Field emission properties of Cu/multiwalled carbon nanotube composite films fabricated by an electrodeposition technique

Composite films of Cu and multiwalled carbon nanotubes (MWCNTs) were fabricated by an electrodeposition technique, and their field emission properties were examined. Commercially available MWCNTs with various diameters (60–150 nm) were used. The microstructure of the composite films was analyzed by scanning electron microscopy and the field emission properties were measured using a diode-type system. Cu/MWCNT composite films with homogeneous dispersion of MWCNTs were fabricated using each type of MWCNT. Bare MWCNTs were present on the surface of the composite films and the ends of the protruding tips were fixed by the deposited copper matrix. The composite films produced clear emission currents and the corresponding Fowler–Nordheim (F–N) plots showed that these were field emission currents. The turn-on electric field tended to decrease with decreasing MWCNT diameter. A light-emitting device incorporating the Cu/MWCNT composite film as a field emitter was fabricated, and its light-emitting properties were investigated. Light emission with a brightness of around 100 cd m^?2 was observed for approximately 100 h.     

A multi-wall carbon nanotube/polymethyl methacrylate composite for use in field emitters on flexible substrates

A polymer-based multi-walled carbon nanotube (MWCNT) field emission device was fabricated from a mixture of dispersed MWCNTs and an aqueous solution of polymethyl methacrylate (PMMA). When the mixture was applied to a substrate, the PMMA formed a strong composite with the MWCNTs, while strongly binding to the substrate. Process optimization was carried out to obtain high field emission performance by controlling the density of the MWCNT emitter tips under good adhesion conditions. The polymer concentration in the MWCNT dispersion and the number of spray coatings of the solution on the substrate served as the variables. The optimized polymer-based MWCNT field emission device showed a low turn-on field of 1.07 V/μm, a high electric field enhancement factor of 2450, highly uniform emission, and long-term stability. The successful application of the developed emitters to a flexible polymer polyethylene terephthalate (PET) substrate was accomplished with good emission uniformity and long stability.     

In-situ studies of electron field emission of single carbon nanotubes inside the TEM

Electron field emission characteristics of individual multi-walled carbon nanotubes (MWCNTs) were investigated in situ inside the transmission electron microscope (TEM). For a single MWCNT it was found that while field-emission can hardly occur from the side of the nanotube, a curved nanotube may result in finite side emission and the best emission geometry is the top emission geometry. Current-voltage (I-V) measurements made at different vacuum conditions and voltage sweeps emphasize the importance of the adsorbates on the electron field emission of MWCNTs. For a contaminated MWCNT, although the field emission current was reduced, the stability of its emission was improved. A current of up to several tens of μA was observed for a single MWCNT, but it was found that long time emission usually results in drastic structure damage that may lead to sudden emission failure.     

Preparation and characterization of multi‐walled carbon nanotube/poly(ethylene terephthalate) nanoweb

Multi‐walled carbon nanotube (MWCNT)/Poly(ethylene terephthalate) (PET) nanowebs were obtained by electrospinning. For uniform dispersion of MWCNTs in PET solution, MWCNTs were functionalized by acid treatment. Introduction of carboxyl groups onto the surface of MWCNTs was examined by Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) analysis. MWCNTs were added into 22 wt % PET solution in the ratio of 1, 2, 3 wt % to PET. The morphology of MWCNT/PET nanoweb was observed using field emission‐scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM). The nanofiber diameter decreased with increasing MWCNT concentration. The distribution of the nanofiber diameters showed a bi‐modal shape when MWCNTs were added. Thermal and tensile properties of electrospun MWCNT/PET nanowebs were examined using a differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA) and etc. Tensile strength, tensile modulus, thermal stability, and the degree of crystallinity increased with increasing MWCNT concentration. In contrast, elongation at break and cold crystallization temperature showed a contrary tendency. Electric conductivities of the MWCNT/PET nanowebs were in the electrostatic dissipation range. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Design and evaluation of the interface between carbon nanotubes and natural rubber

