydrogen mass absorbed in electrodes made from those assemblies can be achieved by significantly improving the signal-to-noise ratio. The hydrogen desorption mass spectra account for the enhanced surface capability for hydrogen adsorption in the electrodes and enable a comparison with the performance of a palladium electrode in similar conditions. A comparative study involving different carbon nanotube electrodes, in similar hydrogen uptake/desorption conditions, clearly confirmed the expectations about their enhanced hydrogen storage capacity and points to the great potential of carbon nanotube assemblies in replacing the heavier metal alloys as electrocatalysts.

Fabrication of superhydrophobic photothermal conversion fabric via layer-by-layer assembly of carbon nanotubes

Photothermal conversion material that generates thermal energy from sunlight is expected to be a promising technology for harvesting and conversion of clean solar energy. However, its photothermal conversion will be affected due to the surface contamination by dirt in outdoor applications, which greatly reduces the solar energy absorption. Herein, a superhydrophobic photothermal conversion fabric was fabricated through layer-by-lay self-assembly of carbon nanotubes (CNTs) on the surface of fibers, and followed by post-treatment with polydimethylsiloxane (PDMS). The CNTs not only impart to the fabric high photothermal conversion capability, but also construct roughening structures on the fiber surface. Consequently, the as-prepared fabric could be rapidly heated to 89.8 °C under one sun (1 kW/m2) irradiation, and showed excellent superhydrophobicity with contact angle 165° ± 0.9° and rolling angle 0.6° ± 0.2°. Meanwhile, the fabric possessed excellent stability to organic solvent, acid/alkali solutions, and UV irradiation. Importantly, the superhydrophobic self-cleaning property prevents the photothermal coating from contamination to guarantee the durability of the photothermal conversion efficiency.

Length-dependent carbon nanotube film structures and mechanical properties

We investigated the microstructures of carbon nanotube (CNT) films and the effect of CNT length on their mechanical performance. 230 μm-, 300 μm-, and 360 μm- long CNTs were grown and used to fabricate CNT films by a winding process. Opposite from the length effect on CNT fibers, it has been found that the mechanical properties of the CNT films decrease with increasing CNT length. Without fiber twisting, short CNTs tend to bundle together tightly by themselves in the film structure, resulting in an enhanced packing density; meanwhile, they also provide a high degree of CNT alignment, which prominently contributes to high mechanical properties of the CNT films. When CNTs are long, they tend to be bent and entangled, which significantly reduce their packing density, impairing the film mechanical behaviors severely. It has also been unveiled that the determinant effect of the CNT alignment on the film mechanical properties is more significant than that of the film packing density. These findings provide guidance on the optimal CNT length when attempting to fabricate high-performance macroscopic CNT assemblies.

Guided Healing of Damaged Microelectrodes via Electrokinetic Assembly of Conductive Carbon Nanotube Bridges.

The subject of healing and repair of damaged microelectrodes has become of particular interest as the use of integrated circuits, energy storage technologies, and sensors within modern devices has increased. As the dimensions of the electrodes shrink together with miniaturization of all the elements in modern electronic devices, there is a greater risk of mechanical-, thermal-, or chemical-induced fracture of the electrodes. In this research, a novel method of electrode healing using electrokinetically assembled carbon nanotube (CNT) bridges is presented. Utilizing the previously described step-wise CNT deposition process, conductive bridges were assembled across ever-larger electrode gaps, with the width of electrode gaps ranging from 20 microns to well over 170 microns. This work represents a significant milestone since the longest electrically conductive CNT bridge previously reported had a length of 75 microns. To secure the created conductive CNT bridges, they are fixed with a layer of electrodeposited polypyrrole (a conductive polymer). The resistance of the resulting CNT bridges, and its dependence on the size of the electrode gap, is evaluated and explained. Connecting electrodes via conductive CNT bridges can find many applications from nanoelectronics to neuroscience and tissue engineering.

Visualization of Thermal Transport within and between Carbon Nanotubes.

Despite the excellent thermal properties of individual carbon nanotubes (CNTs), the thermal characteristics of macroscopic CNT assemblies are poor. This is probably due to the presence of numerous nontrivial intertube boundaries. Currently, clarity on the inherent difference between intra- and inter-CNT thermal conductivities is not well-established. Herein, we report an in situ nanoscale observation on the anisotropic thermal transport of a single bundle of CNTs by monitoring evaporated gold nanoparticles as "thermomarkers". The experimental results indicate that even a small bundle shows colossal thermal anisotropy due to the intertube boundaries. The results are validated by finite element analysis that estimates an anisotropic thermal conductivity ratio greater than 100. The estimated value is much greater than most of the reported values measured on macroscopic specimens and matches with that of highly ordered pyrolytic graphite. Our study reveals the intrinsic thermal anisotropy of bundled CNTs and aids in visualizing nanoscale thermal transport.

