Surface modification of low density polyethylene (LDPE) film by low pressure O2 plasma treatment

In this work, low pressure glow discharge O₂ plasma has been used to increase wettability in a LDPE film in order to improve adhesion properties and make it useful for technical applications. Surface energy values have been estimated using contact angle measurements for different exposure times and different test liquids. In addition, plasma-treated samples have been subjected to an aging process to determine the durability of the plasma treatment. Characterization of the surface changes due to the plasma treatment has been carried out by means of Fourier transformed infrared spectroscopy (FTIR) to determine the presence of polar species such as carbonyl, carboxyl and hydroxyl groups. In addition to this, atomic force microscopy (AFM) analysis has been used to evaluate changes in surface morphology and roughness. Furthermore, and considering the semicrystalline nature of the LDPE film, a calorimetric study using differential scanning calorimetry (DSC) has been carried out to determine changes in crystallinity and degradation temperatures induced by the plasma treatment. The results show that low pressure O₂ plasma improves wettability in LDPE films and no significant changes can be observed at longer exposure times. Nevertheless, we can observe that short exposure times to low pressure O₂ plasma promote the formation of some polar species on the exposed surface and longer exposure times cause slight abrasion on LDPE films as observed by the little increase in surface roughness.     

PMMA Surface Functionalization Using Atmospheric Pressure Plasma for Development of Plasmonically Active Polymer Optical Fiber Probes

In this paper, we demonstrate the development of plasmonically active PMMA optical fiber probes by the attachment of gold nanoparticles to the probe surface functionalized by means of flowing post-discharges from dielectric barrier discharge (DBD) plasmas for the first time. Polymer optical fiber (POF) probes (U shape to improve absorbance sensitivity) were subjected to reactive gas atmospheres in the post-discharge region of a coaxial DBD plasma reactor run at atmospheric pressure in different gases (Ar, Ar + 10 % O₂, O₂, N₂, N₂ + 0.5 % H₂). Plasma treatments in Ar or N₂ gave rise to water-stable electrophilic functional groups on PMMA surface, whereas the amine groups generated by N₂-containing plasmas were not stable. Subsequently, PMMA surfaces were treated with hexamethylene diamine (HMDA) to obtain stable amine groups through the reaction of electrophilic groups. Gold nanoflowers (AuNF, 37 nm, peak 570 nm) binding to the amine functionalized fiber probes was monitored in real-time by recording the optical absorbance changes at 570 nm with the help of a UV–vis spectrometer. Absorbance response from Ar or N₂ plasma treated probes are 100 and 60 times, respectively, that of untreated control probes. A 25 fold improvement in absorbance response was obtained for Ar plasma treated POF in comparison with only HMDA treated POF. The shelf life of the hence fabricated plasmonically active probes was found to be at least 3 months. In addition, plasmonic activity of U-bent fiber probes treated in Ar plasma is better than the conventional wet-chemical activation by environmentally hazardous acid pre-treatment approaches.     

The Role of Dielectric Barrier Discharge Atmosphere and Physics on Polypropylene Surface Treatment

Dielectric barrier discharge (DBD) is the discharge involved in corona treatment, widely used in industry to increase the wettability or the adhesion of polymer films or fibers. Usually DBD's are filamentary discharges but recently a homogeneous glow DBD has been obtained. The aim of this paper is to compare polypropylene surface transformations realized with filamentary and glow DBD in different atmospheres (He, N₂, N₂ + O₂ mixtures) and to determine the relative influence of both the discharge regime and the gas nature, on the polypropylene surface transformations. From wettability and XPS results it is shown that the discharge regime can have a significant effect on the surface transformations, because it changes both the ratio of electrons to gas metastables, and the space distribution of the plasma active species. This last parameter is important at atmospheric pressure because the mean free paths are short (m). These two points explain why in He, polypropylene wettability increase is greater by a glow DBD than by a filamentary DBD. In N₂, no significant effect of the discharge regime is observed because electrons and metastables lead to the same active species throughout the gas bulk. The specificity of a DBD in N₂ atmosphere compared to an atmosphere containing oxygen is that it allows very extensive surface transformations and a greater increase of the polypropylene surface wettability. Indeed, even in low concentration and independently of the discharge regime, when O₂ is present in the plasma gas, it controls the surface chemistry and degradation occurs.     

