Distribution Of Multi-walled Carbon Nanotubes Research Articles

Thermal and electrical properties of aluminoborosilicate glass–ceramics containing multiwalled carbon nanotubes

We report the effects of multiwalled carbon nanotube (MWCNT) dispersions (⩽15 wt.%) on the electrical and thermal conductivities of an aluminoborosilicate glass–ceramic. The electrical conductivity was improved by a factor of ∼106 and the thermal conductivity by ∼70%. The uniform MWCNT distribution achieved with up to 10 wt.% MWCNT resulted in a relatively high electrical percolation threshold. Thermal conductivity was limited by the low thermal conductivities of the CVD MWCNTs, length reduction during processing and interfacial resistance.

Preparation of graphene/multi-walled carbon nanotube hybrid and its use as photoanodes of dye-sensitized solar cells

This study employed a solution-based method to prepare a 3-D hybrid material comprising graphene and acid-treated multi-walled carbon nanotubes (MWCNTs). The adsorption of MWCNTs on graphene reduces the π– π interaction between graphene sheets resulting from steric hindrance, providing a subsequent reduction in aggregation. Optimal proportions of MWCNTs to graphene (2:1) enabled the even distribution of individual MWCNTs deposited on the surface of the graphene. The hybrid 3-D material was incorporated within a TiO 2 matrix and used as a working electrode in dye-sensitized solar cells (DSSCs). The hybrid material provides a number of advantages over electrodes formed of either MWCNTs or graphene alone, including a greater degree of dye adsorption and lower levels of charge recombination. In this study, DSSCs incorporating 3-D structured hybrid materials demonstrated a conversion efficiency of 6.11%, which is 31% higher than that of conventional TiO 2-based devices.

Composites of multi-walled carbon nanotubes and shape memory polyurethane for electromagnetic interference shielding

Multi-walled carbon nanotubes (MWCNTs) and shape memory polyurethane (SMP) were used to prepare MWCNT/SMP composites for electromagnetic interference (EMI) shielding. The uniform distribution of MWCNTs was confirmed by field emission scanning electron microscopy (SEM). The electrical conductivity of the composites was tested by the four-probe method, and the results suggested that the conductivity of the samples was significantly increased by the presence of MWCNTs. The conductivity reached 35 S/m when the MWCNT loading was 9 wt%. Dynamic mechanical analysis (DMA) revealed that the composites exhibited higher storage moduli than pure SMP. In addition, the shielding effectiveness (SE) of composites with various MWCNT loading and thickness were measured over 4–7 and 13–16 GHz. The highest SE achieved was close to 35 dB for MWCNT/SMP composites with the thickness of 2 mm and MWCNT loading of 9 wt%. The SE increased as the thickness and conductivity of the composites increased. Moreover, the SE was enhanced as the frequency increased.

Probing the inter-tube transport in aligned and random multiwall carbon nanotubes

The temperature and magnetic field dependence of conductivity has been used to probe the inter-tube transport in multiwall carbon nanotubes (MWNTs). The scanning electron microscopy images show highly aligned and random distribution of MWNTs. The conductivity in aligned carbon nanotube (ACNT) and random carbon nanotube (RCNT) samples at low temperature follows T1/2 (at T < 8 K) and T3/4 (at T > 8 K) dependence in accordance with the weak localization and electron-electron (e-e) interaction model. The values of diffusion coefficient in ACNT and RCNT are 0.25 × 10−2 and 0.71 × 10−2 cm2 s−1, respectively, indicating that larger number of inter-tube junctions in later enhances the bulk transport. The positive magnetoconductance (MC) data in both samples show that the weak localization contribution is dominant. However, the saturation of MC at higher fields and lower temperatures indicate that e-e interaction is quite significant in RCNT. The T−3/4 and T−1/2 dependence of inelastic scattering length (lin) in ACNT and RCNT samples show that the inelastic e-e scattering is more important in aligned tubes.

Synergistic effect on crystalline structure of polyvinylidene fluoride nanocomposites with multiwalled carbon nanotube loading by a twin screw extruder

AbstractPolyvinylidene fluoride (PVDF)/multiwalled carbon nanotube (MWCNT) composites were prepared by using twin screw extruder at various (0–5 wt %) MWCNT loadings. Field Emission Scanning Electron Microscope (FESEM) micrographs showed a relatively good dispersion and random distribution of MWCNT in PVDF matrix. The physical and dielectric properties increased gradually with the increase in MWCNT content but the thermal stability decreased. The DSC result revealed the increase in crystallinity of the PVDF matrix. Wide angle X‐Ray diffraction (WAXD) result showed a large shoulder at 2θ of 20.78° with increasing in MWCNT content. The experimental percolation threshold for the surface resistance of PVDF/MWCNT composites were estimated and clearly observed at 4 wt % of MWCNT loading. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Maximum natural frequencies of polymer composite micro-beams by optimum distribution of carbon nanotubes

