Microstructure Of Carbon Nanotubes Research Articles

Growth Mechanism of Carbon Nanotubes Revealed by in situ Transmission Electron Microscopy.

Elucidating the growth mechanism of carbon nanotubes (CNTs) is critical to obtaining CNTs with desired structures and tailored properties for their practical applications. With atomic resolution imaging, in situ transmission electron microscopy (TEM) has been a key technique to reveal the microstructure and dynamics of CNTs in real time. In this review, recent advances in the development of in situ TEM with different types of environmental reactors will be introduced. The catalytic growth mechanisms of CNTs revealed by in situ TEM under realistic conditions are discussed from fundamental thermodynamics and kinetics to the detailed nucleation, growth, and termination mechanisms, including the state and phase of active catalysts, interfacial connections between catalyst and growing CNTs, and catalyst-related growth kinetics of CNTs. Great progresses have been made on how a CNT nucleates, grows and terminates, focusing on the interface dynamics and kinetic fluctuations. Finally, challenges and future directions for understanding the atomic dynamics under the real growth conditions are proposed. It is expected that breakthroughs in the fundamental growth mechanisms will pave the way to the ultimate goal of designing and controlling the atomic structures of CNTs for their applications in various devices.

A self-excitation point process model for quantifying nanoparticle agglomeration

ABSTRACT Nanoparticle agglomeration refers to the spontaneous clustering of nanoparticles caused by the attractive forces. Agglomeration impacts the physical and mechanical properties of nanoparticles and their composites. Understanding and controlling nanoparticle agglomeration is crucial for optimizing various applications, from nanomedicine to nanoelectronics. In this work, we formulated a self-exciting point process model to analyse nanoparticle agglomeration based on microstructural input. The model is utilised to categorise a specific set of points within the microstructure as either independent (dispersed) or dependent (agglomerated), along with their respective probabilities. We employed this approach to study two distinct scenarios: (a) Agglomeration in experimentally generated microstructures of titanium nanoparticles, and (b) Analysing agglomeration patterns in simulated microstructures of carbon nanotube networks, generated using a stochastic microstructure model. We obtain a quantitative understanding of the connection between the sonication duration and the level of agglomeration in titanium nanoparticles. As the sonication period increases, both the agglomeration percentage and the size of the agglomerates decrease. Furthermore, our analysis of simulated carbon nanotube microstructures, including equiaxed and rope-like agglomeration, shows a close alignment between results obtained from the point process model and those generated by the stochastic microstructure model.

Lanthanum nanoparticle decorated carbon nanotubes: Facile method of synthesis and studies of their redox stability, cytotoxicity and corrosion inhibition on the magnesium alloy in 3.5 % NaCl environment

Functionalized carbon materials can act as high-temperature coatings and eco-friendly composite materials. We have studied lanthanum-doped carbon nanotube (La-CNT) material redox behavior, cytotoxicity, and corrosion inhibition efficiency. The La-CNT material has been characterized by different techniques to confirm the presence of functional groups. The Fourier transform infrared (FTIR) and Raman studies were performed to investigate the functional groups and carbon defects. Field emission scanning electron microscopy (FESEM) and tunneling electron microscopy (TEM) studies were used to investigate the carbon nanotube microstructure, La nanoparticles were shown to interact with the carbon nanotube surface. X-ray diffraction (XRD) techniques were used to confirm the crystallinity of composite material. Electrochemical methods were used to investigate corrosion inhibition and redox stabilities. After corrosion study on the Mg alloy its microstructure was analyzed to confirm the composite material inhibition efficiency. The composite material showed significant cytotoxicity, and corrosion inhibition efficiency was shown to be 82 % as compared with pristine epoxy-coated Mg alloy.XPS results are suggested that alloy oxide layer formed. The DFT study supported the experimental findings.

Research Progress on Microstructure Design of CNTs Reinforced Al Matrix Composites

Carbon nanotubes (CNTs) have unique characteristics which make them a suitable reinforcing agent in Aluminum Metal Matrix composites. This review summarizes the work carried out in the field of the microstructure design of CNTs/Al composites. By designing the microstructure of CNTs, Al matrix and their composite interface, the problems of agglomeration, entanglement and dispersion of CNTs, wetting and bonding with Al matrix can be effectively solved, and mechanical properties such as Young’s modulus and yield strength can be improved. Such microstructural design includes metal plating on the surface of CNTs, deposition of nano-ceramic particles, Al matrix ball milling and flakes, grain refinement combined with bimodal-grain strengthening of coarse grains.

