Conductive Multi-walled Carbon Nanotubes Research Articles

Numerical Study on Effective Thermal Conductivity of Radial Nanowire Heterostructures with MWCNT Core

The present study aims to investigate numerically the effective thermal conductivity for different radial nanowire heterostructures (RNWHSs), such as core­shell, tubular­shell, and core­shell­shell types, which are used for resolving thermal dissipation problem. The influence of core radius and shell thickness on the effective thermal conductivity was examined by using the boundary/interfacial scattering (BS) method derived from the Casimir theory. It was found that the effective thermal conductivity of the RNWHSs was smaller than the bulk thermal conductivity of multi-walled carbon nanotubes (MWCNTs) because of the diffusive interfacial scattering effect. When the shell thickness was much thinner than the core radius, the thermal conductivity of the core MWCNTwas relatively higher than that of the shell material. Comparing MWCNT/Al2O3 and MWCNT/SiO2 core­shell RNWHSs, the effective thermal conductivities were similar when the core radius was greater than 100 nm or the core porosity was above 0.4, owing to the effect of MWCNT bulk thermal conductivity. Besides, the effective thermal conductivity of the tubular­shell RNWHS with the same cross-sectional area was always lower than that of the core­shell RWNHSs because of additional interfacial scattering at the pores inside the tubular-shell RNWHSs. When the Al2O3 thickness in the core­shell­shell RNWHS of MWCNT/Al2O3/W was less than 135 nm at a fixed MWCNT radius of 100 nm, the effective thermal conductivity increased with core porosity. When the Al2O3 thickness was 1.0 nm, the effective thermal conductivity rapidly decreased with the increase in porosity. [doi:10.2320/matertrans.M2014191]

Electrochemical and Optical Investigation of Conductive Polymer and MWCNT Nanocomposite Film

Composites of multi-walled carbon nanotubes (MWCNT) and conductive polymer with good uniformity were prepared by electropolymerization. Molecular modeling calculations were carried out for electroactive monomer (OAP) polymerization with density functional theory (DFT) level using 6-311G(d,p) basis set for all atoms and Gaussian 03 program package. The reflectance and transmittance amplitudes of the composite were obtained, using the continuity of the tangential components of electrical and magnetic fields at interfaces and solving the algebraic matrix equation. The calculated absorbance spectra as a function of wavelength for MWCNTs dispersed in the conductive polymer are depicted. Band gap of the p-type semiconducting film was obtained from the plot of (αhv)2vs. photon energy.

Hierarchically Structured Ni3S2/Carbon Nanotube Composites as High Performance Cathode Materials for Asymmetric Supercapacitors

The Ni3S2 nanoparticles with the diameters ranging from 10 to 80 nm are grown on the backbone of conductive multiwalled carbon nanotubes (MWCNTs) using a glucose-assisted hydrothermal method. It is found that the Ni3S2 nanoparticles deposited on MWCNTs disassemble into smaller components after the composite electrode is activated by the consecutive cyclic voltammetry scan in a 2 M KOH solution. Therefore, the active surface area of the Ni3S2 nanoparticles is increased, which further enhances the capacitive performance of the composite electrode. Because the synergistic effect of the Ni3S2 nanoparticles and MWCNTs on the capacitive performance of the composite electrode is pronounced, the composite electrode shows a high specific capacitance of 800 F/g and great cycling stability at a current density of 3.2 A/g. To examine the capacitive performance of the composite electrode in a full-cell configuration, an asymmetric supercapacitor device was fabricated by using the composite of Ni3S2 and MWCNTs as the cathode and activated carbon as the anode. The fabricated device can be operated reversibly between 0 and 1.6 V, and obtain a high specific capacitance of 55.8 F/g at 1 A/g, which delivers a maximum energy density of 19.8 Wh/kg at a power density of 798 W/kg. Furthermore, the asymmetric supercapacitor shows great stability based on the fact that the device retains 90% of its initial capacitance after a consecutive 5000 cycles of galvanostatic charge-discharge performed at a current density of 4 A/g.

