Multi-walled Carbon Nanotubes Network Research Articles

Selective distribution and migration of carbon nanotubes enhanced electrical and mechanical performances in polyolefin elastomers

A thermodynamic and kinetic method based on the selective distribution and migration of multi-walled carbon nanotubes (MWCNTs) in polyoxyethylene (PEO)/ethylene-α-octene random copolymer (ORC) composite system was reported to improve the dispersion of MWCNTs in ORC. Scanning electron micrographs and transmission electron micrographs confirmed that MWCNTs could almost completely migrate from the PEO phase to the ORC phase during melt compounding and lead to tremendously improved dispersion of MWCNTs in ORC, compared with traditional melt compounded ORC/MWCNT composites. Rheological analysis revealed that better MWCNTs network was developed at a lower content of MWCNTs with an improved dispersion of MWCNTs in ORC. The percolation threshold was drastically reduced from 3.82 to 0.35 vol % and the electrical conductivity was tremendously improved. The mechanical properties were also fully enhanced in comparison with traditional melt compounded ORC/MWCNT composites owing to the homogeneous dispersion of MWCNTs. These results manifest that, by proper selection of components with a selective distribution of MWCNTs and controlling the migration process of MWCNTs in the composites, the dispersion of MWCNTs in polymer matrix and resulting performance of the nanocomposites can be greatly improved.

Porous UHMWPE Membranes and Composites Filled with Carbon Nanotubes: Permeability, Mechanical, and Electrical Properties

Application of electric fields as a mechanism against membrane fouling is an emerging cleaning process for membranes. Sintering of ultrahigh molecular weight polyethylene powder particles decorated with multiwalled carbon nanotubes (MWCNT) is performed to produce electrically conductive porous filtration membranes. The contact of the molten particle surfaces leads to their fusion through neck formation during sintering. As the MWCNT only cover the surface of the powder particles, they form a conductive network with a high number of inter‐MWCNT contacts in pathways through the polymer matrix. Membranes with an electrical conductivity of 0.9 S m−1 at a MWCNT concentration of 5.0 wt% are prepared. Additionally, a comparison of sintered and compression molded samples shows that after the heating interval, crystallization during cooling strongly influences the formation of the MWCNT network. The study reveals that electrically conductive, porous polymer membranes for microfiltration applications can be prepared using a solvent‐free process. image

Tuning the phase separated morphology and resulting electrical conductivity of carbon nanotube filled PαMSAN/PMMA blends by compatibilization with a random or block copolymer

The mechanism governing the electrical properties for phase separating blends containing multiwall carbon nanotubes (MWNTs) is unravelled by tuning the compatibilization efficiency. Thereto, compatibilization by interfacially segregated block and random copolymers (cp) of poly(styrene-random/block-methyl methacrylate)(PS-r/b-PMMA) was achieved in phase separating blends of poly[(α-methyl styrene)-co-acrylonitrile]/poly(methylmethacrylate) (PαMSAN/PMMA) undergoing spinodal decomposition. A systematic study of the effects of copolymer architecture and molecular weight on the percolating network of selectively localized MWNTs is performed. Effective compatibilization is achieved with block cp irrespective of the ability of the blocks to entangle, whereas for random cp only long random cp having the ability to effectively entangle with the homopolymers are as efficient as long block cp. With increasing copolymer concentration, an increase and subsequent saturation of the electrical conductivity is attained. This originates from an increased connectivity and refinement of the MWNT laden PαMSAN phase, as confirmed by optical microscopy and the linear viscoelastic response of the blends. An effective compatibilizer led to an interfacial tension mediated suppression of an interfacial coarsening of the PαMSAN phase during phase separation, subsequently leading to percolation of MWNTs selectively localized in the PαMSAN phase. Furthermore, the copolymer having the ability to promote the development of a percolated network of MWNTs also allowed the network to be formed at a lower copolymer concentration as compared to that of blends with copolymers leading to restricted improvement in the connectivity of MWNTs. Our robust and simple procedure to tune the blend morphology via the efficiency of the compatibilizers can be used to achieve a synergistic increase in conducting properties.