Optimum distribution of multi-walled carbon nanotubes (MWCNTs) within a polymer composite micro-beam is sought to achieve its highest natural frequencies given a weight percent (wt.%) of MWCNTs. To this end, the micro-beam is divided into ten segments which are perfectly bonded to their neighbors. Each segment is made of low-viscosity, thermosetting polyester epoxy/amine resin LY-5052 and is reinforced by MWCNTs. A computer program, written in the Python programming language, is compiled with ABAQUS to generate a three-dimensional (3D) finite element (FE) model of the micro-beam and subsequently to evaluate an optimum CNT distribution under various vibration modes and boundary conditions. The influence of uniform and optimum MWCNT distributions on the natural frequencies, mode shapes and equivalent stiffness of the micro-beams is investigated and the results are compared with those of the pure polymer micro-beam. Subsequently, after acquiring the optimum distribution of the MWCNTs, two new CNT dispersion functions are proposed for maximizing fundamental frequencies of the clamped-free and clamped–clamped micro-beams. The results of the FE analysis reveal that the optimal reinforcement distribution pattern significantly depends on vibration mode shapes, particularly the micro-beam curvature under each mode. It is observed that fundamental frequencies of clamped-free, clamped-guided and clamped–clamped micro-beams are enhanced up to 15.9%, 13.1% and 12.6%, respectively, by choosing optimum MWCNT distribution profiles along the micro-beam length.

Morphological characterization and modelling of electrical conductivity of multi-walled carbon nanotube/poly(p-phenylene sulfide) nanocomposites obtained by twin screw extrusion

In this study, poly(p-phenylene sulfide) based nanocomposites containing multi-walled carbon nanotubes (MWNTs) were produced by dilution of a 15 wt.% MWNT/PPS masterbatch via twin screw extrusion process. The electrical conductivities of the nanocomposites were measured and percolation threshold was observed below 0.77 vol.% MWNTs. The state of dispersion and distribution quality of MWNTs was analyzed on macro- and nanoscale through transmission light and scanning electron microscopy (SEM). A good deagglomeration of primary macroagglomerates and a homogenous MWNT distribution on nanoscale was found. The dependence of conductivity on MWNT concentration was estimated using statistical percolation theory which matches the experimental data quite well. A new empirical equation was set up to fit the electrical conductivity using quantitative values of visible percolating MWNTs which were detected by charge contrast imaging in SEM.

Electro-responsive Transdermal Drug Release of MWCNT/PVA Nanocomposite Hydrogels

Multi-walled carbon nanotube (MWCNT)/poly(vinyl alcohol) (PVA) nanocomposite hydrogels were prepared by freezingthawing method for the electro-responsive transdermal drug delivery. MWCNTs were used as the functional ingredient to improve both mechanical and electrical properties of MWCNT/PVA nanocomposite hydrogels. The morphology of nanocomposites revealed the uniform distribution of MWCNTs and the good interfacial contact. The compression moduli of hydrogel matrices increased greatly from 40 to 1500 kPa by forming MWCNT/PVA nanocomposites. The swelling ratio of MWCNT/PVA nanocomposites decreased as the content of MWCNTs increased under no electric voltage applied. However, the swelling ratio of MWCNT/PVA nanocomposites increased as the content of MWCNTs increased under electric voltage applied and the applied electric voltage increased. The drug was released in the electro-responsive manner through the skin due to the electro-sensitive swelling characteristics of MWCNT/PVA nanocomposite hydrogels.

PH and electro-responsive release behavior of MWCNT/PVA/PAAc composite microcapsules

The pH and electro-responsive composite microcapsules were prepared by using multi-walled carbon nanotubes (MWCNTs), poly(vinyl alcohol), and poly(acrylic acid). MWCNTs were employed to improve the electro-responsive properties of microcapsules. The surface modification of MWCNTs was carried out by oxyfluorination for the improved dispersion in the microcapsule shell. The morphology of microcapsules and the location of MWCNTs in the microcapsule shell were investigated by SEM and TEM. The dispersion of MWCNTs in the microcapsule shell and the formation of composite microcapsules were improved by using the oxyfluorinated MWCNTs having the hydrophilic functional groups on the surface. The dual pH and electro-responsive release behavior of the composite microcapsules had a close relation with the uniform distribution of MWCNTs in the microcapsule shell.

