Electrical conductivity of carbon black/single-wall carbon nanotube/low-density polyethylene ternary composite foam

In order to obtain high electrical conductive low-density polyethylene (LDPE) foam, carbon black (CB), single-wall carbon nanotube (SWCNT), and LDPE (CB/SWCNT/LDPE) ternary composite foams were successfully fabricated by chemical compression molding method. The electrical conductivity, mechanical properties, microstructure, density, and crystallinity of the foam were studied in detail. It can be found that CB and SWCNT have synergistic effect. For the CB/SWCNT/LDPE composite foam which containing 19 wt % CB and 0.05 wt % SWCNT, its density is only 0.082 g cm⁻¹ and the electrical conductivity can reach at 2.88 × 10⁻⁵ S cm⁻³, which is far more than 15 orders of magnitudes of pure polyethylene and 4 orders of magnitudes times higher than sample which CB content is 19 wt %. It is noteworthy that ultralow concentration of SWCNT could drastically improve the electrical conductivity and reduce the density of LDPE foams. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48382.     

Electrical conductivity of pure carbon nanotube yarns

The porosity of multi-walled carbon nanotube yarns can be varied over a wide range by adjusting the yarn construction, resulting in a dramatic change in yarn electrical conductivity. When the yarn electrical conductivity is converted into specific conductivity, its value remains approximately constant irrespective of the changes in yarn construction and porosity. The process of carbon nanotube yarn production involves two key steps, the formation of a network of carbon nanotube bundles spliced together by the entanglement of individual nanotubes and the compaction of the network into a cylindrical yarn. The splices formed from entangled individual nanotubes play a much greater role in electrical conduction than the cross-over contact formed between CNT bundles by compaction during spinning.     

Length dependent performance of single-wall carbon nanotube thin film transistors

The effects of the length of single-wall carbon nanotubes (SWCNTs) on their thin film transistors (TFTs) were investigated by using SWCNTs sorted in length using size exclusion chromatography. Higher device performances were obtained in longer SWCNTs and it was found that the average length of the SWCNTs is an important factor to determine the device performance. Detailed analyses, in which the SWCNT density was normalized using percolation threshold, confirmed that the dependence of on-current on the normalized density approximately follows percolation theory, independently of the SWCNT length. On the other hand, the behaviors of off-current and on/off ratio showed the considerably different dependence among SWCNT lengths.     

High performance carbon nanotube based composite film from layer-by-layer deposition

So far, preparation of strong carbon nanotube (CNT)/polymer composites still faces big challenges mainly due to the limited controls of CNT dispersion and alignment in polymers. Here, a new “layer-by-layer deposition” method is put forward to prepare CNT/polyvinyl alcohol (PVA) composite films. This is based on intermittent deposition of aligned CNT and PVA layers on a paper tape substrate. The in situ deposition allows PVA to infiltrate into the CNT film efficiently, and, as a result, the mechanical property of CNT/PVA composite film has been improved remarkably. For example, the composite film possesses a tensile strength of 1.7 GPa, which is almost one order of magnitude and 20 times higher than those of the pure CNT and PVA films, respectively. The high performance of the composite film could be ascribed to the role of PVA infiltration, which leads to not only the formation of strong interfacial bonding between CNTs and PVA matrix but also the reduction of film thickness. The novel process offers a new research direction for preparing CNT-based composites and future performance maximization.     

Electrophoretic deposition of surface-modified titanate nanosheets via layer-by-layer assembly and deposited film properties

The surface of H₂Ti₄O₉·xH₂O titanate nanosheets was modified using the sulfonated tetrafluoroethylene-based polymer Nafion^®, via layer-by-layer assembly. The surface modification allowed the titanate nanosheets to be highly dispersed in hydrophobic organic solvents. Thick films of surface-modified nanosheets were prepared on indium tin oxide (ITO)-coated glass substrates as a negative electrode by electrophoretic deposition. The thickness of the films increased with increasing deposition time and grew to more than 8 μm in 600 s under potentiostatic conditions at 7.5 V. The electrophoretically deposited thick films showed significant hydrophobicity with contact angle for water 95°, and enhanced adsorption and higher photocatalytic activity for hydrophobic dyes such as thionine than those of thick films prepared from unmodified titanate nanosheets.     

