Introduction of amino functionalities on ethylene-co-tetrafluoroethylene film surfaces by NH3 plasmas

In order to form active sites for grafting amino groups, a predominant elimination of fluorine atoms from fluoropolymers such as poly(tetrafluoroethylene), ethylene-co-tetrafluoroethylene co-polymer (ETFE) and poly(vinylidene fluoride) was carried out using the plasma irradiation technique, and the possibility that amino functional groups could be formed on the fluoropolymer surfaces was investigated. The NH₃ plasma irradiation led to considerable elimination of fluorine atoms from the fluoropolymers, as well as grafting of nitrogen functionalities. The formation of nitrogen-containing groups was strongly influenced by the magnitude of the W/FM parameter, and the NH₃ plasma operated at a low W/FM parameter of 79 MJ/kg was found to be preferable for the surface modification process. XPS spectra for the NH₃ plasma-modified surfaces showed that the NH₃ plasma attacked predominantly CF₂—CF₂ sequences rather than CH₂—CH₂ sequences in the ETFE polymer. The primary amino groups formed on the ETFE film surfaces were determined by fluorescence measurements. The concentration of the amino groups formed on the surfaces was not constant but varied according to the W/FM parameter. NH₃ plasma operated at a low W/FM parameter of 79 MJ/kg was found to be preferable in grafting amino groups on the ETFE film surfaces.     

Amino group introduction onto multiwall carbon nanotubes by NH3/Ar plasma treatment

Multiwall carbon nanotubes (MWCNTs) were modified by using a microwave-excited NH₃/Ar surface-wave plasma. Changes in the atom composition and structural properties of the modified MWCNTs were studied as a function of gas flow rate, treatment time, microwave power, and bias voltage by using X-ray photoelectron spectroscopy and Raman spectroscopy. The results suggest that nitrogen-containing groups were introduced on the surfaces of the MWCNTs and that the concentration of primary amino groups was affected by gas flow rate, microwave power, and bias voltage. The contact angle of water on the modified MWCNTs decreased and the hydrophilicity of the modified MWCNTs was improved. The surface morphology and structure of the MWCNTs were not destroyed by the plasma treatment.     

Surface modification of graphite encapsulated iron nanoparticles by plasma processing

The graphite encapsulated iron nanoparticles were fabricated by using arc discharge method. The synthesized nanoparticles were pre-treated by an inductively-coupled RF Ar plasma and then post-treated by NH₃ plasma under various gas pressures and treatment times. Analyses of XPS spectra have been carried out to study the effect of the plasma treatment on the surface modification of nitrogen-containing groups. The morphological changes of the particles surface by plasma treatment have also been analyzed by using HR-TEM. Present results show that the highest values of N/C atomic ratio of 5.4 % is obtained by applying 10 min of Ar plasma pre-treatment and 2 min of NH₃ plasma post-treatment conducted in RF power of 80 W and gas pressure of 50 Pa.     

Surface modification of PET films by pulsed argon plasma

The rf power was modulated (discharge on‐time of 10 μs and discharge off‐time of 50–500 μs), for pulsed argon (Ar) and oxygen (O₂) plasmas used to irradiate PET film surfaces to modify the film surfaces. From data regarding the contact angle for the modified PET film surfaces and chemical analyses with XPS, effects of the rf power modulation on the surface modification are discussed. The pulsed Ar and O₂ plasmas are effective in modification of the PET film surface. There is no difference in the contact angle between the pulsed plasma and the continuous plasma. Furthermore, the pulsed Ar plasma is advantageous in formation of hydroxyl groups on the PET film surfaces. The rf power modulation has a possibility to modify into peculiar surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2845–2852, 2002     

Pyrolysis of poly-l-leucine under combustion-like conditions

The protein poly-l-leucine has been used as a model compound for the nitrogen in biomass fuels. It was pyrolysed in a fluidised bed at 700 and 800 °C and the pyrolysis gases were analysed with a FT-IR spectrometer. HCN, NH₃ and HNCO were identified as the main nitrogen-containing species, while neither NO nor N₂O were found among the pyrolysis gases. At 700 °C, as much as 58% of the nitrogen content was converted into HCN and 31% into NH₃. The HCN/NH₃ ratio increased from about 1.9 at 700 °C to above 2.2 at 800 °C. Pyrolysis of another protein, poly-l-proline, at 800 °C gave a HCN/NH₃ ratio close to 10. This revealed that the protein's amino acid composition has a marked impact on the composition of the pyrolysate.     

