Orientation Of Multi-walled Carbon Nanotubes Research Articles

Multi-walled carbon nanotube composite fiber formation in a water coagulation bath and application as wire heater

A type of high-yield multi-walled carbon nanotubes (MWNTs) with a diameter of 4–13 nm was prepared by cracking propylene over Co-Mo/Al2O3-MgO catalyst. The pristine MWNTs were well dispersed in N-Methyl-Pyrrolidone (NMP) solution of an oil soluble non-ion surfactant. Then the MWNT dispersion was extruded out of a spinneret into a rotating water coagulation bath to form a free-standing gel fiber with ribbon shape. The surfactant was insoluble in water while NMP was miscible with water, which promoted the formation of gel fiber. When the gel fiber was dried, a solid MWNT-surfactant composite fiber was obtained. The composite fiber had certain flexibility. However, the tensile strength was only 15.6 ± 1.3 MPa, which was mainly limited by the weak orientation of MWNTs along the fiber and the lack of compactness of MWNTs inside the fiber. In addition, the electrothermal properties of the 3 cm MWNT-surfactant composite fiber as wire heater were also evaluated. The composite fiber possessed rapid temperature response under different voltages. The steady-state temperature reached 48.1 °C, 74.0 °C and 100.2 °C, respectively, at 10 V, 15 V and 17.5 V.

Two-dimensional reinforcement of epoxy composites: alignment of multi-walled carbon nanotubes in two directions

Various applications of reinforced composites demand high two-dimensional (2-D) mechanical properties. For instance, two-dimensional reinforced epoxy composites have the potential to meet the demands of numerous applications in fields such as aerospace and electronics. In this study, 2-D reinforced epoxy composite was prepared by the alignment of multi-walled carbon nanotubes (MWCNTs) in two vertical directions in epoxy matrix. The orientation of MWCNTs in desired directions was controlled by simultaneous application of two alignment methods (magnetic and electric field alignments). Iron oxide-coated MWCNTs with high magnetic susceptibility were prepared to enable aligning them in a magnetic field. The electric field alignment method was also used to orient other non-coated MWCNTs between the field electrodes. Considerable improvements were observed in mechanical properties (up to 28% in tensile strength) of prepared composites in the aligned directions compared to randomly distributed MWCNT-reinforced composites. The alignment of MWCNTs in desired directions was confirmed by TEM images.

Nematic liquid crystal 4-cyano-4′-pentylbiphenyl functionalization of MWNTs for improved thermal and mechanical properties of silicone pressure sensitive adhesives

In this research, nanocomposite modified pressure sensitive adhesives (PSA) (5CB-MWNTs/PSA) with high mechanical and thermal properties were fabricated via nematic liquid crystal 4-cyano-4′-pentylbiphenyl (5CB) functionalized multi-walled carbon nanotubes (MWNTs). The results showed that 5CB interacted with MWNTs via non-covalent interactions e.g. π-π stacking, which not only improved the dispersion and orientation of MWNTs in a silicone PSA but also the compatibility between MWNTs and the silicone material. The tensile strength of 5CB-MWNT/PSA was increased to 14.5 MPa while the mass fraction of MWNTs was 1.0%, which was an enhancement of 943% over that of the MWNTs/PSA and 28 times greater than that of the neat PSA. In addition the thermal conductivity of the PSAs filled with the 5CB-MWNTs were improved to 1.28 W/(m•K) at a mass fraction of 10%, which was increased by 552% over that of the neat PSA and 231% over that of the MWNT/PSA. The resulting thermally conductive and mechanically applicable silicone PSA nanocomposites could be significant in a wide variety of pressure sensitive adhesive applications.

Influence of concentration, length and orientation of multiwall carbon nanotubes on the electromechanical response of polymer nanocomposites

Multiwall carbon nanotube (MWCNT)/polymethyl methacrylate (PMMA) composites were fabricated by solution casting with a range of MWCNT concentrations, two groups of MWCNT lengths and with or without the application of electric field. As-received (CNTs) and fragmented (FCNTs) MWCNTs were used to fabricate composites with MWCNT concentrations between 0.05 wt% and 0.7 wt%. A well-controlled procedure to systematically fragment the MWCNTs based on the application of high-density ultrasonic energy was implemented, and MWCNT length distributions were obtained by a formal statistical analysis. The relationship between the sparseness of the MWCNT network (macroscale morphology), electrical conductivity and piezoresistive sensitivity was evaluated. In order to evaluate the effect of the MWCNT alignment on the composite properties, specific MWCNT concentrations were selected for composites with CNTs and FCNTs under the application of an electric field. Composites with FCNTs exhibited a sparser network, higher transparency, lower electrical conductivity, higher percolation threshold and higher piezoresistive sensitivity than their counterparts with CNTs. On the other hand, composites with electric field-aligned MWCNT bundles presented higher electrical conductivity and piezoresistive sensitivity than their non-aligned counterparts, for both fragmented and non-fragmented cases. The evaluation of the combined effect of carbon nanotube length and alignment on the electromechanical properties of the composites represents an important step on the understanding of the structure-property relation of polymer nanocomposites.

