Relaxation of stresses in polystyrene–carbon microcomposite resistive layers

This paper presents the investigation results on thermoresistive elements made with a styrene–butadiene–styrene (SBS) modified polystyrene binder and carbon filler. Resistive layers were deposited by screen-printing method onto a polyethylene terephthalate (PET) foil. The temperature–resistance dependence of the examined layers was observed. The carbon filler content was precisely selected to obtain high values of TCR, such as 70,000 ppm/°C, for resistive layers with a SBS-modified polystyrene binder in the temperature range from 24 to 100 °C. Because of high TCR the influence of mechanical stresses, which is unfavorable feature of the examined layers, may be omitted. The highest TCR value and stability of electrical parameters during operation were observed for layers containing 42.9% of carbon filler by mass content. The measurements were carried out with the aid of an infrared camera and an oscilloscope because of very fast changes of resistive elements parameters. The analysis of the obtained results allows to draw conclusions about the carbon layer properties and to determine the stress–relaxation rate of the polymer structures.     

UHMWPE/CNTs导电复合体系的电性能

制备了低逾渗值的超高分子量聚乙烯(UHMWPE)/多壁碳纳米管(CNTs)导电复合材料,CNTs分布于UHMWPE粒子的表面和界面处。研究了UHMWPE/CNTs复合材料的温度电阻行为,发现在基体熔点附近,电阻急剧增加,并达到一最大值,然后电阻开始下降,体现负温度电阻效应(NTC)。分析了复合材料电阻松弛时间的升温速率的依赖性,结果表明,升温速率越快,电阻的松弛时间越短。     

Effects of oxygen annealing on gas sensing properties of carbon nanotube thin films

Carbon nanotubes (CNTs) thin films deposited by plasma enhanced chemical vapor deposition have been investigated as resistive gas sensors towards NO₂ oxidizing gas. Effects of air oxidative treatment dramatically influence the nanotubes’ electrical resistance as determined by volt-amperometric measurements. In particular the electrical measurements show that electrical behavior of the CNT films can be converted from semiconducting to metallic through thermal treatments in oxygen. The electrical response was then measured exposing the films to sub-ppm NO₂ concentrations (100 ppb in air) at 165 °C. Upon exposure to NO₂, the electrical resistance of CNTs was found to decrease. The obtained results demonstrate that nanotubes could find use as a sensitive chemical gas sensor for (a) the fast response accompanied by a high sensitivity to sub-ppm NO₂ exposure, and (b) the precise recover of the base resistance value in absence of NO₂ at a fixed operating temperature, likewise indicating that intrinsic properties measured on as prepared nanotubes may be severely changed by extrinsic oxidative treatment effects.     

Carbon nanotube films as a platform to transduce molecular recognition events in metalloporphyrins

Porphyrins have been widely used for many years as functional materials for chemical sensors. Their outstanding chemical features are balanced by some restrictions in terms of transduction techniques. In particular, porphyrin layers are barely conductive, with the consequence that the fabrication of porphyrin based chemiresistors is not possible, except in few rare cases. On the other hand, carbon nanotubes (CNTs) have superior electric properties ranging from metallic to semiconductor in character. Although the conductivity of CNTs is very sensitive to adsorbed molecules, it should be considered that the adsorption onto carbon structures is also scarcely selective and cannot be modified unless other molecular recognition systems are coupled with the CNTs. Following this approach, in this paper we investigated the sensing properties of hybrid CNT-porphyrin films to explore the possibility of transducing the adsorption events occurring in a porphyrin layer into resistance changes of the CNT layers. The results obtained indicate that the presence of the porphyrin films increases the sensitivity of the electric resistance of the CNTs to the concentration of volatile compounds. This enhancement is probably due to the catalytic effect of the metalloporphyrin in conveying the charge transfer from the adsorbate molecule to the CNTs substrate. This property of metalloporphyrins may introduce a further differentiation between porphyrin based sensors that could be positively utilized in sensor array configurations.     

Optimized network of multi-walled carbon nanotubes for chemical sensing

This work reports the design of a resistive gas sensor based on 2D mats of multi-walled carbon nanotubes (MWCNTs) grown by aerosol-assisted chemical vapour deposition. The sensor sensitivity was optimized using chlorine as analyte by tuning both CNT network morphology and CNT electronic properties. Optimized devices, operating at room temperature, have been calibrated over a large range of concentration and are shown to be sensitive down to 27 ppb of chlorine. The as-grown MWCNT response is compared with responses of 2000?°C annealed CNTs, as well as of nitrogen-doped CNTs and CNTs functionalized with polyethyleneimine (PEI). Under chlorine exposure, the resistance decrease of as-grown and annealed CNTs is attributed to charge transfer from chlorine to CNTs and demonstrates their p-type semiconductor behaviour. XPS analysis of CNTs exposed to chlorine shows the presence of chloride species that confirms electron charge transfer from chlorine to CNTs. By contrast, the resistance of nitrogen-doped and PEI functionalized CNTs exposed to chlorine increases, in agreement with their n-type semiconductor nature. The best response is obtained using annealed CNTs and is attributed to their higher degree of crystallinity.     

