Improving the electrical conductivity of multi-walled carbon nanotube networks by H ion beam irradiation

Transparent multi-walled carbon nanotube (MWCNT) networks were irradiated by Ar and H ion beams at 800 K which increased the electrical conductivities of the networks. For networks with transmittances between 40% and 65% at 550 nm, the conductivities could be doubled by H ion irradiation. This increase is ascribed to the formation of covalent bond cross-links between ion irradiated MWCNTs. Moreover, the effect was higher for H ion irradiation than for Ar ion irradiation. This difference is because the damage of H ion irradiation to MWCNTs is weaker than that of Ar ion irradiation.     

Raman study of carbon nanotube purification using atmospheric pressure plasma

Multiwalled carbon nanotubes (MWCNTs) were treated with an atmospheric pressure plasma source using an argon/water mixture. Optical emission diagnostics has shown that hydroxyl radicals (OH) were the major reactive species in the plasma. The structural changes in MWCNTs were monitored by micro-Raman spectroscopy. The observed variation of the D and G band intensity ratio and position dispersion with plasma treatment time was ascribed to the change in structural disorder on MWCNT surfaces. Scanning electron microscopic study showed that some defects can be induced in MWCNTs during plasma treatment. Results of thermogravimetric analysis indicated that atmospheric pressure OH plasma is as effective as traditional wet methods for purifying MWCNTs.     

Comparative study of gamma and ion beam irradiation of polymeric nanocomposite on electrical conductivity

Poly(vinyl alcohol) (PVA) was used to prepare nanocomposites of multi‐wall carbon nanotubes (MWCNT) and functionalized carbon nanotubes (MWCNT‐NH₂) in existence of 2‐carboxyethyl acrylate oligomers (CEA). Radiation‐induced crosslinking of the prepared matrix was carried out via gamma and ion beam irradiation. A comparative study of gamma and ion beam irradiation effect on the electrical conductivity of nanocomposite was conducted. The gelation of the gamma irradiated matrix outperforms the ion beam irradiated matrix. The order of gelation is PVA > (PVA/CEA) > (PVA/CEA)‐MWCNT > (PVA/CEA)‐MWCNT‐NH₂. There is a significant reduction in the swelling of the nanocomposite. The formation of nanocomposites was confirmed by scanning electron microscopy, energy‐dispersive X‐ray (EDX) and FTIR examinations. The direct current electrical properties of PVA/nanocomposites are examined at room temperature by applying electric voltage from 1 to 20 V. The results revealed that the electrical conductivity is increased by adding the carbon nanotubes and irradiation by gamma and ion beam. At an applied electric voltage 20 V, in the electrical conductivity of the unirradiated PVA was from 9.20 × 10^?8 S cm^?1. After adding MWCNT an increase up to 4.70 × 10^?5 S cm^?1 was observed. While after ion beam irradiation, a further increase up to 9.30 × 10^?5 S cm^?1 was noticed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46146.     

Surface modification of tetrafluoroethylene–perfluoroalkyl vinylether copolymer (PFA) by plasmas for copper metallization

Tetrafluoroethylene–perfluoroalkyl vinylether copolymer (PFA) sheet surfaces were modified with argon, helium, oxygen, and hydrogen plasmas. How the four plasmas modified the PFA sheet surfaces was investigated. All plasmas modified the PFA surfaces and at the same time initiated degradation of the PFA polymer chains. The balance between modification and degradation was strongly influenced by the magnitude of the discharge current in the plasmas. Efficiency of the plasmas in modification was hydrogen plasma > oxygen plasma > argon plasma > helium plasma. The modification involved defluorination of CF₂ carbons into CHF and CH₂ carbons and oxidation into O? CH₂, O? CHF, and O? CF₂ groups. The surface‐modification technique (a combination of hydrogen plasma treatment and silane coupling treatment) proposed in this study was applied for copper metallization of the PFA surface. The utility of the technique was confirmed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1087–1097, 2002     

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.     

