基于碳纳米管薄膜电学成像的复合材料结构损伤识别研究

随着纳米技术的飞速发展,碳纳米管因其良好的自感应能力逐渐被应用在结构健康监测领域.提出将碳纳米管薄膜布置在复合材料结构表面作为智能感知层,结合电学成像方法,根据碳纳米管薄膜边界电压值的变化,重建损伤引起的电导率变化分布图像,以确定损伤情况.为提高电学成像效果,采用基于L1范数正则化的最小二乘法重建电导率变化分布,并利用L曲线法选取适当的正则化参数,结合内点法进行反演.搭建了电学成像测试系统并进行了实验研究,实验结果验证了本文所提出方法的可行性和有效性.     

Chemo-sensitivity of latex-based films containing segregated networks of carbon nanotubes

In contrast to conventional hydrophobic Conductive Polymer nanoComposites (CPCs) used to design vapor sensors, which are mostly soluble in organic solvents, monodispersed acrylate copolymer latexes present the double advantage of being more sensitive and selective towards polar vapors such as water. A hierarchically structured latex based CPC film was obtained by co-dispersion of an aqueous acrylic emulsion with multiwalled carbon nanotubes (CNTs), followed by spray layer by layer (sLbL) assembly. The analysis of CPC films morphology by AFM and TEM show that a segregated network of CNT as been achieved by partial coalescence of latex nanoparticles and homogeneously assembled in 3D. Transducer sensitivity was investigated as a function of CNT content, latex glass transition temperature (T_g), organic vapor nature and vapor concentration. The source of the high sensitivity and selectivity observed for these latex-based composites towards water vapor is assumed to mainly result from ionic interaction of SDS with water molecules offering interesting perspectives of development. The different diffusion regimes through the CPC transducer are visualized, modeled and interpreted with the Langmuir-Henry-Clustering (LHC) model, showing that only water is reaching a clustering mode at high vapor concentration. Finally it is believed that the unique hierarchical architecture of BA latex-CNT sensors is responsible for their quick, stable and reproducible responses to vapors.     

基于电容-电阻转换原理的柔性压力传感器

目前,基于碳基纳米材料的柔性压力传感器凭借着其便携性、柔韧性、生物相容性和低成本等特点,在智能医疗、人机交互和智能机器人等领域有着广泛的应用前景,但如何使其在具有较大量程范围的同时保持较高灵敏度,仍是一个严峻的挑战。提出一种基于氧化石墨烯/碳纳米管（Graphene Oxide/Carbon Nanotube, GO/CNT）复合敏感层的柔性压力传感器,同时以热塑性聚氨酯弹性体（Thermoplastic Polyurethanes, TPU）多孔海绵作为传感器骨架。该GO/CNT@TPU柔性压力传感器的量程范围为0～60 kPa,基于电容-电阻转换原理,当受到较小压力（0～5 kPa）时,传感器以电阻感知为主,灵敏度为0.05777 kPa^-1;当受到较大压力（5～60 kPa）时,传感器以电容感知为主,灵敏度为0.33213 kPa^-1。从而有效地实现了传感器的在宽量程内的高灵敏度检测。     

Gas sensing properties of a composite composed of electrospun poly(methyl methacrylate) nanofibers and in situ polymerized polyaniline