Characterization of Polyvinyl Acetate/Multi Walled Carbon Nanotube Nanocomposites

Nanocomposite films from polyvinyl acetate (PVAc) dispersion and multi walled carbon nanotubes (MWCNTs) were prepared by solution casting technique. Stress-strain properties showed increase in elastic modulus and yield strength. Mechanical properties characterized by dynamic mechanical thermal analysis represented increase in storage modulus below glass transition temperature. Studied dielectrical properties of PVAc/MWCNT nanocomposites revealed formation of conductive MWCNT network in PVAc matrix.

Quantitative Analysis of Connectivity and Conductivity in Mesoscale Multiwalled Carbon Nanotube Networks in Polymer Composites

Mesoscale networks of multiwalled carbon nanotubes (CNTs) dispersed in 50/50 PS/PPO (polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide)) are studied. Various dispersion states are formed by several processing methods such as solvent casting (SC) and extrusion (EXT) and followed by compression molding (CM), which alters the topology of the conductive CNT network. This in turn affects the measured electrical conductivity up to 9 orders of magnitude. Quantitative large-area STEM imaging of the representative topology revealed the existence of subtle differences in topology for various dispersion states. The analyses also reveal that strong localized CNT interactions during the SC process result in highly conductive inhomogeneous networks consisting of CNT clusters connected by individual CNTs embedded in the polymer matrix. This leads to a low electrical percolation threshold, so that as compared to a random network a higher local volume fraction than the overall volume fraction of CNTs is present. A dispers...

Stretchable Porous Carbon Nanotube-Elastomer Hybrid Nanocomposite for Harvesting Mechanical Energy.

A stretchable porous nanocomposite (PNC) is reported based on a hybrid of a multiwalled carbon nanotubes network and a poly(dimethylsiloxane) matrix for harvesting energy from mechanical interactions. The deformation-enabled energy-generating process makes the PNC applicable to various mechanical interactions, including pressing, stretching, bending, and twisting. It can be potentially used as an energy solution for wearable electronics.

Sustainable, electrically-conductive bioepoxy nanocomposites

Biobased epoxy nano-composites composed of untreated multi-wall-carbon-nanotubes (MWCNT) and diphenolic acid-derived biobased epoxy: diglycidyl ether of diphenolate n-butyl ester (DGEDP-Bu), were fabricated. Electrical, rheological, and mechanical percolation thresholds were compared between biobased and commercial bisphenol A (DGEBA) epoxy composites. For both epoxies, nanocomposites loaded with 0.05–0.2 wt % MWCNT's exhibited electrical and rheological percolation at 0.05 wt % and 0.2 wt % respectively. DMA and tensile results revealed that DGEDP-Bu composites exhibited equivalent or superior properties to DGEBA composites. With 0.2 wt % MWCNT's, DGEDP-Bu nanocomposites exhibited 68% higher electrical conductivity and a three-fold higher rheological yield stress than those made from DGEBA. Rheological characterization corroborated that continuous MWCNT networks are formed within epoxies between 0.1 and 0.2 wt % MWCNT's. Moreover, upon MWCNT loading, DGEDP-Bu demonstrates equal mechanical performance and better electrical conductivity than DGEBA.

Electropolymerization of β-cyclodextrin onto multi-walled carbon nanotube composite films for enhanced selective detection of uric acid

An amperometric uric acid (UA) sensor incorporating a multi-walled carbon nanotubes (MWCNT) network in Nafion and electropolymerized β-cyclodextrin (β-CD) layer is investigated. The electrochemical sensor is comprised of a glassy carbon electrode modified with Nafion-MWCNT nanocomposite film, a β-CD polymer inner selective layer, and a Hydrothane polyurethane (HPU) outer selective coating. The surface morphology and electronic structure of the electrode material are characterized using transmission electron microscopy (TEM), scanning electron microscope (SEM), and Fourier transform infrared (FTIR) spectroscopy. The electrocatalytic activity of the sensor is studied using cyclic voltammetry (CV), chronocoulometry (CC) and differential pulse voltammetry (DPV). Analytical performance of the electrochemical sensor scheme with and without MWCNT and/or β-CD polymer is determined from direct UA injection during an amperometric analysis. The effective surface area is notably higher for Nafion-MWCNT coated glassy carbon electrodes, which in turn enhanced the sensitivity when coated with β-CD polymer. The results indicated an excellent electrocatalytic property of Nafion-MWCNT/β-CD film for UA detection with enhanced sensitivity (2.11μA·mM−1), wide linear responses over physiologically relevant concentrations, and fast response times. Enhancement is attributed to MWCNT offering increased electroactive surface area and the ability of β-CD to selectively sequester UA.

