Multi-walled carbon nanotube/polyimide composite film fabricated through electrophoretic deposition

Multi-walled carbon nanotube (MWCNT)/polyimide composite films were fabricated through electrophoretic deposition (EPD) of MWCNT-polyamic acid colloidal suspension which was derived from carboxylated-MWCNTs and poly(pyromellitic dianhydride-co-4,4′-oxydianiline) (PMDA-ODA). Under electric field, both negatively charged MWCNTs and PMDA-ODA colloid particles migrate onto a positively charged anode simultaneously, and are converted to a coherent MWCNT/polyimide composite film in the ensuing imidization reaction. Uniform dispersion of MWCNTs in the composite film was observed using transmission electron microscopy. The thickness of the prepared composite film can be tuned by varying processing conditions such as deposition time and anode conductivity. The electrical conductivity of the composite film increased with increasing the concentration of MWCNTs in EPD suspension. The mechanical reinforcement of polyimide using MWCNTs was evaluated by tensile testing and nanoindentation testing.     

High performance field emission of carbon nanotube film emitters with a triangular shape

We report novel two-dimensional (2D) shaped carbon nanotube (CNT) field emitters using triangular-shaped CNT films and their field emission properties. Using the 2D shaped CNT field emitters, we achieved remarkable field emission performance with a high emission current of 22 mA (equivalent to an emission current density >10⁵ A/cm²) and long-term emission stability at 1 mA for 20 h. We also discuss the field emission behavior of the 2D shaped CNT field emitter in detail.     

High performance carbon nanotube spun yarns from a crosslinked network

We report a new method to create covalent crosslinks between carbon nanotubes (CNTs) with reduced intertube and interbundle spaces, for improving the mechanical properties of CNT spun yarns. This is achieved through the pretreatment of a CNT yarn with 4-carboxybenzenediazonium tetrafluoroborate to form reactive carboxyphenyl groups on the CNT sidewalls. These carboxyphenyl groups are then reacted with a multifunctional crosslinker hexa(methoxymethyl) melamine, leading to a highly crosslinked network within the yarn. The CNT yarns were characterized by X-ray photoelectron spectroscopy, focused ion beam scanning electron microscope, and also assessed for their mechanical properties. The results showed that the method developed effectively improved mechanical properties of CNT yarns: we are able to produce CNT yarns with a tensile strength up to 2.5 GPa and Young’s modulus 121 GPa.     

Polymer/carbon nanotube composite film formation: A fluorescence study

In this study, the effect of multi‐walled Carbon nanotube (MWNT) on film formation behavior of Polystrene (PS) latex film was investigated by using steady state fluorescence technique. Films were prepared by mixing of pyrene (P)‐labeled PS latex with different amounts of MWNTs varying in the range between 0 and 20 wt%. After drying, MWNT containing films were separately annealed above glass transition temperature (T_g) of PS ranging from 100 to 270°C for 10 min. In order to monitor film formation behavior of PS/MWNT composites, Scattered light (I_s) and fluorescence intensities (I_P) from P were measured after each annealing step to monitor the stages of film formation. At 0–20 wt% range of MWNT content films, minimum film formation (T_o), void closure (T_v), and healing, (T_h) temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It was observed that while void closure activation energies increased, backbone activation energies decreased as the percent of MWNT is increased in the composite films. POLYM. COMPOS., 35:817–826, 2014. © 2013 Society of Plastics Engineers     

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 binder-free Sn coated carbon nanotube array anode

We report a binder-free Li-ion battery anode based on a tin (Sn) coated vertical-aligned carbon nanotube (VACNT) array. In this anode, the VACNT array, acting as a robust core matrix to support high theoretical capacity active material Sn, offers large inter-wire spacing for Sn expansion during the lithiation/de-lithiation processes and forms direct conductive pathways for electrons transporting. A remarkable enhancement in the capacity retentions abilities of this anode compared with pure Sn film anode has been achieved. A reversible capacity as high as 900 mAh g⁻¹ over 400 cycles at 0.2 C and nearly 400 mAh g⁻¹ over 1000 cycles at 0.5 C has been demonstrated respectively.     