Synthesis and conductivity of multiwalled carbon nanotubes modified poly(vinyl alcohol)/ poly(diallyldimethylammonium chloride) as alkaline anion-exchange membranes

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Transparent and conductive multi walled carbon nanotubes flexible electrodes for optoelectronic applications

Regarding their flexibility, transparency and their ability to conduct, the carbon nanotubes thin films has been a growing interest for applications in optoelectronics. This paper illustrates a process of fabrication for multiwalled carbon nanotubes (MWCNT) thin films on PET (polyethylene terephthalate) substrates to obtain flexible conductive electrodes. Actually, there are several processes to elaborate a flexible conductive electrode using carbon nanotubes, such as: (i) Direct deposition using spin coating, spraying, or incubation produces films, or (ii) deposition by vacuum filtration. In our experiments, we had adopted the deposition by vacuum filtration method to prepare our flexible electrodes using the PET substrate. The optimum result was achieved with a concentration of 1.2mg/ml, corresponding to a sheet resistance (Rs) of 180Ωcm−2 with optical transparence about 81% at 550nm. We will also demonstrate the usage of elaborated flexible conductive electrodes to fabricate organic diodes having the following structure: PET–MWCNTs/P3HT: PC70BM/Al.

Ammonia vapor sensing and electrical properties of fibrous multi-walled carbon nanotube/polyaniline nanocomposites prepared in presence of cetyl-trimethylammonium bromide

Electrically conductive HCl-doped multi-walled carbon nanotube (MWCNT)/polyaniline (Pani) nanocomposites were prepared in the presence of cetyl-trimethylammonium bromide by in situ oxidative polymerization of aniline containing different amount of MWCNTs. Thus prepared Pani@MWCNT nanocomposites were characterized by FTIR, XRD, Raman spectroscopy, SEM and TEM. The stability in terms of their electrical conductivity retention was studied under isothermal and cyclic aging conditions. Pani@MWCNT nanocomposites showed increased thermal stability in terms of DC electrical conductivity retention with increasing MWCNT content. One of the Pani@MWCNT nanocomposites was also tested for ammonia sensing which showed good sensing response and high reproducibility.

Weavable dye sensitized solar cells exploiting carbon nanotube yarns

Weavable Dye Sensitized Solar Cells (DSSC) made with flexible yarns of conductive multiwalled carbon nanotubes (MWNTs) were produced having a power conversion efficiency above 3%. This was achieved with a specific design and careful consideration of the yarn function in the DSSC. Fermat yarns of MWNTs individually coated with mesoporous TiO2 layer were twisted together and coated with more mesoporous TiO2 to create a 3 dimensional photo electrode to overcome electron diffusion length issues. Archimedian yarns of MWNTs coated with a thin layer of platinum worked as a counter electrode to complete the architecture used in this DSSC.

High strain biocompatible polydimethylsiloxane-based conductive graphene and multiwalled carbon nanotube nanocomposite strain sensors

High performance strain sensors were achieved featuring simple, low-cost construction involving the screen printing of combinations of multi-walled carbon nanotube and graphene nano-platelet nanocomposites on biocompatible and flexible polymer substrates. Conductivity and thermal coefficients of resistance of different conductive nanocomposite sensor materials were measured. The zero current resistance and gauge factor of printed sensors was characterized. The combination of high strain operation (up to 40%), high gauge factor (GF > 100), and biocompatible construction pave the way for applications such as minimally invasive in vivo strain measurements.

Functionalization of multi-walled carbon nanotubes with perfluoropolyether peroxide to produce superhydrophobic properties