Surface functionalization of SBA-15 nanorods for anticancer drug delivery

SBA-15 nanorods with high surface area (1010 m² g⁻¹) were functionalized by post grafting method with three different alkoxysilanes including (3-aminopropyl) triethoxysilane (APTES), 3-[bis(2-hydroxyethyl)amino] propyl triethoxysilane (HAPS) and 3-[2-(2-aminoethylamino) ethylamino] propyl trimethoxysilane (AEPS). The prepared materials were used as nanocarriers for an anticancer drug (gemcitabine). The obtained samples were characterized by SAXS, elemental analysis, TGA, N₂ adsorption/desorption, SEM, TEM, FTIR and UV spectroscopies. The adsorption and release properties of all samples were investigated. It was found that the surface functionalization increases the interaction between the carrier and gemcitabine and results in the loading enhancement of the drug. In addition, the adsorption of gemcitabine on the modified mesoporous matrix depends on the type and the amount of alkoxysilanes groups. The maximum content of the deposited drug in the modified SBA-15 nanorods is close to 22 wt.%. The rate of the drug release from the modified samples containing NH₂ groups on their surfaces is pH dependent.     

Improved adhesion of poly(tetrafluoroethylene) by NH3-plasma treatment

—Surface modification of poly(tetrafluor oethylene) (PTFE) by NH₃-plasma treatment was investigated by means of contact angle measurement, XPS, and ATR FT/IR spectroscopy. The modified surfaces were adhesively bonded to nitril rubber. The NH₃-plasma irradiation made PTFE surfaces hydrophilic. The contact angle of water on the modified PTFE surface was 16 deg, and the surface energy was 62-63 mJ/m². The NH₃-plasma irradiation improved adhesion between PTFE and nitril rubber using a phenol-type adhesive. The peel strength of the joints reached 8.1 × 10³ N/m. Carbonyl and amido groups were created on PTFE surfaces by the NH₃-plasma irradiation. The mechanism of the improvement of adhesion by the NH₃-plasma irradiation is discussed.     

Plasma etching treatment for surface modification of boron-doped diamond electrodes

Boron-doped diamond (BDD) thin film surfaces were modified by brief plasma treatment using various source gases such as Cl₂, CF₄, Ar and CH₄, and the electrochemical properties of the surfaces were subsequently investigated. From X-ray photoelectron spectroscopy analysis, Cl and F atoms were detected on the BDD surfaces after 3 min of Cl₂ and CF₄ plasma treatments, respectively. From the results of cyclic voltammetry and electrochemical AC impedance measurements, the electron-transfer rate for Fe(CN)₆^3−/4− and Fe^2+/3+ at the BDD electrodes was found to decrease after Cl₂ and CF₄ plasma treatments. However, the electron-transfer rate for Ru(NH₃)₆^2+/3+ showed almost no change after these treatments. This may have been related to the specific interactions of surface halogen (C-Cl and C-F) moieties with the redox species because no electrical passivation was observed after the treatments. In addition, Raman spectroscopy showed that CH₄ plasma treatment of diamond surfaces formed an insulating diamond-like carbon thin layer on the surfaces. Thus, by an appropriate choice of plasma source, short-duration plasma treatments can be an effective way to functionalize diamond surfaces in various ways while maintaining a wide potential window and a low background current.     

Poly-dimethylsiloxane (PDMS) based micro-reactors for steam reforming of methanol

A miniaturized methanol steam reformer with a serpentine type of micro-channels was developed based on poly-dimethylsiloxane (PDMS) material. This way of fabricating micro-hydrogen generator is very simple and inexpensive. The volume of a PDMS micro-reformer is less than 10 cm³. The catalyst used was a commercial Cu/ZnO/Al₂O₃ reforming catalyst from Johnson Matthey. The Cu/ZnO/Al₂O₃ reforming catalyst particles of mean diameter 50-70 μm was packed into the micro-channels by injecting water based suspension of catalyst particles at the inlet point. The miniaturized PDMS micro-reformer was operated successfully in the operating temperatures of 180-240 °C and 15%-75% molar methanol conversion was achieved in this temperature range for WHSV of 2.1-4.2 h⁻¹. It was not possible to operate the micro-reformer made by pure PDMS at temperature beyond 240 °C. Hybrid type of micro-reformer was fabricated by mixing PDMS and silica powder which allowed the operating temperature around 300 °C. The complete conversion (99.5%) of methanol was achieved at 280 °C in this case. The maximum reformate gas flow rate was 30 ml/min which can produce 1 W power at 0.6 V assuming hydrogen utilization of 60%.     