Surface characterization of plasma‐modified poly(ethylene terephthalate) film surfaces

Poly(ethylene terephthalate) (PET) film surfaces were modified by argon (Ar), oxygen (O₂), hydrogen (H₂), nitrogen (N₂), and ammonia (NH₃) plasmas, and the plasma‐modified PET surfaces were investigated with scanning probe microscopy, contact‐angle measurements, and X‐ray photoelectron spectroscopy to characterize the surfaces. The exposure of the PET film surfaces to the plasmas led to the etching process on the surfaces and to changes in the topography of the surfaces. The etching rate and surface roughness were closely related to what kind of plasma was used and how high the radio frequency (RF) power was that was input into the plasmas. The etching rate was in the order of O₂ plasma > H₂ plasma > N₂ plasma > Ar plasma > NH₃ plasma, and the surface roughness was in the order of NH₃ plasma > N₂ plasma > H₂ plasma > Ar plasma > O₂ plasma. Heavy etching reactions did not always lead to large increases in the surface roughness. The plasmas also led to changes in the surface properties of the PET surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surfaces decreased. Modification reactions occurring on the PET surfaces depended on what plasma had been used for the modification. The O₂, Ar, H₂, and N₂ plasmas modified mainly CH₂ or phenyl rings rather than ester groups in the PET polymer chains to form C? O groups. On the other hand, the NH₃ plasma modified ester groups to form C? O groups. Aging effects of the plasma‐modified PET film surfaces continued as long as 15 days after the modification was finished. The aging effects were related to the movement of C?O groups in ester residues toward the topmost layer and to the movement of C? O groups away from the topmost layer. Such movement of the C?O groups could occur within at least 3 nm from the surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3727–3740, 2004     

Comparison of the effect of excimer laser irradiation and RF plasma treatment on polystyrene surface

Polystyrene (PS) samples were treated with excimer laser, argon and oxygen plasmas. The surface of PS was irradiated using ArF excimer pulsed laser (λ=193 nm). Radio frequency glow discharge (RF) was used to generate the argon and oxygen plasmas. The samples were processed at different number of pulses and treatment times. The changes were characterized by atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM) and contact angle measurements. The data from ATR-FTIR spectra showed the induction process of oxygen-based functional group in both PS samples treated with RF plasma and laser. AFM and SEM observations demonstrated that a specific nanostructure was created on the laser-treated PS surface. Contact angle measurement indicated higher wettability of the treated PS with both argon and oxygen plasmas and lesser wettability of laser-treated samples. The data from in vitro assays showed the significant cell attachment and growth onto plasma-treated surfaces in comparison with laser treated samples.     

On the Use of Atmospheric Pressure Plasma for the Bio-Decontamination of Polymers and Its Impact on Their Chemical and Morphological Surface Properties

Low temperature atmospheric pressure plasma processes can be applied to inactivate micro-organisms on products and devices made from synthetic and natural polymers. This study shows that even a short-time exposure to Ar or Ar/O₂ plasma of an atmospheric pressure plasma jet leads to an inactivation of Bacillus atrophaeus spores with a maximum reduction of 4 orders of magnitude. However, changes in the surface properties of the plasma exposed material have to be considered, too. Therefore, polyethylene and polystyrene are used as exemplary substrate materials to investigate the effect of plasma treatment in more detail. The influence of process parameters, such as type of operating gas or jet-nozzle to substrate distance, is examined. The results show that short-time plasma treatment with Ar and Ar/O₂ affects the surface wettability due to the introduction of polar groups as proofed by X-ray photoelectron spectroscopy. Furthermore, atomic force microscopy images reveal changes in the surface topography. Thus, nanostructures of different heights are observed on the polymeric surface depending on the treatment time and type of process gas.     