Synthesis of carbon nanotube/epoxy composite films with a high nanotube loading by a mixed-curing-agent assisted layer-by-layer method and their electrical conductivity

A mixed-curing-agent assisted layer-by-layer method is reported to synthesize carbon nanotube (CNT)/epoxy composite films with a high CNT loading from ∼15 to ∼36 wt.%. The mixed-curing-agent consists of two types of agents, one of which is responsible for the partial initial curing at room temperature to avoid agglomeration of the CNTs, and the other for complete curing of epoxy resin at high temperature to synthesize epoxy composite films with good CNT dispersion. The electrical conductivity of the composites shows a value up to ∼12 S/m, which is much higher than that for CNT/epoxy composites with a low CNT loading prepared using conventional methods.     

Fabrication of photovoltaic cells using rhenium diimine complex containing polyelectrolytes by the layer-by-layer electrostatic self-assembly method

A series of poly(p-phenylenevinylene)s polycations incorporated with rhenium(I) chlorotricarbonyl bis(phenylimino)acenaphthene complex and pendant pyridinium side groups was synthesized. Due to the presence of ionic pendant groups, the polymers could be used to form multilayer thin films with sulfonated polyaniline (SPAN) by the layer-by-layer (LbL) electrostatic assembly process. The rhenium complexes could function as photosensitizers and SPAN could serve as a charge carrying polymer, and the resulting multilayer films form the active layer of photovoltaic cells. Upon irradiation of the photovoltaic devices by simulated AM 1.5 solar light, the power conversion efficiencies were measured to be of the order of 10⁻⁴%. Measurement of the incident photon-to-electron conversion efficiency (IPCE) at different wavelengths confirmed that the photosensitization was due to the presence of rhenium complexes in the polymer. The photocurrent generation and decay processes could be simulated by triexponential functions, which consisted of a rapid process followed by a relatively slow process. This paper is dedicated to Professor Ian Manners and his scientific accomplishments.     

Electrical conductivity of chemically modified multiwalled carbon nanotube/epoxy composites

The electrical conductivity of oxidized multiwalled carbon nanotubes (MWNT)/epoxy composites is investigated with respect to the chemical treatment of the MWNT. The oxidation is carried out by refluxing the as-received MWNT in concentrated HNO₃ and H₂O₂/NH₄OH solutions, respectively, under several different treatment conditions. The oxidized MWNT are negatively charged and functionalized with carboxylic groups by both solutions. The MWNT oxidized under severe conditions are well purified, but their crystalline structures are partially damaged. It is recognized that the damage to the MWNT has considerable influence on the electrical properties of the MWNT composites, causing the electrical conductivity to be lowered at a low content of MWNT and the percolation threshold to be raised. The MWNT oxidized by the mixture of H₂O₂ and NH₄OH solution provides epoxy composites with a higher conductivity than those produced with the MWNT oxidized by nitric acid over the whole range of MWNT, independently of the oxidation conditions.     

Gradient nanoporous phenolics as substrates for high-flux nanofiltration membranes by layer-by-layer assembly of polyelectrolytes

Thin film composite(TFC) membranes represent a highly promising platform for efficient nanofiltration(NF)processes. However, the improvement in permeance is impeded by the substrates with low permeances. Herein,highly permeable gradient phenolic membranes with tight selectivity are used as substrates to prepare TFC membranes with high permeances by the layer-by-layer assembly method. The negatively charged phenolic substrates are alternately assembled with polycation polyethylenimine(PEI) and polyanion poly(acrylic acid)(PAA)as a result of electrostatic interactions, forming thin and compact PEI/PAA layers tightly attached to the substrate surface. Benefiting from the high permeances and tight surface pores of the gradient nanoporous structures of the substrates, the produced PEI/PAA membranes exhibit a permeance up to 506 L? m~(-2)?h~(-1)?MPa~(-1), which is ～2–10 times higher than that of other membranes with similar rejections. The PEI/PAA membranes are capable of retaining N 96.1% of negatively charged dyes following the mechanism of electrostatic repulsion. We demonstrate that the membranes can also separate positively and neutrally charged dyes from water via other mechanisms.This work opens a new avenue for the design and preparation of high-flux NF membranes, which is also applicable to enhance the permeance of other TFC membranes.     