Poly(methyl methacrylate) (PMMA) nanofibers with different diameters were fabricated by electrospinning and their composites with polyaniline (PANI) were formed by virtue of in situ solution polymerization. The coaxial composite nanofibers so prepared were then transferred to the surface of a gold interdigitated electrode to construct a gas sensor. The structure and morphology of the PANI/PMMA composite fibers were characterized by UV–vis spectroscopy and scanning electron microscopy, which indicated that the coaxial nanofibres of PANI emeraldine salt and PMMA were successfully prepared. The electrical responses of the gas sensor based on the composite nanofibres towards triethylamine (TEA) vapors were investigated at room temperature. It was revealed that the sensor showed a sensing magnitude as high as 77 towards TEA vapor of 500 ppm. In addition, the responses were linear, reversible and reproducible towards TEA vapors ranging from 20 to 500 ppm. The diameters of the electrospun PMMA fibers had an effect on the sensing magnitude of the gas sensor, which is proposed to relate to the difference in the surface-to-volume ratio of the fibers. Furthermore, it was found that the concentration of doping acids only led to changes in resistance of the sensor, but could not affect its sensing characteristics. In contrast, the nature of the doping acids was determinative for the sensing magnitude of the sensor. The gas sensor with toluene sulfonic acid as the doping acid exhibited the highest sensing magnitude, which is explained by taking into account of the sensing mechanism and the interactions of doping acids with TEA vapor.     

Composites of carboxylate-capped TiO2 nanoparticles and carbon black as chemiresistive vapor sensors

Titanium (IV) dioxide (TiO₂) nanoparticles (NPs) with a 1-5 nm diameter were synthesized by a sol-gel method, functionalized with carboxylate ligands, and combined with carbon black (CB) to produce chemiresistive chemical vapor sensor films. The TiO₂ acted as an inorganic support phase for the swellable, organic capping groups of the NPs, and the CB imparted electrical conductivity to the film. Such sensor composite films exhibited a reproducible, reversible change in relative differential resistance upon exposure to a series of organic test vapors. The response of such chemiresistive composites was comparable to, but generally somewhat smaller than, that of thiol-capped Au NPs. For a given analyte, the resistance response and signal-to-noise ratio of the capped TiO₂-NP/CB composites varied with the identity of the capping ligand. Hence, an array of TiO₂-NP/CB composites, with each film having a compositionally different carboxylate capping ligand, provided good vapor discrimination and quantification when exposed to a series of organic vapors. Principal components analysis of the relative differential resistance response of the sensor array revealed a clear clustering of the response for each analyte tested. This approach expands the options for composite-based chemiresistive vapor sensing, from use of organic monomeric or polymeric sorbent phases, to use of electrically insulating capped inorganic NPs as the nonconductive phase of chemiresistive composite vapor sensors.     

Y沸石改善SnO2气体传感器性能的研究

为了改善气体传感器的敏感性能,分别采用SnO2外涂Y沸石的涂覆法和Y沸石与SnO2混合法,用Y沸石对SnO2气体传感器进行改性.用X-射线衍射(XRD)、电子扫描显微镜(SEM)对混合法制备的Y沸石/SnO2复合材料的结构和表面进行了表征与分析.将这两类敏感元件进行了VOC气体的气敏测试.结果表明,与纯SnO2相比,Y沸石与SnO2直接混合的复合材料提高了对丙酮的响应值,而对其他气体响应值基本不变;涂覆法制备的气敏元件不仅提高对丙酮的响应值,而且减小了对乙醇的响应值,对乙醇起到一定抑制作用.初步分析了Y沸石对SnO2气敏特性改善的机理.     

Improvement of gas sensing performance of carbon black/waterborne polyurethane composites: Effect of crosslinking treatment

When carbon black (CB) filled waterborne polyurethane (WPU) composites are exposed to organic solvent vapors, electrical resistance of the materials increases rapidly. They can thus serve as gas sensors. To improve the composites’ performance for practical applications, crosslinking agent was added to the composite latexes, forming intra-molecular crosslinked networks among the matrix polymer of the composites. The method greatly increased the filler/matrix interfacial interaction and reduced the mobility of CB particles. In the composites that had absorbed solvent vapors, reconstruction of conduction paths through re-aggregation of the disconnected filler particulates became difficult. As a result, the unwanted negative vapor coefficient (NVC) effect was significantly weakened, while the gas sensitivity and the performance reproducibility were enhanced as well.     

