In situ polymerized nanocomposites: Polystyrene/CNT and Poly(methyl methacrylate)/CNT composites

Carbon nanotubes (CNTs) were incorporated into polystyrene (PS) and poly(methyl methacrylate) (PMMA) matrices via in situ emulsion and emulsion/suspension polymerization methods. The polymerizations were carried out using various initiators, surfactants, and carbon nanotubes to determine their influence on polymerization and on the properties of the composites. The loading of CNTs in the composites varied from 0 to 15 wt.%, depending on the CNTs used. Morphology and dispersion of the CNTs were analyzed by transmission and scanning electron microscopy techniques. The dispersion of multi-walled carbon nanotubes (MWCNT) in the composites was excellent, even at high CNT loading. The mechanical properties, and electrical and thermal conductivities, of the composites were also analyzed. Both electrical and thermal conductivities were improved.     

A convenient route to disperse pristine carbon nanotubes in polystyrene with no damage of nanotube electronic structure

A convenient route to prepare polystyrene (PS)/pristine carbon nanotube (CNT) nanocomposite was developed; its electronic structure and electrical conductivity were also studied. Using their well-dispersed system in N-methyl-2-pyrrolodone, pristine multi-walled CNTs (MWCNTs), without any surface organo-modification, were greatly debundled and uniformly dispersed in PS matrix via a simple solution blending procedure. The dispersion structure of the prepared PS/pristine MWCNT nanocomposite was confirmed by scanning electron microscope and laser scanning confocal microscopic images. Moreover, Raman spectroscopy indicated that this method could effectively preserve the electronic structure of the pristine CNTs in the prepared nanocomposite, and the PS/pristine MWCNT nanocomposite showed greatly enhanced electrical conductivity.     

Application of cryomilling to enhance material properties of carbon nanotube reinforced chitosan nanocomposites

Cryomilled multiwall carbon nanotube (MWCNT) reinforced chitosan nanocomposites having improved conductivity have been prepared by solution casting method. The MWCNTs were crushed to smaller particles via cryomilling, which was effective in cleaving the nanotubes regularly as well as in reducing the entanglements and agglomeration. The cryomilled CNTs were chemically oxidized by acid and base methods, where basic oxidation generated high graphitic structure. The cryomilled and oxidized CNTs were characterized by XRD, Raman spectroscopy, FTIR and SEM. The conductivity of the nanocomposites was improved by cryomilling and it was further improved by chemical oxidation. Base oxidized cryomilled CNT/chitosan nanocomposites showed large improvement in conductivity compared to all other nanocomposites having 1 wt.% CNT content. Thermal stability and tensile properties of the CNT/chitosan nanocomposites also have been improved significantly by the incorporation of acid and base oxidized cryomilled CNTs. SEM picture of the fractured surface and FTIR showed nano-level dispersion of the functionalized CNTs and good chemical interaction between chitosan and CNTs respectively.     

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.     

碳纳米管在聚合物基体中的分散与有序排列研究--(Ⅰ)碳纳米管在聚合物基体中的分散

聚合物/碳纳米管（CNT）纳米复合材料，可将聚合物良好的加工性能和碳纳米管（CNTs）优异的功能化性质结合起来.目前，面临的主要挑战之一是如何提高CNTs在聚合物基体中的分散性.文中综述了优化物理共混、原位聚合和化学修饰等方法在改善CNTs在聚合物基体中分散性方面的最新研究动态。     

Electrodeposition of Carbon Nanotubes Triggered by Cathodic and Anodic Reactions of Dispersants

The combination of advanced functionalization methods for surface modification and dispersion of carbon nanotubes (CNTs) and electrochemically triggered strategies for coagulation and film formation allowed efficient electrodeposition of CNTs by cathodic and anodic methods. The electrochemical methods involved the application of cationic basic fuchsin or anionic fluorescein dyes. The dyes adsorbed on CNTs provided electrosteric dispersion. The film forming and binding properties of the dyes and their charge neutralization in electrode reactions promoted deposit formation. The proposed methods allowed controlled electrodeposition of CNT films.     

