Suspended Carbon Nanotubes Research Articles

Wet electrospinning-aided self-assembly of multifunctional GO-CNT@PCL core-shell nanocomposites with spider leg bioinspired hierarchical architectures

We report a fast route enabling the multiscale design of nanohybrid structures comprising a 3D fibrous network of polycaprolactone (PCL) wrapped by graphene oxide (GO) sheets onto which carbon nanotube (CNT) brushes are anchored. The method relies on electrospinning PCL solutions onto a suspension of GO and CNTs in ethanol. Self-assembly is due to electrostatic wrapping of GO sheets around PCL fibers and π-π stacking between GO and CNTs. Hierarchical architecture and nanopatterned surface allow gathering the starting properties of PCL, GO and CNTs into lightweight (99% porosity) yet robust (1575% stiffness improvement), amphiphilic monoliths that can remove methylene blue and/or methyl orange from stagnant water with ca.100% efficiency.

High-speed identification of suspended carbon nanotubes using Raman spectroscopy and deep learning

The identification of nanomaterials with the properties required for energy-efficient electronic systems is usually a tedious human task. A workflow to rapidly localize and characterize nanomaterials at the various stages of their integration into large-scale fabrication processes is essential for quality control and, ultimately, their industrial adoption. In this work, we develop a high-throughput approach to rapidly identify suspended carbon nanotubes (CNTs) by using high-speed Raman imaging and deep learning analysis. Even for Raman spectra with extremely low signal-to-noise ratios (SNRs) of 0.9, we achieve a classification accuracy that exceeds 90%, while it reaches 98% for an SNR of 2.2. By applying a threshold on the output of the softmax layer of an optimized convolutional neural network (CNN), we further increase the accuracy of the classification. Moreover, we propose an optimized Raman scanning strategy to minimize the acquisition time while simultaneously identifying the position, amount, and metallicity of CNTs on each sample. Our approach can readily be extended to other types of nanomaterials and has the potential to be integrated into a production line to monitor the quality and properties of nanomaterials during fabrication.

Critical current density for layer-by-layer breakdown of a multiwall carbon nanotube

Electric-current-induced structural changes in a suspended multiwall carbon nanotube (MWCNT) were observed through in situ transmission electron microscopy. The bias voltage and electric current were measured simultaneously as the MWCNT was imaged. The passage of excessive current led to breakdown of the surface of the MWCNT and to subsequent layer-by-layer removal of the broken outermost shell via sublimation of carbon atoms. The surface breakdown of the MWCNT was accompanied by a discrete decrease in the current. Under the assumption that the current passes solely through the outermost shell of the MWCNT, we found that the critical current densities at which the breakdown in the renewed outermost shell occurred after the removal of the broken outermost shell were limited to a remarkably narrow range of (2.4 ± 0.2) × 109 A/cm2, irrespective of the outermost diameter of the MWCNT. The present results provide invaluable information about electron transport phenomena in MWCNTs and about the durability of CNT nanocircuits.

Synthesis, characterization and flocculation efficiency of grafted Moringa gum based derivatives

This paper reports the synthesis of Moringa gum based flocculants with different monomers using aqueous microwave based method. Moringa was grafted with acrylamide, acrylic acid and an assisted hybrid comonomer (PAM-co-PAA) to develop a comprehensive material suited for all kinds of water quality treatment. Grafting was confirmed by different analytical techniques like intrinsic viscosity measurements, molecular weight, elemental analysis, FE-SEM, XRD, FTIR studies and NMR. All these grafted grades were optimized for best performance at different pH (2−10) and temperature (10-60 °C) range. The flocculation efficiency was tested using coal fine, kaolin and multi-walled carbon nanotube (MWCNTs) suspensions. The efficiency of MOG-g-(PAM-co-PAA) was found to be consistently best as compared to MOG-g-PAM and MOG-g-PAA in all the solutions. This may be due to competitive grafting of PAM with respect to PAA. The treatment with 90% (coal fine), 91% (river water) 92% (kaolin) and 98% (MWCNTs) efficiency was achieved. These results indicate that modified Moringa gum based flocculants can be used for many emerging contaminants in future.

