碳纳米管表面处理及其在铜基复合材料中的应用

碳纳米管因特殊结构带来的优异性能而被海内外学者广泛关注,以碳纳米管为增强相制备铜基复合材料是使铜基导体同时具有高强度和高导电性能的有效途径。然而,由于碳纳米管表面能高、表面反应活性低,碳纳米管/铜复合材料制备的过程中存在增强体分散性差和界面结合强度弱两大问题,从而阻碍了复合材料高性能的实现。在碳纳米管/铜复合材料的制备过程中,采用适当的方法对碳纳米管进行表面处理能改变碳纳米管的表面结构和反应活性,在改善碳纳米管的分散性的同时增强碳纳米管与铜基体的界面结合,从而提高碳纳米管的增强效率,保证复合材料良好的综合性能。然而,表面处理过程可能会破坏碳纳米管的结构完整性,影响碳纳米管的本征性能,进而影响其增强效果,或可能在基体中引入其他杂质,影响复合材料的导电和导热性能。因此,在进行表面处理时应综合考虑其对碳纳米管结构性能及复合材料增强作用的影响。近年来,研究者们通过优化碳纳米管表面处理工艺突破了碳纳米管/铜复合材料在制备过程的难点,在保证铜基体优异的导电、导热性能的同时,大幅提高了碳纳米管/铜复合材料的力学性能。碳纳米管表面处理工艺类型大致可分为机械球磨、化学表面改性、表面镀层和联合表面处理四类。传统的机械球磨表面处理对碳纳米管的结构破坏较大;化学表面改性又分为共价表面改性和非共价表面改性,非共价表面改性在保持碳纳米管完整的管状结构和优异性能的同时,提高了碳纳米管在溶液中的分散性,但用于复合材料制备时会给基体引入有机杂质,影响复合材料性能;共价表面改性和表面镀层是铜基复合材料制备过程中最为常用和有效的表面处理方法,其能够在提高碳纳米管在基体中的分散性能的同时改善碳纳米管表面的反应活性,从而形成碳纳米管和铜基体之间强度较高的反应结合界面,实现碳纳米管/铜复合材料高强高导的综合性能。此外,可通过综合利用各种表面处理方法,结合各表面处理工艺的优势,获得更为优异的改性效果。本文从碳纳米管表面处理工艺的基本类型以及碳纳米管表面处理对铜基复合材料结构和性能的影响两方面阐述了碳纳米管表面处理在铜基复合材料中的应用和研究进展,并对其未来的研究方向进行了展望。     

Quantitative image analysis of polyurethane/carbon nanotube composite micostructures

Polyurethane/carbon nanotube (PUR/CNTs) composites are much more functional than pure polyurethanes. High intensity ultrasonic agitation was applied while preparing a mixture of multiwall carbon nanotubes and a monomer. The monomer/MWNT complexes were used to prepare PUR/CNTs nanocomposites. This paper describes the application of quantitative image analysis to characterise the microstructure of the monomer and segmented polyurethane with carbon nanotubes (CNTs). Stereological parameters chosen for analysis were used to evaluate the CNTs' dispersion in the monomer complex and the degree of matrix phase separation in the nanocomposites examined. The nanoparticles induced changes in the structure of the hard and soft domains in the polyurethane matrix and influenced thermal and mechanical properties of the material. Due to the introduction of the nanotubes in the polyurethane matrix, the physical size and glass transition temperature of hard domains increased while the tensile strength and storage modulus decreased.     

