Suspended Carbon Nanotubes Research Articles

Bolometric terahertz detection based on suspended carbon nanotube fibers

Fast and sensitive detection of terahertz radiation is notoriously difficult, especially the detection at the ambient condition. Here, we fabricated bolometric terahertz photodetectors based on suspended carbon nanotube (CNT) fibers. Because the CNT fibers exhibit a very small heat dissipation area, the heat transport from the CNT fibers to the air is negligible. It ensures the devices can work well at the ambient condition. Additionally, the CNT fibers demonstrate a high responsivity up to 0.54 A W−1 and a short response time of 200 μs. This implies a performance that is competitive among the terahertz photodetectors based on CNT.

Spectroscopic signatures of spin-orbit coupling and free excitons in individual suspended carbon nanotubes

We investigate the intrinsic magneto-optical properties of suspended single-walled carbon nanotubes of various chiralities, using a combination of spectrally and time-resolved spectroscopy of individual nanotubes at low temperature. This study elucidates the population and relaxation dynamics of the lowest-energy bright and dark singlet excitons that are mixed with the Aharonov-Bohm effect. The high-quality emission spectra reveal the residual oscillator strength of the dark exciton in zero field, as an optical signature of spin-orbit coupling. They also unveil an asymmetry in the bright exciton recombination line, attributed to the free nature of excitons in these unperturbed nanotubes.

Magnetized suspended carbon nanotubes based nanofluid flow with bio-convection and entropy generation past a vertical cone

The captivating attributes of carbon nanotubes (CNT) comprising chemical and mechanical steadiness, outstanding electrical and thermal conductivities, featherweight, and physiochemical consistency make them coveted materials in the manufacturing of electrochemical devices. Keeping in view such exciting features of carbon nanotubes, our objective in the present study is to examine the flow of aqueous based nanofluid comprising single and multi-wall carbon nanotubes (CNTs) past a vertical cone encapsulated in a permeable medium with convective heat and solutal stratification. The impacts of heat generation/absorption, gyrotactic-microorganism, thermal radiation, and Joule heating with chemical reaction are added features towards the novelty of the erected model. The coupled differential equations are attained from the partial differential equations by exercising the local similarity transformation technique. The set of conservation equations supported by the associated boundary conditions are worked out numerically by employing bvp4c MATLAB function. The sway of numerous appearing parameters in the analysis on the allied distributions is scrutinized and the fallouts are portrayed graphically. The physical quantities of interest including Skin friction coefficient, the rate of heat and mass transfers are assessed versus essential parameters and their outcomes are demonstrated in tabulated form. It is witnessed that the velocity of the fluid decreases for boosting values of the magnetic and suction parameters in case of both nanotubes. Moreover, the density of motile microorganism is decreased versus larger estimates of bio-convection constant. A notable highlight of the presented model is the endorsement of the results by matching them to an already published material in the literature. A venerable harmony in this regard is achieved.

Effects of dispersion state on rheological and electrical characteristics of concentrated multiwalled carbon nanotube suspensions

We report a dispersion state of concentrated multiwalled carbon nanotube (MWCNT) suspensions depending on their iterative milling process. The rheological properties of concentrated suspensions prepared with different milling times were measured using a Couette-typed rotation rheometer, and their electrical characteristics were investigated via an LCR meter. The relationships of the rheological and electrical properties with the dispersion state of the MWCNT were examined. The results of both the rheological and electrical measurements indicated that the de-bundling and dispersion of the MWCNT induced by the iterative milling yielded a percolation microstructure and an electrically conductive structure.

Magnetic segregation effect in liquid crystals doped with carbon nanotubes.

We study the orientational transitions in a suspension of carbon nanotubes in a nematic liquid crystal induced by an external magnetic field. The case of a finite orientational anchoring of liquid crystal molecules at the surface of doped carbon nanotubes is considered. It is shown that in a magnetic field the initial homogeneous planar texture of the liquid crystal–carbon nanotubes mixture is disturbed in a threshold manner (Fréedericksz transition). The orientational and concentration distributions of the suspension are studied for different values of the magnetic field strength and segregation intensity of the impurity subsystem. The optical phase lag between ordinary and extraordinary rays of light transmitted through a layer of a liquid crystal composite is calculated. The possibility of changing the nature of the Fréedericksz transition from second order to first order is shown. This tricritical behavior is related to the redistribution of the carbon nanotubes (segregation effect) inside the layer.