Effects of steel surface treatment with silanized carbon nanotubes on the bonding properties between steel and epoxy adhesive

ABSTRACT The interfacial bonding properties of steel and adhesives are the key factors affecting the application of external bonded fiber reinforced polymer composites to strengthen steel structures. The present study proposed a new method to treat steel surface with carbon nanotubes (CNTs) for modification of the interfacial bond strength between steel and an epoxy adhesive. CNTs were modified in ethanol-water mixture by silane and PVP (Polyvinyl Pyrrolidone) to improve the dispersity of CNTs. Steel plates treated through dip-coating or spray-coating with the modified CNTs suspensions were used for single lap joint tests. Compared to the control samples, the treated steel surfaces resulted in a significant increase in the interface shear strength (i.e., by 52.8%). The desirable enhancement is attributed to the existence of CNT between the steel and adhesives, which is connected to the steel surface through Si-O-Fe covalent.

Fast In-Situ Optical Visualization of Carbon Nanotubes Assisted by Smoke.

The fast visualization and manipulation of individual carbon nanotubes (CNTs) has always been a significant technology for their fundamental research. Here, a fast and facile approach is proposed to realize the optical observation of individual suspended CNTs and CNT networks under conventional optical microscopes with the assistance of tar nanodroplets from smoke. The nanodroplets deposited on CNTs render them with strong light scattering to visible light, thus making the CNTs visible under optical microscopes. This visualization method is controllable, environmentally friendly, low-cost, and can be completed in just a few seconds in ambient conditions. Besides, the tar nanodroplets can be easily removed from the CNTs by laser irradiation. More importantly, the smoke sources are widely available and there are no strict requirements for operating conditions. This smoke-assisted visualization method shows great potential in the fundamental research of CNTs.

Light-induced thermal convection for collection and removal of carbon nanotubes

Carbon nanotubes (CNTs) have exhibited immense potential for applications in biology and medicine, and once their intended purpose is fulfilled, the elimination of residual CNTs is essential to avoid negative effects. In this study, we demonstrated the effective collection and simple removal of CNTs dispersed in a suspension via thermal convection. First, a tapered fiber tip with a cone angle and end diameter of 10° and 3 μm, respectively, was fabricated via a heating and pulling method. Further, a laser beam with a power and wavelength of 100 mW and 1.55 μm, respectively, was launched into the tapered fiber tip, which was placed in a CNT suspension, resulting in the formation of a microbubble on the fiber tip. The temperature gradient on the microbubble and suspension surface induced thermal convection in the suspension, which resulted in the accumulation of CNTs on the fiber tip. The experimentally formed CNT cluster possessed a circular top surface with a diameter of 87 μm and an arched cross-section with a height of 19 μm. Furthermore, this CNT cluster was firmly attached to the fiber tip. Therefore, the removal of CNT clusters can be realized by simply removing the fiber tip from the suspension. Moreover, we simulated the thermal convection that caused CNT aggregation. The obtained results indicate that convection near the fiber tip flows toward it, which pushes the CNTs toward the fiber tip and enables their attachment to it. Further, the flow velocity is symmetrically distributed as a Gaussian function, which results in the formation of a circular top surface and arched cross-sectional profile for the CNT cluster. Our method may be applied in biomedicine for the collection and removal of nano-drug residues.

Resonator-induced quantum phase transitions in a hybrid Josephson junction

We investigate the Josephson current through a suspended carbon nanotube double quantum dot which, at sufficiently low temperatures, is characterized by the ground state of the electronic subsystem. Depending on parameters like a magnetic field or the inter-dot coupling, the ground state can either be a current-carrying singlet or doublet, or a blockaded triplet state. Since the electron-vibration interaction has been demonstrated to be electrostatically tuneable, we study in particular its effect on the current-phase relation. We show that the coupling to the vibration mode can lift the current-suppressing triplet blockade by inducing a quantum phase transition to a ground state of a different total spin. Our key finding is the development of a triple point in the Josephson current parameterized by the resonator coupling and the Josephson phase. The quantum phase transitions around the triple point are directly accessible through the critical current and resilient to moderately finite temperatures. The proposed setup makes the mechanical degree of freedom part of a superconducting hybrid device which is interesting for ultra-sensitive displacement detectors.

Phonon-Induced Pairing in Quantum Dot Quantum Simulator.