A simplified approach for heat conduction analysis of CNT-based nano-composites

The unique thermal properties of carbon nanotubes (CNT) may offer possibilities for the development of fundamentally new composite materials. Numerical simulation for such CNT-based composites usually demands extremely large and expensive computer resources. In preliminary computations, temperature distribution in the CNT has been turned out to be almost uniform, due to its exceptionally high heat conductivity in comparison with the host polymer. This feature allows us to considerably simplify the mathematical model of the heat conduction in CNT composites. In the proposed approach, the host polymer is the only domain which is modeled, while the CNTs are treated as heat superconductors with constant and unknown temperatures constrained at their surfaces. As a result, the computational scale is reduced substantially. The hybrid boundary node method is applied in this study. Numerical examples clearly demonstrate the efficiency and sufficient accuracy of the proposed approach.     

碳纳米管制备及其复合材料导热性能研究进展

随着高集成、高功率电子器件的飞速发展,电子器件对高导热材料需求更加迫切。碳纳米管 因具有独特的一维纳米结构,同时兼具优异的导热、导电和机械性能等,近年来备受国内外科研工作 者广泛的研究关注。该文主要介绍了碳纳米管的 3 种制备方法：石墨电弧法、化学气相沉积法和激光 蒸发法,同时阐述了碳纳米管导热基本机理以及碳纳米管应用于复合材料热传导性能研究,并对碳纳 米管在进一步导热研究中进行了展望。     

Numerical prediction of elastic properties for carbon nanotubes reinforced composites using a multi-scale method

The main aim of this research was to investigate longitudinal elastic and effective modulus of composites reinforced with zigzag and armchair single-walled (CNT) and multi-walled carbon nanotubes (MWCNT) with different volume fractions and aspect ratios via finite element simulation. A three-phased volume element was adopted for the modeling of nanocomposite behavior and nonlinear spring elements were used to model interphase part joints and the effective force between nanotubes and resin were determined based on Lennard-Jones potential. After the evaluation and validation of the model, elastic modulus and Poisson’s ratio of composites reinforced with zigzag and armchair CNTs with different volume fractions and aspect ratios were extracted. It was found that by increasing volume fraction and aspect ratio, elastic modulus of representative volume element of composite was increased and its Poisson’s ratio was decreased. At similar aspect ratio and volume fraction, the elastic modulus of composites reinforced with armchair CNTs and Poisson’s ratio of those reinforced with zigzag CNTs were higher. Also, results showed that elastic modulus of composite was independent from elastic modulus of interphase.

     

Performance of nanocomposites stacked with carbon nanotubes and Nafion films

Nanocomposites stacked layer-by-layer with carbon nanotubes (CNTs), referred to as CNT–Nafion?, are prepared using a spray and reproducible spin-cast deposition methodology. The CNTs used for the nanocomposite film were cylindrical with diameters in the range of 10–15 nm and lengths of up to several micrometers. The CNTs had a high purity of more than 95%. CNT–Nafion? nanocomposites with uniformly spray-coated CNTs provide sufficiently high electrical conductivity throughout, and show enhanced mechanical strength due to laterally aligned CNTs between each interface of the spin-coated Nafion film. Our results indicate that such a layer-by-layer film composed of CNTs and Nafion? is suitable for potential transducer applications at the microscale.     

Estimation of average contact number of carbon nanotubes (CNTs) in polymer nanocomposites to optimize the electrical conductivity

The present paper suggests an equation for the average contact number of carbon nanotubes (CNTs) in CNT-reinforced polymer nanocomposites (PCNT) by two developed equations for electrical conductivity. Several novel parameters in PCNT such as CNT size, CNT concentration, network fraction, interphase depth, tunneling effect, and CNT wettability by the polymer medium are considered to define the average contact number (m). “m” is calculated for some samples and the variation of “m” is explored over a range of parameters’ values. The results show that dense interphase, high fraction of networked CNTs, reedy and short CNTs, low CNT surface energy, high polymer surface energy, low tunneling distance, and small contact diameter increase the “m” improving the conductivity. Moreover, tunneling distance and CNT contact diameter have the greatest effects on the “m”. The optimized level for “m” is necessary to control the nanocomposite’s conductivity.