Ion dynamics in plasma processing for the fabrication of ultrafine structures

The flux, energy and angular distribution of ions generated from inductively coupled argon plasma were measured, using a gridded retarding field ion analyzer, to investigate the dynamics of ions in the plasma. The ion flux and the ion density at the sheath edge were found to increase with power, but to decrease with pressure. The ion energy was modulated, showing two peaks in the argon plasma, because the ratio of the ion transit time to the rf period was less than or comparable to unity. The peak, mean, minimum, and maximum ion energy decreased with increasing pressure, but were nearly constant as power was varied. The ion angular distributions had a Gaussian distribution peaked at zero angle from surface normal. The full-width-at-half-maximum was increased with increasing both power and pressure. The ion temperature was readily obtained from the ion angular distributions, and the value was in the range of 0.08–0.14 eV, agreeing with typical ion temperature values measured previously in inductively coupled plasmas.     

C60 encapsulation inside single-walled carbon nanotubes using alkali-fullerene plasma method

It is reported that alkali-fullerene plasmas consisting of positive alkali-metal ions, negative fullerene ions, and residual electrons are effective in encapsulating fullerenes inside single-walled carbon nanotubes (SWNTs). When positive or negative bias-voltages are applied to SWNTs in plasmas, accelerated negative fullerene or positive alkali-metal ions are irradiated to the SWNTs through the plasma sheath, respectively. Field emission gun transmission electron microscopy (FEG-TEM) clearly shows that drastic structural modifications such as severe bending of SWNT bundles, tube dislocation, and tube tip termination take place after the ion irradiation. Energy dispersive X-ray spectrometry (EDS) confirms the existence of the alkali-metal elements in the sample after the alkali-metal irradiation. In addition to this, the SWNTs encapsulating fullerene molecules are directly observed after only 1 h fullerene-ion irradiation. These results suggest that our experimental system could permit us to intercalate not only fullerenes but also other elements inside the SWNTs by the applied-bias control. Raman scattering spectroscopy is also adopted for the purpose of evaluating pure SWNTs and fullerene encapsulated SWNTs.     

Improved electrical conductivity of very long multi-walled carbon nanotube bundle/poly (methyl methacrylate) composites

Very long and highly dispersible multi-walled carbon nanotube (MWCNT) bundles were synthesized in large quantity by catalytic chemical vapor deposition, and their structural and electrical properties were characterized. It was found that the MWCNTs could be synthesized with either bundled (long-aligned) or short-entangled structure depending on the catalyst system. The aligned MWCNTs were found to be more conductive and more dispersible than the entangled ones. The MWCNT/poly (methyl methacrylate) composites were prepared using both entangled and aligned MWCNTs. The aligned MWCNTs were found to give the composite higher electrical conductivity, which might be attributed to long length and high dispersibility. It was further found that the longer the MWCNT bundle, the higher electrical conductivity of the composite.     

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 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.     

Design of a multi-walled carbon nanotube field emitter with micro vacuum gauge

The variation of vacuum level inside a field emission device when electron is emitted from multi-walled carbon nanotubes (MWCNTs) by electric field was measured where MWCNT gauge packaged with a vacuum device was used to measure the degree of a vacuum until the end of the vacuum device life. It was found that the electrical properties of MWCNTs altered with the degree of a vacuum. We fabricated MWCNT gauge which were printed and pasted by the screen printer. In this paper, we report the successful detection of the ionization of gases in vacuum state.     

Structure and properties of metal-free conductive tracks on polyethylene/multiwalled carbon nanotube composites as obtained by laser stimulated percolation

The fabrication and characterization of conductive tracks by laser irradiation on non-conductive multiwalled carbon nanotube/polyethylene (MWCNT/HDPE) composites is reported. Along the irradiated paths the percolation of MWCNTs is occurring, as demonstrated by field emission scanning electron and atomic force microscopies. An increment of the track conductivity of several orders of magnitude is documented by single pass Kelvin probe force and current sensing atomic force microscopies, together with electrical measurements. The structure of conductive paths has been estimated by secondary electron charge contrast imaging.The investigation has been developed from basic characterization up to industrial scale manufacturing. The method is fast, flexible and innovative, because: (i) highly adherent tracks of any selected pattern on a low cost material can be obtained, (ii) the tracks are metal-free, a fact rendering the composite fully recyclable and (iii) the irradiated materials have application for electrical signals transport; (iv) the tracks are also characterized by piezoresistive properties so allowing their employment as pressure sensors.     

Binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] nanocomposites: formation, characterization and catalytic performance in partial ethanol oxidation

Cuprous oxide agglomerates composed of 4-10 nm Cu2O nanoparticles were deposited on multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNTs to give binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] composites. Di-aqua-bis[2-(methoxyimino)propanoato]copper Cu[O2CCCH3NOMe](2)·2H2O 1 in DMF was used as single source precursor for the deposition of nanoscaled Cu2O. The precursor decomposes either in air or under argon to yield CuO2 by in situ redox reaction. Thermogravimetric coupled mass spectroscopic analysis (TG-MS) of 1 revealed that methanol formed during the decomposition of 1 acts as a potential in situ reducing agent. Scanning electron microscopy (SEM) of the binary [Cu2O/MWCNT] nano-composite shows an increase of cuprous oxide loading depending on the precursor amount, along the periphery of the MWCNTs as well as formation of larger particle agglomerates. Transmission electron microscopy (TEM) of the sample shows crystalline domains of size 4-10 nm surrounded by an amorphous region within the larger particles. SEM and TEM of ternary [Cu2O/ZnO/MWCNT] clearly reveal that Cu2O nanoparticles are primarily deposited on ZnO rather than on MWCNTs. The catalytic activities of the [Cu2O/MWCNT] and [Cu2O/ZnO/MWCNT] binary and ternary composites were studied for the selective partial oxidation of ethanol to acetaldehyde with molecular oxygen. While using binary [Cu2O/MWCNT] (13.8 wt% Cu) as catalyst, acetaldehyde was obtained with a yield of 87% at 355 °C (selectivity 96% and conversion 91%). When nanoscale ZnO is present, the resulting [Cu2O/ZnO/MWCNT] composite shows preferential hydrogen and CO2 formation due to the fact that the dehydrogenation and total oxidation pathway is more favoured compared to the binary composite. Significant morphological changes of the catalyst during the catalytic process were observed.     

SURFACE MODIFICATIONS AND ADHESION OF VULCANIZED SBR RUBBER TREATED WITH RF PLASMAS OF DIFFERENT GASES

The surface modifications produced by treatment of a synthetic vulcanized styrene-butadiene rubber (R1) with oxidizing (oxygen, air, carbon dioxide) and nonoxidizing (nitrogen, argon) RF plasmas have been assessed by ATR-IR and XPS spectroscopy, SEM, and contact angle measurements. The effectiveness of the treatment depended on the gas atmosphere used to generate the RF plasma. In general, acceptable adhesion values of treated R1 rubber were obtained for all plasmas, except for the nitrogen plasma treatment during 15?min, due to the creation of weak layers of low molecular weight moieties on the outermost R1 rubber layer. A toluene wiping of the 15?min N₂-plasma–treated R1 rubber surface removed those moieties, and increased adhesion was obtained. On the other hand, the air, carbon dioxide, and oxygen plasmas produced ablation of the R1 rubber surface, whereas mechanical degradation was not produced by treatment with the Ar plasma.     

Effect of irradiation on mechanical and structural properties of ethylene vinyl acetate copolymers hollow fibers

Effect of irradiation on mechanical and structural properties of ethylene vinyl acetate copolymers (EVA) hollow fibers was studied by the tests such as determination of gel content, density, tensile, FTIR, SEM, and DMA. These effects were discussed based on dose and irradiation environment. The results of gel content depicted that irradiated EVA in ambient conditions had tendency to chain scission while the crosslinking overcame in irradiated samples under nitrogen. Density insignificantly enhanced with irradiation dose. In tensile test, irradiation induced increase in tensile strength and decrease in elongation at break (especially in samples irradiated in nitrogen). Also, changing in layer orientation could be observed by SEM images. In addition, irradiation caused altering peak intensity in FTIR spectrum. DMA results demonstrated that irradiation broaden the elastic zone. Totally, irradiation enhances features especially in irradiated EVA18 in nitrogen. Since, according to stabilization of induced deformation and improvement of mechanical properties (that created by radiation), the irradiated samples can be used in different applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