Adsorption of selected volatile organic vapors on multiwall carbon nanotubes

Carbon nanotubes are expected to play an important role in sensing, pollution treatment and separation techniques. This study examines the adsorption behaviors of volatile organic compounds (VOCs), n-hexane, benzene, trichloroethylene and acetone on two multiwall carbon nanotubes (MWCNTs), CNT1 and CNT2. Among these VOCs, acetone exhibits the highest adsorption capacity. The highest adsorption enthalpies and desorption energies of acetone were also observed. The strong chemical interactions between acetone and both MWCNTs may be the result from chemisorption on the topological defects. The adsorption heats of trichloroethylene, benzene, and n-hexane are indicative of physisorption on the surfaces of both MWCNTs. CNT2 presents a higher adsorption capacity than CNT1 due to the existence of an exterior amorphous carbon layer on CNT2. The amorphous carbon enhances the adsorption capacity of organic chemicals on carbon nanotubes. The morphological and structure order of carbon nanotubes are the primary affects on the adsorption process of organic chemicals.     

Two-dimensional distribution of carbon nanotubes in copper flake powders

We report an approach of flake powder metallurgy to the uniform, two-dimensional (2D) distribution of carbon nanotubes (CNTs) in Cu flake powders. It consists of the preparation of Cu flakes by ball milling in an imidazoline derivative (IMD) aqueous solution, surface modification of Cu flakes with polyvinyl alcohol (PVA) hydrosol and adsorption of CNTs from a CNT aqueous suspension. During ball milling, a hydrophobic monolayer of IMD is adsorbed on the surface of the Cu flakes, on top of which a hydrophilic PVA film is adsorbed subsequently. This PVA film could further interact with the carboxyl-group functionalized CNTs and act to lock the CNTs onto the surfaces of the Cu flakes. The CNT volume fraction is controlled easily by adjusting the concentration/volume of CNT aqueous suspension and Cu flake thickness. The as-prepared CNT/Cu composite flakes will serve as suitable building blocks for the self-assembly of CNT/Cu laminated composites that enable the full potential of 2D distributed CNTs to achieve high thermal conductivity.     

Effect of (Mn + Cr) addition on the microstructure and thermal stability of spray-formed hypereutectic Al–Si alloys

This study aims to investigate the tensile mechanical behavior and fracture toughness of vinyl-ester/polyester hybrid nanocomposites containing various types of nanofillers, including multi- and double-walled carbon nanotubes with and without amine functional groups (MWCNTs, DWCNTs, MWCNT-NH₂ and DWCNT-NH₂). To prepare the resin suspensions, very low contents (0.05, 0.1 and 0.3 wt.%) of carbon nanotubes (CNTs) were dispersed within a specially synthesized styrene-free polyester resin, conducting 3-roll milling technique. The collected resin stuff was subsequently blended with vinyl-ester via mechanical stirring to achieve final suspensions prior to polymerization. Nanocomposites containing MWCNTs and MWCNT-NH₂ were found to exhibit higher tensile strength and modulus as well as larger fracture toughness and fracture energy compared to neat hybrid polymer. However, incorporation of similar contents of DWCNTs and DWCNT-NH₂ into the hybrid resin did not reflect the same improvement in the corresponding mechanical properties. Furthermore, experimentally measured elastic moduli of the nanocomposites containing DWCNTs, DWCNT-NH₂, MWCNTs and MWCNT-NH₂ were fitted to Halphin–Tsai model. Regardless of amine functional groups or content of carbon nanotubes, MWCNT modified nanocomposites exhibited better agreement between the predicted and the measured elastic moduli values compared to nanocomposites with DWCNTs. Furthermore, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to reveal dispersion state of the carbon nanotubes within the hybrid polymer and to examine the CNT induced failure modes that occurred under mechanical loading, respectively. Based on the experimental findings obtained, it was emphasized that the types of CNTs and presence of amine functional groups on the surface of CNTs affects substantially the chemical interactions at the interface, thus tuning the ultimate mechanical performance of the resulting nanocomposites.     

Proliferation of osteoblast cells on nanotubes

Carbon nanotubes (CNT) have a unique structure and feature. In the present study, cell proliferation was performed on the scaffolds of single-walled CNTs (SWCNT), multiwalled CNTs (MWCNT), and on graphite, one of the representative isomorphs of pure carbon, for the sake of comparison. Scanning electron microscopy observation of the growth of osteoblast-like cells (Saos2) cultured on CNTs showed the morphology fully developed for the whole direction, which is different from that extended to one direction on the usual scaffold. Numerous filopodia were grown from cell edge, extended far long and combined with the CNT meshwork. CNTs showed the affinity for collagen and proteins. Proliferated cell numbers are largest on SWCNTs, followed by MWCNTs, and are very low on graphite. This is in good agreement with the sequence in the results of the adsorbed amount of proteins and expression of alkaline phosphatase activity for these scaffolds. The adsorption of proteins would be one of the most influential factors to make a contrast difference in cell attachment and proliferation between graphite and CNTs, both of which are isomorphs of carbon and composed of similar graphene sheet crystal structure. In addition, the nanosize meshwork structure with large porosity is another property responsible for the excellent cell adhesion and growth on CNTs. CNTs could be the favorable materials for biomedical applications.     