Improving the properties of poly(arylene ether nitrile) composites reinforced by covalently modified multi-walled carbon nanotubes

To develop high-performance carbon nanotube (CNT)-based polymer nanocomposites, both the interface control and the dispersion of CNTs within the polymer hosts need to be considered. In this study, we show an effective way to modify the surface of multi-walled CNTs (MWCNTs) by applying a cyclization reaction between nitrile-modified MWCNTs and bis-phthalonitrile. Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to examine the structure and morphology of as-prepared functional CNTs. Phthalocyanines (Pcs) were found to be evenly coated on the surface of MWCNTs, resulting in good dispersion and strong interfacial adhesion between MWNCTs and the poly(arylene ether nitrile) (PEN) matrix. Compared with neat PEN, the tensile strength and tensile modulus of PEN nanocomposites with 2 wt% MWCNTs–Pc increased from 85.6 MPa to 108 MPa and from 2300 MPa to 3350 MPa, respectively. Furthermore, surface-functionalized CNTs can also form the physical MWCNT network within the PEN matrix, as confirmed by rheological and thermal stability tests. Additionally, a low rheological percolation threshold of 0.69 wt% was obtained, and the dielectric constant of PEN nanocomposites was increased from 3.3 for neat PEN to 16.6 with 5 wt% MWCNTs–Pc.

Ce-doped Li4Ti5O12/C nanoparticles embedded in multiwalled carbon nanotube network as a high-rate and long cycle-life anode for lithium-ion batteries application

Spinel-type lithium titanate (Li4Ti5O12) attracts increasing attention for large-scale energy storage as a promising alternative to the graphite in view of superior safety and stability. Nevertheless, the main challenge of Li4Ti5O12 anode is the poor electronic conductivity which restricts its battery performance. Herein, the Ce-doped Li4Ti5O12/C embedded in multiwalled carbon nanotube (MWCNTs) network is successfully fabricated through a conventional sol-gel method. The doped Ce3+-ion and the formed conductive network between the coated carbon and MWCNTs are favorable to improve the kinetics of Li4Ti5O12 toward fast electron transport and Li+-ions diffusion. Such a unique hybrid exhibits superior high-rate and long cycle-life performances when used as an anode material for lithium-ion batteries. It delivers specific capacities of 171.5 and 145.3mAhg−1 at 0.2 and 10C between 1.0 and 2.5V, respectively, and reversible capacity of 129.3mAhg−1 after 600 cycles at high rate of 20C with capacity retention of 98.6%. Moreover, the EIS results reveal that this anode material exhibits high electronic conductivity and fast Li+-ions diffusion. This study provides a new stragety to prepare other electrode materials for high-performance energy storage device.

Leveraging compressive stresses to attenuate the electrical resistivity of buckypaper

Buckypaper (BP) is a planar film that consists of random network of multiwall carbon nanotubes (MWCNTs) held together by weak van der Waals interactions at tube-tube junctions. Although individual carbon nanotubes (CNTs) possess remarkable electrical properties, the electrical resistance of pristine BP is usually too high for practical applications. However, the electrical resistivity of BP can be attenuated by applying modest compressive stresses. Herein, we report an analytical model for predicting the electrical resistivity of BP under defined level of compressive strain. The predictive piezoresistive model of BP was developed by formulating a direct relationship with the structural parameters, physical and electrical properties of CNTs. The basis of the piezoresistive model relied upon the geometrical probability approach in combination with classical Hertzian contact mechanics and constriction resistance techniques. A comparison has been made between the theoretical and experimental results of electrical resistivity of BPs with varying densities. A reasonably good quantitative agreement was obtained between the theory and experiments. The main source of error was caused by the uncertainty in the measurement of the initial BP thickness. Through theoretical modeling, the initial volume fraction of CNTs was found to be one of the key parameters that modulated the piezoresistive behavior of BP.