     

碳纳米管/PDMS复合材料柔性阵列压力传感器制备与实验

以碳纳米管（CNTs）作为导电填料,聚二甲基硅氧烷（PDMS）为基体材料,采用溶液法制备出CNTs/PDMS导电复合材料。研究了碳纳米管浓度对复合材料的电学特性和压阻特性的影响规律,得到碳纳米管在PDMS中的渗滤区域。通过复合材料的压力灵敏度优化碳纳米管浓度。以制备的复合材料为敏感材料,FPCB工艺加工的柔性基板为电极,设计制备了一种简单结构和工艺的柔性阵列压力传感器。用零电势法设计了阵列电阻读出电路与LabVIEW实现的上位机配合,实现信号读取和显示。最后通过一个应用实例表明,该柔性阵列压力传感器及信号处理系统可以实现压力分布与大小的实时监测,可为柔性阵列压力传感器设计与制备提供参考。     

Poly(o-anisidine)-polystyrene composite fibers via electrospinning process: Surface morphology and chemical vapor sensing

The electrospinning technique was utilized to produce camphorsulfonic acid (CSA) doped poly(o-anisidine) (POA)-polystyrene (PS) composite fibers in the non-woven mat form with different fiber characteristics, depending on the proportion of components in spinning solutions. CSA doped POA-PS composite fibers were fabricated onto interdigited gold substrates for use as chemical vapor sensors. The resultant composite fiber sensor responded to high polar volatile chemicals by showing a decrease in electrical resistance during the sensing measurement. The sensitivity of the composite fiber sensor when exposed to water vapor was higher than that of the composite fiber sensor subjected to ethanol vapor due to high polarity together with low vapor pressure of water compared with those of ethanol. The surface morphology of the non-woven composite fiber mat after chemical vapor sensing was unchanged. This work opens up the possibility of using the derivatives of polyaniline as a component in composite fibers for chemical sensing applications by taking advantages of their good solubility in common solvents as well as detectable electrical changes in terms of the relatively small amount of composite fibers needed.     

A novel biosensor using entangled carbon nanotubes layer grown on an alumina substrate by CCVD of methane on FeOx–MgO

Glucose oxidase (GOx) was immobilized on entangled and high surface area carbon nanotubes (CNTs) grown on an alumina substrate, and direct electron transfer reaction between GOx and the electrode was revealed. Fe/MgO catalyst layer was spin-coated on the insulating alumina substrate and the CNT layer was grown on the catalyst by chemical vapor deposition of methane at 950 °C for 15 min. About 20–30 nm bundles of about 1 nm single-wall as well as 10 nm multiwall CNTs are formed. The redox process was surface-controlled and electron transfer coefficient and the rate constant were estimated to be 0.35 and 0.64 s⁻¹, respectively. In addition GOx immobilized on CNT layer showed a linear response range between 12 and 62 μM of glucose concentration. A detection limit and sensitivity of 0.1 μM and 635 μA mM⁻¹ cm⁻², respectively, were obtained for the biosensor.     

Gas sensing properties of platinum derivatives of single-walled carbon nanotubes: A DFT analysis

The limitations of intrinsic carbon nanotube (CNT) based devices to examine toxic gases motivate us to investigate novel sensors which can possibly overcome sensitivity problems. Pt–CNT assemblies (with Pt deposited externally as well as internally Pt-doped ones) interacting with NO₂ and NH₃ are studied and compared with unmodified CNTs. DFT calculations show that Pt can enhance adsorption and charge transfer processes to a very large degree. Incoming gas molecules cause changes in the electronic structure and charge distribution of the Pt-substituted CNTs that are both larger and more far-reaching than in their unmodified counterparts. Their relatively high stability is unaffected by the complexation with NO₂ and NH₃. CNTs with defective surface were also investigated. The sensing performance of Pt-doped CNT is found to be superior to defected CNTs.     