改性活性炭/碳纳米管复合电极脱盐性能研究

采用改性CNT*作为CDI电极导电剂,制备AC*/CNT*复合电极,考察其脱盐性能。利用BET、FTIR和TEM对AC或CNT的表面结构、官能团种类和分散性进行分析。利用电化学工作站和SEM对复合电极的比电容、阻抗和表面形貌进行分析。结果表明,通过改性,AC*的比表面积达到672.48 m2/g,增加了29.43%;CNT*的比表面积为117.39 m2/g,下降了9.94%,但其分散性得到有效改善。根据循环伏安测试和静态脱盐实验结果 ,按AC*∶CNT*∶PVDF=7.2∶0.8∶2质量比制备的电极效果最好,比电容高达130.48 F/g,比吸附量达到7.29 mg/g。     

Electrical conductivity of single-wall carbon nanotube film deposited by electrostatic layer-by-layer assembly with the aid of polyelectrolytes

A single-wall carbon nanotube film was deposited by the sequential deposition of positively charged single-wall carbon nanotube with poly diallyldimethylammonium and negatively charged single-wall nanotube with poly sodium 4-styrenesulfonate. The sequential deposition was repeated 10 times and Al was used as an electrode to measure the electrical conductivity of the film. Electrochemical impedance spectroscopy showed that the film had two semicircles with the resistances of 300 and 1700 Ω, representing single-wall carbon nanotube and polyelectrolyte parts, respectively. The conductivity of the film was enhanced when the water molecules were removed by heat treatment. The analysis of the J-V characteristics indicates that the mechanism of the charge transfer through the single-wall carbon nanotube-polyelectrolyte film is quantum mechanical tunneling.     

Incorporation of carbon nanotube into direct-patternable ZnO thin film formed by photochemical solution deposition

Direct-patterning of ZnO hybrid films containing MWNT was realized without using photoresist and dry etching. Photosensitive 2-nitrobenzaldehyde was introduced into the solution precursors as a stabilizer and contributed to form a cross-linked network structure during photochemical reaction. According to the incorporation of multi-walled nanotube (MWNT) into ZnO films, the transmittance of ZnO hybrid film containing MWNT did not change but the sheet resistance was improved due to the enhancement of charge mobility due to π-bonding nature of MWNT. These results suggested a possibility that a micro-patterned system can be fabricated relatively easily and without high-cost processes, for example, by conventional etching procedure.     

Thermal performance of vertically-aligned multi-walled carbon nanotube array grown on platinum film

Vertically-aligned carbon nanotube array is expected to inherit high thermal conductivity and mechanical compliance of individual carbon nanotube and serve as thermal interface material. In this paper, vertically-aligned multi-walled carbon nanotube arrays have been directly grown on Pt film and the thermal performance has been studied by using laser flash technique. The determined thermal diffusivity decreases from 0.187 to 0.135 cm² s⁻¹ and the thermal conductivity increases from 1.8 to 3.1 W m⁻¹ K⁻¹ as temperature increases from 243.2 to 453.2 K. The fracture surface of the array peeled off the Pt film was characterized by scanning electron microscopy. It has been illustrated that the tearing surface is not smooth but fluffy with torn carbon nanotubes, indicating strong interfacial bonding and consequent small interface resistance between carbon nanotube array and Pt film. According to Raman spectra and transmission electron microscopy image, the possible mechanisms responsible for the thermal transport degradation are low packing density, twist, and the presence of impurities, amorphous carbon, defects and flaws. The influence of intertube van der Waals interactions has been studied by comparing the phonon dispersion relations and is expected to be not significant.     

碳纳米管/SBS复合改性沥青路用性能与相容性研究

为改善SBS改性沥青的路用性能及相容性,采用高速剪切法,将碳纳米管掺入SBS改性沥青中,制备复合改性沥青。采用三大指标、布氏粘度、离析实验、荧光显微镜等对其性能进行评价。结果表明,碳纳米管可以有效改善SBS改性沥青的高温稳定性、粘滞性,并且随着掺入碳纳米管量的增加,性能效果提升越好,但超过0.9%时改善效果趋于饱和;对改性沥青的温度敏感性和低温性能存在不利影响;碳纳米管的掺入限制了SBS颗粒与沥青分子之间的相对运动,使得SBS在沥青中的分散更均匀,改善了相容性与储存稳定性;综合考量碳纳米管/SBS复合改性沥青的各项性能,当其掺量为0.9%时,改性效果达到最佳。     

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.     