Correlation between electrokinetic potential, dispersibility, surface chemistry and energy of carbon nanotubes

This paper proposes the correlation between the electrokinetic potential, dispersibility in solvents, surface energy and oxygen content of carbon nanotubes (CNTs) affected by functionalization. Colloidal systems consisting of CNTs with varying degrees of dispersion are prepared and characterized to evaluate CNT dispersibility and suspension stability in solvents with different polarities. The results show that an absolute value of zeta potential at about 25 mV is closely related to the micro- and macroscopic dispersion of CNTs, whereas a high absolute value of 40 mV is regarded as an indication of high quality CNT dispersion with much enhanced suspension stability in solvents. The absolute zeta potential value increases consistently with increasing degree of CNT functionality, the increase being most pronounced in a hydrophilic liquid such as water. A linear correlation is established between the surface energy of a CNT film and the oxygen to carbon ratio of CNT surface. The CNT dispersibility in a liquid is determined not only by their physical states, but also by the hydrophilicity and surface functionality of CNTs, all of which are reflected by zeta potential.     

Sidewall functionalization of carbon nanotubes through electrophilic substitution

We report a general strategy for functionalizing the sidewalls of carbon nanotubes (CNTs), which is based on electrophilic substitution reactions on phenylated CNTs. By using this strategy, four new functionalized CNTs were prepared, including diphenyl ketone, benzenesulfonyl chloride, benzyl chloride and thiophenol modified CNTs. The benzenesulfonyl chloride and benzyl chloride functinalized CNTs could serve as novel initiators for surface-initiated atom transfer radical polymerization. The thiophenol modified CNTs were used in immobilizing Pd nanoparticles on the CNT surface, and the CNT/Pd hybrid produced exhibits good catalytic efficiency for the electrochemical oxidation of methanol.     

天然有机质对纳米碳管环境行为的影响研究进展

随着纳米技术的快速发展,大量的纳米碳管(CNTs)不可避免地释放到环境中。由于其较大的憎水性表面,CNTs与有机污染物和天然有机质(NOM)强烈地相互作用。综述了NOM存在下CNTs的环境行为,包括NOM对CNTs分散特性和吸附有机污染物特性的影响。着重论述了NOM的理化性质对CNTs分散的影响,"拉拉链"或"胶束包裹"是主要的分散机制。强调应该对不同分散机制下分散的CNTs与有机污染物的相互作用给予更多的关注,提出了目前在液相环境中直接测定CNTs表面积的新思路,并对今后的研究方向进行了展望。     

Theoretical investigation of methane adsorption onto boron nitride and carbon nanotubes

Abstract

Methane adsorption onto single-wall boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) was studied using the density functional theory within the generalized gradient approximation. The structural optimization of several bonding configurations for a CH₄ molecule approaching the outer surface of the (8,0) BNNT and (8,0) CNT shows that the CH₄ molecule is preferentially adsorbed onto the CNT with a binding energy of ?2.84 kcal mol^?1. A comparative study of nanotubes with different diameters (curvatures) reveals that the methane adsorptive capability for the exterior surface increases for wider CNTs and decreases for wider BNNTs. The introduction of defects in the BNNT significantly enhances methane adsorption. We also examined the possibility of binding a bilayer or a single layer of methane molecules and found that methane molecules preferentially adsorb as a single layer onto either BNNTs or CNTs. However, bilayer adsorption is feasible for CNTs and defective BNNTs and requires binding energies of ?3.00 and ?1.44 kcal mol^?1 per adsorbed CH₄ molecule, respectively. Our first-principles findings indicate that BNNTs might be an unsuitable material for natural gas storage.     

Adsorption thermodynamic and kinetic studies of trihalomethanes on multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs) were purified by mixed HNO3/H2SO4 solution and were employed as adsorbents to study adsorption kinetics and thermodynamics of trihalomethanes (THMs) from chlorinated drinking water. The amount of THMs adsorbed onto CNTs decreased with a rise in temperature and high adsorption capacities were found at 5 and 15 degrees C. Under the same conditions, the purified CNTs possess two to three times more adsorption capacities of CHCl3, which accounts for a major portion of THMs in the chlorinated drinking water, than the commercially available PAC suggesting that CNTs are efficient adsorbents. The thermodynamic analysis revealed that the adsorption of THMs onto CNTs is exothermic and spontaneous.     