Isoelectric points of plasma‐modified and aged silicon oxynitride surfaces measured using contact angle titrations

Acid‐base properties of metal oxides and polymers can control adhesion properties between materials, electrical properties, the physical structure of the material and gas adsorption behavior. To determine the relationships between surface isoelectric point, chemical composition and aging effects, plasma‐surface treatment of amorphous silicon oxynitride (SiO_xN_y) substrates was explored using Ar, H₂O vapor, and NH₃ inductively coupled rf plasmas. Overall, the Ar plasma treatment resulted in nonpermanent changes to the surface properties, whereas the H₂O and NH₃ plasmas introduced permanent chemical changes to the SiO_xN_y surfaces. In particular, the H₂O plasma treatments resulted in formation of a more ordered SiO₂ surface, whereas the NH₃ plasma created a nitrogen‐rich surface. The trends in isoelectric point and chemical changes upon aging for one month suggest that contact angle and composition are closely related, whereas the relationship between IEP and composition is not as directly correlated. Copyright © 2010 John Wiley & Sons, Ltd.     

Single-walled carbon nanotubes as stationary phase in gas chromatographic separation and determination of argon, carbon dioxide and hydrogen

A chromatographic technique is introduced based on single-walled carbon nanotubes (SWCNTs) as stationary phase for separation of Ar, CO₂ and H₂ at parts per million (ppm) levels. The efficiency of SWCNTs was compared with solid materials such as molecular sieve, charcoal, multi-walled carbon nanotubes and carbon nanofibers. The morphology of SWCNTs was optimized for maximum adsorption of H₂, CO₂ and Ar and minimum adsorption of gases such as N₂, O₂, CO and H₂O vapour. To control temperature of the gas chromatography column, peltier cooler was used. Mixtures of Ar, CO₂ and H₂ were separated according to column temperature program. Relative standard deviation for nine replicate analyses of 0.2 mL H₂ containing 10 μL of each Ar or CO₂ was 2.5% for Ar, 2.8% for CO₂ and 3.6% for H₂. The interfering effects of CO, and O₂ were investigated. Working ranges were evaluated as 40-600 ppm for Ar, 30-850 ppm for CO₂ and 10-1200 ppm for H₂. Significant sensitivity, small relative standard deviation (RSD) and acceptable limit of detection (LOD) were obtained for each analyte, showing capability of SWCNTs for gas separation and determination processes. Finally, the method was used to evaluate the contents of CO₂ in air sample.     

Activation of Au–Ag Plasmonic Bimetallic Nanocatalysts with Cold Plasma: The Role of Loading Sequence of Plasmonic Metals and Discharge Atmosphere

The activation of Au–Ag plasmonic bimetallic nanocatalyst can make the nanocatalyst exhibit superior visible-light (VL) photocatalytic activity. An efficient activation of Au–Ag nanocatalyst by cold plasma requires the restructuring of Au and Ag species over catalyst surface to form Au–Ag alloy nanoparticles while suppressing agglomeration of the nanoparticles. We here report that the loading sequence of Au and Ag components on titanium dioxide (TiO₂) support during catalyst preparation and discharge atmosphere play important roles in the plasma activation. Preparation of AuAg/TiO₂ nanocatalyst by depositing Ag and Au in sequence could avoid the undesired loss of Ag component, and ensure an effective restructuring of Au and Ag species in O₂ plasma activation. Compared with the reductive (H₂) and inert (Ar and N₂) plasmas, discharge in oxidative O₂ establishes Coulomb field with the negatively charged species over catalyst surface and enable the restructuring and intimate interaction of Au and Ag species. The catalyst characterization and density functional theory calculations suggest that O₂ plasma endows AuAg/TiO₂ nanocatalyst with large numbers of Au–Ag alloy nanoparticles, small size of plasmonic nanoparticles, high density of coordinatively unsaturated sites, and high content of surface oxygen species in the activation, which facilitates the adsorption and activation of O₂, and thus CO oxidation reaction under VL irradiation.

