碳纳米管水泥基复合材料压阻效应的多尺度研究进展

碳纳米管水泥基复合材料具有多尺度的非均一性,其宏观尺度的性能是其各级低阶尺度本质的偶联映射,故而多尺度分析碳纳米管水泥基复合材料性能机理至关重要。本文从宏观、细观、微观和纳观四个尺度,综述了碳纳米管水泥基复合材料压阻效应的多尺度试验、机理和模型等方面的研究进展。总结了现有研究在骨料、孔隙结构、界面过渡区、外部环境因素以及理论模型等方面存在的局限或不足,并提出微纳观结构、理论模型等方面需进一步研究。     

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.     

活性炭/碳纳米管复合电极电吸附机理研究

按活性炭∶碳纳米管∶PVDF=7.2∶0.8∶2质量比制备活性炭/碳纳米管复合电极,并对其构成的EST模块进行吸附动力学、等温吸附和电迁移拟合研究,分析其吸附机理。结果表明,准一级反应动力学模型和Langmuir模型能够很好的拟合、描述活性炭/碳纳米管复合电极在EST脱盐过程中的吸附机理,说明电吸附速率只与一种反应物的浓度有关且是单离子层吸附,EST吸附过程中离子的电迁移率随迁移时间的变化趋势可以用指数形式的方程很好的拟合。     

Electrical ageing of carbon nanotube composite cathode layers

Effect of electrical ageing (EA) on the field emission parameters of thin multiwall carbon nanotube composite (t-MWCNTs-composite) was studied. Initially, t-MWCNTs were mixed with -terpineol and ethyl cellulose and subjected to three roll milling process to obtain t-MWCNTs-composite. Following this, the composite was screen printed on a conducting substrate, annealed for 10 min and employed to the electrical ageing process for a period of 6 h. The ageing, on each cathode layer, was repeated for five times and J–E characteristics have been collected before and after each ageing attempt. The analysis revealed that, the magnitude of threshold turn-on-field gradually increased from its virgin value of 1.223 to 1.968 V µm^− 1 and corresponding mean field enhancement factor, γ_m, gradually decreased from 2700 ± 210 to 1940 ± 30 with a sequential increase in the ageing attempts. The degradation rate, δJ/δt, estimated for untreated and EA samples, indicated that the magnitude of δJ/δt reached to an equilibrium value of ~ 0.785 μA cm^− 2 min^− 1, which shows a stable emission state of the emitters. To investigate the effect of EA on the physical state of the emitters, a few virgin and all EA samples were subjected to scanning electron microscopy, micro Raman spectroscopy and X-ray photoelectron spectroscopy. The details of the analysis are presented.     

Preparation and application of a multiwalled carbon nanotube composite monolithic column

A multiwalled carbon nanotube (MWCNT) composite monolithic column was prepared by the redox initiation method, and MWCNTs were embedded into the monolithic material. In this experiment, 1‐octene was used as monomer, triethylene glycol dimethacrylate was used as the crosslinking agent, propanol and 1‐dodecanol were used as porogens, hydroxyl‐functionalized MWCNTs were used as the inorganic material, and dibenzoyl peroxide and N,N‐dimethyl aniline were used as initiators. The MWCNT composite monolithic column was characterized by scanning electron microscopy, mercury intrusion porosimetry, and nitrogen adsorption–desorption isotherm measurements. The MWCNT composite monolith showed a uniform structure and a high permeability. The MWCNT composite monolithic column uses the high‐performance liquid chromatography to analyze the sample. Compared with the monolithic column without MWCNTs, the MWCNT composite monolith not only improved the column efficiency but also shortened the separation time. Six small molecules were successfully separated by the MWCNT composite monolith in 3 min, with the highest column efficiency reaching 36,000 plates/m In addition, the monolith was also used to separate complex protein samples, including snailase, plasma, and egg white. Therefore, the monolithic column was suitable both for the separation of macromolecules and small molecules. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45070.     