Quantum simulations can provide new insights into the physics of strongly correlated electronic systems. A well-studied system, but still open in many regards, is the Hubbard-Holstein Hamiltonian, where electronic repulsion is in competition with attraction generated by the electron-phonon coupling. In this context, we study the behavior of four quantum dots in a suspended carbon nanotube and coupled to its flexural degrees of freedom. The system is described by a Hamiltonian of the Hubbard-Holstein class, where electrons on different sites interact with the same phonon. We find that the system presents a transition from the Mott insulating state to a polaronic state, with the appearance of pairing correlations and the breaking of the translational symmetry. These findings will motivate further theoretical and experimental efforts to employ nanoelectromechanical systems to simulate strongly correlated systems with electron-phonon interactions.

Stable Near-Infrared Photoluminescence of Single-Walled Carbon Nanotubes Dispersed Using a Coconut-Based Natural Detergent.

We prepared single-walled carbon nanotube (SWNT) suspensions in phosphate buffer solutions containing 1% of a coconut-based natural detergent (COCO) or 1% of sodium dodecyl sulfate (SDS). The suspensions exhibited strong photoluminescence (PL) in the near-infrared region, suggesting that the SWNTs, such as those with (9, 4) and (7, 6) chiralities, were monodispersed. Upon diluting the suspensions with a detergent-free phosphate buffer solution, the PL intensity of the SDS-containing SWNT suspension was significantly lower than that of the COCO-containing SWNT suspension. The COCO-containing SWNT suspension was more stable than the SDS-containing SWNT suspension. The SWNT concentration of the suspensions prepared via bath-type sonication was lower than that of the suspensions prepared via probe-type sonication. However, near-infrared (NIR) PL intensity of the SWNT suspensions prepared via bath-type sonication was much higher than that of the SWNT suspensions prepared via probe-type sonication regardless of the detergent. This suggested that the fraction of monodispersed SWNTs of the suspensions prepared via bath-type sonication was larger than that of the suspensions prepared via probe-type sonication, although the SWNT concentration was low. Our results indicated that COCO favored the fabrication of SWNT suspensions with stable and strong NIR PL, which are useful for various biological applications.

Electrophoretic deposition of carbon nanotubes: recent progress and remaining challenges

ABSTRACT Electrophoretic deposition (EPD) is a powerful technique to assemble carbon nanotube (CNT) coatings and composite films with controlled architectures. This comprehensive review of the EPD of CNTs and CNT-containing composites focuses on achievements within the last 15 years and ongoing challenges. Stable CNT suspensions are a pre-requisite for successful EPD and have been prepared by a variety of strategies, discussed here. The resulting film microstructure is determined by the initial feedstock, the suspension, and the EPD approach applied, as well as a variety of EPD processing parameters. Nanocomposites can be prepared via co-deposition, sequential deposition, or post-deposition treatments, to introduce metallic, ceramic or polymeric phases. There are numerous potential applications for both homogeneous and patterned CNT films, including as structural reinforcements for composites, as field emission, energy storage and conversion devices, as well as in biomedical applications. The advantages and disadvantages of EPD processing in these contexts are discussed.

Electrically driven transport of photoinduced hot carriers in carbon nanotube fibers.

Hot carriers play a significant role in applications of photovoltaics, photodetection, and photocatalysis. However, effective methods for observing the ultrafast dynamic processes of hot carriers are concentrated on the time domain, on which it is difficult and complex to operate. We propose a novel, to the best of our knowledge, and creative strategy to convert the time-domain dynamic process into a spatially thermal redistribution in suspended carbon nanotube fibers. The large average free path of photoinduced hot holes ensures a prominent offset of temperature distribution. The experimental results confirm the theory about electrically driven transport of hot holes, which has rarely been reported.

Indentation behavior of suspended single-walled carbon nanotube films

Suspended thin film carbon nanotubes with suitable mechanical strength are in high demand for applications such as sensors, particle filters, or thermoacoustic speakers. However, researchers working on the production and development of applications for thin films have found difficulty in evaluating their mechanical strength. This research shows the nano-indentation behavior of thin (<26 nm thickness) single-walled carbon nanotube suspended films, to evaluate their mechanical strength. Indentation tests, scanning electron microscopy, and Raman, infrared, reflection spectroscopy showed that the high crystallinity of carbon nanotubes and film thickness uniformity are important for achieving high mechanical strength.