Theoretical investigation of methane adsorption onto boron nitride and carbon nanotubes

Methane adsorption onto single-wall boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) was studied using the density functional theory within the generalized gradient approximation. The structural optimization of several bonding configurations for a CH₄ molecule approaching the outer surface of the (8,0) BNNT and (8,0) CNT shows that the CH₄ molecule is preferentially adsorbed onto the CNT with a binding energy of −2.84 kcal mol⁻¹. A comparative study of nanotubes with different diameters (curvatures) reveals that the methane adsorptive capability for the exterior surface increases for wider CNTs and decreases for wider BNNTs. The introduction of defects in the BNNT significantly enhances methane adsorption. We also examined the possibility of binding a bilayer or a single layer of methane molecules and found that methane molecules preferentially adsorb as a single layer onto either BNNTs or CNTs. However, bilayer adsorption is feasible for CNTs and defective BNNTs and requires binding energies of −3.00 and −1.44 kcal mol⁻¹ per adsorbed CH₄ molecule, respectively. Our first-principles findings indicate that BNNTs might be an unsuitable material for natural gas storage.     

Growth of horizontally aligned dense carbon nanotubes from trench sidewalls

Horizontally aligned, dense carbon nanotubes (HADCNTs) in the form of CNT cantilevers/bridges were grown from selected trench sidewalls in silicon substrate by chemical vapor deposition (CVD). The as-grown CNT cantilevers/bridges are packed with multiwalled carbon nanotubes (MWCNTs) with a linear density of about 10 CNTs μm(-1). The excellent horizontal alignment of these CNTs is mainly ascribed to the van der Waals interactions within the dense CNT bundles. What is more, the Raman intensity ratio I(G)/I(D) shows a gradual increase from the CNT roots to tips, indicating a defect gradient along CNTs generated during their growth. These results will inspire further efforts to explore the fundamentals and applications of HADCNTs.     

Correlation between dispersion state and electrical conductivity of MWCNTs/PP composites prepared by melt blending

Non-conductive polymers filled with conductive carbon nanotubes (CNTs) often do not show detectable conductivity due to poor dispersion of carbon nanotubes in the polymer matrix and the lack of conductive networks formed from CNTs. In this work, we attempted two ways to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) in a polypropylene (PP) matrix: chemical modification of MWCNTs and addition of a master batch as a compatibilizer, followed by melt blending using a micro-compounder. The relationship between the dispersion state of MWCNTs and the electrical conductivity of the CNTs/PP composites have been investigated by controlling several factors such as CNTs modification, compatibilization by a master batch, melt mixing, and post-heat treatment. The enhanced interfacial adhesion between the CNTs and the polymer could improve the dispersion of CNTs but it could also reduce the electrical conductivity of the composites. Meanwhile, it is interestingly found that the post-heat treatment could increase the conductivity remarkably due to the connection of CNTs into networks. Thus, it is concluded that the balance between dispersion of CNTs and the formation of conductive networks plays an important role in enhancing the electrical conductivity of composites.     

Tensile properties of carbon nanotube reinforced aluminum nanocomposite fabricated by plasma spray forming

Uniaxial tensile tests were performed on plasma spray formed (PSF) Al–Si alloy reinforced with multiwalled carbon nanotubes (MWCNTs). The addition of CNTs leads to 78% increase in the elastic modulus of the composite. There was a marginal increase in the tensile strength of CNT reinforced composite with degradation in strain to failure by 46%. The computed critical pullout length of CNTs ranges from 2.1 to 19.7 μm which is higher than the experimental length of CNT, leading to relatively poor load transfer and low tensile strength of PSF nanocomposites. Fracture surface validates that tensile fracture is governed strongly by the constitutive hierarchical microstructure of the plasma sprayed Al–CNT nanocomposite. The fracture path in Al–CNT nanocomposite occurs in Al–Si matrix adjacent to SiC layer on CNT surface.     

Mechanical strength improvement of polypropylene threads modified by PVA/CNT composite coatings

Poly (vinyl alcohol)/carbon nanotube (PVA/CNT) composite was coated on the surface of polypropylene thread for toughness enhancement. Multiwall carbon nanotubes (MWNTs) were treated in acid and alkali to get water-soluble nanotubes, and then embedded into poly (vinyl alcohol) (PVA) matrix, resulting in polymer-carbon composite with homogeneous nanotube dispersion. The stress-strain measurements show that the tensile strength and toughness of the PVA/CNT coated thread increased by 117% and 560%, respectively. These results are supportive of good interfacial bonding between the carbon nanotubes (CNTs) and polymer matrix.