Structural analyses and deposition of purified carbon nanotubes using electrophoretic deposition

This study was conducted to elucidate the analysis of purified carbon nanotubes (CNTs) in dimethylformamide (DMF) that allows good performance in electrophoretic deposition (EPD) process. In this attempt, the effect of mild acid treatment of nitric acid (HNO3) on CNTs of purification process was evaluated. The purified CNTs quality was observed using Thermal Gravimetric Analysis (TGA), Fourier Transformation Infrared Spectroscopy (FTIR), Transmission Electron microscopy (TEM), Scanning Electron Microscope (SEM) and Energy Dispersive x-ray (EDX). Meanwhile for the suspended purified CNTs, the conducted analyses were zeta potential and UV–vis spectroscopy in different solvents (DMF, distilled water, mixture of acetone/ethanol, NMP, and Texanol). The suspension stability was observed for three days prior to EPD process. It was found that the purity of CNTs increased where only 0.03 wt.% of catalyst were left from TGA analyses. Moreover, the TEM and SEM images showed that the catalyst was being removed after purification and functional groups are introduced as observed through FTIR analysis. The UV–vis results showed that the CNTs were suspended longer in DMF and formed more stable suspension as compared to other solvents where constant reading during observations were obtained while the zeta potential result was indicated to have sufficient particle charge (−35.87 mV) for EPD process. In addition, the mechanism of CNTs purifications was studied and it clearly justified the role of functional group as CNTs charge with good reading of zeta potential was obtained. The SEM image of EPD result shows the performance of CNTs suspension in DMF with optimum deposition thickness of 11.98 μm and 0.9 mg of deposition weight.

A Rheological Investigation of Carbon Nanotube Grease.

The use of carbon nanotubes (CNTs) as a thickening agent in polyalphaolefin oils to create CNT-grease has significant merit. Given the abnormally high thermal conductivities of CNTs, it is conceivable that a CNT-grease would exhibit excellent thermal conductivity. The rheological response of CNT-greases is important for two reasons: to determine if the grease will have sufficient lubricating properties and to provide critical information on the structure and particle-particle interactions of CNT suspensions. The viscoelastic response and evidence of creep recovery support the theory of the stable 3 Dimensional network (3D) formation in the CNT-grease. The elastic response indicates that significant energy is needed to dismember the network structure and initiate viscous flow. The macroscopic rheological investigation provides additional information regarding the structure of CNT-grease and particle-particle interactions at high SWNT concentrations, ~10.0 wt. The knowledge gained concerning the structure of CNT suspensions will allow its manipulation to achieve better thermal properties.

Electrophoretic Deposition of MnO2/CNT Composite As Host Material for Efficient Li-S Batteries

Over the past few decades, lithium-sulfur (Li-S) batteries have gained growing attention as the next generation energy storage devices owing to their low cost, relative safety as well as higher theoretical capacity (1675 mAh g-1) and energy density (2600 Wh kg-1) [1]. This work employs the multi-step electrophoretic deposition (EPD) method [2] to fabricate a layered structure of conductive agents on the surface of micron-sized 3D carbon fiber paper (as the current collector). For this purpose, a homogeneous and crack-free film of MnO2/CNT was deposited as the host material (HM) on carbon fiber paper (CFP) by applying uniform DC electric fields of 30-80 V to the stable suspensions of manganese dioxide (MnO2) and carbon nanotubes (MWCNTs) in acetone. The obtained CFP/MnO2/CNT cathode was then impregnated with sulfur using a facile vapor-phase infusion technique at 200 ̊C. The galvanostatic charge-discharge behavior of the coin cells containing CFP/MnO2/CNT as cathode exhibited an initial discharge capacity of around 1000 mAh g-1 and an improved capacity retention rate after up to 50 cycles at 0.1 C. Also, a coulombic efficiency of above 96% was achieved. It is shown that the EPD-deposited carbon and metal oxide-based host materials, as lithium-sulfur cathode, can achieve high discharge capacity and enhanced cycling behavior. In addition, the rate performance tests conducted at 0.1C, 0.5C, 1C, and 2C revealed relatively high capacities at current rates below 2C, implying excellent conductivity and reaction kinetics of the CFP/MnO2/CNT/S composite. It is concluded that the EPD can be employed as a facile binder-free method to fabricate composite cathode structures for Li-S batteries.