碳纳米管增强铝基复合材料的界面研究进展

碳纳米管以其稳定的结构、优异的力学性能,成为复合材料的理想增强相。其增强效果受多方面因素影响,界面是决定其增强效果的关键因素之一,也是金属基复合材料的研究重点。简要介绍了碳纳米管增强铝基(CNTs/Al)复合材料的界面结合机制及界面对复合材料性能的影响,评述了热膨胀系数、制备方法、碳纳米管纯度等多种因素对CNTs/Al复合材料界面的影响,并提出了改善界面的方法。     

Tunable Piezoelectricity of Multifunctional Boron Nitride Nanotube/Poly(dimethylsiloxane) Stretchable Composites

Boron nitride nanotubes (BNNT) uniformly dispersed in stretchable materials, such as poly(dimethylsiloxane) (PDMS), could create the next generation of composites with augmented mechanical, thermal, and piezoelectric characteristics. This work reports tunable piezoelectricity of multifunctional BNNT/PDMS stretchable composites prepared via co-solvent blending with tetrahydrofuran (THF) to disperse BNNTs in PDMS while avoiding sonication or functionalization. The resultant stretchable BNNT/PDMS composites demonstrate augmented Young's modulus (200% increase at 9 wt% BNNT) and thermal conductivity (120% increase at 9 wt% BNNT) without losing stretchability. Furthermore, BNNT/PDMS composites demonstrate piezoelectric responses that are linearly proportional to BNNT wt%, achieving a piezoelectric constant (|d₃₃|) of 18 pmV⁻¹ at 9 wt% BNNT without poling, which is competitive with commercial piezoelectric polymers. Uniquely, BNNT/PDMS accommodates tensile strains up to 60% without plastic deformation by aligning BNNTs, which enhances the composites’ piezoelectric response approximately five times. Finally, the combined stretchable and piezoelectric nature of the composite was exploited to produce a vibration sensor sensitive to low-frequency (≈1 kHz) excitation. This is the first demonstration of multifunctional, stretchable BNNT/PDMS composites with enhanced mechanical strength and thermal conductivity and furthermore tunable piezoelectric response by varying BNNT wt% and applied strain, permitting applications in soft actuators and vibration sensors.     

In situ observation of reversible rippling in multi-walled boron nitride nanotubes

The recent observation of high flexibility in buckled boron nitride nanotubes (BNNTs) contradicts the pre-existing belief about BN nanotube brittleness due to the partially ionic character of bonding between the B and N atoms. However, the underlying mechanisms and relationships within the nanotube remained unexplored. This study reports for the first time the buckling mechanism in multi-walled BNNTs upon severe mechanical deformation. Individual BNNTs were deformed inside a transmission electron microscope (TEM) equipped with an in situ atomic force microscopy holder. High-resolution TEM images revealed that bent BNNTs form multiple rippling upon buckling. The critical strain to form the first ripple was measured as 4.1% and the buckling process was reversible up to 26% strain. As opposed to carbon nanotubes, the BNNTs buckled into V-shaped ripples rather than smooth wavy shapes. The rippling wavelength was quantified in terms of the outer diameter and thickness of the nanotubes. The BNNTs showed a larger rippling wavelength compared to that of CNTs with the same number of walls. This difference was explained by the tendency of BN structures to reduce the number of thermodynamically unfavorable B-B and N-N bonds at the sharp corners in the rippling regions. The BNNTs' structure also exhibited a higher fracture strain compared to their counterpart.     

碳纳米管增强铝基复合材料分散方法研究进展

碳纳米管与铝基体的结合,可以获得导电和导热性良好及综合力学性能优异的复合材料,有望成为新一代轻质高强、结构功能一体化的复合材料.在制备碳纳米管增强铝基复合材料过程中,碳纳米管的团聚将降低界面结合,诱发缺陷产生,导致性能大幅下降,因此,调控优化碳纳米管的分散状态、含量成为获取良好界面结合,获得高性能碳纳米管增强铝基复合材...     

Formation of stainless steel–carbon nanotube composites using a scalable chemical vapor infiltration process

Carbon nanotubes (CNTs) are among the strongest materials known, making their use in composites, a field with very high commercial potential for structural applications. Many of the methods reported to date to form metal composites have an excessive number of steps. Here, a facile chemical vapor deposition method to infiltrate multiwalled carbon nanotubes directly into pure stainless steel pellets and pellets from stainless steel mixed with iron particles is reported. The iron powder was dry-coated before vapor filtration with nanosized iron oxide catalyst precursor, a critical step to increase catalytic activity. This CVD method results in a substantial increase in the elastic modulus, yield strength, and hardness by 47, 104, and over 93 %, respectively, for composites made from mixed, dry-coated particles compared with corresponding control samples without nanotubes. This is the highest enhancement reported, to the best of our knowledge, of the mechanical properties for a metal–nanotube composite prepared using a metal other than copper. The addition of CNTs results in a relatively small increase in corrosion rate which can be mitigated to negligible levels by coating with a thin epoxy–carbon nanotube composite.     