Advanced carbon nanotube/polymer composite infrared sensors

We demonstrate that both single-walled carbon nanotube (SWCNT) types and nanotube-matrix polymer-nanotube (CNT-P-CNT) junctions have profound impact on electro-optical properties of SWCNT/polymer composites. Composite IR sensors based on CoMoCAT^®-produced SWCNTs (SWCNTs_CoMoCAT) significantly outperform those based on HiPco^®-produced SWCNTs (SWCNTs_HiPco). Higher semiconducting nanotube concentration in a SWCNT material is critical to enhance the photo effect of IR light on SWCNT/polymer nanocomposites, whereas CNT-P-CNT junctions play a dominant role in the thermal effect of IR light on supported SWCNT/polymer composite films.     

Ultralight conducting polymer/carbon nanotube composite aerogels

By embedding carbon nanotubes into poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT–PSS) supermolecular hydrogels in the presence of a very small amount of polyvinyl alcohol (PVA), we have presented the fabrication of ultralight conducting polymer/carbon nanotube composite aerogels with the apparent density of 0.04–0.07 g/cm³ made by supercritical CO₂ drying of as-made composite hydrogel precursors. The carbon nanotubes employed here are directly applicable to pristine (MWCNTs) or acid treated (c-MWCNTs) multi-wall nanotubes. Infra-red spectroscopy is used to confirm that PVA used for stabilizing nanotubes during the synthesis of hydrogel precursors has been completely removed by solvent exchange before supercritical CO₂ drying. The morphology and textural properties of the resultant composite aerogels are investigated by scanning electron microscopy, nitrogen adsorption/desorption, and X-ray powder diffraction tests. The thermal stability, together with electrical conductivities, of the resulting composite aerogels is revealed by the thermal gravitational analysis as well as conductivity tests. The results show that embedding of either MWCNTs or c-MWCNTs into PEDOT–PSS aerogel matrix can significantly enhance the specific surface areas (280–400 m²/g), the thermal stability and electrical conductivities (1.2–6.9 × 10⁻² S/cm) of the resulting composite aerogels.     

Piezoresistive effect of individual electrospun carbon nanofibers for strain sensing

Piezoresistive behavior of individual electrospun carbon nanofibers (CNF) was studied for the first time via a microelectromechanical systems platform. The gage factor of CNFs was found to vary from 1.96 to 2.55, not correlating with nanofiber diameter. The measured strain sensitivity of electrical resistance of individual CNFs could not be solely explained based on strain induced dimensional changes of CNFs, pointing to piezoresistivity in nanofibers. The microstructure of CNFs was studied via TEM imaging and Raman spectroscopy, suggesting the presence of sp² and sp³ hybridized carbon atoms in CNFs. The piezoresistivity of CNFs was explained in light of their hybrid structure. A one-dimensional model was adopted to relate CNFs piezoresistivity to their microstructure and electron tunneling between sp² hybridized regions through sp³ hybridized regions. The calibrated model revealed tunneling distances of 0.15–0.3 nm between sp² hybridized atoms. Moreover, our study pointed to the degree of graphitization and elastic mismatch between differently hybridized carbon atom regions in CNFs as critical parameters controlling CNFs’ piezoresistivity. This study sets the stage for the utilization of CNFs, not just as load bearing elements, but also as multifunctional nanoscale components with strain sensing capabilities, for instance in Nanoelectro-mechanical systems applications.     

Well-dispersed single-walled carbon nanotube/polyaniline composite films

Single-walled carbon nanotube (SWNT)/polyaniline (PANI) composite films with good uniformity and dispersion were prepared by electrochemical polymerization of aniline containing well-dissolved SWNTs. The results of atomic force microscopy (AFM) and UV-Vis adsorption spectroscopy show that aniline can be used to solubilize SWNTs via formation of donor-acceptor complexes. The electrochemical deposition of SWNT-aniline solutions have been investigated by cyclic voltammetry. The results show that SWNT-based aniline solutions exhibit a drastic increase in peak current within the potential scanning region. The doping effect of SWNTs on PANI films was investigated by electrochemistry and FTIR spectroscopy. The results indicate that the enhanced electroactivity and conductivity of the SWNT/PANI composite films may be due to the strong interaction between SWNTs and PANI, which facilitates the effective degree of electron delocalization.     