Multiscale material modelling and analysis of carbon fiber/MWCNT/epoxy composites to predict effective elastic constants

Abstract In the current work, the effect of weight percentage and orientation of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of unidirectional (UD) carbon fiber (CF)/MWCNT/epoxy composites was studied by using multiscale material modelling and finite element analysis (FEA). Nanoscale representative elementary volume (RVE) consisting of MWCNTs and microscale RVE consisting of carbon fibers were generated using DIGIMAT FE Software. The equivalent elastic properties obtained from MWCNT/epoxy composites were used to estimate effective elastic constants of UD carbon fiber/MWCNT/epoxy composites. The weight percentage of MWCNTs was varied 0%–5%, while MWCNTs were orientated at 0°, 30°, 45°, 60° and 90°. It was found that the E1, E2, G12, υ12 and υ23 increased by 1.79%, 6.14%, 2.83%, 8.8% and 5% at 5 wt% addition of MWCNTs respectively. It was also found that except transverse young's modulus (E2) all other elastic constants decreased by increasing the orientations and at 90° the transverse Young's modulus (E2) increased by 16.57% compared to 0° orientation at 1 wt% addition of MWCNTs. The multiscale FE analysis results were compared by multiscale micromechanics model.

Structural recovery mechanism after shear induced orientation of multiwalled carbon nanotube in polypropylene matrix

In this work the flow induced orientation and the governing mechanism of structural recovery of multi-walled carbon nanotube (MWCNT) filled polypropylene nanocomposites were investigated. A series of linear and nonlinear melt rheological measurements including stress growth and time sweep experiments were performed at different temperatures to study the structural breakdown, nanoparticles orientation, subsequent structural recovery and MWCNT loadings. The results showed that the structural recovery occurred in two stages. The first stage, initial agglomeration, showed a quick recovery which was independent of temperature, can be interpreted in terms of inter-particle van der Waals interactions. This structural recovery stage had major contribution in the storage modulus increment. The second stage of the recovery, secondary agglomeration, was slower and dependent on temperature, can be attributed to rotary diffusion of nanoparticles. This stage had minor contribution to the storage modulus increase. Storage modulus increment in both of these agglomeration was attributed to the increase of nanotube-nanotube contacts. Both of these stages were confirmed by transmission electron micrographs. These result were in a good agreement with those calculated using van der Waals and diffusion concepts.

Electrical conductivity of carbon nanotube/polypropylene composites prepared through microlayer extrusion technology

Abstract The morphological distribution of carbon nanotubes (CNTs) in polymer matrix has a crucial impact on the performance of CNT-filled polymer composites. A novel microlayer extrusion technology used in the dispersion and orientation of CNTs was proposed, and polypropylene (PP)/multiwalled CNT (MWCNT) composites with different numbers of layers were prepared with it. The MWCNT dispersion was investigated by scanning electron microscopy and Raman mapping method, and the MWCNT orientation was quantified by Raman spectroscopy. The influences of the dispersion and orientation of MWCNTs on the electrical conductivity and crystallization behavior of the composites were investigated. The results showed that the anisotropic conducting properties of the multilayered composites varied distinguishably with the increase of layer numbers and rotation speed. Furthermore, the degree of crystallinity of PP increased when the layer number increased from 1 to 729. All of these results suggest that with the increase of the layer numbers and the rotation speed, the dispersion and orientation of MWCNTs in PP matrix improve greatly. Overall, we provide an efficient and practical approach to control the dispersion and orientation of CNT in polymer matrix, which has a promising application prospect in the field of plastic processing.

Effect of Nanotube Morphologies on Multi-Walled Carbon Nanotubes Based Counter Electrode for Dye-Sensitized Solar Cell.