Effects of amino group on the properties of carbon nanotubes

The surfaces of multi-walled carbon nanotubes were grafted with amino functional groups by reacting acyl-chloride-functionalized carbon nanotubes (CNTs) with hexamethylene diamine, which improves the surfactivity of CNTs. The dispersity, surface morphology, and thermogravimetry of acid-treated and amino-functionalized CNTs were investigated. Amino-functionalized CNTs were added into epoxy resin to analyze the effects of amino functional groups on the properties of resin composites. It was found that the properties of CNTs, such as morphology and scale, were not affected by amino functional groups, but the dispersity in water was highly improved. Amino-functionalized CNTs are better dispersed in resin matrix, and the mechanical properties of composites are improved significantly, whereas the conductivity of composites is not enhanced as expected.     

Vibration damping characteristics of carbon fiber-reinforced composites containing multi-walled carbon nanotubes

Vibration damping characteristic of nanocomposites and carbon fiber reinforced polymer composites (CFRPs) containing multiwall carbon nanotubes (CNTs) have been studied using the free and forced vibration tests. Several vibration parameters are varied to characterize the damping behavior in different amplitudes, natural frequencies and vibration modes. The damping ratio of the hybrid composites is enhanced with the addition of CNTs, which is attributed to sliding at the CNT-matrix interfaces. The damping ratio is dependent on the amplitude as a result of the random orientation of CNTs in the epoxy matrix. The natural frequency shows negligible influence on the damping properties. The forced vibration test indicates that the damping ratios of the CFRP composites increase with increasing CNT content in both the 1st and 2nd vibration modes. The CNT-epoxy nanocomposites also show similar increasing trends of damping ratio with CNT content, indicating the enhanced damping property of CFRPs arising mainly from the improved damping property of the modified matrix. The dynamic mechanical analysis further confirms that the CNTs have a strong influence on the composites damping properties. Both the dynamic loss modulus and loss factor of the nanocomposites and the corresponding CFRPs show consistent increases with the addition of CNTs, an indication of enhanced damping performance.     

碳纳米管增强金属基复合材料电学性能研究进展

碳纳米管(CNTs)具有极高的力学性能、优异的导电和导热性能,被视为理想的复合材料增强相。CNTs增强复合材料已成为一个极为重要的研究领域。然而,由于CNTs与金属基体间相容性、增强体空间分布难以控制、CNTs本身载流量高而电导率相对较低等,CNTs增强金属基复合材料尚未展现出对金属基体电学性能的显著提升,或者无法有效兼顾电学性能和力学性能,整体研究仍处于起步阶段。鉴于此,从预处理、制备方法和电学机制分析等方面概述了CNTs增强金属基复合材料电学性能的研究现状,并展望了该领域的未来发展趋势。      

Fabrication and mechanical/conductive properties of multi-walled carbon nanotube (MWNT) reinforced carbon matrix composites

Multi-walled carbon nanotube (MWNT) reinforced carbon matrix (MWNT/C) composites have been explored using mesophase pitch as carbon matrix precursor in the present work. Results show that carbon nanotubes (CNTs)can enhance the mechanical properties of carbon matrix significantly. The maximal increment of the bending strength and stiffness of the composites, compared with the carbon matrix, are 147% and 400%, respectively. Whereas the highest in-plane thermal conductivity of the composites is 86 W m^− 1 K^− 1 which much lower than that of carbon matrix (253 W m^− 1 K^− 1).At the same time the electrical resistivity of the composites is much higher than that of matrix. It is implicated that CNTs seem to play the role of thermal/electrical barrier in the composites. FSEM micrograph of the fracture surface for the composites shows that the presence of CNTs restrains the crystallite growth of carbon matrix, which is one of factors that improve mechanical properties and decrease the conductive properties of the composites. The defects and curved shape of CNTs are also the affecting factors on the conductive properties of the composites.     