Polycarbonate Composites Containing Carbon Encapsulated “Brick‐Like” Fe3O4 Nanoparticles as Efficient Microwave Absorbers with a Large Bandwidth

AbstractThis study demonstrates lightweight microwave absorber materials designed using polycarbonate (PC) nanocomposites containing multiwall carbon nanotubes (MWNTs) and “brick‐like” lossy magnetic ferrite (Fe3O4) nanoparticles encapsulated with carbon (Fe3O4@C). The designed nanocomposites manifested in exceptional microwave attenuation through absorption (89 %). The unique strategy, of encapsulating ferrites with C, adopted here prevents the disruption of conducting pathway facilitated through the network of MWNTs and overcomes the eddy current effects. In addition, this strategy further led to improved dispersion of ferrites in PC matrix which rather agglomerates during processing. Unlike classical electromagnetic interference (EMI) shielding materials, the PC nanocomposites containing MWNTs and Fe3O4@C resulted in exceptional microwave attenuation in a broad frequency range and mostly through absorption. The absorption ability of these nanocomposites was further assessed by evaluating the reflection loss (RL). For instance, PC nanocomposites containing MWNTs and Fe3O4@C nanoparticles depicted in an exceptional RL of −41.3 dB at 17.7 GHz and with a remarkable bandwidth of 4.4 GHz for a thickness of 1 mm. Unlike previous studies where RL was improved by sacrificing dielectric losses, herein, the adopted strategy enhances both dielectric losses facilitating in enhanced total shielding effectiveness (SET) and RL through suitable impedance matching. This further result in excellent absorption. Therefore, this study provides comprehensive understanding about tailoring the complex microwave properties of the polymer nanocomposites in order to achieve enhanced microwave absorption.

Hierarchical porous nanocomposite architectures from multi-wall carbon nanotube threaded mesoporous NaTi2(PO4)3 nanocrystals for high-performance sodium electrodes

Abstract Rational design and self-assembly of nanostructured electrode materials for high-performance energy-storage devices is highly desirable but still challenging. Herein, we design and synthesize hierarchical porous nanocomposite architectures consisting of mesoporous NaTi 2 (PO 4 ) 3 (MNTP) nanocrystals (NCs) with a pore size of about 10 nm and multi-wall carbon nanotube (MWCNT) networks for high-performance sodium ion batteries (SIBs). Our strategy is based on the hetero-assembly of MWCNTs and nanostructured building units by utilizing the screening effect of electrostatic repulsion in a solution engineered ionic strength using highly soluble ammonium salt to form three-dimensional hierarchical assemblies of MWCNT networks and packed MNTP NCs. Subsequent freeze-drying and calcination convert the assemblies into robust hierarchical porous MWCNTs-threaded particles. Calcination of residual ammonium salt introduces nitrogen into the MWCNTs. Such nanoarchitecture enhances electron/ion conductivity and structural stability as anode materials for SIBs. The nanocomposite has high initial Coulombic efficiency of 99%, high rate capability of 74.0 mAhg −1 at 50C, as well as long-term cycling stability with capacity retention of 74.3 mAhg −1 after 2000 cycles with only 0.012% loss per cycle at 10C. The results provide a general and scalable hetero-assembly approach to different types of nanocomposites for high-performance energy storage devices such as LIBs and SIBs.

Tin Selenide – Multi-Walled Carbon Nanotubes Hybrid Anodes for High Performance Lithium-Ion Batteries

A simple dry physical grinding and solvent mixing approach was used to prepare tin selenide – multiwalled carbon nanotube (MWCNT) hybrid as an anode material for high performance lithium ion batteries (LIBs). The pure tin selenide and their composites with carbon black or graphene oxides were previously reported, however no other groups have reported tin selenide/MWCNT composite as anode materials for LIBs. The new hybrid had superior electrochemical cycling performance with higher reversible (lithiation) capacity of 882 to 651mAhg−1 over 50 cycles compared to pure tin selenide (602 to 58 mAhg−1) or pure MWCNT (339 to 171 mAhg−1) electrodes. The enhanced performance of the tin selenide/MWCNT hybrid was attributed to various factors including alleviation of volume change of tin selenide during lithiation/delithiation by nanoscale network of MWCNT which helped to preserve the electrical connectivity between active particles, reversible decomposition of tin selenide, lithiation/delithiation of MWCNTs and conductive electronic transport pathways provided by MWCNTs.