SURFACE MODIFICATIONS AND ADHESION OF VULCANIZED SBR RUBBER TREATED WITH RF PLASMAS OF DIFFERENT GASES

The surface modifications produced by treatment of a synthetic vulcanized styrene-butadiene rubber (R1) with oxidizing (oxygen, air, carbon dioxide) and nonoxidizing (nitrogen, argon) RF plasmas have been assessed by ATR-IR and XPS spectroscopy, SEM, and contact angle measurements. The effectiveness of the treatment depended on the gas atmosphere used to generate the RF plasma. In general, acceptable adhesion values of treated R1 rubber were obtained for all plasmas, except for the nitrogen plasma treatment during 15 min, due to the creation of weak layers of low molecular weight moieties on the outermost R1 rubber layer. A toluene wiping of the 15 min N₂-plasma-treated R1 rubber surface removed those moieties, and increased adhesion was obtained. On the other hand, the air, carbon dioxide, and oxygen plasmas produced ablation of the R1 rubber surface, whereas mechanical degradation was not produced by treatment with the Ar plasma.     

X-Ray photoemission study of plasma modified polyethylene surfaces

X-Ray photoelectron spectroscopy (XPS) was used to determine plasma induced chemical species on the surface of polyethylene (PE). Argon plasmas were found to have no detectable chemical effect on the PE surface, whereas oxygen and nitrogen plasmas created new chemical species which altered the chemical reactivity of the PE surface. Oxygen plasmas were found to react more rapidly with the PE surface than nitrogen plasmas. The degree of incorporation of new chemical species in the near surface region is approximately 20 at. % at the saturation level for both oxygen and nitrogen plasmas. Core level spectra for oxygen and nitrogen plasma treated PE suggest the formation of primarily C-O-C species in the former and C-N species in the latter. Angle-resolved XPS measurements indicate that the depth of incorporation of new chemical species is confined to the top 25 A.     

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.     

Dielectric properties of irradiated polymer/multiwalled carbon nanotube and its amino functionalized form

The polymer/multiwalled carbon nanotube [poly(vinyl alcohol) (PVA)/carboxyethyl acrylate (CEA)]‐multiwalled carbon nanotube (MWCNT) and its amino functionalized (PVA/CEA)‐MWCNT‐NH₂ nanocomposite samples were successfully synthesized by the chemical method in the form of films. The samples were irradiated with gamma‐ray doses of 50 and 100 kGy and with ion beam fluence of 2.5 × 10¹⁸ and 3.75 × 10¹⁸ ions cm^?2. The prepared nanocomposite samples were characterized using X‐ray diffraction and thermogravimetric analysis. The X‐ray diffraction and thermogravimetric analysis confirm the existence of the chemical crosslinking occurred in the polymer compositions. The AC electrical conductivity, electrical modulus, dielectric constant, and dielectric loss in the frequency range 10²–10⁶ Hz are measured at room temperature. The electrical conductivity is increased with MWCNT doping, gamma‐irradiation, and by ion beam irradiation. A comprehensive analysis of the results revealed that dielectric properties are improved due to the induced physicochemical changes and conductive networks induced by ion beam irradiation. The behavioral effect of these embedded nanoparticles in a PVA matrix on the microstructural, dielectric, and electric properties is analyzed for possible device applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46647.     

Improving Bonding to Piezoelectric Poly(vinylidene fluoride) for Sensor Applications

Argon, oxygen, nitrogen and ammonia plasmas and an acid etch pretreatment were performed on uniaxially stretched piezoelectric poly(vinylidene fluoride) film in order to improve wettability and bonding. Oxygen plasma was found to be too harsh, but nitrogen and argon plasmas improved wettability and resulted in a seven-fold increase in 180° peel strengths. However, this improvement in peel strength was accompanied by a 90% decrease in the piezoelectric properties of the polymer. The acid etch yielded contact angles similar to those of the plasma treated material, and improved peel strengths some twelve times over that of the untreated film. Significantly, no piezoelectric loss resulted from the acid etch.