Formation of NOx precursors during the pyrolysis of coal and biomass. Part V. Pyrolysis of a sewage sludge

A sewage sludge sample from a wastewater treatment plant in China was pyrolysed in a fluidised-bed/fixed-bed reactor and in a fluidised-bed/tubular reactor. HCN was found to be the main NO_x precursor, representing up to about 80% of the nitrogen present in the sludge. The thermal cracking of volatiles is the main route of HCN formation. NH₃ was also an important NO_x precursor formed during the pyrolysis of the sewage sludge. The experimental results indicate that there are at least two distinctive stages of NH₃ formation during the pyrolysis of the sewage sludge at a fast heating rate. The formation of NH₃ at temperatures lower than 400-500 °C is at least partly due to the amino structures in the sludge. The reactions of volatiles in the gas phase make negligible contributions to the observed NH₃ yield.     

Oxygen functionalization of multiwall carbon nanotubes by Ar/H2O plasma treatment

To increase the applicability of multiwall carbon nanotubes (MWCNTs), oxygen-containing functional groups were introduced on the surfaces of MWCNTs by using microwave-excited Ar/H₂O surface-wave plasma. X-ray photoelectron spectroscopy and Raman spectroscopy were used to determine dependencies of Ar/H₂O gas partial pressure, treatment time and microwave power. The oxygen functionalization of MWCNTs by plasma can be achieved very rapidly, about 10 min. The C-O and O-C═O fractions firstly increase and then decrease with increasing Ar partial pressure. The C-O and O-C═O fractions increase with increasing microwave power from 400 W to 700 W. A slight increase of the R (I_D/I_G ratio) value for the treated MWCNTs indicated disordering in the surface microstructure of MWCNTs coincident with the introduction of surface oxygen. The oxygen-containing groups introduced on the surfaces of MWCNTs by plasma treatment are hydrophilic. The dispersion of plasma treated MWCNTs is therefore improved.     

Plasma surface modification of poly(phenylene sulfide) films for copper metallization

Poly(phenylene sulfide) (PPS) films were modified by Ar, O₂, N₂ and NH₃ plasmas in order to improve their adhesion to copper metal. All four plasmas modified the PPS film surfaces, but the NH₃ plasma modification was the most effective in improving adhesion. The NH₃ plasma modification brought about large changes in the surface topography and chemical composition of the PPS film surfaces. The peel strength for the Cu/plasma-modified PPS film systems increased linearly with increasing surface roughness, R _a or R _rms, of the PPS film. The plasma modification also led to considerable changes in the chemical composition of the PPS film surfaces. A large fraction of phenylene units and a small fraction of sulfide groups in the PPS film surfaces were oxidized during the plasma modification process. Nitrogen functional groups also were formed on the PPS film surfaces. The NH₃ plasma modification formed S—H groups on the PPS film surfaces by reduction of S—C groups in the PPS film. Not only the mechanical interlocking effect but also the interaction of the S—H groups with the copper metal may contribute to the adhesion of the Cu/PPS film systems.     

Coupling and reforming of methane by means of low pressure radio-frequency plasmas

Non-oxidative coupling of CH₄/H₂ mixtures was carried out by means of radio frequency (rf) glow discharges for the first time. A central composite design was employed to determine the best experimental conditions for methane transformation into higher hydrocarbons and to fit the experimental data. rf power was the factor showing the highest effect on the results while CH₄/H₂ mole ratio showed the lowest. Conversion was 46.4% at 100 W, 0.07 mbar and CH₄/H₂ mole ratio of 1/2. Selectivity was 56.9% for C₂, 6.9% for C₃, and 36.2% for C₄ hydrocarbons. Least squares fits of quadratic equations yielded approximating functions permitting to predict results of random experiments with errors of about 5%. The same rf system was used for the reforming of methane with CO₂, O₂, and steam plasmas, respectively. The highest oxidation was observed with oxygen whilst steam plasma produced the best results. H₂/CO mole ratio was adjusted by setting specific experimental parameters of the latter. CO₂ free synthesis gas was produced at higher H₂O and CH₄ flow rates, i.e. 0.8 mmol/h and higher power, i.e. 100 W. CO₂ and CO free H₂ was produced at 0.3 and 0.6 mmol/h flow rates of H₂O and CH₄, respectively, and 50 W.     