Suspension‐deposited carbon‐nanotube networks for flexible active‐matrix displays

Abstract— The unique properties of carbon nanotubes (CNTs) promise innovative solutions for a variety of display applications. The CNTs can be deposited from suspension. These simple and low‐cost techniques will replace time‐consuming and costly vacuum processes and can be applied to large‐area glass and flexible substrates. Single‐walled carbon nanotubes (SWNTs) have been used as conducting and transparent layers, replacing the brittle ITO, and as the semiconducting layer in thin‐film transistors (TFTs). There is no need for alignment because a CNT network is used instead of single CNTs. Both processes can be applied to glass and to flexible plastic substrates. The transparent and conductive nanotube layers can be produced with a sheet resistance of 400 Ω/□ at 80% transmittance. Such layers have been used to produce directly addressed liquid‐crystal displays and organic light‐emitting diodes (OLED). The CNT‐TFTs reach on/off ratios of more than 10⁵ and effective charge‐carrier mobilities of 1 cm²/V‐sec and above.     

Uniform carbon‐nanotube emitter for field‐emission displays

Abstract— The synthesis of carbon‐nanotube (CNT) field emitters for FEDs by thermal chemical vapor deposition (CVD) and their structural and emission characterization are described. Multi‐walled nanotubes (MWNTs) were grown on patterned metal‐base electrodes by thermal CVD, and the grown CNTs formed a network structured layer covering the surfaces of the metal electrode uniformly, which realized uniform distribution of electron emission. A technique for growing narrow MWNTs was also developed in order to reduce the driving voltage. The diameter of MWNT depends on the growth temperature, and it has changed from 40 nm at the low temperature (675°C) to 10–15 nm at the high temperature (900–1000°C). Moreover, narrower MWNTs were grown by using the metal‐base electrode covered with a thin alumina layer and a metal catalyst layer. Double‐walled nanotubes (DWNTs) were also observed among narrow MWNTs. The emission from the narrow CNTs showed a low turn‐on electric field of 1.5 V/μm at the as‐grown layer.     

Development of CNT-ISFET based pH sensing system using atomic force microscopy

In recent years, there has been an increasing interest in the monitoring and controlling of pH. It has become an important aspect of many industrial wastewater treatment processes as well as a drinking water quality issue. At the same time, the demand for smaller electronic devices used for various industrial and commercial applications has greatly increased. Nanomaterials such as Carbon Nanotubes (CNTs) are well known for their excellent electrical, mechanical, and thermal properties. Therefore, CNTs are good candidates for the manufacturing of small devices. In this paper, a novel concept combining CNT and Ion Sensitive Field Effect Transistor (ISFET) is proposed for pH-sensing application. Atomic Force Microscope (AFM) based manipulation and electrical property measurements in nano level are involved. Nanochannels are created by AFM-based nanoscratching, and the electrical properties of both multi-walled and single-walled CNTs are tested using Current Sensing AFM. FETs are fabricated to test the possibility of the CNTs’ alignment between the source and the drain electrode using Dielectrophoresis (DEP). The experimental results reveal that CNT is a promising material for improving the performance and lowering the cost of existing pH chemical sensors.     

大变形力敏传感元件温度响应试验研究

利用炭黑/硅橡胶导电复合材料制作了大变形力敏传感元件,对其温度荷载下的电阻响应进行了试验研究,并根据其导电机理对温敏特性进行了深入分析。试验发现制作的大变形力敏传感元件具有正温度系数特性,电阻随温度的升高而增大;温度稳定时,具有电阻弛豫现象。硅橡胶基体随温度变化体积发生变化是造成复合材料温度敏感性的主要原因;同时,温度变化也会影响电子跃迁能力,进而影响到复合材料温度响应。橡胶基体的粘弹性以及试样具有一定厚度的尺寸效应是导致其温度响应滞后性的主要原因。