Multi-walled carbon nanotubes (MWCNTs) with different morphologies were introduced into dyesensitized solar cell (DSSC) as low-cost substitutes for Pt counter electrode (CE). The effect of length and orientation of MWCNTs on the power conversion efficiency (PCE) of DSSC with MWCNTs CE were studied by measuring electrochemical impedance spectroscopy of MWCNTs and the photocurrent density–voltage (J–V ) characteristics of DSSC in this study. Results revealed that the long MWCNTs showed better electrocatalytic activity of reducing triiodide ions than short MWCNTs and yielded the power conversion efficiency of 2.42%. When the aligned multi-walled carbon nanotubes (AMWCNTs) with the same length as the long MWCNTs were used to prepare the CE, the power conversion efficiency of the DSSC reaches 2.95%. In order to further improve the performance of the DSSC, the processing of photoanode and counter electrode were adjusted. The power conversion efficiency of the cell with AMWCNTs as CE prepared by adjusted processing achieved 3.95% and the short circuit current density is superior to the DSSC with Pt as CEs, and it indicated the adjusted processing is beneficial to increase the overall performance of the dye-sensitized solar cell.

Studies on the effect of multi-walled carbon nanotube–reinforced polymer-based nano-composites using finite element analysis software tool

This article confirms experimental results by finite element analysis. The study includes meshing the specimen of size 40 × 12 × 6 mm3. The model is constructed in DesignModeler (ANSYS Workbench). Multi-walled carbon nanotubes are aligned in different angles to correlate the experimental results. The modelling method employed for analysis is based on weight ratio. The proportion of multi-walled carbon nanotubes is 0.25%, 0.5%, 0.75% and 1% by weight of polymer matrix (epoxy resin) for different specimens. Multi-walled carbon nanotubes are dispersed in epoxy matrix using ultrasonic energy. Composite beams were tested under flexure in order to evaluate their mechanical property such as load–deflection criteria by three-point bending test. Finite element method results were in close agreement with the experimental outcomes with different orientation of multi-walled carbon nanotubes into the matrix considered.

Effect of oxidative treatment on the electrochemical properties of aligned multi-walled carbon nanotubes

Vertically aligned multi-walled carbon nanotubes (MWNTs) were grown on the surface of electroconductive silicon substrate by catalytic chemical vapor deposition (CCVD) of a mixture of toluene and ferrocene vapors at 800°С. The anisotropic structure of the array that is due to the mutual orientation of MWNTs makes such materials attractive for use as supercapacitor electrodes. The effect of iron nanoparticles encapsulated in MWNTs as a result of synthesis on the electrochemical capacity of the sample in a 1 М H2SO4 solution was studied. Iron was removed during the thermal treatment of the MWNT array in a 20% H2SO4 solution under the normal or hydrothermal conditions. The contribution of redox processes involving iron was shown to be comparable to the contribution of the double-layer capacity of MWNTs. The hydrothermal treatment allows easy separation of the array from the silicon substrate without any loss of electric coupling of MWNTs.

Covalent functionalization enables good dispersion and anisotropic orientation of multi-walled carbon nanotubes in a poly(l-lactic acid) electrospun nanofibrous matrix boosting neuronal differentiation

A biocompatible porous scaffold obtained via electrospinning a nanocomposite solution of poly(l-lactic acid) and 4-methoxyphenyl functionalized multi-walled carbon nanotubes is presented here for the first time for the enhancement of neurite outgrowth. Optimization of blend preparation and deposition parameters paves the way to the obtainment of defect-free random networks of nanofibers with homogeneous diameters in the hundreds of nanometers length scale. The tailored covalent functionalization of nanotube surfaces allows a homogeneous dispersion of the nanofillers within the polymer matrix, diminishing their natural tendency to aggregate and form bundles. This results in a remarkable effect on the crystallization temperature, as evidenced through differential scanning calorimetry. Furthermore, transmission electron microscopy shows carbon nanotubes anisotropically aligned along the fiber axes, a feature believed to enhance neurite adhesion and growth. Indeed, microscopy images show neurites extension along the direction of nanofibers, highlighting the extreme relevance of scaffold morphology in engineering complex tissue environments. Furthermore, a remarkable effect on increasing the neurite outgrowth results when using the fibrous scaffold containing dispersed carbon nanotubes in comparison with an analogous one made of only polymer, providing further evidence of the key role played by carbon nanostructures in inducing neuronal differentiation.