Field emission properties of carbon nanotubes synthesized by capillary type atmospheric pressure plasma enhanced chemical vapor deposition at low temperature

Carbon nanotubes (CNTs) were grown using a modified atmospheric pressure plasma with NH₃(210 sccm)/N₂(100 sccm)/C₂H₂(150 sccm)/He(8 slm) at low substrate temperatures (?500 °C) and their physical and electrical characteristics were investigated as the application to field emission devices. The grown CNTs were multi-wall CNTs (at 450 °C, 15-25 layers of carbon sheets, inner diameter: 10-15 nm, outer diameter: 30-50 nm) and the increase of substrate temperature increased the CNT length and decreased the CNT diameter. The length and diameter of the CNTs grown for 8 min at 500 °C were 8 μm and 40 ± 5 nm, respectively. Also, the defects in the grown CNTs were also decreased with increasing the substrate temperature (The ratio of defect to graphite (I_D/I_G) measured by FT-Raman at 500 °C was 0.882). The turn-on electric field of the CNTs grown at 450 °C was 2.6 V/μm and the electric field at 1 mA/cm² was 3.5 V/μm.     

Plasma modification of poly(oxybenzoate-co-oxynaphthoate) film surfaces for copper metallization

Poly(oxybenzoate-co-oxynaphthoate) (POCO) film surfaces were modified by four plasma gases, Ar, O₂, N₂ and NH₃, and the effects of the plasma modification were investigated in order to understand the adhesion with copper metal. The Ar, O₂, N₂ and NH₃ plasmas converted the POCO surfaces from hydrophobic to hydrophilic. The effect of the plasma on the hydrophilic modification was in the order: Ar plasma > O₂ plasma > N₂ plasma > NH₃ plasma. The plasma modification contributed to the adhesion between the deposited copper metal and the POCO film. The NH₃ plasma was most effective in improving the adhesion, and the Ar plasma was ineffective. The plasma-modified POCO film surfaces showed quite different C_ls spectra from that of the original POCO film. There were large differences in the C_ls and N_ls spectra between the NH₃ and Ar plasma modifications. The NH₃ plasma modification did not show C_ls component #5 due to π–π^* shake-up satellite, but the Ar plasma modification did show this component. Furthermore, NH₃ plasma modification led to a new N_ls spectrum. The plasmas caused etching of the POCO film surfaces, and the etch rate depended on what plasma was used and how much RF power was used. The NH₃ plasma-modified POCO film surface showed a larger R _a (25.5 nm) than the other plasma-modified surfaces (R _a = 16.4–19.0 nm), which were comparable to that of the original surface (R _a = 14.8 nm). The NH₃ plasma led to a highly-undulated surface, and the other plasmas did not alter the surface roughness. The roughened surfaces showed contribution to enhancement of the adhesion to the deposited copper metal.     

Functionalization of HDPE powder by CF4 plasma surface treatment in a fluidized bed reactor

The surface of HDPE polymer powder was fluorinated by CF₄ plasma in a fluidized bed reactor. Plasma is generated by an inductively coupled electrode at 13.56 MHz (rf) frequency, connected to an auto matching network and an rf power generator. In plasma surface fluorination, the CF₄ gas is diluted with He gas. The experimental variables are treatment time and rf power. The chemical property of the modified powder has been determined by using ESCA and FTIR. Plasma surface fluorination with the powder in a fluidized bed reactor results from the formation of CHF-CF₂, CHF-CHF and CF₂ groups. These fluorine functionalities and the fluorine atomic ratio on the surface increase with the treatment time and rf power. It has been found that the composite parameter is a good measure for determining the effect of total energy input on the plasma surface treatment of polymer powder in a fluidized bed reactor.     