碳纳米管增强树脂力学性能设计

碳纳米管作为增强材料可改善树脂自身性能正备受关注。本文综述了碳纳米管增强树脂力学性能影响因素,同时对目前公开发表的几种预测碳纳米管增强树脂复合材料模量及破坏强度的方法进行了介绍与分析。最后,提出了碳纳米管增强树脂设计研究中面临的问题,并对今后研究动向进行了展望。     

Preparation and characterization of Ni-Cu-P/CNTs quaternary electroless composite coating

Ni-Cu-P/carbon nanotubes (CNTs) quaternary composite coatings were successfully obtained on low carbon steel matrix by electroless plating. The effects of CNTs concentration in the bath on the microstructure of the composite coatings, CNTs content in the composite coatings and the hardness of composite coatings before and after heat treatment at 400 °C have been studied. In addition, the corrosion resistance of Ni-Cu-P/CNTs composite coatings was evaluated by anodic polarization curves in 3.5 wt.% NaCl solution at room temperature. It was noted that the CNTs concentration remarkably influenced the surface morphology of the coatings. With increasing CNTs concentration, both the CNTs content in the composite coatings and the hardness of composite coatings increased at first and then decreased. And the composite coatings after heat treatment provided higher hardness than the as-deposited coatings. The corrosion resistance of Ni-Cu-P/CNTs composite coatings is excellent compared with that of Ni-Cu-P coatings.     

Correlation between dispersion state and electrical conductivity of MWCNTs/PP composites prepared by melt blending

Non-conductive polymers filled with conductive carbon nanotubes (CNTs) often do not show detectable conductivity due to poor dispersion of carbon nanotubes in the polymer matrix and the lack of conductive networks formed from CNTs. In this work, we attempted two ways to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) in a polypropylene (PP) matrix: chemical modification of MWCNTs and addition of a master batch as a compatibilizer, followed by melt blending using a micro-compounder. The relationship between the dispersion state of MWCNTs and the electrical conductivity of the CNTs/PP composites have been investigated by controlling several factors such as CNTs modification, compatibilization by a master batch, melt mixing, and post-heat treatment. The enhanced interfacial adhesion between the CNTs and the polymer could improve the dispersion of CNTs but it could also reduce the electrical conductivity of the composites. Meanwhile, it is interestingly found that the post-heat treatment could increase the conductivity remarkably due to the connection of CNTs into networks. Thus, it is concluded that the balance between dispersion of CNTs and the formation of conductive networks plays an important role in enhancing the electrical conductivity of composites.     

Vibration damping characteristics of carbon nanotubes-based thin hybrid composite spherical shell structures

The present work deals with the evaluation of elastic properties and dynamic analyses of thin hybrid composite shell structures, which consist of conventional carbon fiber as the reinforcing phase and multiwalled carbon nanotubes-based polymer as the matrix phase. The Mori-Tanaka and strength of material method has been implemented to determine the elastic properties of such hybrid composite structures without and with considering agglomerations. An eight-noded shell element, which considers stress resultant-type Koiter's shell theory and transverse shear effect as per Mindlin's hypothesis having five degrees of freedom at each node, has been utilized for discretizing and analysis of such hybrid shell structures. The Rayleigh damping model has been implemented in order to study the effect of carbon nanotubes (CNTs) on damping capacity of such hybrid composite shell structures. Different types of spherical shell panels have been analyzed in order to study the time and frequency responses. Results show that the elastic properties as well as damping properties of such hybrid composite structures improved with the addition of CNTs as compared to conventional carbon fiber reinforced composites laminates; effects of some important parameters on the vibration characteristic of such hybrid composite shell structures have also been presented. The effects of agglomeration parameters on the elastic properties and their influences on the dynamic responses considering different layers and stacking sequences have also been investigated.     

