Morphology,rheological and crystallization behavior in non-covalently functionalized carbon nanotube reinforced poly(butylene succinate) nanocomposites with low percolation threshold

Multi-walled carbon nanotubes (CNTs) were non-covalently functionalized by surface wrapping of poly(sodium 4-styrenesulfonate) (PSS) with the aid of ultrasound. The functionalized CNTs were incorporated into poly(butylene succinate) (PBS) through solution coagulation to fabricate CNTs filled PBS nanocomposites. The morphologies of the PBS/CNT nanocomposites were studied by scanning electron microscope (SEM) and transmission electron microscope (TEM), and the effect of loading of functionalized CNT on the rheological behavior, electrical conductivity and mechanical properties of the nanocomposites was investigated systemically. SEM observation indicates that functionalized CNTs dispersed in PBS matrix without obvious aggregation and showed good interfacial adhesion with the PBS phase. TEM observation reveals that a CNT network was formed when the loading of CNTs increased from 0.1 to 0.3 wt%. Rheological investigation indicates the formation of a CNT network with a percolation threshold of only 0.3 wt%. Significant improvement in electrical conductivity occurred at CNT loading of 0.3 wt%, with the value of electrical conductivity increasing by six orders of magnitude compared to neat PBS. Differential scanning calorimetry indicates that the melt crystallization temperature of PBS was improved by ∼14 °C with addition of only 0.05 wt% functionalized CNTs. Tensile tests indicate that both the yield strength and Young's modulus of PBS were apparently reinforced by incorporation of functionalized CNTs, while the elongation at break was reduced gradually.     

Synergistic effect of functional carbon nanotubes and graphene oxide on the anti‐corrosion performance of epoxy coating

In this work, we reported the synergistic effect of functional carbon nanotubes (CNTs) and graphene oxide (GO) on the anticorrosion performance of epoxy coating. For this purpose, the GO and CNTs were firstly modified by the 3‐aminophenoxyphthalonitrile to realize the nitrile functionalized graphene oxides (GO‐CN) and carbon nanotubes (CNTs‐CN). As modified GO‐CN and CNTs‐CN were characterized and confirmed by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and gravimetric analyzer. It was found that about 19 and 24 wt% of 3‐aminophenoxyphthalonitrile were grafted onto the surface of the GO and CNTs, respectively. The electrochemical impedance spectroscopy results showed that the GO‐CN&CNTs‐CN hybrid materials exhibit a remarkable superiority in enhancing the anticorrosion performance of epoxy coatings. Significant synergistic effect of the lamellar structural GO‐CN and CNTs‐CN on the anticorrosion performance of epoxy composite coatings was designed. Besides, the epoxy coating with 1 wt% of the GO‐CN&CNTs‐CN hybrid exhibited the best anticorrosion performance, in which the impedance showed the largest one (immersion in 3.5 wt% of NaCl solution for 168 hr). Copyright © 2016 John Wiley & Sons, Ltd.     

Epoxy/CNT@X nanocomposite: Improved quasi-static,dynamic fracture toughness,and conductive functionalities by non-ionic surfactant treatment

The present work investigated the effects of non-ionic surfactant treatment on the dispersibility, surface chemistry and structure of carbon nanotube (CNT) particles. Subsequently, the fracture experiments of as-prepared epoxy/CNT@X nanocomposites were carried out under quasi-static and dynamic loading conditions. By simply introducing the steric repulsive force between CNT@X filler and epoxy matrix, improved mode-I critical-stress-intensity factor (K_Ic) and dynamic crack initiation toughness (K_Ii^d) of the epoxy/CNT@X nanocomposite were simultaneously obtained without compromising other desired physical properties, such as electrical properties and electro-thermal behavior. In the case of SHPB impact loading, high-speed imaging along with digital-image-correlation (DIC) technology was utilized to determine dynamic fracture parameters. The results showed a notable reinforcement for the epoxy/CNT@X nanocomposite category, producing maximum increase of ~79% and ~153% in K_Ic and K_Ii^d values relative to epoxy/CNT nanocomposite at such maximum content of 1.0 wt%, respectively. The most delayed crack initiation time (59.9–68.4 μs) and slowest crack-tip velocity (229 ± 28 m/s) were also observed in the epoxy/CNT@X_1.0 case. These results may be explained by improved dispersibility and interfacial adhesion after surfactant treatment.     