Electrochemical determination diethylstilbestrol by a single-walled carbon nanotube/platinum nanoparticle composite film electrode

Platinum nanoparticles (Pt_nano) were prepared and used in combination with single-wall carbon nanotube (SWNT) for fabricating electrochemical sensors with remarkably improved sensitivity toward diethylstilbestrol (DES). The glassy carbon (GC) electrode modified with SWNT/Pt_nano composite film exhibited excellent electrochemical behaviors toward the redox of DES. Compared with the bare GC electrode and SWNTs film modified GC electrode, the redox peak currents at the SWNTs/Pt_nano composite film modified GC electrode was enhanced greatly. The experimental parameters, which influence the peak current of DES, were optimized. Under optimal conditions, a linear response of DES was obtained in the range from 1.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹ (R = 0.997) and with a limit of detect (LOD) of 1.5 × 10⁻⁸ mol L⁻¹. The proposed procedure was successfully applied to determine the active ingredient in the DES tablet with satisfactory results.     

Superhydrophobic carbon nanotube/amorphous carbon nanosphere hybrid film

Fabrication of superhydrophobic surfaces has been widely investigated due to their wide range of applications. Here, synthesis of self-assembled aligned carbon nanotubes (ACNT)/amorphous carbon (a-C) nanosphere hybrid film is reported. Carbon plasma produced by FCVA was used to deposit a-C nanospheres on the ACNT films fabricated by PECVD. The superhydrophobic properties of the surface was investigated by static contact angle (CA) measurement. It is found that the surface morphology of the film which depends on the size of the a-C nanospheres, has a great influence on the hydrophobic properties of the surface. The hydrodynamic properties of the surface is discussed in terms of both Cassie and Wenzel mechanisms. The microstructure of the films is also investigated by XPS and HRTEM. It is shown that the bombardment of the CNTs with high energy carbon ions will damage the crystalline structure of the CNT walls as well.     

Temperature-dependent gas transport performance of vertically aligned carbon nanotube/parylene composite membranes

A novel composite membrane consisting of vertically aligned carbon nanotubes (CNTs) and parylene was successfully fabricated. Seamless filling of the spaces in CNT forests with parylene was achieved by a low-pressure chemical vapor deposition (CVD) technique and followed with the Ar/O₂ plasma etching to expose CNT tips. Transport properties of various gases through the CNT/parylene membranes were explored. And gas permeances were independent on feed pressure in accordance with the Knudsen model, but the permeance values were over 60 times higher than that predicted by the Knudsen diffusion kinetics, which was attributed to specular momentum reflection inside smooth CNT pores. Gas permeances and enhancement factors over the Knudsen model firstly increased and then decreased with rising temperature, which confirmed the existence of non-Knudsen transport. And surface adsorption diffusion could affect the gas permeance at relatively low temperature. The gas permeance of the CNT/parylene composite membrane could be improved by optimizing operating temperature.     

A layer-by-layer deposition mechanism for producing a pyrolytic carbon coating on carbon nanotubes

Pyrolytic carbon (PyC) was deposited on carbon nanotubes (CNTs) in order to modify them by introducing defects to their surface. The deposition of PyC was carried out at temperature between 800 and 1000 °C using propane as carbon source with or without a hydrogen carrier gas at low pressure of 20 kPa. The structure of PyC coatings was examined using transmission electron microscopy. The PyC coating could be distinguished from the original CNT walls due to the difference of the structure, with the coating showing a less orderly layer structure. When H₂ was introduced during deposition, PyC coating started to form at 900 °C, and the deposition rate increased rapidly with increasing temperature. Without H₂, PyC coating with a thickness of a few layers could be formed at temperatures between 800 and 900 °C in 10 min. The outmost layer of the PyC coating showed a structure of rough and curved carbon fragment. A layer-by-layer mechanism is proposed for the deposition consisting of alternating fragment formation (nucleation) and lateral growth to layer.     

