Dispersion of functionalized multi-walled carbon nanotubes in multi-walled carbon nanotubes/liquid crystal nanocomposites and their thermal properties

A novel liquid crystal functionalized multi-walled carbon nanotubes (LC-MWNTs)/2-methyl-N,N′-bis(4′-methoxy benzoyloxy)-terephthalamide liquid crystal (LC) nanocomposite (LC-MWNTs/LC) was prepared via solution blend. The dispersion and thermal property of the nanocomposites with different loadings of LC-MWNTs (0.1-1 wt.%) were investigated using SEM, TGA and DSC. The results show that the dispersion of LC-MWNTs in LC matrix is more homogeneous than purified MWNTs. The decomposition temperature of nanocomposites exhibits obvious decrease at first and then increase with increasing concentration of LC-MWNTs, which is lower than that of LC for 0.1-0.4 wt.% LC-MWNT loadings and higher than that of LC for 0.5-1 wt.% LC-MWNT loadings. The addition of LC-MWNTs has little effects on the texture of smectic mesophase. These results illustrate the LC-MWNTs/LC nanocomposites, which have lower melting point and higher decomposition temperature than those of LC by adding adequate amount of LC-MWNTs, show a wide temperature range of mesophase and high thermostability. The increased mesophase temperature region of LC materials will be beneficial to their practical applications.     

Poly(ethylene-co-vinyl alcohol) functionalized single-walled carbon nanotubes and related nanocomposites

Single-walled carbon nanotubes (SWNTs) were functionalized by poly(ethylene-co-vinyl alcohol) (EVOH) copolymer under carbodiimide-activated esterification reaction conditions. Similar to the parent EVOH copolymer, the EVOH-functionalized carbon nanotubes are soluble in highly polar solvent systems such as DMSO and hot ethanol-water mixtures. The soluble EVOH-SWNT sample was characterized by various techniques, including optical absorption, Raman, NMR, electron microscopy, and thermogravimetric analysis. The common solubility of EVOH and EVOH-SWNT allowed their intimate mixing in solution, and thus the fabrication of nanocomposites in which the SWNTs are homogeneously dispersed in the polymer matrix.     

Chemically functionalized carbon nanotubes

Since their discovery, carbon nanotubes have attracted the attention of many a scientist around the world. This extraordinary interest stems from their outstanding structural, mechanical, and electronic properties. In fact, apart from being the best and most easily available one-dimensional (1D) model system, carbon nanotubes show strong application potential in electronics, scanning probe microscopy, chemical and biological sensing, reinforced composite materials, and in many more areas. While some of the proposed applications remain still a far-off dream, others are close to technical realization. Recent advances in the development of reliable methods for the chemical functionalization of the nanotubes provide an additional impetus towards extending the scope of their application spectrum. In particular, covalent modification schemes allow persistent alteration of the electronic properties of the tubes, as well as to chemically tailor their surface properties, whereby new functions can be implemented that cannot otherwise be acquired by pristine nanotubes.     

Synthesis and properties of amphiphilic block polymer functionalized multi-walled carbon nanotubes and nanocomposites

The grafting of poly(ethylene glycol)-block-polyacrylonitrile (PEG-b-PAN) amphiphilic block polymer onto multi-walled carbon nanotubes (MWCNTs) was achieved by combination of coupling reaction and redox radical polymerization. The chemical structure and yield of the resulting grafted polymer were characterized and confirmed by FT-IR and TGA. Transmission electron microscopy (TEM) images clearly indicated that the nanotubes were coated with a polymer layer. The concentrated DMF dispersions of MWCNT-g-(PEG-b-PAN) nanocomposite were stable for months, the viscoelasticity being monitored by rheometer. MWCNT-g-(PEG-b-PAN) hybrid nanocomposite membranes were fabricated by phase inversion in a wet process. The results showed that high concentration of MWCNTs could be dispersed in the polymer matrix. The morphology and surface hydrophilicity characteristics of the membrane could be controlled by the composition of MWCNT-g-(PEG-b-PAN) nanocomposite membrane.     