Flame retardancy of epoxy resin nanocomposite with a novel polymeric nanoflame retardant

A wrapped nanoflame retardant, designated as polyhedral oligomeric silsesquioxane (POSS)‐poly(4‐bromostyrene) (PBS)‐carbon nanotubes (CNTs), was synthesized via π‐π stacking interactions between the walls of multiwalled carbon nanotubes and the silicon‐bromine containing hybrid copolymer (designated as POSS‐PBS) that was copolymerized by 4‐bromostyrene and acryloyloxyisobutyl polyhedral oligomeric silsesquioxane. The POSS‐PBS‐CNTs exhibited good dispersibility in epoxy resin (EP) without obvious aggregation. Furthermore, the fire behaviors of this flame‐retardant EP (FR‐EP) nanocomposites were examined via limited oxygen index (LOI) and cone calorimeter (CONE) tests. The FR‐EP had an ideal LOI value of 35.3% and its residual char yield obtained from CONE test was significantly enhanced from 5.9% to 15.3% with the incorporation of 4 wt% POSS‐PBS‐CNTs and 1.33 wt% Sb₂O₃ into EP matrix. Additionally, the addition of 4 wt% POSS‐PBS‐CNTs or POSS‐PBS can efficiently decrease the peak heat release rate (PHRR) of EP matrix by 41.0% or 45.6%, respectively.     

High-performance fiberglass/epoxy reinforced by functionalized CNTs for vehicle applications with less fuel consumption and greenhouse gas emissions

Carbon Nanotubes (CNTs) is among the most promising nanofiller materials that could be used for enhancing the properties of fiberglass/epoxy laminates for vehicle industries with less CO₂ emission (the key player in the climate change). However, usually the commercialized CNTs are supplied in the shape of heavily entangled tubes what leads to random dispersion of CNTs in the polymer matrix and decrease in their performance, especially at industrial scale. Within this frame, the chemical functionalization process was used in the present research to avoid this problem and to modify the surface properties of CNTs at the same time, thus improving compatibility and solubility of CNTs in epoxy solutions. Afterwards, probe sonicator (pre-dispersion), ultrasonic path (main dispersion), mechanical mixer (mixed CNTs/Epoxy solutions with hardener), and vacuum infiltration (to remove air bubbles) were used to disperse functionalized CNTs with different concentrations (in the range 0.05–0.4 wt%) in the epoxy-hardener solutions. Then, vacuum-assisted resin transfer technique followed by curing process were used to prepare 4 layers-fiberglass/CNTs/epoxy panels. The mechanical and impact properties of the prepared panels were tested according to ASTM D7025 and ISO 6603-2 standards, respectively. Also, thermal behavior of the panels was investigated using thermogravimetric (TG-DTG). Finally, the environmental performance in terms of greenhouse gas emission (GHGE) was evaluated according to ISO-14040 standard, taking the resulting strength and changes in density into account. The results showed that 0.35 wt% of FCNTs were enough to improve the strength of panels by ~60%, compared to pure sample. Which means that weight structure of vehicles can decrease by 23%. Also, fuel consumption and GHGE can decrease significantly by 16% and ~26%, respectively. In addition, thermal stability and energy impact absorption at the same concentration of CNTs were improved by 5% and 31%, respectively.     

Combined effect of graphene oxide and MWCNTs on microwave absorbing performance of epoxy composites

Currently, carbon nanotube (CNT) ‐based composites have been considered as microwave absorbers because of the fascinating properties of CNTs. In this work, multi‐walled CNTs (MWCNTs) and graphene oxide (GO) ‐based epoxy composites (i.e. MWCNT/EPr and GO‐MWCNT/EPr), with sample thickness of 2 mm, were prepared to study microwave absorbing properties in the frequency band of 8–18 GHz. Uniform dispersion of MWCNTs in the organic solvent and polymer matrix was achieved by preparation of GO. The test for electromagnetic parameters, i.e. complex permittivity and the permeability of the samples, was carried out with vector network analyzer (VNA) using reflection‐transmission waveguides. Results showed that GO‐MWCNT/EPr composites have better absorption capability than MWCNT/EPr composites. The improved reflection loss for the composites with 0.4 wt% and 0.6 wt% of GO (out of total filler loading 6 wt%) were ?14.32 dB and ?14.29 dB, respectively. The improvement in reflection loss and absorption bandwidth for GO‐MWCNTs composites suggested that MA features are synergistically effected by GO and MWCNTs. Further skin depth and shielding effectiveness terms are studied to observe overall mechanism of electromagnetic (EM) shielding which showed that multiple reflections also play a role in EM shielding. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbon Nanotube Reinforced Supramolecular Hydrogels for Bioapplications

