反复机械拉伸法在聚合物中定向排列单壁纳米碳管

在原位聚合过程中,采用反复机械拉伸的方法,将半干状态的SWNTs／PMMA复合体系沿同一方向反复拉伸,合成了SWNTs在PMMA基体中定向排列并均匀分散的SWNTs／PMMA复合材料SEM和TEM照片分析表明,SWNTs沿拉伸方向排列且均匀分散;不同入射角度下的偏振拉曼光谱分析也表明其定向性良好;电学和力学性能测量结果进一步表明复合材料表现出显著的各向异性,且电导率和力学性能沿SWNTs排列方向得到明显提高;建立了SWNTs在拉伸过程中定向排列的动力学模型,理论分析了SWNTs在流股剪切力作用下在复合体中沿拉伸方向定向排列的机理。     

单壁纳米碳管/纳米铝基复合材料的增强效果

用半连续氢电弧法和活性氢等离子蒸发法分别制备出单壁纳米碳管(SWNTs)和纳米A1粉体，然后用提纯后的SWNTs和纳米A1粉体制备出SWNTs含量(质量分数)分别为0、2．5％、5．0％、7．5％和10.0％的单壁纳米碳管／纳米铝基块体复合材料．SWNTs对高强度纳米A1基体具有显著的增强作用，当SWNTs含量小于5．0％时，材料的硬度随着SWNTs含量的提高线性上升．其中5％SWNTs和纳米A1的复合增强效果最好，其硬度可达2.89GPa，大约是粗晶A1(0．15GPa)的20倍．当SWNTs含量超过5．0％时，增强效果开始缓慢的下降．讨论了单壁纳米碳管增强纳米铝基复合材料的强化机制．     

单壁纳米碳管增强纳米铝基复合材料的制备

将用氢电弧法制备的单壁纳米碳管（SWNTs）提纯后与纳米Al粉体混合，在室温下冷压成型，再在260～480℃真空热压处理，制备出相对密度大于90%，SWNTs弥散分布于纳米Al基体中的单壁纳米管增强纳米复合材料，含量为2.5%（质量分数）的SWNTs对纳米Al基体的增强效果约为55%，SWNTs/纳米Al复合材料的硬度随热压温度的升高而增加，热压温度为380℃时硬度达到峰值2.21GPa，大约是粗晶Al的15倍，比同样温度热压出来的纳米Al块体的硬度高36.4%。     

具有高压阻重复性和敏感性的纳米碳管复合硅橡胶

通过比较不同长径比的多壁纳米碳管复合硅橡胶的渗流特性发现长径比大于10000(长200μm,直径20nm)的长纳米碳管具有与长径比小于100(长2μm,直径20nm)的短纳米碳管显著不同的渗流特性,测量发现:随着导电相质量分数的增加,短纳米碳管呈现压阻系数由正到负的变化规律,而长纳米碳管即使导电相体积分数较低时也未呈现单调正的压阻系数,通过比较TEM和SEM照片,渗流曲线图以及对实验结果的分析,表明导电相的形貌对弹性体复合材料的压阻特性有很大影响。测量还表明对应最显著压阻变化率的质量分数长,短纳米碳管复合硅橡胶明显高于短纳米碳管复合硅橡胶,并且具有更高的压阻重复性,其在高体积分数下的高压阻敏感性、高补强作用及高压阻重复性使得该材料能用于柔性力敏传感器。     

油基纳米流体的电导率

以1种典型成品油和2种典型原油为基液,采用两步法制备油基纳米流体,研究含不同质量分数的球形氧化铁纳米颗粒与大长径比碳纳米管对油样电导率的影响,分析油基纳米流体电导率变化的主要机理。结果表明:氧化铁油基纳米流体电导率没有明显增大,碳纳米管油基纳米流体电导率均显著增大;碳纳米管成品油基纳米流体的渗流阈值(质量分数,以下同)为0.27%,添加质量分数为2%的碳纳米管分散液的成品油基纳米流体电导率增大5.83×1010倍;2种添加碳纳米管的原油基纳米流体与成品油基纳米流体的电导率变化规律类似,渗流阈值为0.1%~0.3%,添加质量分数为0.5%的碳纳米管分散液的原油基纳米颗粒电导率增大近1 000倍;大长径比碳纳米管通过在原油中建立电桥,有效增大了原油电导率。     

反复拉伸法制备单壁碳纳米管定向排列的SWCNT／PMMA复合材料

采用反复机械拉伸法制备了单壁碳纳米管(SWCNTs)均匀分散且定向排列的SWCNT/聚甲基丙烯酸甲酯(PMMA)复合材料.将半干状态的SWCNT/PMMA复合体沿同一方向反复拉伸100次,每次的拉伸比为50,每次拉伸完以后,将聚合物沿拉伸的方向反复重叠.SEM,偏振拉曼光谱分析均表明SWCNTs沿拉伸方向排列.电学与力学测试结果表明:与PMMA相比,复合材料的电导率、弹性模最、拉伸强度和延伸率均得到明显提高,并表现出显著各向异性,复合材料滑拉伸方向的电学和力学性能显著高于其垂直于碳纳米管排列方向的值.     