Continuous synthesis of carbon nanotubes using a metal-free catalyst by CVD

This study demonstrates the first example of the use of a metal-free catalyst for the continuous synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD). In this paper silica nanoparticles produced from the thermal decomposition of PSS-(2-(trans-3,4-Cyclohexanediol)ethyl)-Heptaisobutyl substituted (POSS) were used as catalyst and ethanol was served as both the solvent and the carbon source for nanotube growth. The POSS/ethanol solution was nebulized by an ultrasonic beam. The tiny mists were continuously introduced into the CVD reactor for the growth of CNTs. The morphology and structure of the CNTs have been investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The obtained CNTs have a multi-walled structure with diameters mainly in the size range from 13 to 16 nm. Detailed investigations on the growth conditions indicate that the growth temperature and POSS concentration are important for achieving high-quality nanotubes, and that the existing of small amount of water in ethanol is effective to remove amorphous carbon species during the formation of CNTs. The mass production of CNTs without any metal contaminant will provide a chance for investing and understanding the intrinsic properties of CNTs and applications particularly in nanoelectronics and biomedicines.     

Experimental study to assess the effect of carbon nanotube addition on the through-thickness electrical conductivity of CFRP laminates for aircraft applications

The present paper tests experimentally the through-thickness electrical conductivity of carbon fiber-reinforced polymer (CFRP) composites laminates for aircraft applications. Two types of samples were prepared: Type A samples with carbon nanotubes (CNTs) and Type B samples without CNTs. During the electrical experiments, electrical currents of several mA were injected through the specimens. Electrical resistance was monitored simultaneously in order to deduce the changes in the through-the-thickness electrical conductivity caused by the addition of CNTs. Improvement of electrical conduction by two orders of magnitude was achieved through the addition of 1 wt% carbon nanotubes as compared to classic CFRP without CNTs. For moisture saturated samples, the influence of moisture absorption on such measures was found to be negligible.     

用ECR-CVD方法制备定向碳纳米管

以FeaO4纳米粒子为催化剂,CH4和H2为气源,采用电子回旋共振微波等离子体化学气相沉积技术(ECR-CVD)在多孔硅基底上制备出定向生长的碳纳米管.研究了气氛组成、气压、温度和反应时间对碳纳米管生长特性的影响.使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和拉曼光谱(Raman spectrum)表征了样品的形貌和结构.结果表明:气氛组成和气压影响了反应腔内离解碳的浓度,从而影响碳纳米管的成核、生长速度及定向生长;温度的变化改变催化剂的尺寸从而改变碳纳米管的直径,在过低的温度下碳纳米管不能实现定向生长;碳纳米管随着反应时间的延长而不断增长,但超过一定时间后催化剂颗粒被碳包覆而失去催化作用,生长停止.     

Elaboration of single wall carbon nanotubes-based gas sensors: Evaluating the bundling effect on the sensor performance

In this article, carbon nanotube (CNT)-based sensors have been prepared using dispersion techniques. Sensors are obtained from a dispersion of CNTs using either chloroform as a solvent or sodium dodecylbenzene sulfonate as a surfactant. These sensors are prepared by drop-cast deposition of the solutions on interdigitated electrodes. The organic solvent processing leads to CNT layers where carbon nanotubes are obtained as larger bundles, whereas smaller bundles and individual tubes are predominantly formed in the surfactant processing. Under gas exposure (NO₂), both sensors respond to low gas concentrations; however, the sensing layers composed of larger bundles of CNTs present a slightly different behaviour (in terms of rapid stabilisation and sensitivity) compared to those made of individual CNTs.     

碳纳米管/聚乙烯咪唑纳米复合材料的制备与表征

采用化学改性手段制备了一类新型的碳纳米管／聚乙烯咪唑(CNTs／PVI)纳米复合材料。并通过红外光谱、扫描电镜、透射电镜和X射线衍射等手段表征CNTs／PVI产物。有机杂环聚合物引入碳纳米管材料体系以后,会显著改善碳纳米管在有机溶剂中的分散均匀性和可加工性,并将碳纳米管具有的优异力学、热稳定性能和杂环聚合物具有的优良溶解性等结合起来,得到一种新型的综合性能优异的光电功能材料。     

Synthesis and characterization of carbon nanotubes via ultrasonic spray pyrolysis method on zeolite

Ultrasonic spray pyrolysis method for the synthesis of carbon nanotubes (CNTs) has been investigated with zeolite supporting material. Single wall carbon nanotubes (SWCNTs) were obtained at 850 °C in nitrogen environment. Such deposition system makes it possible to grow CNTs without reducing agent at atmospheric pressure in a simple setup. Iron and cobalt acetate were used as catalyst and ethanol as carbon source for the synthesis of CNTs. Results show that nature of zeolite and cobalt concentration play important roles for SWCNTs production. Interestingly, we notice that in catalyst particles of sharp shape, nucleation of a nanotubes cap occurs dominantly in the forward direction.     