Thermal behavior of functionalized conventional polyaniline with hydrothermally synthesized graphene/carbon nanotubes

Abstract

Conventional polyaniline (PANI) was mixed as a binder polymer matrix with carbonous materials. Hydrothermal technique was utilized to fabricate a nanocomposite of graphene (G)/carbon nanotubes (CNTs). The morphological features and quality of the synthesized PANI, G/CNTs, and their mixtures were investigated. Scanning electron microscopy (SEM) images confirm the formation of wide area graphene sheets with folds around the edges. In addition, the hydrothermally fabricated G/CNTs exhibited a uniform distribution with partial agglomeration. However, adding their mixture to PANI generated a mesh like porous morphology which demonstrates an enhancement in surface area and providing 3D conduction network. Moreover, Raman spectra confirm the quality of the synthesized samples. The generated disorder and defects within the structure, and the ratio of quinoid ring (Q) to benzenoid (B) ring in the fabricated samples were depicted. In addition, the enhancement in thermal parameters and reversing the thermo-electric carrier type into N-type after doping were attributed to the generated facile conduction paths of G/CNTs.     

功能化碳纳米管的应用研究进展

碳纳米管具有独特的管状结构和优异的性能,由于其表面活性、分散能力的制约,影响了碳纳米管的应用。从共价修饰和非共价修饰两方面,介绍了目前碳纳米管功能化修饰的方法和研究状况。从光电通信、医疗、材料等方面着重介绍了功能化修饰后的碳纳米管一些最新应用进展,展望了碳纳米管的发展与应用前景。     

Ozonolysis of functionalized single-walled carbon nanotubes

Room temperature ozonolysis of fluorinated SWNT and phenyl-sulfonated SWNT have been studied in perfluoropolyether (PFPE) solvents. Etching at the end caps (approximately 70 nm/hour for fluorinated SWNT/PFPE suspension with 1 g/l concentration) has been demonstrated to be the dominating effect during the ozonolysis of fluorinated SWNT. Base on characterization by AFM analysis, X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy, fluorination along the SWNT sidewalls protects F-SWNT from extensive functionalization by ozonolysis. An ozone reaction with fluorinated SWNT has been found to improve its solubility in 96% sulfuric acid. This allows oxidative cutting by ammonium peroxydisulfate without defluorination. In comparison to fluorinated SWNT, phenyl-sulfonated SWNT was found to be effectively and homogeneous cut by ozonolysis in a water suspension.     

Mechanical properties of functionalized carbon nanotubes

Carbon nanotubes (CNTs) used to reinforce polymer matrix composites are functionalized to form covalent bonds with the polymer in order to enhance the CNT/polymer interfaces. These bonds destroy the perfect atomic structures of a CNT and degrade its mechanical properties. We use atomistic simulations to study the effect of hydrogenization on the mechanical properties of single-wall carbon nanotubes. The elastic modulus of CNTs gradually decreases with the increasing functionalization (percentage of C-H bonds). However, both the strength and ductility drop sharply at a small percentage of functionalization, reflecting their sensitivity to C-H bonds. The cluster C-H bonds forming two rings leads to a significant reduction in the strength and ductility. The effect of carbonization has essentially the same effect as hydrogenization.     

Synthesis of epoxy ferrite nanocomposites in supercritical carbon dioxide

A series of epoxy ferrite nanocomposites (EFNCs) was synthesised through dispersing ferrite nanoparticles (5.0 phr, parts per hundred of resin) into diglycidylether of bisphenol A (0.1 mol) in supercritical carbon dioxide at 85 ± 1°C, 1600 psi over 1 h followed by curing with triethylene tetramine (15 phr) at 40 ± 1°C. For this purpose, ferrite nanoparticles were synthesised through size-controlled precipitation method. The size of ferrite nanoparticles was calculated through XRD and further verified through transmission electron microscopy. The synthesised EFNCs were characterised through UV-Vis, FT-IR, laser-induced breakdown spectra, X-ray diffraction, scanning electron microscopy and vibrational sample magnetometry. The results showed that, with the decrease in size, the concentration of ferrite nanoparticle in EFNCs was increased ranging 3.843–4.042 phr. This resulted in a substantial increase in the compression, tensile, impact strength and Rockwell hardness of EFNCs. The effect of particle size on wear behaviour of EFNCs was investigated at various combinations of hydraulic end load ranging 1.0–3.0 bar and disc speed 230 rpm, which showed that a decrease in the size of ferrite nanoparticles imparts a remarkable reduction in wear volume over epoxy composite. All such EFNCs showed superparamagnetic behaviour with saturation magnetisation ranging 15.8–39.91 emu g^?1.     

Field-effect transistors assembled from functionalized carbon nanotubes

We have fabricated field-effect transistors from carbon nanotubes using a novel selective placement scheme. We use carbon nanotubes that are covalently bound to molecules containing a hydroxamic acid functionality. The functionalized nanotubes bind strongly to basic metal oxide surfaces, but not to silicon dioxide. Upon annealing, the functionalization is removed, restoring the electronic properties of the nanotubes. The devices thus fabricated show excellent electrical characteristics.     