     

Characterization of surface modifications of stainless steel samples after electron and ion bombardment by SEM, AES, and XPS

The interaction of inert or reactive gas plasmas with the surface of stainless steel has been investigated with the aim, to modify the surface and hence to reduce the outgassing rate of the material, an important factor for the production of an ultrahigh vacuum. The plasma treatments investigated may be an alternative to the common used in situ baking. The samples have been exposed to electrons, argon and oxygen ions either in a DC glow discharge or in a microwave discharge. The DC glow discharge in Ar/O₂, the most effective plasma treatment reduces the outgassing rate by a factor of 10. After this treatment the surfaces of the samples have been investigated with respect to the topography and the chemical composition (depth profile) by Secondary Electron Microscopy (SEM), Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS), respectively. The surface modifications resulting from the different treatments of the samples have been correlated to the outgassing rate.     

Gas transport behavior of mixed-matrix membranes composed of silica nanoparticles in a polymer of intrinsic microporosity (PIM-1)

Recently, high-free volume, glassy ladder-type polymers, referred to as polymers of intrinsic microporosity (PIM), have been developed and their reported gas transport performance exceeded the Robeson upper bound trade-off for O₂/N₂ and CO₂/CH₄. The present work reports the gas transport behavior of PIM-1/silica nanocomposite membranes. The changes in free volume, as well as the presence and volume of the void cavities, were investigated by analyzing the density, thermal stability, and nano-structural morphology. The enhancement in gas permeability (e.g., He, H₂, O₂, N₂, and CO₂) with increasing filler content shows that the trend is related to the true silica volume and void volume fraction.     

Mass spectrometer-wall probe diagnostic of Ar discharges containing SF6 and/or O2: Reactive ions in etching plasmas

Positive and negative ions of Ar/SF₆ and Ar/SF₆/O₂ plasmas (etching plasmas) and of Ar/O₂ plasmas (cleaning plasmas) in Pyrex tubes have been investigated using a mass spectrometer-wall probe diagnostic technique. The measurement of negative ions proved to be a very sensitive method for the detection of wall material. In etching plasmas with small admixtures of SF₆, oxygen was found as the only representative of wall material. At larger amounts of SF₆, silicon could be detected. In cleaning plasmas with small admixtures of O₂ applied to a previously etched Pyrex surface, fluorine was found, indicating the reversal of fluoridation by oxygenation.     

Properties of low-molecular-weight polyethylene treated with gas plasma

Polyethylene films were evaporated in gas plasmas of Ar, N₂, O₂, and H₂O. The deposits were analyzed by infrared (IR) spectroscopy to determine the concentration of characteristic functional groups. The deposit prepared in Ar-atmosphere had a rather high concentration of methyl group and many double bonds were produced in the film. The deposits prepared in Ar- and N₂-plasmas produced similar spectra, which showed twice the concentration of methyl group than the deposit in Ar-atmosphere and also contained a few carbonyl and hydroxyl groups. The film treated in O₂-plasma contained the largest amount of carbonyl group and the lowest number of double bonds among the plasma-treated deposits. Dielectric loss curves against temperature for the deposits treated in these plasmas showed a broad peak near 20°C. For O₂-plasma-treated film the loss tangent curves showed a sharp maximum. The activation energy for the relaxation of Ar-, O₂-, and H₂O-plasma-treated films had the same value of 50.6 kcal/mol. The observed relaxation in the films prepared in gas plasmas was considered due to the β process and was attributed to the motion of oxidized branched polyethylene.     