Effect of Ultrafine Additives on the Morphology of Cement Hydration Products

The present research is focused on the investigation of the influence of ultrafine additives on the structure formation of hardened cement paste and the establishment of the mechanisms of the morphological transformations, which determine the properties of hydrated products. In the course of the research, the modification of ordinary Portland cement was performed by the suspension of multi-walled carbon nanotubes (MWCNTs), carbon black (CB) paste, and silica fume (SF). Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) microanalysis, X-ray diffraction (XRD) analysis, thermal analysis, and Fourier-transform infrared (FTIR) spectroscopy were used to study cement hydration products. The morphology of hardened cement paste depends on the chemical reactivity of additives, their geometry, and their genesis. The action mechanism of the inert carbon-based additives and pozzolanic silica fume were considered. The cement hydration products formed in the process of modification by both types of ultrafine additives are described. In the case of the modification of cement paste by inert MWCNTs and CB paste, the formation of cement hydration products on their surface without strong adhesion was observed, whereas in the case of the addition of SF separately and together with MWCNTs, the strong adhesion of additives and cement hydration products was noted.

Proposal for a Nanomechanical Qubit

Mechanical oscillators have been demonstrated with very high quality factors over a wide range of frequencies. These also couple to a wide variety of fields and forces, making them ideal as sensors. The realization of a mechanically-based quantum bit could therefore provide an important new platform for quantum computation and sensing. Here we show that by coupling one of the flexural modes of a suspended carbon nanotube to the charge states of a double quantum dot defined in the nanotube, it is possible to induce sufficient anharmonicity in the mechanical oscillator so that the coupled system can be used as a mechanical quantum bit. This can however only be achieved when the device enters the ultrastrong coupling regime. We discuss the conditions for the anharmonicity to appear, and we show that the Hamiltonian can be mapped onto an anharmonic oscillator, allowing us to work out the energy level structure and how decoherence from the quantum dot and the mechanical oscillator are inherited by the qubit. Remarkably, the dephasing due to the quantum dot is expected to be reduced by several orders of magnitude in the coupled system. We outline qubit control, readout protocols, the realization of a CNOT gate by coupling two qubits to microwave cavity, and finally how the qubit can be used as a static force quantum sensor.

Carbon Nanotubes Flex as Qubits

A suspended carbon nanotube coupled to a double quantum dot makes a mechanical oscillator that serves as a qubit.

Hydration and Microstructure of Nano Modified Cement Paste

Hydration of cement systems modified by nano additives requires the understanding of its mechanisms. The present research is focused on the investigation of hydration processes in cement pastes modified by multi-walled carbon nanotubes (MWCNTs) suspension. The ultrasonication method was used for homogenization of MWCNTs in the volume of an aqueous suspension. The hydration of cement pastes was assessed by the calorimetry test. The prolongation of cement hydration in case of modification by MWCNT suspension was observed. The microstructure observation by scanning electron microscopy (SEM) was performed for identification of MWCNT's dispergation in hardened cement pastes and for the observation of cement hydration products. The compressive and flexural strength were tested to evaluate the effect of MWCNT on mechanical properties of hardened cement paste.

Generation of entanglement between quantum dot molecule with the presence of phonon effects in a voltage-controlled junction

We investigate the generation of entanglement through a quantum dot molecule under the influence of vibrational phonon modes in a bias voltage junction. The molecular quantum dot system is realized by coupled quantum dots inside a suspended carbon nanotube. We consider the dynamical entanglement as a function of bias voltage and temperature by taking into account the electron-phonon interaction. In order to generate the robust entanglement between quantum dots and preserve it to reach the maximal achievable amount steadily, we introduce an asymmetric coupling protocol and apply the easy tunable bias voltage-driven field. For an oscillating bias voltage, the time-varying entanglement can periodically reach the maximum revival. In thermal entanglement dynamics, the phenomena of thermal entanglement degradation and thermal entanglement revival are observed which are intensively affected by the strength of phonon decoherence. The revival of entanglement shows a larger value for a higher phonon coupling.