To design the interface between carbon nanotubes and natural rubber (NR), a silane coupling agent, bis(3‐triethoxysilylpropyl) tetrasulfide (TESPT), was used to modify the surface of multiwalled carbon nanotubes (MWCNTs) in a two‐step method, and the silane‐modified multiwalled carbon nanotubes (s‐MWCNTs) were combined with NR by solvent casting. The s‐MWCNTs with an amorphous layer were visualized by transmission electron microscopy, the functional groups of which were confirmed by Raman and Fourier transform infrared analyses, and the functionalization degree was characterized by thermogravimetric analysis. The interface between s‐MWCNTs and NR was investigated by Raman analysis and field emission scanning electron microscopy (FESEM). Raman analysis showed a shift from 1,340 to 1,353 cm⁻¹ of D band of s‐MWCNTs in the NR/s‐MWCNT composite, and FESEM observation indicated that s‐MWCNTs were embedded deeply in NR. All of these results proved that s‐MWCNTs were grafted with TESPT and they reacted with the active double bonds of NR to form a strong interface. The improved interface resulted in an extreme nonlinear viscoelastic behavior and enhanced dynamic mechanical property of NR/s‐MWCNT composite as compared to NR/MWCNT composite. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

A facile,efficient, and rapid covalent functionalization of multi-walled carbon nanotubes with natural amino acids under microwave irradiation

Covalent surface functionalization of multi-walled carbon nanotubes (MWCNT)s with different natural amino acids was successfully carried out under microwave irradiation. The process is fast, one-pot, simple and resulted in a high degree of functionalization as well as dispersibility in organic solvents. Surface functionality groups and morphology of MWCNTs were analyzed by Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy, thermogravimetric analysis, X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The results consistently confirmed the formation of amino acid functionalities on MWCNTs which is available for further chemistry, while the structure of MWCNT has remained relatively intact. These results illustrate a direct pathway to functionalize MWCNTs for building nanostructures. The amino acid-functionalized MWCNTs could be easily dispersed in common organic solvents.     

Multi-walled carbon nanotube/Co composite field emitters fabricated by in situ spray coating

Multi-walled carbon nanotube(MWCNT)/Co composite powders, in which MWCNTs are homogeneously implanted in Co nanoparticles, were fabricated by polyol method. Homogeneous field emitters were fabricated by in situ spray coating of MWCNT/Co composite powders without using polymer binder and followed by sintering MWCNT/Co composite powders to form powder-powder bonding and powder-substrate bonding. Field emission properties of MWCNT/Co composite field emitters made by in situ spray coating were enhanced compared to those of MWCNT/Co composite field emitters made by screen printing due to self-activation of MWCNTs and minimization of contamination and structural defects of MWCNTs.     

Characterizations on the amidized multiwalled carbon nanotubes grafted with polyaniline via in situ polymerization

A multiwalled carbon nanotubes (MWCNTs) were carboxylated after refluxing with sulfuric and nitric acids. These attached carboxylic acid groups were further condensated with o‐phenylene diamine into amide catalyzed by dicyclohexyl carbodiimide (DCC). The obtained amidized MWCNTs were in situ‐polymerized with aniline monomers to graft a conducting polyaniline (PANI) onto MWCNT (ES‐g‐MWCNTs) through the polymerization occurring in the ortho‐ and meta‐positions. The reduced conductivity of the MWCNT after carboxylation can be recovered after grafting with PANI, which owns a strong λ_max at the near infrared region due to the extended conjugation from MWCNTs to PANI. Transmission electronic microscopic pictures show a gradual broadening of the MWCNT diameter after carboxylation, amidization, and polymerization. The weight loss from the thermogravimetric thermograms due to the carboxylations of MWCNTs, amidized MWCNTs, and the PANI grafted MWCNTs into CO₂ can be used to estimate the degree of carboxylation, amidization, and grafting of PANI. The degree of carboxylation of MWCNT calculated from ESCA spectrum is around 23% close to that estimated from TGA thermogram. The doping level of redoped PANI‐grafted MWCNT is found to be 27.78% much less than the maximum 50% of neat PANI. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Multi-walled carbon nanotube/ribonucleic acid hybrid field emitters fabricated by spray deposition

Multi-walled carbon nanotubes (MWCNTs) are shown to disperse in water, and be functionalized using RNA so that MWCNT/RNA hybrids can be fabricated on substrates by spray method. The material has strong adhesion on glass substrates or metal wires. A liquid elastomer surface treatment is used to make the field emitter tips protrude from the cathode. Possible methods of realizing field emitter sources, including X-ray sources, are discussed. The MWCNT/RNA hybrids have a higher emission current density and more uniform emission image than the MWCNTs on their own, since the RNA coated MWCNTs attach more strongly to the substrate. A diode configuration field emission X-ray source using the MWCNT/RNA hybrids on tungsten wire tip was tested and found to provide clear X-ray images.     