Hydrogen Storage Properties of Mg-Ni Alloy Catalysed by Multi-Walled Carbon Nanotubes

The hydrogen storage performance of ball-milled sample of cast Mg-6 wt% Ni alloy was investigated. Morphology and microstructure of the cast sample and achieved powders were evaluated by high-resolution scanning electron microscopy. The activation characteristics of ball-milled alloy are compared with those of the materials obtained by ball-milling of 5 wt% multi-walled carbon nanotubes (MWCNTs) for 2 hours. MWCNTs enhanced the absorption kinetics considerably. The hydrogen content of modified powder by MWCNTs reached to the maximum hydrogen capacity within two minutes of exposure to hydrogen at 370°C and 2MPa pressure. The evidence is provided that nucleation and growth of hydrides accelerate drastically by homogenously distribution of MWCNTs on the surface of ball-milled powders.

Ternary Poly(styrene‐co‐acrylonitrile)/Poly(vinyl chloride) Blend Composites with Multi‐Walled Carbon Nanotubes and Enhanced Physical Characteristics

AbstractWe report a ternary system of poly(styrene‐co‐acrylonitrile) (SAN), poly(vinyl chloride) (PVC), and multi‐walled carbon nanotube (MWCNT) composites prepared by both a solution blending method and the SOAM. The MWCNT content in the composites was optimized by both TGA and mechanical characterization of binary mixtures of SAN/MWCNT and PVC/MWCNT composites. The dispersion of MWCNTs in the miscible SAN/PVC blends was characterized by FT‐Raman spectroscopy, FE‐SEM, and FE‐TEM. The distribution of MWCNTs in the SAN/PVC blends was examined in terms of their wetting coefficients and minimization of the interfacial energy. Composites prepared using the SOAM method showed superior physical properties to the SAN/PVC blends and SAN/PVC/MWCNT composites prepared using the solution blending method.magnified image

Photothermal Response of Tissue Phantoms Containing Multi-Walled Carbon Nanotubes

Inclusion of multi-walled carbon nanotubes (MWNTs) into tissue prior to laser therapy has the potential to enhance the selectivity and effectiveness of cancer therapy by providing greater and more controlled thermal deposition. The purpose of this study was to investigate the optical and thermal response of tissue representative phantoms containing MWNTs to optical radiation. Tissue representative phantoms 20 mm in diameter and 1 mm in thickness were created from sodium alginate. Following the inclusion of MWNTs (900 nm in length, 40-60 nm in diameter) in phantoms, the distribution of MWNTs was observed using transmission electron microscopy. A predominantly, evenly dispersed and randomly oriented distribution of MWNTs was observed with a rare presence of MWNT clustering or clumping. In order to characterize the response of MWNT inclusion on optical properties of phantoms, the transmittance and reflectance spectra of phantoms with and without MWNT inclusion were measured with a spectrophotometer over a wavelength range of 200-1400 nm. Inclusion of MWNTs in phantoms dramatically enhanced light absorption across the entire wavelength range as evidenced by a diminished transmittance and reflectance compared with phantoms without MWNTs. In order to evaluate the spatiotemporal temperature distribution associated with laser irradiation of phantoms with and without MWNTs, the temperature was measured at discrete radial distances from the center of the incident laser beam using thermocouples. The rate of temperature increase and peak temperature for phantoms containing MWNTs was much greater compared with phantoms without MWNTs at all measurement locations. In conclusion, MWNT inclusion in tissue phantoms increases the optical absorption and temperature elevation, which may enable more effective photothermal therapies of human disease utilizing lasers.

Microstructure and activation characteristics of Mg–Ni alloy modified by multi-walled carbon nanotubes

An Mg–6 wt% Ni alloy was fabricated by a casting technique and the drilled chips ball-milled by high energy ball milling to be examined for their hydrogenation modified with multi-walled carbon nanotubes (MWCNTs). The activation characteristics of ball-milled alloy are compared with those of the materials obtained by ball milling with 5 wt% MWCNTs for 0.5, 1, 2, 5 and 10 h. MWCNTs enhanced the absorption kinetics considerably in all cases. The hydrogen content of the modified powder with MWCNTs reached maximum hydrogen capacity within 2 min of exposure to hydrogen at 370 °C and 2 MPa pressure. X-ray diffraction analysis provided evidence that no carbon-containing phase was formed during milling. However, milling with MWCNTs reduced the crystallite size, even if the milling was carried out for only an hour. The rate-controlling steps of the hydriding reactions at different milling times were determined by fitting the respective kinetic equations. Evidence is provided that nucleation and growth of hydrides are accelerated drastically by a homogenous distribution of MWCNTs on the surface of the ball-milled powders. We show that MWCNTs are very effective at promoting the hydriding/dehydriding kinetics, as well as in increasing the hydrogen capacity of the magnesium alloy.