Multi-walled carbon nanotubes (MWCNTs) have been functionalized through perfluoropolyether (PFPE) radicals obtained by thermal decomposition of linear PFPE peroxide. The reactivity of MWCNTs with PFPE peroxide has been compared with the direct fluorination of MWCNTs using elemental fluorine in mild conditions. The experimental results indicated that the functionalization with PFPE peroxide and the direct fluorination with elemental fluorine were suitable techniques to modify and control the physical-chemical properties of MWCNTs. After the introduction of PFPE chains on the MWCNT surface, the wettability of MWCNTs changed from hydrophilic to superhydrophobic, because the low surface energy properties of PFPE were transferred to the MWCNT surface. However, the linkage of PFPE chains weakly influenced the electrical properties of conductive MWCNTs. The amount of PFPE chains linked to the carbon nanotubes, the PFPE fluids obtained by homocoupling side-reactions and the decomposed portion of PFPE have been evaluated by mass balance. The modified MWCNTs have been characterized by X-ray photoelectron spectroscopy, thermal gravimetric analysis, X-ray diffraction, scanning electron microscopy, contact angle and surface area measurements. The effects of the chemical treatment on the conductive properties of MWCNTs have been studied by resistivity measurements at different applied pressures.

Multi-Wall Carbon Nanotubes Deposited on Gold Electrode for Bacteria Detection

In this paper, we describe a new strategy for E. coli bacteria detection using an immunosensor based on multi-wall carbon nanotubes (MWCNTs) deposited onto a gold electrode. Cyclic voltammetry and impedance spectroscopy were performed before and after MWCNTs deposition. The deposition of MWCNTs on the gold surface was further confirmed by obtaining transmission electron microscopy (TEM) images. The MWCNTs modified with carboxyl groups were functionalized with polyclonal antibodies and were used for E. coli detection. The specificity of the immunosensor was tested against Lactobacillus fermentium bacteria. A limit of detection of 10 CFU/mL was obtained with good reproducibility. Such a low detection limit is obtained due to the high conductivity of multiwall carbon nanotubes.

Viscosity and thermal conductivity of dispersions of gum arabic capped MWCNT in water: Influence of MWCNT concentration and temperature

Experiments were carried out on the measurement of viscosity and thermal conductivity of multi-walled carbon nanotubes (MWCNT)-water nanofluids prepared using gum arabic as dispersant. The influence of temperature (28–60°C), MWCNT concentration (0.14–0.24vol%) on viscosity and effective thermal conductivity has been investigated. Our results on the effect of MWCNT concentration on relative viscosity and thermal conductivity ratio are in qualitative agreement with those reported in literature. Thermal conductivity ratios increase strongly with temperature, especially above 45°C. Relative viscosities too increased with temperature above 45°C at relatively higher MWCNT concentration indicating the potential role of Brownian motion.

Facile synthesis of MoS3/carbon nanotube nanocomposite with high catalytic activity toward hydrogen evolution reaction

Hydrogen has been proposed as a future energy carrier in the transition from the current hydrocarbon economy. Exploring advanced materials for electrocatalytic and photoelectrochemical water splitting has become one of the most important issues for bulk and inexpensive hydrogen production. In this study, the nanocomposite of MoS3 and multi-walled carbon nanotubes (MWCNTs) with the high catalytic activity toward hydrogen evolution reaction (HER) was easily synthesized using wet chemistry process. With the aid of functional groups present in MWCNTs, amorphous MoS3 nanoparticles were highly dispersed over MWCNT surface. It was found that MoS3 on the MWCNTs was electrochemically reduced to MoS2 before HER and thus the amorphous MoS2 was identified as the actual catalyst for HER. Furthermore, MoS2 with amorphous structure exhibited the higher HER activity than crystalline MoS2 due to the fact that the former had a higher number of exposed edges. In addition, the catalytic activity of nanocomposite of MoS3 and MWCNTs was increased with decreasing the loading amount of MoS3 on MWCNTs and the optimal MoS3 loading on MWCNTs was 33wt%. Based on the extensive transmission electron microscopy analysis and capacitance measurements, the catalytic activity of the nanocomposite was highly correlated to its active surface area which was controlled by MoS3 morphology on MWCNT surface. The nanocomposite of MoS3 and MWCNTs exhibited excellent HER activity with a small overpotential of ∼0.13V, large cathodic currents and a Tafel slope as small as 40mV/decade. The impedance measurements suggested that the high catalytic activity of nanocomposite of MoS3 and MWCNTs was stemmed from the synergistic effect from the highly exposed edges of amorphous MoS3 nanoparticles and the excellent electrical coupling to the conductive MWCNT network. Furthermore, it was found that the current density of this hybrid catalyst was decreased to 88% of the initial value after the continuous 500 cycling, which showed the reasonable stability in the long-term operation. The present work suggested that the highly active and stable nanocomposite of MoS3 and MWCNTs showed a great potential as a low cost alternative to Pt in water splitting.