High dispersion ability of fluorene‐based polyester as a polymer matrix for carbon nanotubes

The high compatibility of fluorene‐based polyester (FBP‐HX) as a polymer matrix for multiwalled carbon nanotubes (MWCNTs) is discussed. A low surface resistivity due to the fine dispersion of MWCNTs in FBP‐HX and polycarbonate (PC) is reported. With a solution‐casting method, a percolation threshold with the addition of between 0.5 and 1.0 wt % MWCNTs was observed in the MWCNT/PC and MWCNT/FBP‐HX composites. Because of the coverage of FBP‐HX on the MWCNTs, a higher surface resistivity and a higher percolation ratio of the MWCNT/FBP‐HX composites were achieved compared with the values for the MWCNT/PC composites. In the MWCNT/FBP‐HX composites, MWCNTs covered with FBP‐HX were observed by scanning electronic microscopy. Because of the coverage of FBP‐HX on the MWCNTs, FBP‐HX interfered with the electrical pathway between the MWCNTs. The MWCNTs in FBP‐HX were covered with a 5‐nm layer of FBP‐HX, but the MWCNTs in the MWCNT/PC composites were in their naked state. MWCNT/PC sheets demonstrated the specific Raman absorption of the MWCNTs only with the addition of MWCNTs of 1 wt % or above because of the coverage of the surface of the composite sheet by naked MWCNTs. In contrast, MWCNT/FBP‐HX retained the behavior of the matrix resin until a 3 wt % addition of MWCNTs was reached because of the coverage of MWCNTs by the FBP‐HX resin, induced by its high wettability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Aminofunctionalization effect on the microtribological behavior of carbon nanotube/bismaleimide nanocomposites

Original multiwalled carbon nanotubes (O‐MWCNTs) and aminofunctionalized ethylenediamine‐treated multiwalled carbon nanotubes (MWCNTs‐EDA) were mixed with bismaleimide (BMI) resin to prepare O‐MWCNT/BMI and MWCNT‐EDA/BMI composites, respectively. Raman spectroscopy, thermogravimetric analysis, and infrared spectroscopy were used to investigate the influence of aminofunctionalization on the multiwalled carbon nanotube (MWCNT) framework. Dynamic mechanical analysis, scanning electron microscopy images of the fractured surface, and field emission scanning electron microscopy of the worn surface were used to determine the possible friction and wear mechanisms of the system. The MWCNT‐EDA/BMI composite exhibited a higher friction coefficient value and a lower wear loss rate value than the O‐MWCNT/BMI composite, which was attributed to the larger number of defects caused by the aminofunctionalization of the MWCNTs, the stronger interfacial adhesion formed between the MWCNTs‐EDA and the BMI resin, and the better dispersive state of the MWCNTs‐EDA in the BMI matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ultrasonic synthesis of highly dispersed Pt nanoparticles supported on MWCNTs and their electrocatalytic activity towards methanol oxidation

A new method of synthesis of highly dispersed Pt nanoparticles with large catalytic surface area on multi-walled carbon nanotubes (MWCNTs) under high-intensity ultrasonic field was developed. The method, with low processing temperature at 25 °C, took only about 5 min. The surface characterization of MWCNTs was carried out by fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy methods. The electrochemical surface area and pore volume of MWCNTs were also examined. The result showed that functional groups of the MWCNTs which favored the high loading and high dispersion of particles and electrochemical surface area of MWCNTs were reinforced in the case of high-intensity ultrasonic field. The Pt/MWCNT catalysts were characterized by energy dispersion X-ray spectra analysis (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements. The prepared Pt nanoparticles were uniformly dispersed on the MWCNT surface. The mean size of Pt particles was 3.4 ± 0.2 nm. The electrocatalytic properties of Pt/MWCNT composites and kinetic characterization for methanol electro-oxidation were investigated by cyclic voltammetry. The Pt/MWCNT catalysts prepared for 5 min in ultrasonic field present excellent electrochemical activities. The schematic of the reaction was also introduced.     