Surface modification of Kevlar 149 fibers by gas plasma treatment

Kevlar 149 fibers have been surface treated with NH₃-, 0₂-, or H₂O-plasm to modify the fiber surfaces. SEM (scanning electron microscopy) is used to characterize the surface topography of fibers etched by gas plasmas. The chemical compositions and functional groups of the fiber surfaces are identified by ESCA (electron spectroscopy for chemical analysis) and SSIMS (static secondary ion mass spectroscopy), respectively. The contact angle of water on modified PPTA [poly(p-phenylene terepbthalamide)] film prepared from using Kevlar 149 fibers is also used to investigate the wettability. The results show that the etching abilities of gas plasmas are dependent on the type of gas used for plasma treatments. The contact angle data indicate that all the three gas plasma treatments are effective in rendering the surface of PPTA more hydrophilic. The ESCA analysis results show that the surface compositions of plasma-treated fibers are highly dependent on the type of gas used and treatment time. Changes in surface compositions of fibers treated by NH₃-, O₂-, and H₂O-plasma are observed. Increasing nitrogen and oxygen contents are observed for the NH₃-plasma treatment, and the O₂- and H₂O-plasma treatments, respectively. Furthermore, the incorporation of amino groups into fiber surfaces by NH₃-plasma treatment and the extensive damage of the aromatic ring and the polymer backbone by H₂O-plasma and O₂-piasma are evidenced by SSIMS.     

High anticorrosion chromate-free passive films made by Titanate and waterborne polyurethane on galvanized steel sheet

In this study, environmental friendly hybrid passive films on galvanized steel sheet were prepared from waterborne polyurethane and Titanate. The experimental results show that the optimized composition in passive solution was 30 g/L TiOSO₄, 5 g/L (NH₂)₂CS, 10 g/L NH₄F and 150 g/L WPU. The samples were dipped into passive solution for 10 s, dried at 120 °C for 15 s. Though the film's thickness is just 0.5 μm, the white rust resistance is excellent.     

Fabrication and laser behaviors of Nd:YAG ceramic microchips

Transparent Nd:YAG ceramic microchips were fabricated through the slip casting shaping directly from the slurry formed by the commercial Al₂O₃/Y₂O₃/Nd₂O₃ powders, and followed by the vacuum sintering procedure. Viscosity of the slurries, the phase evolution and the densification behavior were investigated. For the Al₂O₃/Y₂O₃/Nd₂O₃ compound slurries system, the optimal condition is 0.5 wt.% NH₄PAA dispersant and 30 wt.% solid loading at pH ≥ 8. The YAG phase started to form at 1250° C and pure YAG phase could be obtained at 1400° C. The optical in-line transmittance of the Nd:YAG ceramics with thickness of 2 mm was about 83.8% at 1064 nm and 82.5% at 400 nm, which hit the upper limit of the theoretically calculated value. For the 1.0 at.% Nd:YAG ceramic microchip, the slope efficiency was 43% for 1.0 at.% Nd:YAG ceramic pumped by 920 mW cw Ti:sapphire tunable laser, and the maximum laser output power 246 W was obtained for 2.0 at.% Nd:YAG ceramics pumped by 925 W LD.     

Fast and clean functionalization of carbon nanotubes by dielectric barrier discharge plasma in air compared to acid treatment

Multi-walled carbon nanotubes (MWCNTs) have been functionalized by a dielectric barrier discharge plasma in air and compared to those functionalized in HNO₃. The MWCNTs were prepared by chemical vapor deposition of xylene using ferrocene as a catalyst at 850 °C. Air oxidation followed by acid treatment was used to purify the MWCNTs, which were then annealed in helium. The MWCNTs were functionalized in air in a plasma reactor at room temperature. Quantitative analyses of gases evolved during the temperature programmed desorption of the functionalized nanotubes were carried out using Fourier transform infrared spectroscopy and gas chromatography. The influence of plasma parameters, including power in the range of 8-90 W and treatment time in the range of 1-9 min, on the number of the functional groups was investigated. It is shown that the extent of functionalization increases with increasing discharge power, provided that the exposure time of the MWCNTs in the plasma atmosphere does not exceed a certain period of time. Compared to acid treatment, plasma functionalization offers the advantages of much shorter treatment time, and produces less damage.