A mesoporous composite template composed of self-assembled silica nanotube and multi-walled carbon nanotube

The multi-walled carbon nanotubes (MWNTs) were successfully embedded in the hexagonally-arranged silica tubular structure by the self-organization of two surfactant systems providing a MWNT-incorporated silica nancomposite template. The anionic surfactant (sodium dodecyl sulfate, SDS) adsorbed on the MWNT surfaces allowed the MWNTs to interact with the outer surface of the self-assembled non-ionic surfactant, poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer. Due to the hydrophilic–hydrophilic interaction between the PEO blocks and the sulfate group of SDS, the MWNTs were most possibly surrounded by the outer wall of the SBA-15 hexagonal tubes aligning in the longitudinal and transverse directions to the silica tube direction. According to the interplanar distances, electron microscopy images, and N₂ adsorption–desorption isotherms, the synthesized SBA-15/MWNT system exhibited the structural integrity of silica-tube arrangement and structural characteristics of MWNTs in terms of BET surface area and micropore volume. This work made it clear that the developed SBA-15/MWNT template could be used to synthesize various MWNT-incorporated 2-D replicas.     

Investigation on sensitivity of a polymer/carbon nanotube composite strain sensor

Extensive numerical simulation and experimental measurements have been conducted to understand the effects of processing parameters and material properties on sensor sensitivity in polymer/carbon nanotube (CNT) composite sensors. The numerical simulation was based on an improved three-dimensional statistical resistor network model incorporating the tunneling effect between the neighbouring nanotubes, and a fiber reorientation model. The behaviors of a sensor subjected to both tensile and compressive strains were investigated. Both numerical and experimental results indicate that a higher tunneling resistance or higher ratio of the tunneling resistance to the total resistance of the sensor leads to a higher sensor sensitivity. Processing conditions and material properties, such as weight fraction, diameter and conductivity of CNTs, curing temperature, mixing rate and barrier height of polymer matrix all play a role in determining the sensor sensitivity.     

半纤维素/碳纳米管复合凝胶的溶胀性能

采用 (NH4)2S2O8-Na2SO3为引发剂体系,N,N-亚甲基双丙烯酰胺（BIS）为交联剂,利用自由基聚合法成功制备了半纤维素/碳纳米管复合凝胶。用SEM对凝胶的结构形态进行了研究分析;研究了单体比例、碳纳米管含量和pH值对凝胶溶胀率的影响;并应用溶胀动力学方程对试验数据进行拟合。研究结果表明：半纤维素/碳纳米管复合凝胶的溶胀率随着甲基丙烯酸/半纤维素比例的增加而减小,随着碳纳米管含量的增加而减小;pH≤11时随pH值的增加而增大,pH>11时随pH值的增加而减小。拟合结果表明整个溶胀过程符合Schott二级动力学模型。     

纳米CuO粒子填充多壁碳纳米管复合材料的制备与表征

采用超声辅助的混酸处理方法对多壁碳纳米管(MWCNTs)进行酸化改性,用湿化学方法制备了填充CuO的MWCNTs复合材料(CuO@MWCNTs)。考察了MWCNTs直径、Cu(NO3)2溶液浓度及煅烧温度对CuO填充形貌的影响。借助FTIR、TEM、HRTEM、XRD测试手段对酸化MWCNTs(AMWCNTs)、CuO@MWCNTs进行了表征与分析。结果表明,直径40～60 nm的MWCNTs,在Cu(NO3)2浓度0.2 mol/L和600℃条件下,可得到CuO粒子均匀紧致分布的CuO@MWCNTs,CuO粒子粒径分布在10～15 nm。     

The effect of nanotube alignment on stress graphitization of carbon/carbon nanotube composites

Carbon nanotubes, when used as filler in a glass-like carbon matrix, has been reported to induce stress graphitization in the matrix. The effects on stress graphitization of the amount of carbon nanotube loading and nanotube orientation in the composite were investigated through microscopy and X-ray diffraction analyses. Results showed that an increase in nanotube content and nanotube alignment could increase the extent of formation of anisotropic regions, thereby hastening stress graphitization. It was shown that the distance between nanotubes could affect the formation of the anisotropic structures, such that they could develop in a circumferential manner around the nanotubes when the nanotubes are situated far from each other or develop continuous regions between nanotubes when they are closer together. The development of these microstructures and its relationship to the residual stresses that accumulate in the material during heat treatment is discussed here.     

Synthesis and mechanical properties of carbon nanotube/diamond-like carbon composite films

Diamond-like carbon (DLC) coatings were successfully deposited on carbon nanotube (CNT) films with CNT densities of 1 × 10⁹/cm², 3 × 10⁹/cm², and 7 × 10⁹/cm² by a radio frequency plasma-enhanced chemical vapor deposition (CVD). The new composite films consisting of CNT/DLC were synthesized to improve the mechanical properties of DLC coatings especially for toughness. To compare those of the CNT/DLC composite films, the deposition of a DLC coating on a silicon oxide substrate was also carried out. A dynamic ultra micro hardness tester and a ball-on-disk type friction tester were used to investigate the mechanical properties of the CNT/DLC composite films. A scanning electron microscopic (SEM) image of the indentation region of the CNT/DLC composite film showed a triangle shape of the indenter, however, chippings of the DLC coating were observed in the indentation region. This result suggests the improvement of the toughness of the CNT/DLC composite films. The elastic modulus and dynamic hardness of the CNT/DLC composite films decreased linearly with the increase of their CNT density. Friction coefficients of all the CNT/DLC composite films were close to that of the DLC coating.     

The effect of electro-degradation processing on microstructure of polyaniline/single-wall carbon nanotube composite films

Mesostructured polyaniline/single-wall carbon nanotube (PAni/SWCNT) composite film has been prepared through electrochemical polymerization/degradation processing. The microstructures of the films are observed before and after electro-degradation. Initial twisty SWCNT bundles are broken down and linked by the polymerization of PAni. Both crystalline and disordered PAni regions coexist in the PAni/SWCNT composite nanowires. The disordered regions are gradually dissolved while the crystalline regions are basically preserved after electro-degradation. The formation mechanism of the composite with special construction has been proposed. In addition, cyclic voltammetry measurements demonstrate that the electroactive performance of PAni/SWCNT composite is enhanced after electro-degradation. It is found that the specific capacitance of electro-degraded composite reaches up to 848.7 F/g, more than twice over the untreated film, which is ascribed to its profitable charge accessible interface and increased available crystalline PAni regions.     

Dual frequency conductivity switching in a carbon nanotube/liquid crystal composite

We report dielectric and conductivity measurements on a composite of carbon nanotubes and a liquid crystal possessing dual frequency switching characteristics. The conductivity increases by two orders of magnitude with respect to that for the host liquid crystal, and achieves negligible temperature dependence. The frequency dependence of the ac conductivity is explained by the extended pair approximation model, although the exponent is slightly higher than generally seen. We demonstrate that the current through the sample can be field-driven between the two anisotropic values (170:1) by simply changing the frequency of the applied voltage, and exhibiting at least a millisecond response.     

Mechanical properties of carbon nanotube/carbon fiber reinforced thermoplastic polymer composite

Carbon nanotube (CNT)/carbon fiber (CF) hybrid fiber was fabricated by sizing unsized CF tow with a sizing agent containing CNT. The hybrid fiber was used to reinforce a thermoplastic polymer to prepare multiscale composite. The mechanical properties of the multiscale composite were characterized. Compared with the base composite (traditional commercial CF), the multiscale composite reinforced by the CNT/CF hybrid fiber shows increases in interlaminar shear strength (ILSS) and impact toughness. Laminate containing CNTs showed a 115.4% increase in ILSS and 27.0% increase in impact toughness. The reinforcing mechanism was also discussed by observing the impact fracture morphology. POLYM. COMPOS., 38:2001–2008, 2017. © 2015 Society of Plastics Engineers     

Size effect of X-shaped carbon nanotube junctions

Systematic calculations have been performed for X-shaped junctions formed between two crossed identical carbon nanotubes (armchair or zigzag tubes) with diameters ranging from 3.92 Å to 9.49 Å using an empirical potential method. The formation energy of X junctions is found to be a function of the diameter of the tubes. The formation temperature is dependent on the curvature of tubes. The calculations show that it is energetically favorable to form X junctions by the direct heating method if the tube diameter is less than 0.85 nm.     

碳纳米管复合材料的最新研究进展

介绍了碳纳米管的历史和结构特点,然后重点阐述碳纳米管复合材料的制备方法及在各个领域的最新应用情况,最后对碳纳米管复合材料未来的研究方向进行展望。