Investigation of MnFeO3/Multiwalled Carbon Nanotubes Composite As Potential Anode for Lithium-Ion Batteries

MnFeO3, explored for its application in sensors, catalysis and semiconductors has been validated for the first time as anode for lithium-ion batteries, facilitated through the formation of composite containing multiwalled carbon nanotubes. MnFeO3 nanoparticles, derived from combustion method upon sonication with multiwalled carbon nanotubes (MWCNT) form MnFeO3/MWCNT composite that has been explored for the first time as anode material in lithium-ion battery applications. Scalable and highly reproducible sonochemical process has been adopted to form the composite, wherein the interweaved MWCNT ensures better electronic conductivity and the desirable pinning of pristine MnFeO3 particles with a conductive coating. The observed capacity and rate capability behavior of MnFeO3/MWCNT composite anode are found to be superior than pristine MnFeO3 anode in such a manner that a steady state reversible capacity of 840 mAh g-1 has been obtained at 0.5 A g-1 even after 50 cycles against an inferior capacity of 200 mAh g-1 offered by MnFeO3. Further, MnFeO3/MWCNT composite anode shows excellent rate capability and reversibility with respect to various current density conditions ranging from 0.5 to 10 A g-1, wherein appreciable capacity values of 2960 and 410 mAh g-1 have been obtained at 0.5 and 10 A g-1 respectively. The impressive electrochemical performance of MnFeO3/MWCNT composite anode could be correlated to the multifarious advantages offered by MWCNT, such as increase in the electronic conductivity, maintenance of structural stability upon cycling and mitigation of inherent and exorbitant volume changes observed upon cycling. In particular, the synergistic effect of conversion cum redox reaction triggered electrochemical activity of MnFeO3 and the increased electronic conductivity rendered by the conducting carbon network of MWCNT, possessing larger surface area and appreciable mechanical strength contributes to the improved electrochemical behaviour, observed with the currently prepared MnFeO3/MWCNT anode in a significant manner. These results suggest that the currently synthesized MnFeO3/MWCNT nanocomposite anode could be considered as a promising candidate for next generation hybrid energy storage applications. The present study is bestowed with the identification and demonstration of earth abundant, environment friendly and low cost metals viz., Mn and Fe based composite anode for high capacity and high rate lithium-ion battery applications, which is noteworthy.

Interphase tuning for stronger and tougher composites.

The development of composite materials that are simultaneously strong and tough is one of the most active topics of current material science. Observations of biological structural materials show that adequate introduction of reinforcements and interfaces, or interphases, at different scales usually improves toughness, without reduction in strength. The prospect of interphase properties tuning may lead to further increases in material toughness. Here we use evaporation-driven self-assembly (EDSA) to deposit a thin network of multi-wall carbon nanotubes on ceramic surfaces, thereby generating an interphase reinforcing layer in a multiscale laminated ceramic composite. Both strength and toughness are improved by up to 90%, while keeping the overall volume fraction of nanotubes in a composite below 0.012%, making it a most effective toughening and reinforcement technique.

C-doped mesoporous anatase TiO2 comprising 10 nm crystallites

We report a C-doped mesoporous anatase TiO2 with high surface area synthesized using multi-walled carbon nanotube (MWCNT) mat as a “rigid” template and carbon doping source. The characterization by SEM, HRTEM, X-ray diffraction and nitrogen adsorption revealed that TiO2 samples have a porous structure which are figuratively a inverse copy of MWCNT network and pore walls are formed by interconnected TiO2 nanoparticles with average diameter of ∼10nm. We found that annealing temperatures from 400 to 1000°C before MWCNT template removal had very limited effect on particle size (∼10nm), surface area (112–129m2/g) and total pore volume (0.74–0.85m2/g) of the samples through a significantly delayed phase transition from anatase to rutile started at 800°C, resulting in only ∼9.1% conversion at 1000°C. The pore size distribution is in mesopore range from 6 to 60nm peaked at ∼24nm. XPS analysis showed a relatively strong C1s peak at 288.4eV, indicating C doping at Ti sites, which is responsible for red shift of adsorption edge of UV–vis spectra and photocatalytic activity in visible-light region.

