Thermoluminescence of thin polymeric films obtained in a glow discharge plasma

The thermoluminescence and radiothermoluminescence were studied of thin polymeric films produced in a glow discharge plasma. It was shown that during the formation of polymeric films in the plasma, not only radical states but also ionic states are stabilized in them. Four luminescence maxima were detected on the radiothermoluminescence curves of the films. The possible assignment of the position of these maxima on a temperature scale to the relaxational transitions in the films is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 743–747, November–December, 1988.     

Investigation of glow discharge plasma for surface modification of polypropylene

Material surface properties of polymers, plastics, ceramics and textiles can be modified by atmospheric or low‐pressure glow discharge plasma. The aim of the present work is to study the surface modification of biaxially oriented polypropylene (BOPP) film in order to improve its hydrophilic and wetting properties. In this article we used low‐pressure, low‐temperature oxygen plasma for the surface treatment of BOPP. Scanning electron microscopy indicates that plasma treatment causes mainly physical changes by creating microcraters and roughness on the surface and increasing surface friction. Attenuated total reflectance infrared spectra show oxygen‐containing groups such as ? OH at 3513 cm^?1 and C?O at 1695 cm^?1. Microscopic investigations of water droplets on BOPP (treated, untreated) show that the interfacial adhesion of treated surfaces is increased. Copyright © 2003 John Wiley & Sons, Ltd.     

Oxidation of polyethylene surface by glow discharge and subsequent graft copolymerization of acrylic acid

Plasma-induced graft copolymerization of acrylic acid, which was incorporated into PE films, was investigated here. The influence of plasma conditions such as plasma treatment gases, power, pressure, time, monomer concentration, and graft copolymerization time on polymerization yield was determined. The samples were characterized by ESCA, IR, and water contact angle. A respective chemical shift of the C1s signal of Ar or O₂ plasmatreated and untreated PE films was revealed by ESCA, in which the presence of the grafted PAAc was also verified. An increase in polymerization yield with plasma treatment duration and power was found. That the grafted copolymerization was limited to a very thin surface region was revealed by optical microscopy on the cross section of the grafted film. © 1993 John Wiley & Sons, Inc.     

Aqueous p-nitrotoluene oxidation induced with direct glow discharge plasma

A plasma induced degradation process has been studied to treat 4-nitrotoluene (4-NT) present as an aqueous pollutant. The plasma was locally generated from a glow discharge around a tip of a platinum anode in an electrolytic solution. The influence of initial pH and Fe²⁺ on the degradation was examined. Major intermediates resulting from the degradation process were identified. Amongst the aromatic intermediates, p-hydroxybenzoic acid was the predominant degradation product. The formation of oxalic acid, malic acid was also observed. The final products of degradation were NH ₄ ⁺ , NO ₃ ⁻ and CO₂. Based on the analysis of intermediates and the kinetic considerations, the degradation was shown to follow a pseudo-first order reaction hence, a possible reaction pathway was proposed.     

Enhancement of wettability in low density polyethylene films using low pressure glow discharge N2 plasma

Low pressure glow discharge nitrogen plasma has been used to improve wettability in a low density polyethylene (LDPE) film for technical applications. The plasma treatment was carried out at a power of 300 W for different exposure times in the 1–20 min range. Wettability changes were analyzed using contact angle measurements. In addition to this, plasma‐treated samples were subjected to an aging process to determine the durability of the plasma treatment. X‐ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy were used for surface characterization. The nitrogen plasma treatment considerably reduced contact angle values thus indicating an increase in surface wettability. The spectroscopic study showed presence of oxygen‐based species on the plasma‐treated samples, which are mainly generated after the plasma treatment as a consequence of air exposure. These polar species contribute to improve surface functionalization, but this is almost lost during aging due to the hydrophobic recovery process. Microscopic studies revealed that also small changes in surface roughness occurred during the plasma treatment but these are very low compared to surface activation. The results confirmed that low pressure nitrogen can be considered as an environmentally efficient process to improve wettability in low density polyethylene films. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2390–2399, 2007     

Surface oxidation of polyethylene using an atmospheric pressure glow discharge with liquid electrolyte cathode

This study investigated the action of an atmospheric pressure air glow discharge (APGD) with aqueous electrolyte cathode onto the surface of polyethylene (PE) films. Distilled water and aqueous solutions of KCl and HCl were utilized as a cathode. The surface properties of PE were characterized by contact angle measurement followed by surface free energy calculation, Fourier transform infrared by attenuated total reflectance (FTIR-ATR), and XPS. After treating the PE surface, we observed OH groups, CO groups in ester, ketone, and carboxyl groups, and CO groups in unsaturated ketones and aldehydes. For a treatment time of 20 min and a discharge current of 40 mA, atomic concentrations of O and N were 12% and 2%, respectively, under distilled water application. Modification processes were able to improve the surface free energy of PE.     