Enhanced anisotropic heat conduction in multi-walled carbon nanotubes

Anisotropy of heat conduction in multi-walled carbon nanotubes (MWNTs) is investigated by measuring heat flows in a pristine MWNT and in a MWNT with defects. The in- and out-of-shell thermal conductivities of each MWNT graphite shell are determined, and differences of more than four orders of magnitude are obtained because of the inter-shell gaps. This enhanced anisotropy reduces the conductance by 74% compared with that of the pristine MWNT because of the presence of outer shell defects, which comprise only 2.8% volume ratio. Furthermore, the anisotropy-assisted length dependence of thermal conductivity is demonstrated, even though there is no ballistic phonon transport.

Pulse electrodeposition of CoS on MWCNT/Ti as a high performance counter electrode for a Pt-free dye-sensitized solar cell

Because of the large specific surface area and superior electrical conductivity of multi-wall carbon nanotubes (MWCNTs) and the high electrocatalytic activity of cobalt sulfide (CoS), CoS/MWCNT hybrid films are deposited onto Ti foil substrates by sequential electrophoresis and pulse potentiostatic electrodeposition. Field-emission scanning electron microscopy observes that the surface of the MWCNTs is wrapped with a nano-honeycomb CoS thin film of ∼55 nm in thickness. Cyclic voltammograms, electrochemical impedance spectroscopy, and Tafel polarization characterization indicate that the CoS/MWCNT/Ti counter electrode (CE) has better electrocatalytic activity for I3− reduction than Pt CE. Under full sunlight illumination (100 mW cm−2, AM 1.5 G), the dye-sensitized solar cell based on the CoS/MWCNT/Ti CE achieves a power conversion efficiency of 8.05%, which exceeds that of the device based on Pt/Ti CE (6.39%).

Electrically conductive superhydrophobic octadecylamine-functionalized multiwall carbon nanotube films

Electrically conductive, superhydrophobic multiwall carbon nanotube (MWCNT) thin films were prepared by direct amination of MWCNTs with up to 14wt.% of octadecylamine (ODA) by vacuum filtration method. The ODA-functionalized MWCNT films exhibit a high water contact angle of 165° and electrical conductivity of 860S/m. The liquid–air–solid interface is directly observed from above the water droplet using an optical microscope. The observation indicates that the wettability state of the MWCNTs has changed from relatively hydrophilic to superhydrophobic state upon functionalization with ODA. The fundamental mechanisms responsible for the unusual combination of surface superhydrophobicity and high electrical conductivity of the MWCNT films are described and their implications are discussed.

An aligned macro-porous carbon nanotube/waterborne polyurethane sensor for the detection of flowing organic vapors

Abstract We report a conductive multi-walled carbon nanotube (MWNT)/waterborne polyurethane (WPU) sensor with an ultra-regular aligned macro-porous structure obtained simply by a directional freeze-drying process. This novel polymer material can broaden the application area of polymer based gas sensors from static or quasi-static organic vapors to flowing organic vapors such as acetone, n-hexane, toluene and tetrahydrofuran, and is particularly suitable for monitoring the latter. Because of the unique micro-phase separation structure of WPU, the conductive MWNT/WPU sensor has a broad applicability to flowing organic vapors from nonpolar to polar.