Surface functionalization of carbon nanotubes by biological adhesive polymers carbopol for developing high‐permittivity polymer composites

Surface functionalization of carbon nanotubes (CNTs) by biological adhesive polymers carbopol (CP) was developed by simply mixing CNT suspension and an aqueous solution of CP without any toxic solvents. CP can be easily coated onto CNTs through hydrogen bonds OCOH⋯NH2CO and electrostatic interaction between COO on CP and NH3+ on CNTs. After modification, the surface of the CNT is endowed with a large number of carboxyl groups, which can effectively prevent the reaggregation of CNT by electrostatic repulsion between the ionized carboxyl groups. Hence, highly dispersed functionally modifying CNT by CP (CP‐CNT) filler in polydimethylsiloxane (PDMS) matrix can be obtained. More important, with the help of adhesive properties of CP, the interfacial compatibility between fillers and matrix can also be improved. Thus, the CP‐CNT/PDMS composites exhibited higher dielectric permittivity comparing with CNT/PDMS composites at the same filler content. We present a potential and green approach of surface functionalization of CNT for preparing high‐permittivity polymer composites. J. VINYL ADDIT. TECHNOL., 26:165–172, 2020. © 2019 Society of Plastics Engineers

High Purity Semiconducting Single-Walled Carbon Nanotubes for Printed Electronics

We demonstrate a technique to improve the purity of semiconducting component extracted from single walled carbon nanotube (CNT) suspension by “Electric-field inducing Layer Formation (ELF)”. Separa...

A ultra-wideband thin microwave absorber using inkjet-printed frequency-selective surfaces combining carbon nanotubes and magnetic nanoparticles

A ultra-wideband microwave absorber (UWMA) combining frequency-selective surfaces (FSS) and dielectric layers is proposed. FSS patterns are printed by inkjet on dielectric layers using a resistive magnetic ink made of suspended carbon nanotubes decorated with $${\text {Fe}}_3{\text {O}}_4$$ nanoparticles. The UWMA exhibits a huge fractional bandwidth of 140%, corresponding to reflectivity lower than − 10 dB and absorption higher than 90%, observed from 7 GHz to 43 GHz, meaning a 36 GHz bandwidth, for a thickness of only 0.26 $$\lambda$$. This performance is achieved through a proper selection of FSS surface resistance, tuned by the number of printed layers. Excellent agreement is observed between designed and measured low reflectivity and high absorption.

Statistical theory of magnetic field induced phase transitions in negative diamagnetic anisotropy liquid crystals doped with carbon nanotubes

A statistical mean-field theory is proposed for describing the magneto-orientational ordering of a composite material, namely a liquid crystal suspension of carbon nanotubes. A nematic liquid crystal with negative anisotropy of diamagnetic susceptibility with the molecules, which have long axes tending to be orthogonal to the applied magnetic field, has been considered as a dispersion medium. Since carbon nanotubes possess positive anisotropy of the diamagnetic susceptibility, they tend to align parallelly to the field, causing competition with the ordering of the liquid crystal matrix. Phase transitions induced by temperature and magnetic field have been studied for different values of the coupling energy of carbon nanotubes with a liquid crystal matrix. It is shown that depending on the temperature, magnetic field induces the transition from a highly ordered nematic phase to a weakly ordered paranematic phase with both the positive and the negative value of the order parameter of the liquid crystal, which respectively corresponds to the orientational anisotropy of the “easy-axis” and “easy-plane” types.