Immobilization of carbon nanotubes decorated gold nanoparticles on anodized aluminium oxide (Au-CNTs-AAO) membrane for enhanced catalytic performance

In recent years, the integration of nanostructure assemblies has led to unprecedented levels of control over the fabrication and functional properties of materials, with numerous potential applications. Here, we highlight the recent contributions towards the fabrication of multi-layered assemblies of carbon nanotubes (CNTs) decorated with gold nanoparticles (Au NPs) on porous materials. In this study, a three-component composite consisting of functionalized carbon nanotubes (CNTs), anodized aluminium oxide (AAO), and Au NPs was designed and synthesized in the form of a free-standing catalyst using a simple and unsophisticated technique for the first time. The AAO were coated with carbon nanotubes and gold nanoparticles and used as the supports for the catalytic. The CNTs-AAO composite was prepared by spin-coating of CNTs on the AAO surface. The Au NP layers were incorporated into the CNTs-AAO composite by immersing the composite in a gold solution. The Au-CNTs-AAO assemblies were tested for catalytic performance in the reduction of p-nitrophenol (p-NP) to p-aminophenol (p-AP). The Au-CNTs-AAO exhibited superior catalytic activity, with a reaction rate (k) of 0.678 min −1, higher than those of Au-CNTs and Au-AAO. Additionally, the Au-CNTs-AAO assemblies prepared with support of different AAO porosities showed that the catalytic activity increased as the pore diameter increased from 40 to 80 nm. Subsequently, it was demonstrated that the surface functionalization of CNTs with the silane moiety leads to higher catalytic activity compared to unfunctionalized CNTs. This efficient approach to the design and construction of this porous support improved the catalyst's properties in the reduction of p-NP, such as the catalytic performance, thermal stability, natural separation and reusability. These layered assemblies can potentially serve as a platform for various catalytic activities.

Melamine-induced formation of carbon nanotubes assembly on metal-organic framework-derived Co/C composites for lightweight and broadband microwave absorption.

Extending effective absorption bandwidth at a low filling ratio is still a challenge for metal-organic framework-derived microwave absorbing materials. Herein, varied complex structures based on CNTs have been built on Co/C particles derived from ZIF-67 via melamine-involved annealing routes. It was found that cobalt nanoparticles derived from ZIF-67 act as catalysts for the growth of CNTs, effectively promoting and controlling the content of melamine. Due to the effective control of the CNT-containing complex structure, excellent microwave absorption performance was achieved at a rather low filling ratio of 20 wt%, which can be attributed to improved attenuation ability and ameliorated impedance matching. Results show that highly graphitic CNTs benefit the formation of the electron transport network and enhancement of conduction loss. Unique one-dimensional complex structure and abundant Co/C interfaces strengthen the polarization loss. When the dielectric loss was optimized at different frequencies, appropriate impedance matching was also gained to realize a broad effective absorption bandwidth of 5.6 and 4.4 GHz in Ku and X bands, respectively. This work may provide novel insights into the synthesis and design of CNT-containing metal-organic framework-derived materials with lightweight features and wide frequency response.

Fabrication of scalable, aligned and low density carbon nanotube/silicon carbide hybrid foams by polysilazane infiltration and pyrolysis

Polymer-derived ceramic (PDC) process is an attractive technique that has high ceramic yield. This versatile method allows for fabrication of porous carbon nanotube (CNT)/ silicon carbide (SiC) hybrid materials that is important high temperature structural applications. Although several forms of CNT assemblies have been used with the PDC approach, the fabricated CNT/ceramic nanocomposites were either one or two dimensional. Herein, we report, for the first time, the fabrication of a low density, three-dimensional (3D) and scalable CNT/SiC structure using PDC technique. It was synthesized by impregnating preceramic polysilazane (PSZ) into ultralow density, anisotropic, and highly aligned CNT foams, followed by thermosetting and pyrolysis processes. The ceramic phase conformally coated the CNTs. The X-ray diffraction (XRD) diffractogram confirmed the presence of β-SiC crystalline phase. The resulting hybrid foam inherited the morphology and form factor of the original CNT foam, and possessed mechanical robustness, improved electrical properties, and extraordinary thermal stability.