Multifunctional microneedle patches with aligned carbon nanotube sheet basement for promoting wound healing

Wound healing has become a health concern and economic burden worldwide for its high incidence and complexity. Attempts to improve wound treatment tend to develop biomedical patches with delicate structure design and functionality. In this paper, we present novel multifunctional microneedle patches with aligned carbon nanotube (CNT) sheet basement for promoting wound healing. Because of the outstanding biocompatibility, biodegradability and non-immunogenicity, hyaluronic acid (HA) is utilized to construct the CNT-integrated microneedle patch with vascular endothelial growth factor (VEGF) encapsulation. It was found that the aligned CNT layer basement could not only impart the composite microneedle patch with orientation morphology, but also endow the patch with controllable release performance, due to its photo-thermal or electro-thermal conversion capacity. Based on these features, we have demonstrated that the highly ordered microstructure of CNT could effectively induce the orientation of fibroblasts; while VEGF release could facilitate tubular formation of endothelial cells. Thus, the aligned CNT and VEGF-loaded multifunctional patch is beneficial to the wound repair process in a typical animal experiment. These results indicate that the proposed microneedle patch is potentially promising for regeneration medicine.

Tribological Properties of Carbon Nanotube and Carbon Nanofiber Blended Polyvinylidene Fluoride Sheets Laminated on Steel Substrates

Nanostructured carbon dispersed polymer nanocomposites are promising materials for tribological applications. Carbon nanofiber (CNF) and carbon nanotube (CNT) dispersed polyvinylidene fluoride (PVDF) nanocomposite was prepared by chemical synthesis route. Morphology and microstructure of well-dispersed CNF and CNT in PVDF were specified by scanning electron microscope and X-ray diffraction, respectively. Moreover, chemical and functional characteristics were examined by Raman spectroscopy and FTIR investigation. The friction coefficient of PVDF nanocomposite laminated on steel substrate decreased with an increase in the dispersed quantity of CNF and CNT. The friction coefficient of PVDF is approximately 0.27; however, the addition of carbon nanomaterial in PVDF will further decrease the friction coefficient between 0.24 and 0.17. This value was significantly less in CNT dispersed PVDF nanocomposite. This could be explained by easy shearing and rolling action contact interfaces.

Hollow microneedle array fabrication using a rational design to prevent skin clogging in transdermal drug delivery.

Microneedle (MN) technology is promising to replace hypodermic needles for practical use and painless drug delivery. However, the complex top-down fabrication process of functional MN arrays is a bottleneck that hinders their widespread use. Here, we fabricate the tapered hollow MN array using a unique bi-level-tip by combining strain-engineering and capillary self-assembly of carbon nanotube (CNT) microstructures. Strain-engineering facilitated by the offset pattern of the catalyst enables the growth of bent, bi-level CNT microstructures while capillary self-assembly helps in constituting the tapered geometry of MNs. The bottom-up fabrication that consists of only two standard photolithography steps and CNT growth to form the scaffold of MNs followed by a polymer (polyimide) reinforcement step to impart mechanical stiffness to MNs provides scalable and fewer processing steps. The tapered shape of the MN allows an 8 times smaller force to pierce and penetrate the skin compared to the straight MN. The liquid delivery rate of the bi-level-tip MN is measured to be 26% better than the flat tip MN of the same lumen size as its geometry reduces skin clogging effect at the needle tip. In addition, cytotoxicity tests verify that the polyimide reinforced CNT-MNs are biocompatible for future in vivo applications.

Iron, nitrogen and fluorine co-modified carbon nanotubes as an effective catalyst for oxygen reduction reaction

A carbon catalytic material was synthesized using a heteroatomic doping strategy to improve its electrochemical performance on oxygen reductionreaction. Iron, nitrogen and fluorine were doped together to regulate the microstructure of carbon nanotubes through subsequently thermal treatment on iron phthalocyanine(FePc) and fluorinated carbon nanotubes(FCNT). The electrocatalytic activity of FePc/FCNT800 is higher than that of FCNT, FePc/FCNT and commercial Pt/C catalysts, with an Eonset of 1.05 V and E1/2 of 0.9 V in 1.0 M KOH solution. The result demonstrated the synergistic ORR catalytic effect in Fe, N and F co-modified carbon material. It also exhibits a perfect stability during the ADT test after 5000 cycles and the 20 h long-term chronoamperometry (CA) test in 1.0 M KOH solution.