Multi-scale investigation of electronic transport and electromechanical behavior in carbon nanotube materials

Using home-built experimental setups, electrical properties and electromechanical characterization of two systems based on multiwalled carbon nanotubes (MWNTs) were investigated at room temperature. The first system is formed by carbon nanotubes (CNTs) either isolated or in small groups on a gold substrate, while the second one concerns a macroscale three-dimensional entanglement of CNTs in powder form. The local electrical resistance on systems of the first type was measured using an atomic force microscopy with a conductive tip and showed a narrow distribution of resistance values as well for isolated CNTs as for small groups of them. However, in this latter case the average resistance value has been found to be one order of magnitude higher than that of individual CNTs, which was attributed to the contact resistance between CNTs. This parameter was then studied from a statistical viewpoint through electromechanical tests performed at a macroscopic scale. They consisted in applying an external compression to CNTs powder samples and measuring the evolution of the electrical resistance across the pressed material. These tests demonstrated an outstanding decrease of the electrical resistance resulting from the increasing number of random connections between CNTs under compression, and the experimental curves were fitted with an analytical model. Furthermore, it was deduced from this model that the elementary contact resistance between CNTs decreases under compression. The stability of this electrical contact was verified over several durations and under different constant applied loads.     

Effect of CNT functionalization on crack resistance of a carbon/epoxy composite at a cryogenic temperature

In this study, the authors attempted to enhance the crack resistance of a carbon/epoxy composite by adding carbon nanotubes (CNTs) into the resin formulation. Prior to applying CNTs, a chemical surface treatment, amino-functionalization, was conducted to enhance the interfacial bonding between CNTs and epoxy resin. The resultant increase in tensile strength was attributed to good interfacial bonding quality. Two kinds of 3-phase carbon/CNT-epoxy unidirectional prepregs were fabricated via a hot-melting process with the addition of CNTs. The CNT-reinforcing and -functionalizing effects were investigated through DCB tests and measurement of the acoustic emission (AE) signal of a cross-ply specimen both at RT and at ?150 °C. The carbon/epoxy composite containing functionalized-CNTs showed improved interlaminar fracture toughness and transverse crack resistance at the cryogenic temperature.     

A comparative study of 1/f noise and temperature coefficient of resistance in multiwall and single-wall carbon nanotube bolometers

The 1/f noise and temperature coefficient of resistance (TCR) are investigated in multiwall carbon nanotube (MWCNT) film bolometers since both affect the bolometer detectivity directly. A comparison is made between the MWCNT film bolometers and their single-wall carbon nanotube (SWCNT) counterparts. The intrinsic noise level in the former has been found at least two orders of magnitude lower than that in the latter, which outweighs the moderately lower TCR absolute values in the former and results in higher bolometer detectivity in MWCNT bolometers. Interestingly, reduced noise and enhanced TCR can be obtained by improving the inter-tube coupling using thermal annealing in both SWCNT and MWCNT films, suggesting much higher detectivity may be achieved via engineering the inter-tube coupling.     

碳纳米管应用于聚合物抗静电纤维的研究

基于聚合物与抗静电载体混纺而形成的“海岛”型内部结构,通过极化放电而消除静电的抗静电原理,将碳纳米管应用于聚合物抗静电纤维。摩擦静电荷测试结果显示,碳纳米管由于具有优异的导电性,强化抗静电载体周围的电场,从而显著地提高了聚合物纤维的抗静电能力。经过改性处理的碳纳米管,如空气活化和酸处理等,抗静电效果更加显著,尤其是金属沉积处理的碳纳米管,抗静电效果最为显著。说明碳纳米管在抗静电聚合物纤维领域是很有应用前途。     

Influence of plasma treatment on CNT absorption of cotton fabric and its electrical conductivity and antibacterial activity

In this study, effect of plasma pretreatment on the absorption of carboxilated carbon nanotubes (CNTs) on the surface of cotton fabrics was investigated. Treated samples were characterised using a Raman spectrophotometer. Also, the morphological properties of samples were studied using a scanning electron microscope. Electrical resistance and interactions between CNTs and plasma-treated cotton functional groups at the surface were also evaluated. Antibacterial activity of cotton fabric when modified by low temperature plasma and stabilised with CNTs was also investigated. Results showed a uniform coating of CNTs on the plasma-treated cotton fabric and it was found that the plasma treatment is effective on improving CNTs absorption by cotton fabric. Generally, cotton fabric characterisation, such as antibacterial activity and electrical conductivity, after plasma treatment and loading CNT are improved.