In Situ Surface Plasmon Resonance Investigation of the Assembly Process of Multiwalled Carbon Nanotubes on an Alkanethiol Self-Assembled Monolayer for Efficient Protein Immobilization and Detection

In situ surface plasmon resonance (SPR) was used to study the assembly process of multiwalled carbon nanotubes (MWCNTs) quantitatively on an alkanethiol self-assembled monolayer (SAM) surface, showing that MWCNTs can follow the Langmuir adsorption kinetics to assemble spontaneously whereas the assembly temperature has an essential influence on the assembly kinetics and the surface distribution of MWCNTs. To further in situ investigate protein attachment on the MWCNT surface and its sensing application quantitatively, goat IgG was immobilized by three strategies: direct adsorption, covalent binding, and 1-pyrenebutanoic acid, succinimidyl ester (PBSE)-assisted attachment, of which the covalent binding approach provides the best protein loading capacity. The SPR label-free detection of anti-goat IgG demonstrates excellent performance with high sensitivity, good specificity, and rapid response in comparison to that with a plain substrate without MWCNT assembly reported in our previous work. This is contributed by the 3D MWCNT assembly matrix providing a high probe immobilization capability and superb accessibility for the target to enhance its sensing performance significantly.

Biodegradable Poly(butylene succinate)/Multi-Walled Carbon Nanotubes Nanocomposite at Low Carbon Nanotubes Loading: Morphology, Crystallization and Mechanical Property

Biodegradable nanocomposite based on poly(butylene succinate) (PBSU) and multi-walled carbon nanotubes (MWNTs) was prepared by solution blending method at 1 wt% MWNTs loading. Scanning electron microscopic observation illustrates a homogeneous distribution of MWNTs in the PBSU matrix. Differential scanning calorimetry, optical microscopy, and wide angle X-ray diffraction were used to study the nonisothermal crystallization, isothermal crystallization kinetics, spherulitic morphology, and crystal structure of neat PBSU and its nanocomposite. The presence of MWNTs enhances the crystallization of PBSU in the nanocomposite due to the heterogeneous nucleation effect while the crystallization mechanism and crystal structure of PBSU do not change. Moreover, the incorporation of a small quantity of MWNTs has improved significantly the mechanical property of PBSU in the nanocomposite compared with that of neat PBSU.

Distribution and persistence of pleural penetrations by multi-walled carbon nanotubes

BackgroundMulti-walled carbon nanotubes (MWCNT) are new manufactured nanomaterials with a wide spectrum of commercial applications. The durability and fiber-like dimensions (mean length 3.9 μm long × 49 nm diameter) of MWCNT suggest that these fibers may migrate to and have toxicity within the pleural region. To address whether the pleura received a significant and persistent exposure, C57BL/6J mice were exposed by pharyngeal aspiration to 10, 20, 40 and 80 μg MWCNT or vehicle and the distribution of MWCNT penetrations determined at 1, 7, 28 and 56 days after exposure. Following lung fixation and sectioning, morphometric methods were used to determine the distribution of MWCNT and the number of MWCNT fiber penetrations of three barriers: alveolar epithelium (alveolar penetrations), the alveolar epithelium immediately adjacent to the pleura (subpleural tissue), and visceral pleural surface (intrapleural space).ResultsAt 1 day 18%, 81.6% and 0.6% of the MWCNT lung burden was in the airway, the alveolar, and the subpleural regions, respectively. There was an initial, high density of penetrations into the subpleural tissue and the intrapleural space one day following aspiration which appeared to decrease due to clearance by alveolar macrophages and/or lymphatics by day 7. However, the density of penetrations increased to steady state levels in the subpleural tissue and intrapleural from day 28 - 56. At day 56 approximately 1 in every 400 fiber penetrations was in either the subpleural tissue or intrapleural space. Numerous penetrations into macrophages in the alveolar airspaces throughout the lungs were demonstrated at all times but are not included in the counts presented.ConclusionsThe results document that MWCNT penetrations of alveolar macrophages, the alveolar wall, and visceral pleura are both frequent and sustained. In addition, the findings demonstrate the need to investigate the chronic toxicity of MWCNT at these sites.