Electrically conductive superhydrophobic octadecylamine-functionalized multiwall carbon nanotube films

Electrically conductive, superhydrophobic multiwall carbon nanotube (MWCNT) thin films were prepared by direct amination of MWCNTs with up to 14 wt.% of octadecylamine (ODA) by vacuum filtration method. The ODA-functionalized MWCNT films exhibit a high water contact angle of 165° and electrical conductivity of 860 S/m. The liquid–air–solid interface is directly observed from above the water droplet using an optical microscope. The observation indicates that the wettability state of the MWCNTs has changed from relatively hydrophilic to superhydrophobic state upon functionalization with ODA. The fundamental mechanisms responsible for the unusual combination of surface superhydrophobicity and high electrical conductivity of the MWCNT films are described and their implications are discussed.     

Electrical and mechanical tuning of 3D printed photopolymer–MWCNT nanocomposites through in situ dispersion

An electric field-assisted in situ dispersion of multiwall carbon nanotubes (MWCNTs) in polymer nanocomposites, fabricated through stereolithography three-dimensional (3D) printing technique, was demonstrated. The introduction of MWCNTs increased the elasticity modulus of the polymer resin by 77%. Furthermore, the use of an electric field for in situ MWCNT dispersion helped improving the average elongation at break of the samples with MWCNTs by 32%. The electric field also increased the ultimate tensile strength of the MWCNT reinforced nanocomposites by 42%. An increase of over 20% in the ultimate tensile strength of in situ dispersed MWCNT nanocomposites over the pure polymer material was observed. Finally, it was demonstrated that the magnitude and direction of the electrical conductivity of MWCNT nanocomposites can be engineered through the application of in situ electric fields during 3D printing. An increase of 50% in the electrical conductivity was observed when MWCNTs were introduced, while the application of the electric field further improved the electrical conductivity by 26%. The presented results demonstrated the feasibility of tuning both electrical and mechanical properties of MWCNT reinforced polymer nanocomposites using in situ electrical field-assisted 3D printing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47600.     

Sonochemical hybridization of carbon nanotubes with gold nanoparticles for the production of flexible transparent conducing films

We have demonstrated the fabrication of flexible, transparent, conducting multiwalled carbon nanotube (MWCNT)/gold nanoparticle hybrid films with improved optoelectronic properties by combining the ionic liquid-assisted sonochemical method (ILASM) for hybrid synthesis with the vacuum filtration (VF) method for thin film preparation. Au nanoparticles (NPs) with diameters of 10.3 ± 1.5 nm were uniformly distributed onto the sidewalls of MWCNTs through ILASM, and flexible, transparent, conducting films of Au/MWCNT hybrids (HBs) were reproducibly fabricated by the VF method. In particular, the sheet resistance of Au-MWCNT-HB films was more than 2-fold lower than the sheet resistance of pristine MWCNT films due to the well-interconnected three-dimensional nanotube network structure and the synergistic effect of hybridization of MWCNTs with Au-NPs.     

Influence of silane concentration on the silanization of multiwall carbon nanotubes

The relationship between the concentration of silane, the degree of surface coverage and the functionalization of multiwall carbon nanotubes (MWCNTs) upon silanization is experimentally investigated. MWCNT silanization is conducted using a γ-methacryloxypropyltrimethoxy silane varying its concentration with respect to the weight of the MWCNTs from 3.5% to 1000% (10×). Physicochemical characterization of the MWCNTs points out that the optimum range of silane concentration required to generate adequate surface coverage on the MWCNTs is between one and two times the weight of the MWCNTs. This optimum range of silane concentration is further confirmed by mechanical testing of silanized MWCNT/vinyl ester polymer composites.     