Entropy Generation and Heat Transfer Analysis in MHD Unsteady Rotating Flow for Aqueous Suspensions of Carbon Nanotubes with Nonlinear Thermal Radiation and Viscous Dissipation Effect.

The impact of nonlinear thermal radiations rotating with the augmentation of heat transfer flow of time-dependent single-walled carbon nanotubes is investigated. Nanofluid flow is induced by a shrinking sheet within the rotating system. The impact of viscous dissipation is taken into account. Nanofluid flow is assumed to be electrically conducting. Similarity transformations are applied to transform PDEs (partial differential equations) into ODEs (ordinary differential equations). Transformed equations are solved by the homotopy analysis method (HAM). The radiative source term is involved in the energy equation. For entropy generation, the second law of thermodynamics is applied. The Bejan number represents the current investigation of non-dimensional entropy generation due to heat transfer and fluid friction. The results obtained indicate that the thickness of the boundary layer decreases for greater values of the rotation parameter. Moreover, the unsteadiness parameter decreases the temperature profile and increases the velocity field. Skin friction and the Nusselt number are also physically and numerically analyzed.

Suspended CNT-Based FET sensor for ultrasensitive and label-free detection of DNA hybridization

A suspended carbon nanotube (SCNT)-based field effective transistor (SCNT-FET), which was fabricated by utilizing the surface tension of liquid silver to suspend a CNT between two Pd electrodes, was proposed for the detection of DNA hybridization. Benefits from the separation between the CNT and the substrates could be observed; namely, the conductivity of a SCNT-FET was much higher (two orders of magnitude) than that of a FET based on an unsuspended CNT and about 50% sensing surface of CNT was freed from substrate. The Slater-Koster tight-binding method was adopted for geometry optimization and transport property calculation of the SCNT bound with DNA. The result showed that the conductance (G = 1/R) of the SCNT decreased in order with the binding of single-stranded DNA (SSDNA, probe DNA) and double-stranded DNA (DSDNA) and that the ability of DSDNA to weaken the conductivity of the SCNT was several times higher than that of SSDNA. SEM and Raman spectroscopy were used to demonstrate that DNA could be bound successfully onto the SCNT using a 1-pyrenebutanoic acid succinimidyl ester (PBASE) as a linkage. Ultra-high sensitivity detection of DNA [with a limit of detection (LOD) as low as 10 aM] was obtained using such an SCNT-FET, which showed a lower value than that of a previously reported FET DNA biosensor whose sensing materials were in direct contact with the substrate.

(Invited) Ultra-Low Power Light Emission Via Avalanche and Sub-Avalanche Breakdown in Suspended Carbon Nanotubes

We report near-infrared light emission in suspended carbon nanotube field effect transistors over a wide range of gate and bias voltages. An abrupt increase in both the electric current (90 μA/V) and electroluminescence intensity is observed at high bias voltages (∼3.5 V), when gated in the “off’ state (i.e., Vgate > 0 V). For bias voltages below the threshold for avalanche breakdown, we observe light emission due to the creation of exitons by impact ionization under these high electric fields. Here, we find that there is a relatively small region over which low power (∼nW) light emission is observed. By plotting the relative luminescence efficiency (i.e., light intensity/electrical power) as a function of the gate and bias voltages, we observe a very sharp feature corresponding to avalanche emission at which the electroluminescence efficiency is 2−3 orders of magnitude higher than that under all other conditions of gate and bias voltage. A steep increase in the current with bias voltage (i.e., large dI/dVb) is observed at the same gate and bias conditions of the highly efficient electroluminescence and signifies the onset of the avalanche process. We believe that these results demonstrate additional mechanistic evidence for achieving highly efficient light emission in carbon nanotubes via avalanche breakdown.