Combination of glow-discharge and arc plasmas for CF4 abatement

Decomposition of CF₄ by glow-discharge and arc plasmas was studied using a tubular quartz reactor, a disk type, and a T-type quartz reactor. The effects of different metal electrodes, input voltage, and reactor type on the efficiency of CF₄ total destruction (DRE) were studied. The T-shape reactor was more efficient in CF₄ destruction than either the disk or tubular type due to a combined effect of glow discharge and arc plasmas. Several hydrogen and oxygen sources, such as H₂O, H₂, O₂, and CH₄, were used to convert CF₄. Using H₂ and O₂ as the hydrogen and oxygen sources presented better DRE than using H₂O. The effect of different hydrogen and oxygen sources on the conversion of CF₄ followed the trend: (H₂ + O₂) > (CH₄ + O₂) > H₂O. The maximum DRE of 95% was observed with 0.5% CF₄ using H₂ and O₂. A mass spectrometer and an emission spectroscope equipped with a charge-coupled detector (CCD) were used to characterize the products and intermediates. Mass spectrometric studies indicated that the reaction products were HF, CO₂, and trace amounts of NO. N₂ first negative and second positive emission lines were observed in the glow discharge plasmas as well as in the arc plasmas of N₂. However, C and F intermediates were observed only in arc plasmas of CF₄. Reactions occurring in the glow discharge plasmas and arcs seem to follow different mechanisms.     

Determination of trace amounts of permanent gases in ultra pure hydrogen by gas chromatography

Summary A HP-5880A gas Chromatograph equipped with TCD and FID has been used to determine trace amounts of O₂+Ar, N₂, CO, CH₄ and CO₂ in pure and ultra pure hydrogen. Utilizing the preconcentration technique, the minimum detectability with a 10-liter sample is around 0.2 ppb (v/v) for O₂+Ar, 0.4 ppb (v/v) for N₂, 0.05 ppb (v/v) for CO, 0.2 ppb (v/v) for CH₄ and 0.3 ppb (v/v) for CO₂. Calculation of results in trace gas analysis is discussed and a calculation method is proposed for the concentration of impurities in the sample calculated from the difference of successive sampling volumes and peak areas.

---

Spurenbestimmung von permanenten Gasen in hochreinem Wasserstoff mit Hilfe der Gas-Chromatographie

     

Effect of nonsolvent additive on the surface morphology and the gas separation performance of poly(2,6-dimethyl-1,4-phenylene)oxide membranes

Integrally skinned asymmetric membranes were prepared from poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) using different nonsolvent additives. These nonsolvent additives consisted of branched and linear alcohols ranging from C₃ to C₁₀. Permeation data of these membranes were obtained from a constant pressure permeation system for pure gases of CO₂, CH₄, O₂ and N₂. An empirical correlation relating the pure gas permeance ratio of CO₂/CH₄ and the structural components of the nonsolvent additives has been proposed. The membranes were characterized by atomic force microscope (AFM) and intrinsic viscosity measurements. It was observed that there were two types of surface morphologies: merged nodules and discrete nodules. The appearance of the nodules were reflected in the mean roughness data, R_a. It was revealed that membranes with smaller and merged nodules resulted in higher pure gas permeance ratios for O₂/N₂ and CO₂/CH₄ with the exception of 3,5,5-trimethyl-1-hexanol and 3-ethyl-2,2-dimethyl-3-pentanol. The microscopic studies showed that the membranes containing discrete nodules resulted in lower pure gas permeance ratios for O₂/N₂ and CO₂/CH₄. It was observed that nonsolvent additives that possess a long straight hydrocarbon chain such as 2-ethyl-1-hexanol, 1-octanol and 2-decanol produced the highest pure gas permeance ratios.     