纳米碳管改善氧化铝填充硅橡胶复合材料的导热与机械性能(英文)

纳米碳管由于其优异的特性可以用于改善复合材料的导热和机械性能。本文通过传统的机械混合工艺,采用氧化铝粉体和少量纳米碳管填充甲基乙烯基硅橡胶,研究了氧化铝粉体的质量分数、表面改性和纳米碳管的添加对复合材料热导率、杨氏模量和硬度的影响。结果表明:氧化铝粉体的质量分数越高,复合材料的热导率越高;当氧化铝粉体的质量分数固定时,对其表面改性和添加纳米碳管能够明显提高复合材料的热导率、杨氏模量和硬度,发现改性氧化铝和纳米碳管并用可以协同增强填料与橡胶间的界面作用,促进橡胶基底中更好的导热通道和网络结构的形成,从而改善复合材料的导热和机械性能。     

单壁碳纳米管束的排布

流体排布法是实现碳纳米管定向排列的一种简单的方法。采用流体排布法在具有浸润性图案化的基底上成功地对单壁碳纳米管(SWNTs)束进行了水平方向上的排布。将SWNTs悬浮液滴入光刻胶制成的微通道中,在流体剪切力作用下,弯曲的SWNTs在一定程度上会被拉伸并且平行地排列在纳米级宽度的微通道中。将排列好的SWNTs阵列转移到一些不同间距的金电极对上面,制作成碳纳米管场效应晶体管(CNTFET)。CNTFET的电性能测试结果表明,制备的SWNTs束可以制造出不同电极间距同时具有良好电性能的CNTFET。     

石墨烯/尼龙66导电纳米复合材料的制备与性能研究

通过溶液共混法制备了石墨烯(G)/尼龙66(PA66)复合材料,通过热压得到了导电纳米复合材料试样。改变石墨烯在尼龙66中的含量,制备了不同比例的G/PA66复合材料,通过室温电导率测试发现,当石墨烯含量达到1.338%(体积分数)时,复合材料的直流体积电导率上升到9.72×10~(-3)S/m,导电渗流阚值为0.734%(体积分数);复合材料的交流体积电导率和介电常数也随石墨烯含量的上升而增加。研究表明:分散良好的石墨烯显著提高了复合材料的导电性。采用扫描电镜(SEM)、万能力学试验机及热重分析仪(TGA)对复合材料的微观形貌、力学性能、热稳定性进行了研究。结果表明,复合材料的拉伸模量升高,热稳定性增强。     

多壁碳纳米管/环氧树脂复合材料的制备及性能

以化学修饰法在多壁碳纳米管上成功接枝了四乙烯五胺,并用溶液共混法制备出多壁碳纳米管/环氧树脂复合材料。使用电子拉力试验机、Agilent 4294A、差示扫描量热(DSC)和扫描电镜(SEM)对复合材料进行研究。结果表明,修饰后的碳纳米管能均匀分散在基体中,添加经修饰后的碳管比添加原始碳管更能提高环氧树脂的力学强度、热稳定性和介电性能。当经修饰后的碳管质量分数为1.5%时拉伸强度和断裂伸长率分别增加了84.3%和150%,玻璃化转变温度提高了32℃,复合材料的介电常数高达25.8。     

The effects of CNT alignment on electrical conductivity and mechanical properties of SWNT/epoxy nanocomposites

The single-walled carbon nanotubes (SWNTs) filled nanocomposite SWNT/epoxy resin composite with good uniformity, dispersion and alignment of SWNTs and with different SWNTs concentrations was produced by solution casting technique. Subsequently, the semidried mixture was stretched repeatedly along one direction at a large draw-ratio of 50 for 100 times at ambient atmosphere manually to achieve a good alignment and to promote dispersion of SWNTs in the composite matrix. Composite showed higher electrical conductivities and mechanical properties such as the Young’s modulus and tensile strength along the stretched direction than perpendicular to it, and the electrical property of composite rise with the increase of SWNT concentration. The percolation threshold value of electrical conductivity along the stretching direction is lower than the value perpendicular to the SWNTs orientation. In addition, the anisotropic electric and mechanical properties results, SEM micrograph and the polarized Raman spectra of the SWNT/epoxy composite reveal that SWNTs were well dispersed and aligned in the composites by the repeated stretching process.     