Solar-Thermal Conversion Characteristics of Surfactant-Free Gold Nanoparticles Produced By Plasma-Based Synthesis Method

Gold nanoparticles (Au NPs), with their unique plasmonic absorption in the visible spectrum, are promising candidates for the use as nanofluids for enhancing the solar-thermal conversion (STC) process in direct-absorption solar collectors (DASCs) [1-4]. Their absorption performance mainly depends on their size and morphology [5] controlled by the synthesis technique used [4], such as the widely-used wet chemistry-based methods. These chemical methods rely on the use of surfactants for controlling the nanoparticles size and shape, as well as achieving stability within the hosting fluid. However, utilizing chemical additives results in undesired by-products, which require washing, purification and recycling processes and also they eliminate the possibility of further functionalization of the produced Au NPs [6, 7]. Besides, surfactants increase the thermal resistance between the nanoparticle and the hosting fluid [8] and could also decompose and degrade over time, at operating temperatures as low as 70 °C [9].In the present work, the optical properties and STC characteristics of three types of Au NPs produced by different synthesis methods were experimentally investigated. The first type was produced using a plasma-induced non-equilibrium electrochemistry system, to form surfactant-free nanoparticles (sf-Au NPs). The second type was synthesized using Turkevich method to form PEGylated nanoparticles (p-Au NPs), while the third type is citrate-capped nanoparticles (c-Au NPs), supplied by Sigma. After washing and drying the Au NPs powder of each type, they were separately re-dispersed in ethylene glycol (EG) as a base fluid to give Au NPs concentration of 39.4 mg/L forming nanofluids of sf-Au NPs/EG, p-Au NPs/EG and c-Au NPs/EG.XPS results of the untreated and treated gold precursors, used for the synthesis process, showed that no gold ions were found in the treated sample, indicating the full reduction of the gold precursors. In addition, TEM images showed that all samples have the same average nanoparticle size of ~32 nm. However, the size and morphology of sf-Au NPs showed a broad range of sizes and shapes, while the other two samples have nanoparticles of fine spherical shapes and narrow size distribution. Furthermore, the optical properties results for a wavelength range of 280-900 nm, using UV-VIS spectroscopy, showed sf-Au NPs/EG nanofluid exhibited a broad plasmonic absorption peak over the visible spectrum, while the other two nanofluids have similar narrow peaks. Moreover, measurements from Zetasizer Nano ZS system showed that sf-Au NPs have a zeta potential of -25.8 mv, while the p-Au NPs and c-Au NPs have slightly higher values of -35.6 mV and -38.6 mV, respectively, which could be considered as good stabilization.A lab-scale DASC was built for investigating the STC performance of each nanofluid, under a uniform radiation intensity of ∼1000 W/m2 for 25 min, during which the nanofluids temperature change was recorded. Results revealed that sf-Au NPs/EG nanofluid achieved the highest solar-thermal conversion efficiency and specific absorption rate, compared to the other two surfactant-based Au NPs/EG nanofluids. The STC efficiency was enhanced to above 80%, compared to the efficiency of the base fluid, while 50-60% enhancement was reached by the surfactant-based nanofluids, highlighting the advantages of using plasm-liquid treatment method for the synthesis of sf-Au NPs for the use as nanofluids for solar energy harvesting in DASCs. 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BEM modeling and experiment verification for thermoacoustic response of suspended nano thin films

A kind of novel suspended nano thin films that exhibit excellent thermoacoustic effects is introduced as a promising candidate and a new approach for acoustic wave generation without mechanical vibration. Although several analytical models have been established in the past to determine thermoacoustic fields and to aid design optimization, there still show many limitations. In particular, those analyses in the past are mostly only available for one-dimensional problems. In this paper, a new numerical approach based on the boundary element method (BEM) is developed for predicting acoustic fields excited from a suspended thermoacoustic (TA) nano thin film with an arbitrary three-dimensional configuration. To substantiate the numerical model, experimental studies on the thermoacoustic emission of carbon nanotube (CNT) thin films are performed to verify the proposed method and excellent agreement is observed. By using the numerical approach, the accuracy and applicability of two recently developed analytical models for suspended CNT thin films are evaluated and discussed in detail. Furthermore, the influence of irregular deformation of CNT thin films on the acoustic field is investigated.