Effects of different hot pressing processes and NFC/GO/CNT composite proportions on the performance of conductive membranes

In this study, both nanofibrillated cellulose (NFC) and graphene oxide (GO) as dispersant and binder, were employed to effectively disperse and assemble carbon nanotube (CNT) via ultrasonic dispersion. A NFC/rGO (reduced graphene oxide)/CNT conductive composite membrane was prepared via a low-temperature and efficient hot pressing treatment with the synergistic effect of drying, reduction, and densification, which exhibited good conductivity, mechanical performance, and thermal stability. After the composite membrane (mass ratio of NFC:GO:CNT was 2:4:4) was hot pressed under 3 MPa at 170 °C for 30 min, its sheet resistance reduction rate reached to 61.1% (decreased from 19.8 ± 3.1 Ω sq.−1 to 7.7 ± 1.1 Ω sq.−1), while its Young's modulus increased from 1496.3 ± 250.9 MPa to 3178.3 ± 356.2 MPa. Hot pressing at the low temperature can reduce oxygen-containing groups on GO, by which the carbon-to‑oxygen ratio was increased from 2.28 to 5.05. The presented controllable method helps to construct a conductive network in the composite membrane, and provides a new strategy to enhance performance of the low-dimensional carbon composite membrane.

Preparation of NiO decorated CNT/ZnO core-shell hybrid nanocomposites with the aid of ultrasonication for enhancing the performance of hybrid supercapacitors

Supercapacitor (SC) electrodes fabricated with the combination of carbon nanotubes (CNTs) and metal oxides are showing remarkable advancements in the electrochemical properties. Herein, NiO decorated CNT/ZnO core-shell hybrid nanocomposites (CNT/ZnO/NiO HNCs) are facilely synthesized by a two-step solution-based technique for the utilization in hybrid supercapacitors. Benefitting from the synergistic advantages of three materials, the CNT/ZnO/NiO HNCs based electrode has evinced superior areal capacity of ~67 µAh cm−2 at a current density of 3 mA cm−2 with an exceptional cycling stability of 112% even after 3000 cycles of continuous operation. Highly conductive CNTs and electrochemically active ZnO contribute to the performance enhancement. Moreover, the decoration of NiO on the surface of CNT/ZnO core-shell increases the electro active sites and stimulates the faster redox reactions which play a vital role in augmenting the electrochemical properties. Making the use of high areal capacity and ultra-long stability, a hybrid supercapacitor (HSC) was assembled with CNT/ZnO/NiO HNCs coated nickel foam (CNT/ZnO/NiO HNCs/NF) as positive electrode and CNTs coated NF as negative electrode. The fabricated HSC delivered an areal capacitance of 287 mF cm−2 with high areal energy density (67 µWh cm−2) and power density (16.25 mW cm−2). The combination of battery type CNT/ZnO/NiO HNCs/NF and EDLC type CNT/NF helped in holding the capacity for a long period of time. Thus, the systematic assembly of CNTs and ZnO along with the NiO decoration enlarges the application window with its high rate electrochemical properties.

High-Performance Flexible Electrochemical Heavy Metal Sensor Based on Layer-by-Layer Assembly of Ti3C2Tx/MWNTs Nanocomposites for Noninvasive Detection of Copper and Zinc Ions in Human Biofluids

A flexible electrochemical heavy metal sensor based on a gold (Au) electrode modified with layer-by-layer (LBL) assembly of titanium carbide (Ti3C2Tx) and multiwalled carbon nanotubes (MWNTs) nanocomposites was successfully fabricated for the detection of copper (Cu) and zinc (Zn) ions. An LBL drop-coating process was adopted to modify the surface of Au electrodes with Ti3C2Tx/MWNTs treated via ultrasonication to fabricate this novel nanocomposite electrode. In addition, an in situ simultaneous deposition of "green metal" antimony (Sb) and target analytes was performed to improve the detection performance further. The electrochemical measurement was realized using square wave anodic stripping voltammetry (SWASV). Moreover, the fabricated sensor exhibited excellent detection performance under the optimal experimental conditions. The detection limits for Cu and Zn are as low as 0.1 and 1.5 ppb, respectively. Furthermore, Cu and Zn ions were successfully detected in biofluids, that is, urine and sweat, in a wide range of concentration (urine Cu: 10-500 ppb; urine Zn: 200-600 ppb; sweat Cu: 300-1500 ppb; and sweat Zn: 500-1500 ppb). The fabricated flexible sensor also possesses other advantages of ultra-repeatability and excellent stability. Thus, these advantages provide a great possibility for the noninvasive smart monitoring of heavy metals in the future.