Electrical, rheological and mechanical characterization of multiscale composite materials based on poly(etherimide)/short glass fibers/multiwalled carbon nanotubes

Composites based on poly(etherimide) matrix (PEI) with nanoscale reinforcements (multiwalled carbon nanotubes (MWCNTs)) and multiscale reinforcements (MWCNTs and Glass Fibers (GFs)) are processed by melt blending. For nanocomposite materials, we demonstrate that addition of MWCNTs (i) significantly improve electrical conductivity of PEI matrix, (ii) do not significantly improve the mechanical properties (young and flexural modulus) but strongly degrades the strain at break. In the case of multiscale composite materials PEI_GF_MWCNT, strain at break increases with the nanofiller content, and the electrical properties are the same than that in the case of nanocomposites. TEM observations are performed at the PEI/GF interfaces and clearly show a preferential location and orientation of MWCNTs along and perpendicularly to the GFs which explain the evolution of the strain at break for the multiscale composite materials.

Self-Assembly of Aligned Multi-Walled Carbon Nanotubes in Polypropylene-Coated Multi-Walled Carbon Nanotubes Composites

Polypropylene (PP)-coated multi-walled carbon nanotubes (MWNTs) composite with MWNTs exceptional alignment dispersed and improved mechanical properties was prepared with maleic anhydride (MAH) as a compatibilizer and poly (butyl methacrylate) (PBMA) as a binding. Scanning electron microscopy (SEM) results showed that MWNTs within composite were aligned without aggregation and the oriented MWNTs were connected by matrix. High-resolution transmission electron microscopy (HRTEM) results demonstrated that the nanotubes were densely coated with a PP layer. Infrared spectroscopy (IR) results revealed that there was covalently linkage of MWNTs with PP via MAH. The interactions between MWNTs-PP and MWNTs-PBMA induced orientation of MWNTs. The improved mechanical properties of PP - coated MWNTs composite was also shown.

Composite fibers from poly(vinyl alcohol) and poly(vinyl alcohol)‐functionalized multiwalled carbon nanotubes

AbstractHigh‐strength composite fibers were prepared from poly(vinyl alcohol) (PVA) and multiwalled carbon nanotubes (MWNTs) functionalized with PVA matrix. Esterification between MWNTs and PVA was confirmed by Fourier transform infrared, Raman spectroscopy, thermogravimetric analysis, transmission electron microscope, and atomic force microscope. Homogeneous dispersion of PVA‐functionalized MWNTs in dimethyl sulfoxide was affirmed by optical micrographs and particle size analysis. The PVA‐functionalized MWNTs/PVA (1 wt %) composite fibers prepared by gel spinning and hot‐drawing process exhibited tensile strength and modulus as high as 2.1 and 34 GPa, respectively, showing a 75% increase in tensile strength and 35% increase in modulus compared with pure PVA fibers. The mechanical properties were also much higher than untreated MWNTs/PVA (1 wt %) composite fibers and carboxylated MWNTs/PVA (1 wt %) composite fibers. From wide‐angle X‐ray diffraction, scanning electron microscopy, and Raman spectra analysis, higher mechanical properties of PVA‐functionalized MWNTs/PVA composite fibers are attributable to homogeneous dispersion of MWNTs in PVA matrix, stronger interfacial adhesion between MWNTs and PVA matrix, and uniaxial orientation of MWNTs along fiber axis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The electrical conductivity of carbon nanotube/carbon black/polypropylene composites prepared through multistage stretching extrusion

We reported the design of a grape-cluster-like conductive network in a polypropylene (PP) matrix, where oriented multi-walled carbon nanotubes (MWCNTs) served as branches and provided charge transport over large distances while grape-like carbon black (CB) aggregates enriched around MWCNTs and linked these conductive tubes through charge transport over small distances. The key for construction of this grape-cluster-like conductive network was the extension and orientation of MWCNTs, which was achieved in this work by multistage stretching extrusion with an assembly of laminating-multiplying elements (LMEs, which divide and recombine polymer melts). The highest efficient grape-cluster-like conductive network was obtained at a CB:MWCNT weight ratio of 6. The experimental results showed that this novel grape-cluster-like conductive network provided a low percolation threshold for PP/CB/MWCNT composites due to the synergistic effect of CB and oriented MWCNTs. When the combined CB and MWCNT content was about 6.9vol%, the electrical resistivity of PP/CB/MWCNT composites prepared by multistage stretching extrusion with 6 LMEs decreased to only 0.63Ωcm.