Characterization of a glow discharge plasma as a function of sampling orifice potential

Plasma diagnostic studies have been carried out on the discharge source of a commercial glow discharge quadrupole mass spectrometer. Plasma parameters were determined using an electrostatic probe with the objective of determining the dependence (if any) of these parameters on the voltage placed on an auxiliary electrode immersed in the plasma. The biased electrode utilized in this study was the sampling orifice element itself. Our results indicate that, for positive orifice voltages with respect to the grounded anode, variations in the plasma potential and ion energy can be correlated directly to the bias placed on the sampling orifice. The dependence of the electron temperature on this parameter is observed to be more complex in nature, and electron number densities show little significant variation with respect to sampling orifice bias. In addition, increased orifice voltages result in an increase in the ion signal intensity measured with the mass spectrometer. Based on the results obtained here, we feel that this increase is due primarily to an increase in ion transmission to the quadrupole arising from the increased ion energy.     

Reduction of supported noble-metal ions using glow discharge plasma

A novel plasma reduction method has been developed to reduce supported noble-metal ions without the use of any reducing chemicals. H2PtCl6, PdCl2, AgNO3, and HAuCl4 supported on nonporous TiO2 and porous gamma-Al2O3 and HZSM-5 were reduced using an Ar glow discharge plasma. Optical absorption spectra and X-ray photoelectron spectroscopy show that the supported metal ions are completely reduced to metallic species. Transmission electron microscopy shows that the prepared metals are amorphous clusters and homogeneously distributed with nanoscale sizes. X-ray diffraction also confirms that the plasma-reduced metals exist as small crystallites or amorphous clusters. Thermal annealing of plasma-reduced samples at elevated temperature transforms the clusters into crystals with a slight increase in particle sizes, but the sizes are still smaller than those of H2-reduced metals. O2 glow discharge plasma can also reduce noble-metal ions, accompanied by production of a small amount of oxides. Plasma reduction is very promising for the preparation of metal nanoparticles and supported metal catalysts.     

Surface properties of polyethylene after low-temperature plasma treatment

The effect of oxygen and ammonia plasma treatments on changes of the surface properties of linear high-density polyethylene (HDPE) was studied. Surface energies of the polymer substrates were evaluated by contact angle measurements using Lifshitz-van der Waals acid-base approach. The surface energy of untreated HDPE is mainly contributed by Lifshitz-van der Waals interactions. After 5 min of plasma treatment, hydrogen bonds are formed on the surface, which is reflected in predominant acid-base interactions. The SEM results obtained demonstrate considerable changes of the surface roughness due to different types of the plasma gas used. Evolution of oxygen- or amino-containing moieties was detected by XPS and ATR FT IR. The prepared polyethylene surfaces were used as a basic support for further fabrication of novel hybrid biocomposite sandwich structures.     

Emission spectroscopic studies of Grimm-type glow discharge plasma with argon-helium gas mixtures

The effect of argon/helium pressure ratios on the emission intensity of various Ar II lines is investigated for a Grimm-type glow discharge radiation source, operated with Ar-He mixtures. The relative intensities of the Ar II lines are altered significantly by mixing helium with argon. It is found that the population of the Ar⁺ excited states can be redistributed through He-Ar collisional energy transfer. The energy level of the He singlet metastable state (¹S₀,20.62 eV) is very important for these processes. If the excitation energy of Ar II lines is higher than that of the He singlet metastable, strong quenching of the Ar II line intensity is observed. However, when the excitation energy is slightly lower, some of the Ar II lines are enhanced by adding helium to the argon plasma. Energy exchanges between the Ar⁺ doublet term states and the He singlet metastable are favoured because the total spin remains unchanged before and after the He-Ar collisions. Furthermore, the helium mixing also exerts a great influence on the emission intensities of the elements sputtered from the cathode of the discharge lamp. The enhancement of Al I and Al II emission intensities at suitable Ar-He mixture ratios is discussed for when aluminum is employed as a cathode material.     

Modification of surface properties of high and low density polyethylene by Ar plasma discharge

Structural changes induced by Ar plasma discharge in low and high density polyethylene (LDPE and HDPE) were studied by different techniques. AFM and SEM methods were used to determine surface morphology, the changes in chemical structure were followed using FTIR and UV-vis spectroscopy. The content and the depth profile of incorporated oxygen was determined by RBS method. The degree of polymer ablation was determined gravimetrically. Standard goniometry was used to determine contact angle and to follow aging of plasma modified polymer. As a result of plasma treatment a lamellar structure or spherulites appear on the surface of HDPE and LDPE, respectively. Pronounced increase of the surface roughness is observed on HDPE contrary to LDPE. Plasma treatment for 400 s leads to the ablation of the surface layer of about 0.6 and 1 μm thick for LDPE and HDPE, respectively. Plasma treatment results in oxidation of the polymer surface layer which is more pronounced in HDPE. Concentration maximum of incorporated oxygen lies 25 nm beneath the sample surface in both polymer types. After exposure to plasma discharge carbonyl, carboxyl and amide groups were detected in the polymer surface layer together with CC bonds either in aromatic or in aliphatic structures. Immediately after the plasma treatment strong decline of the contact angle is observed, the decline being larger in HDPE. Later, in aged specimens the contact angle increases rapidly. The increase, which may be due to rearrangement of degraded structures, is stronger in the specimens exposed to plasma for longer times.     