Raman spectroelectrochemistry of a single-wall carbon nanotube bundle

Raman microscopy and spectroelectrochemistry with polymer electrolyte gating is developed to study the effect of charging on Raman spectra of individual single-wall carbon nanotubes (SWCNTs) and bundles. The Raman spectra of a small bundle, consisting of well-separated features from a metallic and a semiconducting SWCNT, have been obtained at different electrochemical charging levels. The broad Fano peak of the metallic SWCNT exhibits an appreciable frequency upshift and simultaneous line narrowing when the charging level, either positive or negative, is increased, in agreement with the presence of a Kohn anomaly in metallic SWCNTs. The radial breathing mode of the metallic tube also shows a similar but much weaker dependence on the charging potential. While the G mode frequencies of the semiconducting SWCNT also increase with the increasing charging level, the magnitude of such change is much smaller than in the metallic SWCNT. At high negative charging potentials the G⁻ peak of the semiconducting SWCNT exhibits a larger upshift than its G⁺ peak, leading to the observation of merging of these two peaks. However, both G⁺ and G⁻ peaks of the semiconducting SWCNT become broader at high charging levels, which are not predicted from previous theoretical studies.     

Electrical conductivity of single walled and multiwalled carbon nanotube containing wool fibers

The main purpose of this study was producing conductive wool fabric applying carbon nanotubes. Raw and oxidized wool samples were treated with carbon nanotubes in the impregnating bath in the presence of citric acid as a crosslinking agent and sodium hypophosphite as a catalyst while sonicating them in the ultrasonic bath. Electrical resistance, washing durability, and color variation of treated samples were assessed. Through SEM images, the surface morphology of treated samples was studied confirming the surface coating through carbon nanotubes. According to the results, the electrical resistance of treated wool with carbon nanotubes reduced substantially. However, the single‐walled carbon nanotubes are more useful to increase the conductivity. In addition, the wool color changed into gray after the treatment. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrical conductivity and Joule heating of polyacrylonitrile/carbon nanotube composite fibers

Carbon nanotube (CNT) can exhibit electrical conductivity and introduce electric current into polymer. Using dry-jet-wet spin technology, polyacrylonitrile (PAN)/CNT composite fibers with 15 wt% and 20 wt% of CNT content were fabricated. The electrical conductivity of PAN/CNT fibers was enhanced by the annealing process at different temperatures and changed with time. These fibers could also respond to stretching, and the electrical conductivity decreased by 50% when the elongation reached 3%. In addition, electrical current can induce Joule heating effect and thermally transform PAN/CNT composite fibers. With the application of various electrical currents up to 7 mA at a fixed length, conductivity was enhanced from around 25 S/m to higher than 800 S/m, and composite fibers were stabilized in air. The temperature of composite fibers can increase from room temperature to several hundreds of degree Celsius measured by an infra-red (IR) microscope. Joule heating effect can also be estimated according to one-dimensional steady-state heat transfer equation, which reveals the temperature can be high enough to stabilize or carbonize fibers. As a result, this research provides a new idea of heating fabrics for thermal regulation, and a new approach for stabilizing and carbonizing PAN-based carbon fibers.     

Tuning the photophysical properties of soluble single-wall carbon nanotube derivatives by co-functionalization with organic molecules

The photophysical characterization of three soluble derivatives of single-wall carbon nanotubes (SWCNTs), functionalized with poly(ethylene glycol) (PEG), co-functionalized with PEG and aminofluorene and co-functionalized with PEG and aminoanthracene is reported. The peculiar excellent solubility of these derivatives allows, for the first time in covalently functionalized SWCNTs, the study of their excitation dynamics by monitoring the near-infra-red emission. Moreover, the aminoanthracene derivative shows higher photoluminescence efficiency in the visible range than the aminofluorene derivative, demonstrating the possibility to tune extensively the photophysical properties of these functionalized SWCNTs.     

Synthesis of millimeter-long vertically aligned carbon nanotube arrays on aluminum oxide buffer prepared by layer-by-layer assembly of boehmite nanoplates

To synthesize vertically aligned carbon nanotube (VA-CNT) arrays longer than a millimeter using chemical vapor deposition (CVD), aluminum oxide buffer has to be deposited on supporting substrates to prevent diffusion and aggregation of catalyst nanoparticles. Currently, reliable deposition has to be made using expensive and time-consuming e-beam evaporation or thermal sputtering. Here, we report a simple, low-cost, and scalable method for buffer preparation using layer-by-layer assembly of boehmite nanoplates followed by thermal annealing. On top of buffer prepared using this method, we have grown VA-CNT arrays consisting of CNTs with a length of 1.3(±0.1) mm, an inner diameter of 5.6(±1.3) nm, and a wall number of 4(±1) by using CVD with iron as catalyst and ethylene as carbon source.     