Anisotropic properties of aligned SWNT modified poly (methyl methacrylate) nanocomposites

The poly (methyl methacrylate) (PMMA)/single-walled carbon nanotube (SWNT) composites with good uniformity, dispersion and alignment of SWNT were fabricated in an improved figuration process. The semidried mixture was stretched along one direction at a drawing ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The transmission electron microscopic (TEM) observation demonstrated that SWNT in the PMMA/SWNT composite tends to align in the stretching direction owing to a torque exerting on it in the stretching process. The electrical and mechanical properties of PMMA/SWNT composite were studied as a function of SWNT orientation and concentration. The aligned SWNT modified PMMA/SWNT composite presented highly anisotropic properties. The experimental results showed that the electrical conductivity and mechanical properties of composite rise with the increase of SWNT concentration, and that composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The thermogravimetric analysis (TGA) revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.     

Properties of well aligned SWNT modified poly (methyl methacrylate) nanocomposites

The PMMA/SWNT composites with good uniformity, dispersion and alignment of SWNT were fabricated in a stretching process. The semidried mixture was stretched along one direction at a draw ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The TEM and SEM observation demonstrated that SWNT in the PMMA/SWNT composite tend to align in the stretching direction. The electrical conductivity and the mechanical properties of composite rise with the increase of SWNT concentration, composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The TGA revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.     

Multifunctional Composites of Ceramics and Single‐Walled Carbon Nanotubes

Polycrystalline ceramic/single‐walled carbon nanotube (SWNT) composites possess unique grain boundaries, containing 1D tortuous SWNTs bundles that form 2D tangled embedded nets. This unprecedented grain‐boundary structure allows tailoring of multifunctional ceramic/SWNTs composites with unique combinations of desirable mechanical (toughness, strength, creep) and transport (electrical, thermal) properties. A brief discussion and analysis of recent developments in these composites are presented.     

Role of structure and morphology in the elastic modulus of carbon nanotube composites

The nature of nanoscale reinforcements in the carbon nanotube composites indicates nanocomposite properties are heavily dependent on the micro/nano-structure and morphology. Macroscopic parameter-based properties estimation may lead to deviation as large as 30%. In this paper, a modified shear-lag model, combined with probability statistical theory and composites morphology, is established to investigate the elastic properties of single wall carbon nanotubes (SWNTs)-reinforced polymer composites. The computational results indicated that elastic modulus of nanocomposite was remarkably dependent on the micro/nano-structure, including diameter, length, and orientation of the dispersed SWNTs. Microstructure-dependent shape factor and orientation effect factor played a key role on achieving high-performance nanocomposites. Elastic modulus of nanocomposite with well-dispersed carbon nanotubes was more susceptible to the orientation. Similarly, nanocomposite modulus was more subject to the dispersion influence when SWNTs were well-aligned. The maximal modulus was located in the zone of small rope diameters and small orientation angles when adequate interfacial bonding was provided. The computational results were also compared with experimental outcome and demonstrated good consistence.     

Effect of constructive rehybridization on transverse conductivity of aligned single-walled carbon nanotube films

Alignment of densely packed single-walled carbon nanotubes (SWNTs) largely preserves the extraordinary electronic properties of individual SWNTs in the alignment direction, while in transverse direction the films are very resistive due to large energy barriers for tunneling between adjacent SWNTs. We demonstrate that chromium atoms inserted between the sidewalls of parallel SWNTs effectively coordinate to the benzene rings of the nanotubes via hexahapto bonds that preserve the nanotube-conjugated electronic structure and serve as a conduit for electron transfer. The atomically interconnected aligned SWNTs exhibit enhanced transverse conductivity, which increases by ～2100% as a result of the photoactivated organometallic functionalization with Cr. The hexahapto mode of bonding the graphitic surfaces of carbon nanotubes with transition metal atoms offers an attractive route to the reversible chemical engineering of the transport properties of aligned carbon nanotube thin films. We demonstrate that a device fabricated with aligned SWNTs can be reversibly switched between a state of high electrical conductivity (ON) by light and low electrical conductivity (OFF) by applied potential. This study provides a route to the design of novel nanomaterials for applications in electrical atomic switches, optoelectronic and spintronic devices.     