Thermal Conductivity Enhancement of Epoxy Composites by Interfacial Covalent Bonding for Underfill and Thermal Interfacial Materials in Cu/Low-K Application

Nowadays with enhanced performance and reduced profile, electronics and photonics devices demand efficient heat dissipation and low operation temperature. Thereby, instead of traditional fillers (e.g., fused silica), thermally conductive silicon carbide (SiC) particles and multiwall carbon nanotubes (MWNTs) are applied here as fillers in composites for underfill and thermal interfacial materials (TIMs), respectively. SiC particles are coated with an ultrathin layer of silicon oxide by thermal oxidation at 800°C in air and consequently functionalized by γ-glycidoxypropyl-trimethoxysilane in order to graft epoxides on their surface. Moreover, MWNTs were chemically functionalized with carboxyls and hydroxyls in a concentrated acid mixture. Transmission electron microscopy, Fourier-transform infrared spectrascopy, and thermogravimetric analysis characterization indicates that both of the fillers are successfully functionalized, which makes their surface reactive with epoxy resin, resulting in interfacial covalent chemical bonding between the thermally conductive fillers and epoxy resin. It is found that interfacial chemical bonding across the interface between these functionalized fillers and polymer matrix can promote significant thermal conductivity enhancement of epoxy composites, which is promising for underfill and TIMs in Cu/low-K application.

In situ TEM study on changes in structure and electrical conductance of carbon nanotube-gold contact induced by local joule heating

Electrical conductance of multi-walled carbon nanotubes (MWCNTs) with closed and open tips contacting with a gold (Au) electrode was studied by in situ transmission electron microscopy. When a current density through the contact region reached a threshold value of 2.6 × 108 A/cm2, the MWCNT tip was embedded into the Au surface by local melting of Au, and the total resistance was reduced with the increase of the contact area. Conductance per unit area at the contact between the MWCNT and Au electrode for the open-ended MWCNT is four times larger than that for the close-ended one, which is due to the direct connection of inner walls of the open-ended MWCNT with the Au surface.

Concentration effect of multiwalled carbon nanotube and poly(3, 4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) conjugated film on the catalytic activity for counter electrode in dye sensitized solar cells

Conductive and catalytic multiwalled carbon nanotube (MWCNT)/poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) composite films were prepared by dispersing MWCNT in the PEDOT:PSS aqueous solution using ultrasonication without any oxidation process. The effect of the MWCNT loading in the PEDOT:PSS solution was studied in terms of the conductivity and catalytic activity. The MWCNT/PEDOT:PSS composite films showed much lower sheet resistance in the range of 730–2150 Ω/□ and higher surface roughness in the range of 25–110 nm than the pure PEDOT:PSS film (980 kΩ/□ and 0.82 nm) depending on the MWCNT content in the composite. The high conductivity and roughness of MWCNT/PEDOT:PSS films enhanced its performance as a catalytic counter electrode in the dye-sensitized solar cell (DSSC). The interface resistance between the MWCNT/PEDOT:PSS film and the electrolyte was evaluated with electrochemical impedance spectroscopy (EIS) and it was confirmed that as the content of MWCNT in PEDOT:PSS solution was increased, the resistance was decreased. The cell efficiency of DSSC with MWCNT/PEDOT:PSS counter electrode was highly improved as the MWCNT concentration in MWCNT/PEDOT:PSS film increases and especially, the DSSC with FTO-free spray coated MWCNT/PEDOT:PSS counter electrode showed excellent sell performance (Jsc: 10.9 mA/cm2, F.F.: 60.6% and n: 5.4%), which is comparable with that with platinum on FTO counter electrode system (Jsc: 13.9 mA/cm2, F.F.: 62.8% and n: 7.1%).

Molecular dynamics simulations of heat conduction in multi-walled carbon nanotubes

Heat conduction in multi-walled carbon nanotubes (MWNTs) was studied using non-equilibrium molecular dynamics simulations. This research focuses on the effects of the multi-wall structure of the MWNTs on the heat conduction. The results show that the thermal conductivity of a MWNT is almost the same as that of the corresponding single-walled carbon nanotubes (SWNTs) rather than much smaller as has been suggested. Thus, the multi-wall structure does not significantly affect the thermal conduction in the MWNTs. Analysis of the temperature profiles and the phonon density of states confirms that there is almost no heat transport between the MWNT layers and that each layer conducts heat nearly independently along parallel channels. This is physically reasonable since the weak inter-wall interactions and large interfacial thermal resistances make the MWNT layers behave like parallel thermal circuits.