Strongly anisotropic field emission from highly aligned carbon nanotube films

The field electron emission properties of carbon nanotube (CNT) films composed of densely packed and highly aligned CNTs were investigated. The CNT films were produced by a continuous film casting process and are spooled into long lengths with the CNTs aligned lengthwise in the film. The anisotropic nature of the CNT film morphology was confirmed by performing specific conductivity measurements in directions both parallel and perpendicular to the aligned CNT microstructure. Field emission experiments were performed on 5 and 10 mm wide films that were mechanically cut into small samples and then vertically mounted so that the emission occurred from the film edge. The films were mounted with the aligned CNT microstructure oriented either parallel or perpendicular to the direction of the applied electric field. The highest emission currents were produced by films mounted in the parallel alignment configuration. Additional experiments were performed on films that were folded, which eliminated surface irregularities at the film edge due to the cutting process. SEM imaging performed at the ridge of the folded film before and after field emission (FE) experiments showed that films mounted in the parallel alignment configuration had minimal surface damage after FE, while films mounted in the perpendicular alignment configuration showed substantial damage. The effective emission area and field enhancement factor were extracted from the FE data using the orthodox Fowler–Nordheim theory. Folded CNT film cathodes mounted in the parallel alignment configuration produced the highest emission currents, while demonstrating a larger emission area and lower field enhancement factor.

Effect of pretreatment on the microstructure of multiwalled carbon nanotubes

Four kinds of multi-walled carbon nanotubes pretreated by different methods were studied. Chemically functionalized (hydroxylation and carboxylation) CNTs were prepared by oxidizing original CNTs in H2SO4 solutions of different temperatures and concentrations by KMnO4. Graphitized CNTs were prepared by heat-treating original CNTs in an inert gas at 2800°C for 20 hours. CNTs Nickel plating on the surface was obtained by electroless plating. The effect of pretreatment on the surface state and microstructure of carbon nanotubes was also studied. The results showed that Chemical functionalization could form some functional groups on the surface of CNTs, which could not only improve the compatibility of CNTs with some solvents, but also purified CNTs, which had a positive effect on the preparation of composite materials. High-temperature graphitization treatment could significantly increase the degree of crystallization of carbon nanotubes and reduce structural defects. After electroless nickel plating, evenly distributed nano-sized metal particles were formed on the surface of the CNTs, and the interface between the two was well bonded.

In-situ continuous growth of carbon nanotubes on the surface of carbon fibres

An efficient method for growing carbon nanotubes (CNTs) on the surface of continuously moving carbon fibres has been developed by a unique open-ended chemical vapor deposition (CVD) furnace. Scanning electron microscopy (SEM) is used to observe the morphological characteristics of CNTs grown on carbon fibre surfaces, and high-resolution transmission electron microscopy (HRTEM) is used to study the microstructure of CNTs. The results show that the CNTs achieve uniform and orderly growth. In the process of CNTs growth, the cross-linking of adjacent graphite crystallites is formed and the damage of the catalyst nanoparticles to the fibres is repaired, so the tensile strength is increased compared to the carbon fibres undergoing reduction. CNTs-grown carbon fibres can be used to fabricate the flexible supercapacitor electrodes to improve electrochemical capacitance and promote electrochemical stability.

Optimizing electromagnetic wave absorption performance: Design from microscopic bamboo carbon nanotubes to macroscopic patterns

Achieving ideal electromagnetic wave absorbing materials and effective artificial super structures design are increasingly attractive for their irreplaceable role in aerospace stealth structure, Over the Air (OTA) test and civil wireless communication systems. In this work, the bamboo carbon nanotubes (CNTs) were prepared by a simple thermal treatment method. The microstructure and yields of bamboo CNTs were tunable by changing the feeding amounts of polypropylene fabrics precursors. The optimal reflection losses (RL) value of as-prepared bamboo CNTs was up to −54.5 dB at 14.45 GHz with 1.85 mm, meanwhile the effective bandwidth (fe) covered from 12.31 to 17.76 GHz. With subsequent macroscopic honeycomb architecture design based on the as-fabricated bamboo CNTs, the artificial structures with variable radius, thickness and height exhibited more than 90% absorption in 8.5–18 GHz. The results suggested that combination of developing microscopic microwave absorbers and macroscopic structure design would fundamentally optimize the electromagnetic wave absorption with low matching thickness and extensive effective bandwidth.