Alignment of SWNTs by protein-ligand interaction of functionalized magnetic particles under low magnetic fields

Carbon nanotubes (CNTs) have attracted considerable attention for applications using their superior mechanical, thermal and electrical properties. A simple method to controllably align single-walled CNTs (SWNTs) by using magnetic particles embedded with superparamagnetic iron oxide as an accelerator under the magnetic field was developed. The functionalization of SWNTs using biotin, interacted with streptavidin-coupled magnetic particles (micro-to-nano in diameter), and layer-by-layer assembly were performed for the alignment of a particular direction onto the clean silicon and the gold substrate at very low magnetic forces (0.02-0.89 T) at room temperature. The successful alignment of the SWNTs with multi-layer film was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By changing the orientation and location of the substrates, crossed-networks of SWNTs-magnetic particle complex could easily be fabricated. We suggest that this approach, which consists of a combination of biological interaction among streptavidin-biotin and magnetite particles, should be useful for lateral orientation of individual SWNTs with controllable direction.     

Solvent-free preparation of high-toughness epoxy--SWNT composite materials

Multicomponent nanocomposite materials based on a high-performance epoxy system and single-walled carbon nanotubes (SWNTs) have been prepared. The noncovalent wrapping of nitric acid-treated SWNTs with a PEO-based amphiphilic block copolymer leads to a highly disaggregated filler with a boosted miscibility in the epoxy matrix, allowing its dispersion without organic solvents. Although direct dispersion of acid-treated SWNTs results in modestly improved epoxy matrix mechanical properties, the incorporation of wrapped SWNTs produces a huge increase in toughness (276% improvement at 0.5 wt % loading) and impact strength (193% at 0.5 wt % loading) with no detrimental effect on the elastic properties. A synergistic effect between SWNTs and the block copolymer is revealed on the basis of tensile and impact strength results. Atomic force microscopy has been applied, obtaining stiffness mappings that identify nanostructure features responsible of the dynamic mechanical behavior. The electrical percolation threshold is greatly reduced, from 0.31 to 0.03 wt % SWNTs when block copolymer-wrapped SWNTs are used, and all the measured conductivity values increased up to a maximum of 7 orders of magnitude with respect to the baseline matrix (1 wt % wrapped-SWNTs loading). This approach provides an efficient way to disperse barely dispersible SWNTs without solvents into an epoxy matrix, and to generate substantial improvements with small amounts of SWNTs.     

Mechanical properties of epoxy nanocomposites reinforced with very low content of amino-functionalized single-walled carbon nanotubes

Functionalized single-walled carbon nanotubes (SWNTs) with amino groups were prepared by oxidation, acylation, and amidation of SWNT surfaces. Epoxy/SWNT composite membranes were fabricated using a very low content of amino-grafted SWNTs (< or = 0.08 wt%) as fillers. SWNTs with amino groups acted as a curing agent, covalently bonding to the epoxy matrix. The influence of SWNT content on the mechanical properties of epoxy/amino-functionalized SWNT composite membrane was investigated. It is found that the tensile strength of composites is enhanced with the increase of SWNTs. Only 0.01 wt% of SWNT-R-NH, leads to improvement of the epoxy tensile strength by 9.5%, and 0.08 wt% of SWNT-R-NH2 increased tensile strength by 13.6%. For comparison purposes, epoxy/pristine-SWNT films were also prepared. The improvement of the tensile strength of the amino-functionalized SWNTs system is more remarkable than that of pristine SWNT system at very low weight-percentage loading. The amino groups on the surface of SWNTs can be covalently attached to the epoxy matrix, which effectively improves the dispersion and adhesion of SWNTs in epoxy. This leads to the enhancement in mechanical properties of the epoxy composite. Mechanical results between functionalized and pristine nanotubes are discussed in detail.     

Stretching-induced crystallinity and orientation to improve the mechanical properties of electrospun PAN nanocomposites

Polyacrylonitrile-based carbon fibers, embedded with single-walled carbon nanotubes have been prepared by the electrospinning technique. The as-spun nanofibers were hot-stretched in an oven to enhance the orientation and crystallinity which has been confirmed by X-ray diffraction and DSC etc. With the hot-stretched process and the introduction of SWNTs, the mechanical properties of PAN nanofibers such as the modulus and tensile strength will be enhanced correspondingly. In addition, the electrical conductivities of the PAN/SWNTs nanofiber composites were also enhanced. It was concluded that the hot-stretched nanofibers and the PAN/SWNTs nanofiber composites can be used as a potential precursor to produce high-performance carbon nanocomposites.