Nanocomposite hydrogels based on carbon nanotubes (CNTs) are known to possess remarkable stiffness, electrical, and thermal conductivity. However, they often make use of CNTs as fillers in covalently cross‐linked hydrogel networks or involve direct cross‐linking between CNTs and polymer chains, limiting processability properties. Herein, nanocomposite hydrogels are developed, in which CNTs are fillers in a physically cross‐linked hydrogel. Supramolecular nanocomposites are prepared at various CNT concentrations, ranging from 0.5 to 6 wt%. Incorporation of 3 wt% of CNTs leads to an increase of the material's toughness by over 80%, and it enhances electrical conductivity by 358%, compared to CNT‐free hydrogel. Meanwhile, the nanocomposite hydrogels maintain thixotropy and processability, typical of the parent hydrogel. The study also demonstrates that these materials display remarkable cytocompatibility and support cell growth and proliferation, while preserving their functional activities. These supramolecular nanocomposite hydrogels are therefore promising candidates for biomedical applications, in which both toughness and electrical conductivity are important parameters.     

Enhancement of water barrier properties and tribological performance of hybrid glass fiber/epoxy composites with inclusions of carbon and silica nanoparticles

Water barrier properties and tribological performance (hardness and wear behavior) of new hybrid nanocomposites under dry and wet conditions were investigated. The new fabricated hybrid nanocomposite laminates consist of epoxy reinforced with woven and nonwoven tissue glass fibers and two different types of nanoparticles, silica (SiO₂) and carbon black nanoparticles (C). These nanoparticles were incorporated into epoxy resin as a single nanoparticle (either SiO₂ or C) or combining SiO₂ and C nanoparticles simultaneously with different weight fractions. The results showed that addition of carbon nanoparticles with 0.5 and 1 wt% resulted in maximum reduction in water uptake by 28.55% and 21.66%, respectively, as compared with neat glass fiber reinforced epoxy composites. Addition of all studied types and contents of nanoparticles improves hardness in dry and wet conditions over unfilled fiber composites. Under dry conditions, maximum reduction of 47.26% in weight loss was obtained with specimens containing 1 wt% carbon nanoparticles; however, in wet conditions, weight loss was reduced by 17.525% for specimens containing 0.5 wt% carbon nanoparticles as compared with unfilled fiber composites. Diffusion coefficients for different types of the hybrid nanocomposites were computed using Fickian and Langmuir models of diffusion. Copyright © 2017 John Wiley & Sons, Ltd.     

Facile approach to obtain individual‐nanotube dispersion at high loading in carbon nanotubes/polyimide composites

A big challenge in making a composite lies in achieving individual‐nanotube dispersion of carbon nanotubes (CNTs) in a polymer matrix, without aggregation and entanglement and excellent interfacial adhesion between the CNTs and the polymers matrix. In this communication, using polyethylene glycol‐200, we successfully prepared CNT‐reinforced polyimide composites that exhibit individual‐nanotube dispertion in the matrix at high‐loading CNT's. The content of CNTs in a composite can reach 43 wt%. Copyright © 2007 John Wiley & Sons, Ltd.     

A feasible strategy to constructing hybrid conductive networks in PLA‐based composites modified by CNT‐d‐RGO particles and PEG for mechanical and electrical properties

Carbon nanotubes (CNTs) and reduced graphene oxide (RGO) were successfully assembled by chemical reaction to obtain CNT‐d‐RGO particles. Then, a home‐made dynamic impregnating device was used to prepare hybrid CNT‐d‐RGO/polyethylene glycol (PEG). Next, the different modifiers, including CNTs, GO, CNT‐d‐RGO, PEG, and CNT‐d‐RGO/PEG, were, respectively, added into poly‐(lactic acid) (PLA) matrix via melt‐compounding. The dispersed morphology for these different modifiers within the PLA matrix was confirmed by SEM and TEM observations. Especially, compared with the identical weight ratio of CNT‐d‐RGO, the hybrid CNT‐d‐RGO/PEG within the PLA matrix exhibited an excellent exfoliated and interconnected networks morphology. Moreover, compared with pure PLA, not only the crystallinity of all PLA‐based composites notably improved, but half‐crystallization time was also shortened. Furthermore, despite the addition of different modifiers, the crystal form of PLA‐based composites remained unchanged. Noticeably, compared with those of pure PLA, the tensile stress, strain, and modulus of PLA composite added with CNT‐d‐RGO/PEG increased by 29.4%, 4.1%, and 56.1%, respectively, and the V‐notch impact strength slightly improved. In addition, compared with pure PLA, volume resistivity of the PLA composite added with 1 wt% CNT‐d‐RGO/PEG decreased by 93.1%, and its volume conductivity increased by five orders of magnitude.     