Electrodeposition of composite materials containing functionalized carbon nanotubes

New methods have been developed for the synthesis and electrodeposition of functionalized single-walled carbon nanotubes (f-SWNTs). Polystyrene sulfonate functionalized nanotubes (PSS-f-SWNTs) and poly(ethylene imine) functionalized nanotubes (PEI-f-SWNTs) were co-deposited with cationic chitosan macromolecules. It was shown that chitosan promotes cathodic deposition of anionic PSS-f-SWNTs. The strategies for charging and electrodeposition of PEI-f-SWNTs include partial protonation of PEI in acidic chitosan solutions or formation of cationic Ag⁺–PEI complexes. The thickness of chitosan–PSS-f-SWNTs and chitosan–PEI-f-SWNTs composite films was varied in the range of up to 0.5–5 μm. The amount of f-SWNTs in the deposits was varied by controlling the SWNT concentration in the solutions. It was shown that the use of chitosan enabled co-deposition of other materials, such as hydroxyapatite (HA). The proposed method enabled the fabrication of composite films.     

Creep behavior of polyurethane nanocomposites with carbon nanotubes

The polyurethane (PU) nanocomposites containing carbon nanotubes (CNTs) were prepared through in situ polymerization for the creep study. The results show that the presence of CNTs leads to a significant improvement of creep resistance of PU. However, this creep resistance does not increase monotonously with increase of CNT contents because it is highly dependent on the dispersion of CNTs. Several theoretical models were then used to establish the relations between CNT dispersion and final creep and creep–recovery behaviors of nanocomposites. The as-obtained viscoelastic and viscoplastic parameters of PU matrix and structural parameters of CNTs further confirmed the retardation effect by CNTs during creep of the nanocomposite systems. Besides, the time–temperature superposition (TTS) principle was also employed in this work to make a further evaluation on the creep of PU/CNT nanocomposites with long-term time scale.     

环氧化功能碳纳米管改性氨基PPS

聚苯硫醚（PPS）是绝缘和疏水性材料,一定程度上限制了其在某些特定领域的应用。利用氨基改性PPS（NPPS）,并利用环氧功能化多壁碳纳米管（EFMWCNTs）与NPPS共价作用形式,采用溶液共混制备了EFMWCNTs/NPPS导电复合材料。利用FTIR、XPS、XRD、FESEM、TEM、DSC、TGA和半导体粉末电导率测试仪系统表征了复合材料的结构与性能。表征结果显示:PPS的链段上引入氨基后,PPS的熔融峰和结晶峰消失。NPPS利用EFMWCNTs进一步改性后,EFMWCNTs/NPPS导电复合材料的热稳定性相比NPPS增加,原因是EFMWCNTs与NPPS之间的共价作用有效提高了EFMWCNTs在NPPS中的分散性。EFMWCNTs/NPPS复合材料的电导率随EFMWCNTs添加量增加而增加,添加10wt%的EFMWCNTs时,复合材料的电导率为6.1×10-2 S/cm。      

Advances and prospects on biomolecules functionalized carbon nanotubes

In recent years, functionalization of carbon nanotubes (CNTs) with biomolecules such as nucleotide acids, proteins, and polymers as well as cells have emerged as a new exciting field. Theoretical and experimental studies of structure and function of bio-inspired CNT composites have made great advances. The importance of nucleic acids, proteins, and polymers to the fundamental developments in CNT-based bio-nano-composites or devices has been recognized. In particular, biomechanics, biochemistry, thermodynamics, electronic, optical, and magnetic properties of the bio-inspired CNT composites have become a new interdisciplinary frontier in life science and nanomaterial science. Here we review some of the main advances in this field over the past few years, explore the application prospects, and discuss the issues, approaches, and challenges, with the aim of stimulating a broader interest in developing CNT-based bio-nanotechnology.     

Potential of functionalized single walled carbon nanotubes in flexible thermoelectrics

Journal of Materials Science - It is well known that chemical functionalization of surfaces has demonstrated to be an important strategy to modify electron transport mechanism of single walled...     

Implementation of functionalized multiwall carbon nanotubes on magnetorheological elastomer

This work studies the effects of loading various functionalized multiwall carbon nanotubes (carboxyl, –COOH-MWCNTs) on the morphological and the field-dependent rheological properties of magnetorheological elastomers (MREs). A new type of MRE, which is reinforced by various loading from 0 to 1.5 wt% of COOH-MWCNT, is fabricated and experimentally investigated. The morphology of COOH-MWCNT and MRE with COOH-MWCNTs is characterized using field emission scanning electron microscopy and transmission electron microscopy. The results indicate that the COOH-MWCNTs are well embedded and dispersed randomly in the MRE structures. The rheological properties under different magnetic fields are evaluated using parallel plate rheometers. The influence of COOH-MWCNT content on the viscoelastic performance of the MRE is systematically investigated. It is found that when a higher content of COOH-MWCNT (up to 1.0 wt%) is added in the MRE, the MRE exhibits a higher MR effect of up to 17.5%. It is also shown that COOH-MWCNT acts as a reinforcing agent that leads to an enhancement in MR performance.     