Electric-field-induced microstructure modulation of carbon nanotubes for high-performance supercapacitors

The growth direction, morphology and microstructure of carbon nanotubes (CNTs) play key roles for their potential applications in electronic and energy storage devices. However, effective synthesis of CNTs in high crystallinity and desired microstructure still remains a tremendous challenge. Here we introduce an electric field for controlling the microstructure formation of CNTs. It reveals that the electric field not only make CNTs aligned parallel but also improve the density of CNTs. Especially, the microstructures of CNTs gradually change under electrical field. That is, graphite sheets are transformed from the “herringbone” structure to a highly crystalline structure, facilitating the transportation of electrons. Due to the improved aligned growth direction, high density and highly crystalline microstructure, the electrochemical performance of CNTs is greatly improved. When the CNTs are applied in supercapacitors, they present a high specific capacitance of 237 F/g, three times higher than that of the CNTs prepared without electrical field. Such microstructure modulation of CNTs by electric field would help to construct high performance electronic and energy storage devices.

Enhancement of thermal conductivity by the introduction of carbon nanotubes as a filler in paraffin/expanded perlite form-stable phase-change materials

In this study, the effect of the introduction of carbon nanotubes (CNTs) as a filler for enhancing the thermal conductivity of paraffin-carbon nanotubes/expanded perlite form-stable composite phase change materials (PA-CNTs/EP FS-CPCMs) was experimentally investigated. Four samples of PA-CNTs/EP FS-CPCMs with different CNT mass fractions were prepared by vacuum impregnation. Scanning electron microscopy was employed to investigate the morphology and microstructure of CNTs, EP, and PA-CNTs/EP FS-CPCMs. Differential scanning calorimetry was employed to examine the thermal properties of PA-CNTs/EP FS-CPCMs, and results indicated that the latent heat and phase-change temperatures of the PA-CNTs/EP FS-CPCMs slightly change with the CNTs mass fractions. The thermal conductivity of PA-CNTs/EP FS-CPCMs5.27 (0.516Wm−1K−1) was 4.82 times that of PA-CNTs/EP FS-CPCMs0. The thermal storage and release properties of PA-CNTs/EP FS-CPCMs were significantly improved as compared with those of PA-CNTs/EP FS-CPCMs0. Results obtained from Fourier transform infrared spectroscopy, thermogravimetric analysis, and thermal cycling tests showed that PA-CNTs/EP FS-CPCMs exhibit good chemical and thermal stabilities. The as-prepared PA-CNTs/EP FS-CPCMs demonstrate considerable potential as thermal energy storage materials.

Characteristics of plasma sprayed coatings produced from carbon nanotube doped ceramic powder feedstock

Incorporation of carbon nanotubes (CNT) in thermally sprayed ceramic coatings is expected to improve its properties. Three ceramic powders were doped with CNT using three methods, namely, dry mixing, mixing in alcohol and heterocoagulation, a colloidal processing technique. Plasma sprayed coatings prepared from these powders were characterized for their microstructure, phases, retention and distribution of CNT, hardness, porosity, fracture toughness, elastic modulus and ultrafine microstructural features. Raman spectroscopy revealed that the CNT could be protected during plasma spraying with limited damage, and CNT was distributed homogeneously in the coatings produced from the heterocoagulated powders. The coating obtained from the heterocoagulated powder was found to possess the highest hardness and least porosity among the coatings investigated. CNT had been found to bridge the splats and thus, enhance coating cohesion. Compared to pure alumina coatings, heterocoagulated coatings demonstrated around 23% and 20% increase in the indentation fracture toughness and elastic moduli, respectively, with the addition of 1wt% CNT. Transmission electron micrographs showed the formation of an interlayer in the matrix-CNT interface.

Predictive Synthesis of Freeform Carbon Nanotube Microarchitectures by Strain-Engineered Chemical Vapor Deposition.