Overall behavior and microstructural deformation of R-CNT/polymer composites

Carbon nanotubes (CNTs) are an excellent candidate for the reinforcement of composite materials owing to their distinctive mechanical and electrical properties. Reticulate carbon nanotubes (R-CNTs) with a 2D or 3D configuration have been manufactured in which nonwoven connected CNTs are homogeneously distributed and connected with each other. A composite reinforced by R-CNTs can be fabricated by infiltrating a polymer into the R-CNT structure, which overcomes the inherent disadvantages of the lack of weaving of the CNTs and the low strength of the interface between CNTs and the polymer. In this paper, a 2D plane strain model of a R-CNT composite is presented to investigate its micro-deformation and effective stiffness. Using the two-scale expansion method, the effective stiffness coefficients and Young’s modulus are determined. The influences of microstructural parameters on the micro-deformation and effective stiffness of the R-CNT composite are studied to aid the design of new composites with optimal properties. It is shown that R-CNT composites have a strong microstructure-dependence and better effective mechanical properties than other CNT composites.     

陶瓷/碳纳米管复合材料的制备、性能及韧化机理

评述和讨论了碳纳米管增强陶瓷基复合材料的制备工艺,包括碳纳米管在陶瓷基体上的分散和材料的烧结成型,添加碳纳米管后材料力学性能、导电和导热等物理性能的改善以及韧化机理,指出碳纳米管在陶瓷材料基体上的均匀分散,碳纳米管在组织中存活,碳纳米管与陶瓷基体的界面结合状态是影响碳纳米管增强陶瓷基复合材料性能提高的关键.     

Activation of boron nitride nanotubes and their polymer composites for improving mechanical performance

Boron nitride nanotubes (BNNTs) are inappropriate for further chemical derivatization because of their chemical inertness. We demonstrate covalent activation of chemically inert BNNTs by isophorone diisocyanate (IPDI) to form isocyanate group (NCO)-terminated BNNT precursors with an 'NCO anchor' ready for further functionalization. As identified by Fourier transform infrared spectroscopy, a number of molecules or polymers with -COOH, -OH or -NH? groups are readily attached to the activated IPDI-BNNTs. The IPDI-BNNT-involving polymer composites have shown mechanical properties are considerably improved due to the good dispersibility of IPDI-BNNTs in the polymer matrix and the strong interfacial interactions between BNNTs and polymers. The methodology reported here provides a promising method to promote the chemical reactivity of BNNTs and covalently modify polymer nanocomposites with improved mechanical performance.     

Boron Nitride Nanotubes

The current status of research on boron nitride nanotubes (BNNTs)—carbon nanotube structural analogues—is discussed. Latest achievements in BNNT synthesis, morphology, and atomic structure analysis as well as physical, chemical, and functional property evaluations are reviewed. Similarities and differences between structural parameters and properties of BNNTs in comparison with conventional carbon nanotubes are particularly highlighted. Recent breakthroughs in BNNT filling, doping and functionalization, morphology, and electronic structure engineering are examined. Finally, prospective BNNT applications for fabricating field‐effect transistors, gas accumulators, and reinforcing polymer films are presented.     

Effects of interface characteristics on mechanical properties of carbon nanotube reinforced polymer composites

Abstract

Carbon nanotubes (CNTs) possess exceptional mechanical properties and are therefore suitable candidates for use as reinforcements in composite materials. To take full advantage of their exceptional properties, load sharing mechanisms needs to be understood in the composite materials. Load transfer in composites is achieved through the fibre/matrix interface. In the present paper, finite element method is used to investigate the effects of interface behaviour on carbon nanotube based composite mechanical properties. The effective nanocomposite mechanical properties are evaluated using a three-dimensional nanoscale representative volume element (RVE). In this RVE approach, a single nanotube and the surrounding polymer matrix are modelled. Two cases of perfect bonding and an elastic interface are considered. In addition, the rule of mixtures relations is used to validate the results of numerical models. The results indicate that mechanical properties of nanocomposite materials are significantly influenced by the interface strength.     