Magnetic field-guided orientation of carbon nanotubes through their conjugation with magnetic nanoparticles

Low intensity magnetic fields (22mT) rendered by a pair of bar magnets have been used to achieve in situ precise orientation of multiwalled carbon nanotubes (MWCNTs) and their directional deposition on solid substrates. The nanotubes were imparted magnetic characteristics through Fe3O4 (magnetite) nanoparticles covalently attached to their surface. The side walls of nanotubes were first acid oxidized with H2SO4/HNO3 (3:1 v/v) mixture and amine-functionalized magnetic nanoparticles were then interfaced to ends and side walls of the nanotubes through covalent linkages in the presence of a zero length cross linker, 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide. Fourier transformed infrared spectroscopic investigations affirmed the functionalization of nanostructures and formation of a magnetic nanohybrid. Transmission electron microscopy results revealed the attachment of nanoparticles along the side walls of MWCNTs. A flow cell was utilized to orient magnetic nanohybrid in the desired direction and also to create thin films of aligned MWCNTs. Further, directional assembly of magnetic MWCNTs at different orientation angles on solid substrates was studied by field emission scanning electron microscopy and optical microscopy. The procedure can be scaled to align CNTs on large surface areas for numerous applications, e.g., nanosensors, field emitters, and composites.

Nanobubbles stability and multiwall carbon nanotubes straightening on few-layer graphene surfaces

The formation of nanobubbles, straightening, and orientation of multiwalled carbon nanotubes (MWCNTs) are investigated by preparing thin films employing dip casting of colloidal solutions on few-layer graphene (FLG) surfaces. In contrast to what is known, it is observed that nanobubbles are formed on an ultrathin dewetted layer of 0.5 nm thickness and exhibit unusual stability at ultrahigh vacuum conditions. Further, nanobubble rings are observed at atmospheric pressure. The results provide direct experimental evidence of the interaction between MWCNTs and nanobubbles at air–liquid–solid triple contact line and at lower step edge of the FLG, which together lead to the alignment of MWCNTs. Due to the balance between the surface tension forces and the strain forces arising from tube bending, MWCNTs attained straight rod-like shape. This enabled us to evaluate the elastic modulus of the MWCNT as E = 0.9 TPa.

Extension‐induced mechanical reinforcement in melt‐spun fibers of polyamide 66/multiwalled carbon nanotube composites

AbstractIn this work, polyamide 66 (PA66) and its composites with multiwalled carbon nanotubes (MWNTs) were melt spun into fibers at different draw ratios. PA66 fibers at high draw ratio demonstrate a 40% increase in tensile strength, 66% increase in modulus and a considerable increase in toughness. It is demonstrated that this reinforcement can be mainly attributed to high‐draw‐ratio‐induced good dispersion and orientation of MWNTs, particularly the enhanced interfacial adhesion between MWNT and matrix thanks to interfacial crystallization. Our work provides a simple but efficient method to achieve good dispersion and strong interfacial interaction through melt spinning. Copyright © 2011 Society of Chemical Industry

Properties and structure of MWNTs/cellulose composite fibers prepared by Lyocell process

AbstractLyocell fiber is a new kind of regenerated cellulose fiber and expected to replace the Rayon fiber to be not only used in the textile field but also used in the fields of industry and aerospace after being modified. In this work, the multi‐walled carbon nanotubes (MWNTs)/Lyocell composite fibers were prepared under different draw ratios by dry‐wet spinning and their electrical properties, mechanical properties, and structure were investigated. It was found that an appropriate amount of MWNTs could be dispersed homogeneously in the Lyocell matrix and could improve the mechanical and thermal properties of composite fiber. The results of wide angle X‐ray diffraction (WAXD) showed that the MWNTs in the composite fiber almost aligned along the axis of the fibers and the orientation of MWNTs increased with the increasing draw ratio. Furthermore, it was found that more MWNTs content and lower draw ratio could improve the electrical conductance of the composite fiber. The composite fiber containing 5 wt % MWNTs has a volume conductivity of 8.8 × 10−4 S/cm, which is five orders higher than that of pure Lyocell fiber. These results indicate that the MWNTs/Lyocell composite fiber has potential applications in the areas of precursor of carbon fiber and conductive fiber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Development of conductive network of multiwalled carbon nanotubes in polycarbonate melt

AbstractThe effect of applied thermal history on the rheological properties in a molten state and the electric properties in a solid state is evaluated using mechanically blended samples composed of polycarbonate and multiwalled carbon nanotubes (MWNTs). It is found that MWNTs orient perpendicular to the applied compression direction owing to the squeeze flow at compression molding, which is prominent for the sample compressed at low temperature. The orientation of MWNTs reduces the interparticle contacts between MWNTs and thus decreases the electrical conductivity. Postprocessing annealing procedure at high temperature, however, leads to random orientation due to Brownian motion and then improves the electrical conductivity. The transition from an electrical insulator to a conductor by the redistribution process, which is called dynamic percolation, is well detected by the rheological measurements. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers