Recent advances in hybrids of carbon nanotube network films and nanomaterials for their potential applications as transparent conducting films

The use of carbon nanotubes (CNTs) as transparent conducting films is one of the most promising aspects of CNT-based applications due to their high electrical conductivity, transparency, and flexibility. However, despite many efforts in this field, the conductivity of carbon nanotube network films at high transmittance is still not sufficient to replace the present electrodes, indium tin oxide (ITO), due to the contact resistances and semi-conducting nanotubes of the nanotube network films. Many studies have attempted to overcome such problems by the chemical doping and hybridization of conducting guest components by various methods, including acid treatment, deposition of metal nanoparticles, and the creation of a composite of conducting polymers. This review focuses on recent advances in surface-modified carbon nanotube networks for transparent conducting film applications. Fabrication methods will be described, and the stability of carbon nanotube network films prepared by various methods will be demonstrated.     

Synthesis,characterizations, and physical properties of carbon nanotubes coated by conducting polypyrrole

A new type of carbon nanotube (CNT) (diameter of <100 nm) coated by conducting polypyrrole (PPY) was synthesized by in situ polymerization on CNTs. The structure of the resulting complex nanotubes (CNT‐PPY) was characterized by elemental analysis, X‐ray photoelectron spectroscopy, Raman spectra, and X‐ray diffraction. These indicated no significant chemical interaction between PPY and the CNT. The electrical, magnetic, and thermal properties of the complex nanotubes were measured and showed the physical properties of the CNTs were modified by conducting PPY. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2605–2610, 1999     

Carbon nanotube-based nanocomposites and their applications

The purpose of the current review article is to present a compherensive understanding regarding pros and cons of carbon nanotube–related nanocomposites and to find ways in order to improve the performance of nanocomposites with new designs. Nanomaterials including carbon nanotubes (CNTs) are employed in industrial applications such as supercapacitors, and biosensors, and etc. The present article has been prepared in three main categories. In the first part, carbon nanotube types have been presented, as single-walled carbon nanotubes, multi-walled carbon nanotubes, and also equivalent circuit models, which have been used to more clarify the experimental measurements of impedance. In the second part, nanocomposites with many carbon, inorganic and polymeric materials such as polymer/CNT, activated carbon/CNT, metal oxide/CNT, and carbon fiber/CNT have been investigated in more detail. In the third part, the focus in on the industrial applications of CNTs. including supercapacitors, biosensors, radar absorbing materials, solar cells, and corrosion protection studies. This review article explains the latest advances in carbon nanotubes and their applications in electrochemical, electrical and optical properties of nanocomposites.     

Mechanical properties and electrical conductivity in a carbon nanotube reinforced silicon nitride composite

The influence of carbon nanotubes (CNTs) addition on basic mechanical, thermal and electrical properties of the multiwall carbon nanotube (MWCNT) reinforced silicon nitride composites has been investigated. Silicon nitride based composites with different amounts (1 or 3 wt%) of carbon nanotubes have been prepared by hot isostatic pressing. The fracture toughness was measured by indentation fracture and indentation strength methods and the thermal shock resistance by indentation method. The hardness values decreased from 16.2 to 10.1 GPa and the fracture toughness slightly decreased by CNTs addition from 6.3 to 5.9 MPa m^1/2. The addition of 1 wt% CNTs enhanced the thermal shock resistance of the composite, however by the increased CNTs addition to 3 wt% the thermal shock resistance decreased. The electrical conductivity was significantly improved by CNTs addition (2 S/m in 3% Si₃N₄/CNT nanocomposite).     

Tailoring optical and electrical properties of carbon nanotube networks for photovoltaic applications

Maximizing the electrical conductivity and optical transmittance of a carbon nanotube (CNT) network is critical for using CNTs as electrodes of solar cells. In this paper, the effect of CNT network morphology on its electrical and optical properties is investigated both experimentally and theoretically, indicating that a network consisting of loosely-percolated small long nanotube bundles or individual CNTs showed outstanding transparency and electrical conductivity. Further removal of surfactant absorbed onto the CNTs or treating them with nitric acid significantly increased the electrical conductivity of CNT films without sacrificing the transparency. The optimized CNT network demonstrated a surface resistivity of 205 ohm/square with 65% optical transmittance. These results will significantly facilitate the application of CNTs in solar cells and other electronic devices.     

Fabrication of high mechanical performance UHMWPE nanocomposites with high-loading multiwalled carbon nanotubes

Using conventional mixing techniques, the mechanical properties of prepared carbon nanotube (CNT)/polymer composites are not impressive enough, because of their aggregation problem at a high loading of CNTs. In this article, high mechanical performance ultrahigh molecular weight polyethylene (UHMWPE) nanocomposites with high loading of multiwalled CNTs were successfully fabricated by a new manufacturing technique. Specifically, the tensile strength and storage modulus at 25 °C of UHMWPE nanocomposites with 32 wt % of nanotubes prepared by the novel technique reaches 107.6 MPa and 6.0 GPa, respectively, about 4.7 times and 5.0 times of that of pure UHMWPE resin, which are also very high experimental results compared with polyethylene nanocomposite prepared by traditional hot-compression techniques. These attractive results suggest that the high-loading CNTs without sacrificing their dispersion and the impregnation quality of polymer-impregnated buckypapers are essential for fabricating CNTs/polymer composites with superior mechanical properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48667.     

Simple approach for the fabrication of carbon nanotube field emitter using conducting paste

A conducting layer using carbon nanotube (CNT) paste was prepared by mixing multi-walled CNT (MWNT), organic vehicles and spin on glass (SOG). The effect of SOG on the properties of the CNT paste was evaluated and compared to that of CNT paste with a glass frit. CNT powders were coated on the conducting CNT film either by sprinkling CNT powders onto the overall conducting layer area or by dropping a solution containing well dispersed CNTs. CNTs were strongly fixed by the formation of silica after heat treatment. The samples showed good field emission characteristics with turn-on electric fields of approximately 1.6 ∼ 2.2 V/μm. SOG was found to be an efficient inorganic binder for CNTs in the CNT paste.     

Processing and properties of carbon nanotube/poly(methyl methacrylate) composite films

A systematic study of the reinforcement of single‐walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes, and vapor‐grown carbon nanofibers (VGCNFs) in poly(methyl methacrylate) (PMMA) is reported. SWNT/PMMA composite films with various SWNT concentrations (from 0.5 to 50 wt % with respect to the weight of PMMA) were processed from nitromethane. Two types of SWNTs were used: SWNT‐A, which contained 35 wt % metal catalyst, and SWNT‐B, which contained about 2.4 wt % metal catalyst. Properties of different nanotubes containing composites were compared with 15 wt % carbon nanotubes (CNTs). Property enhancement included electrical conductivity, mechanical properties, and solvent resistance. The thermal degradation of PMMA in the presence of CNTs in air and nitrogen environments was studied. No variation in the thermal degradation behavior of PMMA/CNT was observed in nitrogen. The peak degradation temperature increased for the composites in air at low CNT loadings. Dynamic and thermomechanical properties were also studied. At a 35 wt % SWNT loading, a composite film exhibited good mechanical and electrical properties, good chemical resistance, and a very low coefficient of thermal expansion. Property improvements were rationalized in terms of the nanotube surface area. Composite films were also characterized with Raman spectroscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterisation of silica–carbon nanotube hybrid microparticles and their effect on the electrical properties of poly(vinyl alcohol) composites

Hybrid silica–carbon nanotube (CNT) particles with a radial symmetry were produced by the growth of nanotubes onto spherical, mesoporous silica gel particles using the floating catalyst chemical vapour deposition (FC-CVD) method. Characterisation of the hybrid particles, using electron microscopy, Raman spectroscopy and thermogravimetry showed the geometry and porosity of the silica particles to influence the alignment and density of the CNTs produced. CNT growth initiated in the pores of the gel particles and three hours of CVD growth were required to get extensive surface coverage. In the early stages of growth, the reactants diffused inside the mesoporous silica and consequently the CNTs grew mainly within the silica gel rather than on the surface. Some indication of catalyst templating was observed within the smaller (<10 nm) pores, but this templating did not result in aligned CNTs. Composite films of hybrid silica–CNT particles in poly(vinyl alcohol) were cast and their impedance measured. An electrical percolation threshold of 0.62 wt.% was found for the hybrid particles, of which 0.20 wt.% were CNTs.     

Electrical and mechanical properties of multi‐walled carbon nanotubes reinforced PMMA and PS composites

The use of multi‐walled carbon nanotubes (MWCNT) as reinforcing material for thermoplastic polymer matrices, polymethyl methacrylate (PMMA), and polystyrene (PS) has been studied. MWCNT were synthesized by chemical vapor deposition (CVD) technique using ferrocene‐toluene mixture. As‐prepared nanotubes were ultrasonically dispersed in toluene and subsequently dispersed in PMMA and PS. Thin polymer composite films were fabricated by solvent casting. The effect of nanotube content on the electrical and mechanical properties of the nanocomposites was investigated. An improvement in electrical conductivity from insulating to conducting with increasing MWCNT content was observed. The carbon nanotube network showed a classical percolating network behavior with a low percolation threshold. Electromagnetic interference (EMI) shielding effectiveness value of about 18 dB was obtained in the frequency range 8.0–12 GHz (X‐band), for a 10 vol% CNT loading. An improved composite fabrication process using casting followed by compression molding and use of functionalized MWCNT resulted in increased composites strength. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Conducting polymer/carbon nanotube composite films made by in situ electropolymerization using an ionic surfactant as the supporting electrolyte

We have demonstrated a simple and general strategy, namely in situ electropolymerization by using an ionic surfactant as the electrolyte, for alignment of disordered CNTs within conducting polymer/carbon nanotube composite films. The single- or multi-walled CNTs were first dispersed in an aqueous solution containing SDS (sodium dodecyl sulfate), then electroactive monomer pyrrole or N-methylpyrrole was added into the above mixture, finally electrochemical reaction was proceeded at the surface of the Au electrode and correspondingly a series of conducting polymer/carbon nanotube composite films with the orientation of carbon nanotubes were obtained.     

Synthesis of carbon nanotube/epoxy composite films with a high nanotube loading by a mixed-curing-agent assisted layer-by-layer method and their electrical conductivity

A mixed-curing-agent assisted layer-by-layer method is reported to synthesize carbon nanotube (CNT)/epoxy composite films with a high CNT loading from ∼15 to ∼36 wt.%. The mixed-curing-agent consists of two types of agents, one of which is responsible for the partial initial curing at room temperature to avoid agglomeration of the CNTs, and the other for complete curing of epoxy resin at high temperature to synthesize epoxy composite films with good CNT dispersion. The electrical conductivity of the composites shows a value up to ∼12 S/m, which is much higher than that for CNT/epoxy composites with a low CNT loading prepared using conventional methods.     

Tribological application of carbon nanotubes in a metal-based composite coating and composites

Ni-P-carbon nanotube (CNT) composite coating and carbon nanotube/copper matrix composites were prepared by electroless plating and powder metallurgy techniques, respectively. The effects of CNTs on the tribological properties of these composites were evaluated. The results demonstrated that the Ni-P-CNT electroless composite coating exhibited higher wear resistance and lower friction coefficient than Ni-P-SiC and Ni-P-graphite composite coatings. After annealing at 673 K for 2 h, the wear resistance of the Ni-P-CNT composite coating was improved. Carbon nanotube/copper matrix composites revealed a lower wear rate and friction coefficient compared with pure copper, and their wear rates and friction coefficients showed a decreasing trend with increasing volume fraction of CNTs within the range from 0 to 12 vol.% due to the effects of the reinforcement and reduced friction of CNTs. The favorable effects of CNTs on the tribological properties are attributed to improved mechanical properties and unique topological structure of the hollow nanotubes.     

In situ preparation of polyimide/amino‐functionalized carbon nanotube composites and their properties

In order to improve the dispersion of carbon nanotubes (CNTs) in polyimide (PI) matrix and the interfacial interaction between CNTs and PI, 4,4′‐diaminodiphenyl ether (ODA)‐functionalized carbon nanotubes (CNTs‐ODA) were synthesized by oxidation and amidation reactions. The structures and morphologies of CNTs‐ODA were characterized using Fourier transform infrared spectrometer, transmission electron microscopy, and thermal gravimetric analysis. Then a series of polyimide/amino‐functionalized carbon nanotube (PI/CNT‐ODA) nanocomposites were prepared by in situ polymerization. CNTs‐ODA were homogeneously dispersed in PI matrix. The influence of CNT‐ODA content on mechanical properties of PI/CNT‐ODA nanocomposites was investigated. It was found that the mechanical properties of nanocomposites were enhanced with the increase in CNT‐ODA loading. When the content of CNTs‐ODA was 3 wt%, the tensile strength of PI/CNT‐ODA nanocomposites was up to 169.07 MPa (87.11% higher than that of neat PI). The modulus of PI/CNTs‐ODA was increased by 62.64%, while elongation at break was increased by 66.05%. The improvement of the mechanical properties of PI/CNT‐ODA nanocomposites were due to the strong chemical bond and interfacial interaction between CNTs‐ODA and PI matrix. POLYM. COMPOS., 35:1952–1959, 2014. © 2014 Society of Plastics Engineers     

Incorporation of 4‐aminobenzene functionalized multi‐walled carbon nanotubes in polyaniline for application in formic acid electrooxidation

Incorporation of carbon nanotubes (CNTs) in conducting polymer can lead to new composites with enhanced electrical and mechanical properties. However, the development of such composites has been hampered by the inability to disperse CNTs in polymer matrix due to the lack of chemical compatibility between polymers and CNTs. Covalent sidewall functionalization of carbon nanotube provides a feasible route to incorporate carbon nanotube in polymer. In this work, 4‐aminobenzene groups were grafted onto the surface of multi‐walled carbon nanotube (MWNT) via C? C covalent bond. Polyaniline (PANI)/MWNT composites were fabricated by electrochemical polymerization of aniline containing well‐dissolved functionalized MWNTs. The obtained composites can be used as catalyst supports for electrooxidation of formic acid. Cyclic voltammogram results show that platinum particles deposited in PANI/MWNT composite films exhibit higher electrocatalytic activity and better long‐term stability towards formic acid oxidation than that deposited in pure PANI films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modified and unmodified multiwalled carbon nanotubes in high performance solution-styrene-butadiene and butadiene rubber blends

The outstanding properties of carbon nanotubes have generated scientific and technical interests in the development of nanotube-reinforced polymer composites. Therefore, we investigated a novel mixing approach for achieving a good dispersion of multiwalled carbon nanotubes (CNTs) in a rubber blend. In this approach the CNTs were incorporated into a 50:50 blend of solution-styrene-butadiene rubber and butadiene rubber. First, the CNTs were predispersed in ethanol and then this CNT-alcohol suspension was mixed with the rubber blend at elevated temperature. The rubber nanocomposites prepared by such method exhibit significantly enhanced physical properties already at very low nanotube concentrations. Additionally, we have analysed the dielectric and thermal properties of the compound. The high aspect ratio of the carbon nanotubes enabled the formation of a conductive percolating network in these composites at concentrations below 2 wt.%. In contrast to the electrical conduction behaviour, the thermal conductivity of the composites has not been influenced significantly by the presence of carbon nanotubes. Dynamic mechanical analysis indicates that the incorporation of CNTs affects the glass transition behaviour by reducing the height of the tan δ peak considerably. Above the glass transition temperature the storage modulus has been increased after incorporation of a small amount of CNTs. Finally, the ‘Payne effect’, an indication of filler-filler interactions, was observed at very low concentrations of CNT in the rubber matrix.     

A method of mobilizing and aligning carbon nanotubes and its use in gel spinning of composite fibres

We report a method of improving the alignment of carbon nanotubes (CNTs) in a solid strand prepared from a CNT forest without dispersing and regrouping them. The use of a lubricant loosens the interconnections between the carbon nanotubes so that they can slide relative to each other and align themselves longitudinally. A highly stretchable polymer gel fibre is used as a carrier to apply the lubricant to a continuous length of the carbon nanotube strand so that the strand can be drawn uniformly and continuously by a series of drawing operations. The lubricant is then extracted to produce a highly aligned carbon nanotube reinforced polymer composite fibre that demonstrates a remarkable reinforcement effect. The CNT strength utilisation in the composite fibre is one order of magnitude greater than that in a pure carbon nanotube spun yarn.     

Reversible transformation of hydrophobicity and hydrophilicity of aligned carbon nanotube arrays and buckypapers by dry processes

Dry treatment using a combination of UV and ozone can readily change the surface of vertically aligned carbon nanotubes from superhydrophobic to superhydrophilic. This treatment is also effective for buckypapers. Heating in a vacuum at an elevated temperature (650-750 °C) can reverse the surface state from superhydrophilic to superhydrophobic. The UV & ozone treatment causes the least amount of damage to the stripe-like carbon nanotube patterns. The effect of rough surface on apparent contact angles of CNT forests was discussed to explain the origin of superhydrophilicity and superhydrophobicity.     

锌/碳纳米管复合电沉积薄膜性能研究

通过复合电沉积技术制备了纳米叠层锌/碳纳米管和光亮锌/碳纳米管2种复合薄膜,薄膜的拉曼光谱验证了锌与碳纳米管的共沉积。薄膜表面的场发射扫描电子显微镜观测显示碳纳米管表面的金属包覆层连续且均匀,预示着良好的界面结合。在2种薄膜的断口和裂纹处分别发现了被拔出基体和桥联的碳纳米管,证实了碳管对基体具有有效的增强作用。     

Effect of surface treatment for carbon nanotubes on morphological and rheological properties of poly(ethylene oxide) nanocomposites

Poly(ethylene oxide) nanocomposites filled with functionalized multi‐walled carbon nanotubes are prepared and characterized using rheological and morphological measurements. This study investigates how the surface treatment of carbon nanotubes (CNTs) affects the CNT dispersion state. It is found that the nanocomposites have a higher effective volume fraction than the real volume fraction of the CNTs. The dispersion state of the CNTs is identified by using field emission scanning electron spectroscope and transmission electron microscope. The rheological findings indicate that there exists a percolated network structure of the CNTs in the nanocomposites, which was confirmed by electrical conductivity measurements as well as morphological observation. POLYM. ENG. SCI., 46:1350–1357, 2006. © 2006 Society of Plastics Engineers