Fabrication and electrochemical capacitance of hierarchical graphene/polyaniline/carbon nanotube ternary composite film

A film composed of graphene (GN) sheets, polyaniline (PANI) and carbon nanotubes (CNTs) has been fabricated by reducing a graphite oxide (GO)/PANI/CNT precursor prepared by flow-directed assembly from a complex dispersion of GO and PANI/CNT, followed by reoxidation and redoping of the reduced PANI in the composite to restore the conducting PANI structure. Scanning electron microscope images indicate that the ternary composite film is a layered structure with coaxial PANI/CNT nanocables uniformly sandwiched between the GN sheets. Such novel hierarchical structure with high electrical conductivity perfectly facilitates contact between electrolyte ions and PANI for faradaic energy storage and efficiently utilizes the double-layer capacitance at the electrode–electrolyte interfaces. The specific capacitance of the GN/PANI/CNT estimated by galvanostatic charge/discharge measurement is 569 F g⁻¹ (or 188 F cm⁻³ for volumetric capacitance) at a current density of 0.1 A g⁻¹. In addition, the GN/PANI/CNT exhibits good rate capability (60% capacity retention at 10 A g⁻¹) and superior cycling stability (4% fade after 5000 continuous charge/discharge cycles).     

High performance, freestanding and superthin carbon nanotube/epoxy nanocomposite films

We develop a facile, effective and filter free infiltration method to fabricate high performance, freestanding and superthin epoxy nanocomposite films with directly synthesized Sing-Walled Carbon Nanotubes (SWNTs) film as reinforcement skeleton. It is found that the thicknesses of the nanocomposite films can be easily controlled in the range of 0.5-3 μm by dripping target amount of acetone diluted epoxy through the skeleton film. The consequent measurements reveal that the mechanical and electrical properties of SWNTs/epoxy nanocomposite films could be tailored in a quite wide range. For examples, the Young's modulus of nanocomposite films can be tuned from 10 to 30 GPa, and the electrical conductivity can be ranged from 1000 S·cm(-1) to be insulated. Moreover, high load transfer efficiency in the nanocomposite films is demonstrated by the measured ultrahigh Raman bands shift rate (-30 ± 5 cm(-1)/% strain) under strain. The high effective modulus is derived as 774 ± 70 GPa for SWNTs inside this nanocomposite film.     

Polyaniline/carbon nanotube composite Schottky contacts

Schottky contacts were fabricated on composites of high molecular weight polyaniline and pristine multiwalled carbon nanotubes. Physical and electrical characteristics of these organic composite materials were studied by using atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrical measurements. The RMS surface roughness of the composite films was found to be 4 nm. From the IV characteristics of these composite devices, it appears that the current follows Ohm's law at lower voltages and Child's law at higher voltages, indicating a space‐charge‐limited emission mechanism in the presence of a distribution of shallow traps.     

Perylene derivative sensitized multi-walled carbon nanotube thin film

Perylene-sensitized multi-walled carbon nanotubes (PV-MWNT) have been prepared by a π-stacking between nanotubes and perylene derivatives, N,N′-diphenyl glyoxaline-3,4,9,10-perylene tetracarboxylic acid diacidamide (PV). The resultant nanocomposites have been characterized by transmission electron microscope (TEM), UV-vis absorption, photoluminescence (PL) and photocurrent spectra. Long range ordering can be observed in the form of PV-MWNT via π-stacking by TEM. Red-shift in the optical spectra consisting of the UV-vis absorption and PL spectra with the attraction of PV on the surface of the MWNTs were observed. The evident quenching in PL spectra of PV-MWNT was ascribed to the absorption and transfer of recombination energy by MWNT. Photosensitivity spectra demonstrated an increasing photocurrent in the ultraviolet region and a broadening photosensitivity in the red spectral region for solar cells based on PV-MWNT.