Largely enhanced thermal and electrical conductivity via constructing double percolated filler network in polypropylene/expanded graphite – Multi-wall carbon nanotubes ternary composites

In this study, we report a sharp increase of both thermal and electrical conductivity in polypropylene (PP) via formation of double percolated filler network with dense small-sized multi-wall carbon nanotubes (MWCNT) network located within loosened large-sized expanded graphite (EG) network. The electrical conductivity of PP/EG composites which levels off after the percolation threshold can be further enhanced by adding MWCNT and is increased two orders of magnitude as the content of MWCNT reaches to its threshold. Besides, the thermal conductivity of PP/EG-MWCNT increases by 38.5% compared to PP/EG and is much higher than PP/MWCNT. Furthermore, an excellent electromagnetic interference shielding effectiveness of ∼60 dB is obtained at the sample thickness of only 1.3 mm. Then, effective medium theory model is applied to analyze the mechanism for the largely enhanced thermal and electrical conductivity. It is suggested that formation of double percolated filler network, in which three types of connections exist between EG and EG, EG and MWCNT as well as MWCNT and MWCNT, could effectively reduce the interface thermal resistance. Our work is important and provides some new idea for the preparation of polymer composites with excellent thermal and electrical conductivity via constructing double percolated filler network.

Tunable morphology and its influence on electrical, thermal and mechanical properties of carbon nanostructure-buckypaper

In this study, free-standing buckypapers (BPs) made up of a three-dimensional network of multi-walled carbon nanotubes (MWCNTs) that are branched, cross-linked, and share common walls, defined henceforth as multi-walled carbon nanostructures (MWCNSs) are characterized to obtain their electrical, thermal and mechanical properties. Two types of free-standing sheets are studied, namely uncompressed buckypapers (UBPs) and compressed buckypapers (CBPs). Both are processed via a vacuum filtration method, with subsequent compressive force applied between platen presses to obtain CBP. CBPs are found to exhibit improved thermal and electrical conductivities since higher density of CNT networks leads to more conductive pathways. However, mechanical properties of CBPs and UBPs are approximately the same. Local anisotropic behavior of both BPs allows them to have either positive or negative Poisson's ratio. While UBP is suitable for membrane applications due to its mechanical stability and well-defined pore characteristics, the CBP offers a compact structure that can reduce penetration of the polymer matrix in composite applications such as for integrated circuit packaging and EMI shielding.

In situ growth and performance of spherical Fe2F5·H2O nanoparticles in multi-walled carbon nanotube network matrix as cathode material for sodium ion batteries

The multi-wall carbon nanotubes wired spherical Fe2F5·H2O particles (MWCNTs-wired Fe2F5·H2O) are synthesized via an ionic liquid (IL) based precipitation route as the cathode material for sodium ion batteries (SIBs), in which the IL 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMMimBF4) is used as environmentally friendly fluorine source, appropriate solvent and binder. The structure, morphology and electrochemical performance of the as-prepared samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), charge/discharge tests, cyclic voltammetric measurements (CV). The results show that the MWCNTs-wired spherical Fe2F5·H2O particles present the cubic crystal structure with the cell volume of 1.12821 nm3. Moreover, the SEM and TEM images show that the spherical Fe2F5·H2O particles and disentangled MWCNTs are intertwined together to form a chestnut-like micrometer-sized aggregates. Furthermore, the MWCNTs-wired spherical Fe2F5·H2O particles show a high initial discharge capacity of 251.2 mAh g−1 at 20 mA g−1 in the voltage of 1.0–4.0 V, and the corresponding reversible discharge capacity is 197.4 mAh g−1. Comparing with bare Fe2F5·H2O, the discharge capacity of the MWCNTs-wired spherical Fe2F5·H2O particles still can maintain about 115.0 mAh g−1 after 50 cycles when the current density increased to 100 mA g−1, and the corresponding capacity retention reaches 90.2%.