The influence of surfactants on the processing of multi‐walled carbon nanotubes in reinforced cement matrix composites

AbstractFive surfactants [sodium dodecyl benzene sulfonate (SDBS), sodium deoxycholate (NaDC), Triton X‐100 (TX10), Arabic gum (AG), and cetyltrimethyl ammonium bromide (CTAB)] were employed separately or jointly as superficial active agents (SAAs), to enhance solubilization/dispersion of multi‐walled carbon nanotubes (MWNTs) in aqueous solution and cement matrix. The stabilizations of MWNTs in 12 SAAs solutions were estimated through sedimentation time of each suspension with centrifugation or sitting in 60 days. The mechanical and electrical properties as well as microstructures of MWNTs/cement composites (MNT/CCs) using the SAAs of SDBS, NaDC, AG, or the mixture of SDBS and TX10 were investigated. It was found that the capability of SAAs in dispersing MWNTs roughly decreases in the order as SDBS&TX10, SDBS, NaDC&TX10, NaDC, AG, TX10, and CTAB. The SAA of SDBS and TX10 with a mixing ratio of 3:1 by weight exhibits the best solubilization/dispersion capability. The delaminating time of the suspension of the above SAA with or without centrifugation is 80 min and 60 days, respectively. The microscopy observation indicates that the nanotubes form a stable network in the MNT/CC using SDBS&TX10 SAA. In addition, compared to the Plain/C, the corresponding MNT/CC increases in flexural strength, compressive strength, and the electrical conductivity by 29.10%, 20.8%, and two orders of magnitude, respectively. The enhancements are attributed to the uniform and stable distribution of MWNTs with the suitable surfactants and the ultrasonic dispersion method.

Fabrication and Characterization of HA-ZrO2-MWCNT Ceramic Composites

In this article, a new kind of hydroxyapatite-zirconia-carbon nanotube (HA-ZrO2-MWCNT) ceramic composites was fabricated to enhance the mechanical properties of a hydroxyapatite (HA) ceramic for satisfying various requirements in bone rehabilitation. A new dispersing process was proposed to ensure a homogeneous distribution of multi-wall carbon nanotubes (MWCNTs) in the HA ceramic matrix. The flexural strength and fracture toughness of the HAZrO2-CNT composites were enhanced by about 126% and 124%, respectively, as compared with those of the unmodified HA ceramics. The X-ay diffraction analysis revealed that a small quantity of HA decomposed in the composites with introduction of strengthening phases. The in vitro test results showed that the sample surfaces were covered with a new apatite layer after immersion in simulated body fluid for 10 days, indicating good biocompatibility of the composites.

Mechanical performance of highly compressible multi-walled carbon nanotube columns with hyperboloid geometries

Multi-walled carbon nanotube (MWCNT) columns are formed from the frit compression of a random distribution of MWCNTs in a casting solvent; its drying led to the formation of hyperboloid geometry. Uniaxial loading of MWNT columns mimics an open-cell foam behaviour and possesses an expansion rate in excess of 250 mm min −1 and an elastic modulus of 10–12 MPa, thus superior to conventional low-density flexible foams. Successive compression–expansion cycling within the Hookean region reveals a hysteresis loop in the stress–strain curve that stabilises at a final value of ε F = 18%, but on contact with its casting solvent and subsequent drying, the sample can be regenerated to within ε R = 6% according to a memory effect and is repeatable in successive stress cycles and solvent regeneration. The system was modelled for the macroscopic stress–strain behaviour of the MWCNT column to reveal the contributions of linear dependence, elasticity–plasticity and elasticity–plasticity with hardening, revealing good agreement with the stress–strain data. MWCNT columns should prove useful as an energy adsorbing device.

Toxicity and imaging of multi-walled carbon nanotubes in human macrophage cells

Multi-walled carbon nanotubes (MWNTs) have been proposed for use in many applications and concerns about their potential effect on human health have led to the interest in understanding the interactions between MWNTs and human cells. One important technique is the visualisation of the intracellular distribution of MWNTs. We exposed human macrophage cells to unpurified MWNTs and found that a decrease in cell viability was correlated with uptake of MWNTs due to mainly necrosis. Cells treated with purified MWNTs and the main contaminant Fe 2O 3 itself yielded toxicity only from the nanotubes and not from the Fe 2O 3. We used 3-D dark-field scanning transmission electron microscopy (DF-STEM) tomography of freeze-dried whole cells as well as confocal and scanning electron microscopy (SEM) to image the cellular uptake and distribution of unpurified MWNTs. We observed that unpurified MWNTs entered the cell both actively and passively frequently inserting through the plasma membrane into the cytoplasm and the nucleus. These suggest that MWNTs may cause incomplete phagocytosis or mechanically pierce through the plasma membrane and result in oxidative stress and cell death.