Interlaminar Fracture Toughness Characterization of Laminated Composites: A Review

Abstract

Interlaminar fracture toughness had been the subject of great interest for several years and is still interesting to the research community. In this article, a comprehensive analysis of fracture toughness in FRP laminates is presented. Primarily, toughness studies are undertaken on glass and carbon fiber reinforced composites under mode-I and mode-II loading conditions. The fracture behavior and its failure pattern depend on a number of parameters: fiber sizing/coating, matrix modification, insert film, fiber volume fraction, stacking sequence, specimen geometry, loading rate and temperature change. In fact, a state-of-the-art process enables increasing fracture resistance with “matrix toughening by carbon nanotubes (CNT) inclusion”. It enables production of materials having ultra-high strength and low weight. The present study has highlighted the available techniques of CNT incorporation: mechanical mixing, grafting and interleaving. Other aspects, such as the dispersion level, matrix viscosity, fiber surface roughness, loading weight %, bonding strength with epoxy, height and density of grown CNT, energy absorption mechanism during delamination, etc., have been examined as well. Although a clear correlation of all these parameters with fracture toughness is hard to establish, there is growing understanding of the surface-grown CNTs and interleaving processes as they ensure significant increase in fracture toughness.     

Toughening of Epoxy Nanocomposites: Nano and Hybrid Effects

In this paper, we review recent progress made in the field of epoxy-based binary and ternary nanocomposites containing three-, two-, and one-dimensional (i.e., 3D-, 2D-, and 1D) nano-size fillers with a special focus on their fracture behaviors. Despite investigations conducted so far to evaluate the crack-resistance of epoxy nanocomposites and attempts made to clarify the controlling toughening mechanisms of these materials, some questions remain unsolved. It is shown that silica nanoparticles can be as effective as rubber particles in improving the fracture toughness/energy; but incorporation of carbon nanotubes (CNTs) or clay platelets in epoxy matrices delays crack growth only modestly. The “nano” effects of silica (<25 vol.%) and rubber (>10 wt.%) nanoparticles in toughening epoxy resin are confirmed by comparison with silica and rubber micro-particles of the same loading. There is clear evidence of both synergistic and additive toughening effects in the silica/rubber/epoxy ternary nanocomposites. In addition, positive hybrid toughening effect has been observed in the nano-rubber/CNT/epoxy composites; however, a negative hybrid effect is predominant in nano-clay/nano-rubber/epoxy ternary nano-composites. Future research directions for epoxy-based nanocomposites towards multi-functional applications are discussed.     

Kinetics studies on the accelerated curing of liquid crystalline epoxy resin/multiwalled carbon nanotube nanocomposites

A new class of nanocomposite has been fabricated from liquid crystalline (LC) epoxy resin of 4,4′‐bis(2,3‐epoxypropoxy) biphenyl (BP), 4,4′‐diamino‐diphenyl sulfone (DDS), and multiwalled carbon nanotubes (CNTs). The surface of the CNTs was functionalized by LC epoxy resin (ef‐CNT). The ef‐CNT can be blended well with the BP that is further cured with an equivalent of DDS to form nanocomposite. We have studied the curing kinetics of this nanocomposite using isothermal and nonisothermal differential scanning calorimetry (DSC). The dependence of the conversion on time can fit into the autocatalytic model before the vitrification, and then it becomes diffusion control process. The reaction rate increases and the activation energy decreases with increasing concentration of the ef‐CNT. At 10 wt % of ef‐CNT, the activation energy of nanocomposite curing is lowered by about 20% when compared with the neat BP/DDS resin. If the ef‐CNT was replaced by thermal‐insulating TiO₂ nanorods on the same weight basis, the decrease of activation energy was not observed. The result indicates the accelerating effect on the nanocomposite was raised from the high‐thermal conductivity of CNT and aligned LC epoxy resin. However, at ef‐CNT concentration higher than 2 wt %, the accelerating effect of ef‐CNTs also antedates the vitrification and turns the reaction to diffusion control driven. As the molecular motions are limited, the degree of cure is lowered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Improving Thermal and Flame Retardant Properties of Epoxy Resin with Organic NiFe‐Layered Double Hydroxide‐Carbon Nanotubes Hybrids