Effects of nanotube helical angle on mechanical properties of carbon nanotube reinforced polymer composites

Carbon nanotubes (CNTs) possess exceptional mechanical properties and are therefore suitable candidates for use as reinforcements in composite materials. The CNTs, however, form complicated shapes and do not usually appear as straight reinforcements when introduced in polymer matrices. This results in a decrease in nanotube effectiveness in enhancing the matrix mechanical properties. In this paper, theory of elasticity of anisotropic materials and finite element method (FEM) are used to investigate the effects of CNT helical angle on effective mechanical properties of nanocomposites. Helical nanotubes with different helical angles are modeled to investigate the effects of nanotube helical angle on nanocomposite effective mechanical properties. In addition, the results of models consisting of helical nanotubes are compared with the effective mechanical properties of nanocomposites reinforced with straight nanotubes. Ultimately, the effects of helical CNT volume fraction on nanocomposite longitudinal modulus are investigated.     

Preparation and properties of powder styrene-butadiene rubber composites filled with carbon black and carbon nanotubes

Carbon nanotubes (CNTs) and carbon black (CB) filled powder styrene-butadiene rubber (SBR) composites were prepared by spray drying of the suspension of CNTs and CB in SBR latex. The powders were sphere like and fine with uniform diameters of 10-15 μm. Experimental results showed that the introduction of CNTs into the matrix was beneficial to improve the security of the vulcanization of the rubber composites, and the dynamic and basic mechanical properties of the CNTs/SBR composites were better than those of CB/SBR and neat SBR composites. Observations on the microstructure of the composites indicated that CNTs were well dispersed in the matrix. Morphology of the fracture confirmed that the bonding between CNTs and rubber matrix was strong and load can be transferred to CNTs efficiently during the mechanical property tests. Moreover, the powder SBR composites containing well-dispersed CNTs could be perfect candidate as additives for other polymers.     

Microstructure and properties of polyurethane nanocomposites reinforced with methylene-bis-ortho-chloroanilline-grafted multi-walled carbon nanotubes

Methylene-bis-ortho-chloroanilline (MOCA), an excellent cross-linker widely used to prepare cured polyurethane (PU) elastomers with high performance, was used to modify a multi-walled carbon nanotube. PU/carbon nanotube (CNT) nanocomposites were prepared by incorporation of the MOCA-grafted CNT into PU matrix. Fourier transform infrared spectra have shown that the modified CNTs have been linked with PU matrix. The microstructure of composites was investigated by Field-Emission Scanning Electron Microscopy. The results of Dynamic Mechanical Thermal Analysis and Differential Scanning Calorimetry have investigated the grafted CNTs as cross-linker in the cured composites. The studies on the thermal and mechanical properties of the composites have indicated that the storage modulus and tensile strength, as well as glass transition temperature and thermal stability are significantly increased with increasing CNT content.     

An assessment of the science and technology of carbon nanotube-based fibers and composites

This paper examines the recent advancements in the science and technology of carbon nanotube (CNT)-based fibers and composites. The assessment is made according to the hierarchical structural levels of CNTs used in composites, ranging from 1-D to 2-D to 3-D. At the 1-D level, fibers composed of pure CNTs or CNTs embedded in a polymeric matrix produced by various techniques are reviewed. At the 2-D level, the focuses are on CNT-modified advanced fibers, CNT-modified interlaminar surfaces and highly oriented CNTs in planar form. At the 3-D level, we examine the mechanical and physical properties CNT/polymer composites, CNT-based damage sensing, and textile assemblies of CNTs. The opportunities and challenges in basic research at these hierarchical levels have been discussed.