A review on conducting carbon nanotube fibers spun via direct spinning technique

Due to our modern standard of living, the demand of electrical energy is growing rapidly. To meet this exigency, the conventional metal wires have become obsolete to meet highly efficient electrical energy supply demands. The suitable alternative to metal wires must exhibit good electrical and thermal conductivity, low mass density, negligible skin effects and non-corrosive properties. The axially aligned carbon nanotubes (CNT) assemblies, the CNT fibers, are among the most promising materials to meet these requirements. The CNT fibers hold great potential for highly fuel-efficient electric vehicles and low-power nanochips in ever-advancing computer hardware where conventional wires have no future. This article provides an overview of the conducting nature of CNT fibers. First, CNTs as futuristic conducting material will be elucidated briefly, followed by synthesis techniques of CNT fiber. Specific attention is devoted to the direct spinning technique (FC-CVD) as the fiber produced by this method has quite high electrical conductivity (EC) and of limitless length. Then, the effect of various parameters (during synthesis like carrier gas or feedstock flow rate and after synthesis like doping of metallic nanomaterials, coating of polymers or interaction with the acidic environment) on its EC is discussed. This study would pave the way for the bright future of CNT fiber to be used as electrical wiring by concentrating on current challenges confronting this field.

Multi-dimensional ZnO@MWCNTs assembly derived from MOF-5 heterojunction as highly efficient microwave absorber

Metal-organic framework (MOF) derivatives have been arousing great attention in microwave absorption (MA) applications because of the adaptable morphological and component variance. However, it is still a huge challenge to construct multi-dimensional assembly with special heterostructure based on MOF and conductive carbon materials for excellent MA performance. Here, we successfully synthesized the cube-like assembly of multi-walled carbon nanotubes (MWCNTs) and ZnO (ZnO@MWCNTs) with unique multi-dimensional architecture via controlling the pyrolysis time of MOF-5 wrapped by MWCNTs. The ZnO@MWCNTs-4h are composed of zero-dimensional ZnO nanoparticles, one-dimensional MWCNTs, and three-dimensional micro-scale porous carbon framework. These various dimensional components confined within the cube space lead to the strong reflection loss (RL) at different frequencies, thus resulting in exceptional MA performance. The ZnO@MWCNTs-4h can reach a RL peak of −34.4 dB at only 1.5 mm thickness. More importantly, the maximum RL can achieve −47.4 dB at 2.7 mm with a mass loading as low as 20%. The optimized MA performance can be ascribed to high-density polarized sites, tightly interwoven MWCNTs conductive network, and strong multiple scattering that all induced by the multi-dimensional structures and components. Therefore, novel ZnO@MWCNTs composites are promising as a lightweight and highly efficient microwave absorber.

Full on-line preparation of polymer composites reinforced with aligned carbon nanotubes

Carbon nanotubes (CNTs) reinforced composite materials have been widely studied, but the long-standing technical issues with poor dispersion, low CNT content, and low CNT alignment remain to be solved. In this study, a CNT/polymer composite material is prepared by continuously winding a highly aligned CNT assembly with the polymer resin introduced and cured on-line. CNTs are mixed with the resin at the molecular level, and their alignment is maintained. Effects of critical experimental parameters such as winding rate, curing temperature, and curing time are studied. Under optimal conditions, the composite material with a high CNT content of 65 wt% exhibits a high tensile strength of 751 MPa and elongation at break of 6%. All the preparation processes are completed in air and on line without any post off-line processing as involved in previous conventional techniques. Therefore, this study provides a new strategy for manufacturing cost-effective composite materials in large scale and structural components of different sizes for wide applications.

Flexible and high-performance piezoresistive strain sensors based on carbon nanoparticles@polyurethane sponges

In this work, flexible and high-performance piezoresistive strain sensors were fabricated by simple layer-by-layer electrostatic self-assembly of carbon nanoparticles on commercial polyurethane (PU) sponges. It was shown that the sponge-based strain sensors exhibited obviously positive and negative piezoresistive characteristics under tensile and compressive strains, respectively. The alternate assembly of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) contributed to the construction of a more complete conductive network and significantly improved the sensing performance of the sensor due to the synergistic effect between CNTs and GNPs. Compared with the CNT@PU and CNT/GNP@PU sponge strain sensors, the CNT/GNP/CNT@PU sensor had a larger strain detection range and higher linearity. Besides, the CNT/GNP/CNT@PU sponge strain sensor showed high sensitivity (GF = 43,000 at 60% tensile strain and GF = −1.1 at 50% compressive strain), responsive capability to very small strain (0.05%) and outstanding stability during 3000 loading cycles. Due to its excellent sensing performance, the CNT/GNP/CNT@PU sensor enabled monitoring of various physiological activities, including finger movements, wrist bending and walking etc. In addition, a 5 × 5 sensor array based on the sponge-based strain sensor was prepared to achieve accurate identification of weight distribution. This study provides valuable information for the development of flexible strain sensors with high-performance and low-cost.