To improve the dispersion of carbon nanotubes (CNTs) and flame retardancy of layered double hydroxide (LDH) in epoxy resin (EP), organic nickel‐iron layered double hydroxide (ONiFe‐LDH‐CNTs) hybrids were assembled through co‐precipitation. These hybrids were further used as reinforcing filler in EP. EP/ONiFe‐LDH‐CNTs nanocomposites containing 4 wt% of ONiFe‐LDH‐CNTs with different ratios of ONiFe‐LDH and CNTs were prepared by ultrasonic dispersion and program temperature curing. The structure and morphology of the obtained hybrids were characterized by different techniques. The dispersion of nanofillers in the EP matrix was observed by transmission electron microscopy (TEM). The results revealed a coexistence of exfoliated and intercalated ONiFe‐LDH‐ CNTs in polymer matrix. Strong combination of the above nanofillers with the EP matrix provided an efficient thermal and flame retardant improvement for the nanocomposites. It showed that EP/ONiFe‐LDH‐CNTs nanocomposites exhibited superior flame retardant and thermal properties compared with EP. Such improved thermal properties could be attributed to the better homogeneous dispersion, stronger interfacial interaction, excellent charring performance of ONiFe‐LDH and synergistic effect between ONiFe‐LDH and CNTs.     

Facile and green solvothermal synthesis of palladium nanoparticle-nanodiamond-graphene oxide material with improved bifunctional catalytic properties

We developed a selective solvothermal synthesis of palladium nanoparticles on nanodiamond (ND)–graphene oxide (GO) hybrid material in solution. After the GO and ND materials have been added in PdCl₂ solution, the spontaneous redox reaction between the ND–GO and PdCl₂ led to the creation of nanohybrid Pd@ND@GO material. The resulting Pd@ND@GO material was characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectrometry, scanning electronic microscopy (SEM), and atomic absorption spectrometry methods. The Pd@ND@GO material has been used for the first time as a catalyst for the reduction for 2-nitrophenol and the degradation of methylene blue in the presence of NaBH₄. GO plays the role of 2D support material for Pd nanoparticles, while NDs act as a nanospacer for partly preventing the re-stacking of the GO. The Pd@ND@GO material can lead to high catalytic activity for the reduction reaction of 2-nitrophenol and degradation of methylene blue with 100% conversion within ~15 s for these two reactions even when the content of Pd in it is as low as 4.6 wt%.     

Enhanced photocatalytic activity of mesoporous TiO2 aggregates by embedding carbon nanotubes as electron-transfer channel

Mesoporous multiwalled carbon nanotubes/titanium dioxide (CNTs/TiO(2)) nanocomposites with low loading amounts (0-0.5 wt%) of CNTs embedded inside mesoporous TiO(2) aggregates has been prepared by a simple one-pot hydrothermal method using titanium sulfate as titanium source. The as-prepared CNTs/TiO(2) samples are carefully characterized, analyzed and discussed. In contrast to previous reports with high CNT loading, our results indicate that a low CNT loading slightly influences the textural properties (including crystallite size, degree of crystallinity, specific surface areas, and pore volume etc.) and UV-light absorption of the mesoporous TiO(2) aggregates. The SEM and TEM results demonstrate that the CNTs are mostly embedded in the mesoporous TiO(2) aggregates. Moreover, chemical bonds are formed at the interface between CNTs and TiO(2), which is confirmed by the Raman, IR and XPS analyses. Significantly, we point out that PL analysis in terms of intensity of PL signals seems to not be a reliable way to monitor the recombination rate in the CNTs/TiO(2) composite, due to the quenching effect of CNTs. Instead, the analysis of transient photocurrent responses is introduced, which definitely reflects CNTs as fast electron transfer channels in chemically-bonded CNTs/TiO(2) composites with low CNT loading. Notably, the positive synergy effects of CNTs and TiO(2) depend on both the CNT loading amount and the state of interfacial contacts. In our study, only these chemically bonded CNTs/TiO(2) nanocomposites with appropriate loading amounts (<0.1 wt%) favor the separation of photogenerated electron-hole pairs and decrease their recombination rate and thus display significantly enhanced photocatalytic activity for degrading acetone in air under UV irradiation, as compared with pristine TiO(2) counterparts and commercial P25 photocatalyst. In contrast, a high CNT loading (>0.1 wt%) results in a decrease in photocatalytic activity; a simple mechanical mixing of CNTs and TiO(2) without forming chemical bonds at the interface also results in inferior photocatalytic performance.     