Influence of the gas pressure on single-wall carbon nanotube formation

Experiments and modeling are performed to predict the effect of gas pressure on species distributions and nanotube growth rate under specific conditions of synthesis of single-wall carbon nanotubes (SWCNTs) by arc discharge. Numerical results are compared with experiments in order to find a consistent correlation between the nanotube growth and the pressure. We use argon and helium as buffer gases with a total pressure varied between 0.1 and 1 bar. We experimentally observe that both the anode erosion rate and the Brunauer-Emmett-Teller (BET) surface area of the as-produced nanotube soot material are very sensitive to the total gas pressure in the reactor.     

Characterisation of carbon nanotube films deposited by electrophoretic deposition

Electrophoretic deposition (EPD) was shown to be a convenient method to fabricate uniform coatings of carbon nanotubes (CNTs) with desired thickness and excellent macroscopic homogeneity. The CNT deposition kinetics are controlled by the applied electric field and deposition time which, in turn, prove to be linearly correlated with the deposition yield and thickness. The CNT films were characterised by using a range of techniques including high resolution scanning electron microscopy, nanoindentation and atomic force microscopy. Nanoindentation results revealed differences in the local microstructure of CNT deposits leading to variations of Young’s modulus and hardness, which were ascribed to differences in the packing density of CNTs, as observed also by AFM. A mathematical model for the kinetic of EPD of CNTs based on Hamaker’s law was proposed and the predictions of the model were shown to be in good agreement with experimental results.     

Fabrication of the single-wall carbon nanotube compound polymer film electrode and the simultaneous electrochemical behavior of aminophenol isomers

We describe a simple, rapid and selective voltammetry for simultaneous determination of electroactive isomers using nanometer composite electrode. The electrode was constructed by electropolymerization of 4-aminopyridine at single-wall carbon nanotubes modified glassy carbon electrode (SWNTs/POAPE). The configuration and electrochemical properties of SWNTs/POAPE were characterized by scanning electronic micrographs (SEM) and voltammetry. The SWNTs/POAPE showed an excellent electrocatalytic activity to the oxidation of aminophenol isomers and capability of determining three aminophenol isomers simultaneously. The oxidation peak potential difference between m-aminophenol and o-aminophenol was 416 mV, o-aminophenol and p-aminophenol 119 mV, indicating that the o-, m- and p-aminophenol could be identified entirely at the SWNTs/POAPE. The proposed electrode has been applied to the simultaneous voltammetric determination of aminophenol isomers in mixture without previous chemical or physical separations.     

Electrical conductivity of poly(vinylidene fluoride)/carbon nanotube composites with a spherical substructure

Poly(vinylidene fluoride) (PVDF)/multiwalled carbon nanotube (MWCNT) conducting composites were prepared with a percolation threshold as low as 0.07 wt%. The MWCNTs in a PVDF solution can lead to the formation of spherical PVDF/MWCNT composite particles by sonication. The MWCNTs coated on the surfaces of the spherical particles form a conduction network when the spheres coalesce to form a solid composite. The existence of the spherical particles with a substructure results in the reduction in MWCNT content and improves the electrical conductivity of the composites.     

Amperometric glucose biosensor prepared with biocompatible material and carbon nanotube by layer-by-layer self-assembly technique

Prussian Blue (PB) based glucose biosensor was prepared by immobilizing glucose oxidase (GOD) in layer-by-layer (LBL) films with chitosan (Chi) and multi-walled carbon nanotubes (MWNTs). With the increasing of Chi/MWNTs/GOD layers, the response current to glucose was changed regularly and reached a maximum value when the number of layer was six. At the optimized condition, the biosensor exhibits excellent response performance to glucose with a linear range from 1 to 7 mM and a low detection limit of 0.05 mM. The biosensor also shows a high sensitivity of 8.017 μA mM⁻¹ cm⁻², which is attributed to the biocompatible nature of the LBL films. Furthermore, the biosensor shows rapid response, good reproducibility, long-term stability and freedom of interference from other co-existing electroactive species such as ascorbic acid and acetaminophen.