High-throughput fabrication of microstructured surfaces with multi-directional, re-entrant, or otherwise curved features is becoming increasingly important for applications such as phase change heat transfer, adhesive gripping, and control of electromagnetic waves. Toward this goal, curved microstructures of aligned carbon nanotubes (CNTs) can be fabricated by engineered variation of the CNT growth rate within each microstructure, for example by patterning of the CNT growth catalyst partially upon a layer which retards the CNT growth rate. This study develops a finite-element simulation framework for predictive synthesis of complex CNT microarchitectures by this strain-engineered growth process. The simulation is informed by parametric measurements of the CNT growth kinetics, and the anisotropic mechanical properties of the CNTs, and predicts the shape of CNT microstructures with impressive fidelity. Moreover, the simulation calculates the internal stress distribution that results from extreme deformation of the CNT structures during growth, and shows that delamination of the interface between the differentially growing segments occurs at a critical shear stress. Guided by these insights, experiments are performed to study the time- and geometry-depended stress development, and it is demonstrated that corrugating the interface between the segments of each microstructure mitigates the interface failure. This study presents a methodology for 3D microstructure design based on "pixels" that prescribe directionality to the resulting microstructure, and show that this framework enables the predictive synthesis of more complex architectures including twisted and truss-like forms.

Hierarchical Assemblies of Carbon Nanotubes for Ultraflexible Li-Ion Batteries.

The flexible batteries that are needed to power flexible circuits and displays remain challenging, despite considerable progress in the fabrication of such devices. Here, it is shown that flexible batteries can be fabricated using arrays of carbon nanotube microstructures, which decouple stress from the energy-storage material. It is found that this battery architecture imparts exceptional flexibility (radius ≈ 300 μm), high rate (20 A g(-1) ), and excellent cycling stability.

Densification kinetics and mechanical properties of carbon/carbon composites reinforced with carbon nanotubes produced in situ

Carbon nanotube reinforced carbon/carbon composites were fabricated via in situ growth of carbon nanotubes directly on needle-punched felts following direct resistive heating thermal gradient chemical vapor infiltration. The infiltration kinetics, mechanical properties and microstructure of carbon nanotube reinforced carbon/carbon composites were studied. The results show that rough laminar pyrocarbon is obtained owing to CNTs favoring the formation of high-textured pyrocarbon. When nickel nitrate content is 0.10 ml/L, carbon nanotubes with the diameter about 30 nm are obtained together with continuous network on the carbon fibers. The flexural strength and interlaminar shear strength of the composites obtained with 0.1 mol/L nickel nitrate contents are increased by nearly 44.2% and 40.7%, respectively, compared to that of the composite containing no carbon nanotubes.

Effect of sintering temperature on the mechanical properties and microstructure of carbon nanotubes toughened TiB2 ceramics densified by spark plasma sintering

TiB2-based composites containing 15vol% multi-walled carbon nanotubes were synthetized at the temperature of 1600°C to 1800°C for 10min under a uniaxial load of 20MPa by spark plasma sintering. Microstructure, mechanical properties and densification behavior of the composites were studied. It was shown that mechanical properties were increased by introduction of carbon nanotubes, especially for the fracture toughness. The fracture toughness was ∼9.1MPam1/2, which was much higher than that of monolithic TiB2 ceramics. The dense microstructure was the primary factor to improve the mechanical properties. The toughening mechanisms were crack deflection and carbon nanotubes pull-out. The results presented here provide a potential method for improving the fracture toughness of TiB2 ceramics.

Surface pressure and microstructure of carbon nanotubes at an air-water interface.

This article reports the surface pressure and microstructure of two different types of carbon nanotubes (CNTs) at an air-water interface; namely, as-produced CNTs (nf-CNTs) and CNTs functionalized with carboxyl groups (f-CNTs). Both types of CNTs formed 3D aggregates upon compression using a Langmuir-Pockels trough. However, f-CNTs showed a lower degree of aggregation compared with that of nf-CNTs. This is attributed to the deprotonation of the carboxyl groups within the water subphase, leading to additional electrostatic repulsion between f-CNTs. For the same initial amount of CNTs spread onto the interface, the actual coverage of f-CNTs was higher than that of nf-CNTs at a given trough area. At high compression, f-CNTs formed aligned CNT domains at the interface. These 2D domains resembled 3D liquid-crystalline structures formed by excluded volume interactions. The denser packing and orientational ordering of f-CNTs also contributed to a compressional modulus higher than that of nf-CNTs, as calculated from the surface pressure isotherms. A Volmer equation of state was applied to model the measured surface pressure containing both thermodynamic and mechanical contributions. The Volmer model, however, did not consider the loss of CNTs from the interface due to 3D aggregation and consequently overestimated the surface pressure at high compression. The actual coverage of CNT during compression was back calculated from the model and was in agreement with the value obtained independently from optical micrographs. The findings of this work may have a broader impact on understanding the assembly and collective behavior of rod-like particles with a high aspect ratio at an air-water interface.