Polymorphism and transcrystallization of syndiotactic polystyrene composites filled with carbon nanotubes

Syndiotactic polystyrene (sPS) composites filled with well-dispersed multi-walled carbon nanotubes (CNTs) were readily prepared through a coagulation method. Fourier-transform infrared spectroscopy and wide-angle X-ray diffraction revealed the effect of CNTs on the polymorphism of sPS. When crystallized from the melted state, the formation of the β-form was always favored after CNT addition regardless of crystallization conditions (isothermal or non-isothermal). In the case where liquid nitrogen was used to quench the melt, the uncrystallized material that was not able to crystallize in the extremely short crystallization time crystallized in the α form upon subsequent cold crystallization. Regardless of the CNT content, the glass transition and equilibrium melting temperature of the sPS matrix were unchanged at ∼96 and 290 °C, respectively. With a gradual increase in CNT loading, the sPS crystallization rate initially increased but then reached a plateau value at high CNT concentrations because of the reduction in chain mobility. Moreover, the Avrami exponent was changed from 2.8 for samples at low CNT contents to 2.0 for samples with a CNT concentration above 0.1 wt.%, at which the rheological threshold was approached and a polymer-CNT hybrid network was formed. The enhanced crystallization kinetics was attributed to the high nucleating ability of CNTs to induce a transcrystalline layer (TCL) at its surface, as revealed by transmission electron microscopy. For composites with low levels of CNT, the growth of sPS spherulites in the bulk between CNTs prevailed. Provided that the CNT-related networks were developed, the two-dimensional growth of cylindrical TCL at the CNT surface became dominant and led to the expected Avrami exponent.     

A novel hybrid based on carbon nanotubes and heteropolyanions as effective catalyst for hydrogen evolution

Heteropolyanions of tungstophosphoric acid (PWA) have been successfully hybridized with carbon nanotubes (CNTs) by a severe mechanical milling. The obtained hybrid is electroactive for hydrogen evolution (HE) at potentials as positive as −0.16 V vs. Ag/AgCl in 0.2 M HClO₄ aqueous solution and its electrocatalysis is up to the level of Pt/CNTs (20 wt% Pt) for HE, indicating a vigorous alternative to Pt group metals. The HE mechanism of the hybrid was also studied and it was found that the tungsten oxycarbides are the electroactive components for HE.     

Polymer Nanocomposites Using Urchin‐Shaped Carbon Nanotube‐Silica Hybrids as Reinforcing Fillers

Summary: Carbon nanotubes (CNTs) have been grown on MCM‐41 supported Fe nanoparticles and the as‐prepared (no further purification) CNT‐silica hybrid was directly incorporated into nylon‐6 (PA6) by simple melt‐compounding. The urchin‐shaped CNT‐silica hybrid filler was observed to be homogeneously dispersed throughout the matrix by scanning electron and transmission electron microscopy. Compared with neat PA6, the tensile modulus and strength of the composite are greatly improved by about 110%, with incorporation of only 1 wt.‐% CNT‐silica filler.

SEM image and schematic representation showing polymer chains wrapping around the urchin‐shaped CNT‐silica hybrid filler.     

Quantitative analysis of electron field-emission characteristics of individual carbon nanotubes: the importance of the tip structure

Electron field-emission measurements on individual carbon nanotubes (CNTs) were performed inside the transmission electron microscope (TEM). The field-emission characteristics of CNTs with different tip structures were compared, and their field conversion factor and emission area were studied systematically. It was found that the field-emission characteristics of a CNT depend sensitively on its tip structure, and in particular an opened CNT was shown to be superior to a capped CNT. High-resolution TEM observations revealed that the tip of an opened CNT may, in general, be regarded as being composed of irregular shaped graphitic sheets, and these graphitic sheets have been found to improve dramatically the field-emission characteristics, but the sharp edge may result in larger error in the calculated emission area. The influence of uncertainty in the work function of the CNTs on the field conversion factor and emission area calculation was also investigated.