Dispersion and reinforcing mechanism of carbon nanotubes in epoxy nanocomposites

Carbon nanotube based epoxy composites have been fabricated at room temperature and refrigeration process using sonication principle. Flexural moduli, electrical conductivity, glass transition temperature of epoxy resin as well as nanocomposite samples have been determined. Distribution behaviour of carbon nanotubes in the epoxy matrix was examined through scanning electron microscopy. Composite samples showed better properties than resin samples due to strengthening effect of the filled nanotubes. Refrigerated nanocomposites obtained increasing mechanical property because of better dispersion due to low temperature settlement of polymers. Improvement of electrical conductivity was due to the fact that aggregated phases form a conductive three-dimensional network throughout the whole sample. The increasing glass transition temperature was indicative of restricting movement of polymer chains that ascribe strong interaction presented between carbon nanotubes and epoxy chains that was again supplemented by Raman study and SEM.     

Modeling electrical conductivities of nanocomposites with aligned carbon nanotubes

We have developed an improved three-dimensional (3D) percolation model to investigate the effect of the alignment of carbon nanotubes (CNTs) on the electrical conductivity of nanocomposites. In this model, both intrinsic and contact resistances are considered, and a new method of resistor network recognition that employs periodically connective paths is developed. This method leads to a reduction in the size effect of the representative cuboid in our Monte Carlo simulations. With this new technique, we were able to effectively analyze the effects of the CNT alignment upon the electrical conductivity of nanocomposites. Our model predicted that the peak value of the conductivity occurs for partially aligned rather than perfectly aligned CNTs. It has also identified the value of the peak and the corresponding alignment for different volume fractions of CNTs. Our model works well for both multi-wall CNTs (MWCNTs) and single-wall CNTs (SWCNTs), and the numerical results show a quantitative agreement with existing experimental observations.     

Mechanical properties of carbon nanotubes and their polymer nanocomposites

More than 10 years have passed since carbon nanotubes (CNT) have been found during observations by transmission electron microscopy (TEM). Since then, one of the major applications of the CNT is the reinforcements of plastics in processing composite materials, because it was found by experiments that CNT possessed splendid mechanical properties. Various experimental methods are conducted in order to understand the mechanical properties of varieties of CNT and CNT-based composite materials. The systematized data of the past research results of CNT and their nanocomposites are extremely useful to improve processing and design criteria for new nanocomposites in further studies. Before the CNT observations, vapor grown carbon fibers (VGCF) were already utilized for composite applications, although there have been only few experimental data about the mechanical properties of VGCF. The structure of VGCF is similar to that of multi-wall carbon nanotubes (MWCNT), and the major benefit of VGCF is less commercial price. Therefore, this review article overviews the experimental results regarding the various mechanical properties of CNT, VGCF, and their polymer nanocomposites. The experimental methods and results to measure the elastic modulus and strength of CNT and VGCF are first discussed in this article. Secondly, the different surface chemical modifications for CNT and VGCF are reviewed, because the surface chemical modifications play an important role for polymer nanocomposite processing and properties. Thirdly, fracture and fatigue properties of CNT/polymer nanocomposites are reviewed, since these properties are important, especially when these new nanocomposite materials are applied for structural applications.     

Hydrogen peroxide vapor sensor using metal-phthalocyanine functionalized carbon nanotubes

We have developed a process for preparation of composites by blending and ultrasonification of multi-walled carbon nanotubes with metal-phthalocyanines and have used the same as very selective and sensitive sensor for detection of H₂O₂ vapors. A combination of sensors made from composites of cobalt-phthalocyanine and copper-phthalocyanine with multiwall carbon nanotubes has been found to show opposite conductivities to H₂O₂ vapors while the pair shows similar response to other chemical vapors. This unusual behavior makes this paired sensor as a reliable method to selectively identify the presence of H₂O₂ vapors with response and recovery times of few seconds. Our developed sensors work at room temperature and show resistivity in the range of 10⁴ to 10⁵ Ω cm. They can be employed for detection of H₂O₂ based explosives, to monitor levels of H₂O₂ in industrial units and other applications.