Argon glow discharge and vapor-phase grafting of vinyl monomers on wettability of polyethylene

Argon glow discharge-induced vapor-phase grafting of vinyl monomers containing various polar pendant groups onto PE films was investigated. Relationships between the enhanced wetting properties and the level of grafting, the types of pendant groups, and the surface topographical features were established. Improved wettability of the grafted PE surfaces is attributed to both the increased surface polarity and topographical features. On AA-grafted PE surfaces with optimal wettability, microcracks, with depths of 130 ∼ 250 nm, lengths over 10 µm, and widths between 1.5 and 6.0 µm, are proved to be a topographical feature necessary for improved wettability. With sufficient microcracks, grafting with vinyl monomers containing carbonyl groups, i.e., carboxyl, aldehyde, and ketone groups, improved surface wetting more than grafting with those containing either hydroxyl and epoxy groups. The acquired wettability of vinyl monomer-grafted PE surface is attributed to the physicochemical synergism between the microcracks and the polar groups. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1145–1159, 1997     

Spatially-resolved observation of glow discharge plasma for atomic emission spectrometry.

An imaging spectrograph equipped with a CCD detector was employed to measure two-dimensional emission images from a glow discharge plasma in atomic emission spectrometry. The emission images at Zn I 334.50 nm for a zinc sample and at Cu I 324.75 nm for a copper sample could be obtained. Their emission intensities were not uniform in the radial direction of the plasma region but became weaker at larger distance from the central zone. The two-dimensional distribution would result from a spatial variation in the excitation efficiency of the plasma and thus provide useful information for understanding the excitation processes occurring in the plasma.     

Penetration of plasma surface modification. I. Cf4 and C2F4 glow discharge plasmas

Plasma treatment of a polymeric surface could involve at least three major mechanisms: (1) direct interaction of reactive species in the low-temperature plasma state with the surface (line of sight irradiation effect), and (2) chemical reactions of plasma-induced reactive species with the surface, and (3) reactions among reactive species and the surface (plasma polymerization). The first and the third effects are considered to be limited to the surfaces which directly contact with plasma (glow). The second effect is not limited to the surfaces that contact with plasma state but can penetrate beyond the plasma zone by diffusion. Using an assembly of fibers, of which only the top layer contacts with plasma (glow), the penetration of chemical changes caused by plasma exposure was investigated. Results indicate that the fluorination effect (incorporation of fluorine-containing moieties on the surface of polymeric substrate) penetrates through a considerable thickness of the assembly of fibers, depending on the porosity (gas permeability) of the system. Chemical reactions of plasma-induced (chemically) reactive but nonpolymerizing species with the substrate fibers seems to predominate. The direct interactions of energetic species, such as ions, electrons, and electronically excited species, with polymeric surfaces seems to play relatively minor roles in the plasma treatment investigated. The major role of plasma, in this case, seems to be creating such chemically reactive species. © 1994 John Wiley & Sons, Inc.     

Solid sample atomic absorption analysis after glow discharge sputtering

Summary The use of the Atomsource atomizer and a double-beam/two-channel AA instrument shall be described at first. It seems that this relatively new combination of sputtering chamber and atomic absorption measurement needs a long time to be applied. Both these techniques are not used normally in one laboratory by the same operators. May be the different aims to analyse solutions by AA and solids by glow discharge sputtering makes it more difficult to see the advantages. These are given, especially in the case of analysis of metals and other conducting materials, by the short time needed for sputtering and the accuracy, simplicity, and flexibility caused by AA meausurements. In addition, AA becomes available to determine elements like B, Ce, La, Nb or Zr much better than before.     

Thermoluminescence from extended-chain crystals of polyethylene

Thermoluminescence (TL) has been observed in γ-irradiated extended-chain crystals of polyethylene above room temperature. The TL curve, which exhibits four peaks at 50, 90, 120, and 140°C, is different from that given by folded-chain crystals, in both shape and intensity. In particular, a shape, strong glow peak is observed at 140°C, corresponding to the melting temperature of the extended chain crystals. These results are discussed in relation to independent measurements by differential scanning calorimetry and electron spin resonance.     

The kinetics of erosion of polyamide films under the action of a glow discharge plasma

Infrared internal reflection and absorption spectroscopy was used to study the kinetics of erosion of AL 60/40 polyamide films under glow discharge treatment. The degree of erosion was estimated quantitatively.