Curve fitting on experimental data of a new hybrid nano-antifreeze viscosity: Presenting new correlations for non-Newtonian nanofluid

In this paper, the rheological behavior of a mixture of water and ethylene glycol containing a combination of multi-walled carbon nanotubes and aluminum oxide in a temperature range of 25 to 50 °C was investigated experimentally. Homogeneous and stable samples with different concentrations were made by suspending carbon nanotubes and aluminum dioxide in a 50–50 mixture of water and ethylene glycol using a two-step method. The viscosity of nanofluid samples at different shear rates was measured by the DV-I PRIME Brookfield digital viscometer, which uses a rotating cylinder method. The results showed that, despite the Newtonian behavior of the base fluid, all nanofluid samples showed a non-Newtonian behavior. It was also observed that non-Newtonian behavior of nanofluid follows the Power law model. Thus, using the curve fitting, the consistency index and the power law index were obtained. Moreover, mathematical correlations were proposed as a function of temperature and volume fraction for obtaining consistency index and the power-law index. Comparisons showed the accuracy of proposed correlations.

Layering Transition in Superfluid Helium Adsorbed on a Carbon Nanotube Mechanical Resonator.

Helium is recognized as a model system for the study of phase transitions. Of particular interest is the superfluid phase in two dimensions. We report measurements on superfluid helium films adsorbed on the surface of a suspended carbon nanotube. We measure the mechanical vibrations of the nanotube to probe the adsorbed helium film. We demonstrate the formation of helium layers up to five atoms thickness. Upon increasing the vapor pressure, we observe layer-by-layer growth with discontinuities in both the number of adsorbed atoms and the speed of the third sound in the adsorbed film. These hitherto unobserved discontinuities point to a series of first-order layering transitions. Our results show that helium multilayers adsorbed on a nanotube are of unprecedented quality compared to previous works. They pave the way to new studies of quantized superfluid vortex dynamics on cylindrical surfaces, of the Berezinskii-Kosterlitz-Thouless phase transition in this new geometry, and perhaps also to supersolidity in crystalline single layers as predicted in quantum MonteCarlo calculations.

Instigated magnetic field effect on carbon nanotubes suspensions encompassing variable thermophysical characteristics

This communication aims to explore the instigated magnetic field and partial slip influence on nanofluid transport towards the curved stretching surface by taking into the account temperature and nanoparticles volume fraction dependent viscosity. The single and multi-wall carbon nanotubes (CNTs) are incorporated in the traditional industrial fluids namely, water and propylene glycol. The Curvilinear coordinate system is opted to model the physical flow problem and simplification is performed by utilizing appropriate transformation. The velocity, pressure, induced magnetic field and temperature distributions accompanied by surface drag force and heat flux are computed numerically by employing implicit finite difference scheme. Graphs and bar charts are drawn to examine the effects of prominent substantial parameters. Some pivotal findings are that the Nusselt number was increasing function of ϕ,λ* and Rd and decreasing function of k and N. The present study is a prototype and a benchmark in exploring induced magnetic field effects on CNTs transport over a curved surface and will lead to further investigation in future and may be beneficial in polymer industry and nanotechnology.

Miniature pressure sensor based on suspended MWCNT

Conventional pressure sensors rely on diaphragms with large surface areas, which deform in response to pressure. Down scalability of these devices is one of the major challenges of the technology along with reducing the overall actuation voltage and achieving ultra-high sensitivity. We present a sensitive miniature pressure sensor based on the change in the physisorbed gases with the pressure of the surrounding air. The sensor consists of a suspended individual multiwall carbon nanotube (MWCNT) clamped on Au electrodes by electron-beam-induced deposition (EBID) of Pt. The variation in the surrounding pressure is shown to be tracked by monitoring the change in the resistivity, hence resistance, of the MWCNT bridge structure due to the change in percentage of oxygen and humidity in the surrounding medium with pressure. The experimental data reveal the practicability and simplicity of the proposed pressure sensor.

Modification of cement systems by carbon nanotubes

The nanoparticles and nanostructures such as nano silica, nano metakaolin, titanium dioxide and aluminium oxide nanoparticles, graphite nanomaterials, carbon nanotubes are used for modification of composite materials in construction industry. The considerable attention of researchers is focused on the investigation of cement systems modified by carbon nanotubes (CNT). The present research describes the generalized data about modification of cement systems by CNT suspension in fresh and hardened state. The influence of carbon nanotubes on setting time of cement paste, rheological and mechanical properties of nanomodified cement systems are demonstrated in the present research.