Mechanical and thermal properties of polyphenylene sulfide/multiwalled carbon nanotube composites

Polyphenylene sulfide (PPS)/multiwalled carbon nanotube (MWCNT) composites were prepared using a melt‐blending procedure combining twin‐screw extrusion with centrifugal premixing. A homogeneous dispersion of MWCNTs throughout the matrix was revealed by scanning electron microscopy for the nanocomposites with MWCNT contents ranging from 0.5 to 8.0 wt %. The mechanical properties of PPS were markedly enhanced by the incorporation of MWCNTs. Halpin‐Tsai equations, modified with an efficiency factor, were used to model the elastic properties of the nanocomposites. The calculated modulus showed good agreement with the experimental data. The presence of the MWCNTs exhibited both promotion and retardation effects on the crystallization of PPS. The competition between these two effects results in an unusual change of the degree of crystallinity with increasing MWCNT content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanism of cone-shaped carbon nanotube bundle formation by plasma treatment

Formation of the cone-shaped multi-walled carbon nanotube (MWCNT) bundles was investigated with the consideration of the induced dipole moments of the MWCNTs interaction under the ion irradiation which is accelerated by the applied sheath electric field for the various argon, hydrogen, nitrogen, and oxygen plasmas. Vertically grown MWCNTs were irradiated by energetic ion whose energy and dose were controlled by the sheath formed on the MWCNT substrate. Plasma irradiation was carried out in a downstream region separated from the plasma source region, providing that the irradiated ion density and energy could be controlled precisely with the sheath electric field. In argon and hydrogen plasmas, the cone-shaped MWCNT bundle was not fabricated, while it was formed successfully in nitrogen and oxygen plasmas. Especially, the oxygen plasma was the most effective in the formation of the bundle. The mechanism of the bundle formation could be explained by a model explaining the interaction between the induced dipole moment of the MWCNT and the sheath electric field. For the nitrogen and oxygen plasma irradiated MWCNT, the induced dipole moment could be enhanced by C-N and C-O bonds so the size of the bundle is proportional to the ion irradiation and the sheath electric field.     

Enhancement in mechanical properties of multiwalled carbon nanotube‐reinforced epoxy composites: Crosslinking of the reinforcement with the matrix via diamines

In this study, the effect of diamine molecular structure, attached to the multiwalled carbon nanotubes (MWCNTs), on the interfacial interactions of the MWCNTs and the epoxy matrix was studied. Pristine MWCNTs were successfully functionalized with multiple aliphatic and aromatic diamines. It has been found that, compared to aliphatic molecules, aromatic diamines can yield higher functionalization degree, due to higher activity and longer half‐life of aromatic intermediates. However, at the same functionalization degree, the aliphatic ligands were more successful in reacting with epoxy chains and forming covalent bonds between the MWCNTs and the matrix. Considerable improvements were achieved in the mechanical properties of functionalized MWCNT‐reinforced epoxy composites in comparison with the pristine MWCNT‐reinforced composites. Fractography observations revealed distinct differences in the failure modes of reinforced composites after functionalization of the MWCNTs with diamines. POLYM. ENG. SCI., 59:1905–1910, 2019. © 2019 Society of Plastics Engineers     

Multi-walled carbon nanotube/polyimide composite film fabricated through electrophoretic deposition

Multi-walled carbon nanotube (MWCNT)/polyimide composite films were fabricated through electrophoretic deposition (EPD) of MWCNT-polyamic acid colloidal suspension which was derived from carboxylated-MWCNTs and poly(pyromellitic dianhydride-co-4,4′-oxydianiline) (PMDA-ODA). Under electric field, both negatively charged MWCNTs and PMDA-ODA colloid particles migrate onto a positively charged anode simultaneously, and are converted to a coherent MWCNT/polyimide composite film in the ensuing imidization reaction. Uniform dispersion of MWCNTs in the composite film was observed using transmission electron microscopy. The thickness of the prepared composite film can be tuned by varying processing conditions such as deposition time and anode conductivity. The electrical conductivity of the composite film increased with increasing the concentration of MWCNTs in EPD suspension. The mechanical reinforcement of polyimide using MWCNTs was evaluated by tensile testing and nanoindentation testing.