The effect of two gases forming supercritical fluids (Xe and CO2) on the spectral characteristics and analytical capabilities of microwave induced plasmas

A comparative study of the effect of CO₂ and Xe added along with the plasma gas to He and Ar microwave induced plasmas (MIPs), simulating possible conditions to be used when a MIP is employed as specific detector for supercritical fluid chromatography (SFC), has been carried out. The proportions of CO₂ and Xe to the plasma gas investigated are comparable to the typical percentages used for SFC-MIP couplings. The study has been performed with two different MIP systems: an atmospheric pressure discharge held in a Beenakker cavity TM₀₁₀ and a reduced pressure surfatron-MIP.The influence of CO₂ and Xe addition on the spectrochemical properties of the discharge has been studied by using the atomic emission of mercury and some typical non-metals (chlorine, carbon and sulfur) at different wavelengths (atomic and ionic lines). Results showed that ion line emission intensities are always reduced more significantly than atom line emissions by both dopant gases on study, whatever the pressure. In general terms, however, the effect of adding Xe is less severe, both for atom and ion lines, than that of CO₂; in most cases the detection limits (DLs) observed are better for Xe than for CO₂ as dopant gas. In fact, the DLs obtained for the selected lines of mercury measured were practically unaltered by the addition of 0.2% Xe to atmospheric pressure Ar or He MIPs. CO₂ addition (0.2%) produced about 1.5 times worsening of the observed DLs for mercury. For non-metal analyses better DLs were also obtained, in general terms, with Xe than with CO₂ as dopant gas.     

Surface modification of ethylene‐co‐tetrafluoroethylene films by remote plasmas

The surface modifications of ethylene‐co‐tetrafluoroethylene (ETFE) surfaces by six plasmas (direct H₂, Ar, and O₂ plasmas and remote H₂, Ar, and O₂ plasmas) were investigated with two questions in mind: (1) what plasma could effectively modify ETFE surfaces and (2) which of the CF₂? CF₂ and CH₂? CH₂ components in ETFE was selectively modified? The plasma exposure led to a weight loss from the ETFE surfaces and changes in the chemical composition on ETFE surfaces. The weight‐loss rate showed a strong dependence on what plasma was used for the modification. The remote H₂ plasma led to the lowest rate of weight loss in the six plasma exposures, and the direct O₂ plasma led to the highest rate of weight loss. During exposure to the plasmas, defluorination occurred, and two new C_1s components [? CH₂? CHF? CH₂? and ? CH₂? CH(O? R)? CF_x? , and ? CH₂? CHF? CF₂? , ? CH₂? C(O)? CF_x? , and ? CF_x? C(O)? O? ] were formed on the modified ETFE surfaces. Defluorination was strongly influenced by what plasma was used for the modification. The remote H₂ and Ar plasmas showed high defluorinations of 55 and 51%, respectively. The remote O₂ plasma showed a low defluorination of only 25%. Conclusively, the remote H₂ and Ar plasma exposure effectively modified ETFE surfaces. With the exposure of these surfaces to the remote H₂ plasma, the CF₂? CF₂ component was predominantly modified, rather than the CH₂? CH₂ component. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2871–2882, 2002     

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.     

On the Control of Plasma Parameters and Active Species Kinetics in CF<Subscript>4</Subscript> + O<Subscript>2</Subscript> + Ar Gas Mixture by CF<Subscript>4</Subscript>/O<Subscript>2</Subscript> and O<Subscript>2</Subscript>/Ar Mixing Ratios

The effects of both CF₄/O₂ and Ar/O₂ mixing ratios in three-component CF₄ + O₂ + Ar mixture on plasma parameters, densities and fluxes of active species determining the dry etching kinetics were analyzed. The investigation combined plasma diagnostics by Langmuir probes and zero-dimensional plasma modeling. It was found that the substitution of CF₄ for O₂ at constant fraction of Ar in a feed gas produces the non-monotonic change in F atom density, as it was repeatedly reported for the binary CF₄/O₂ gas mixtures. At the same time, the substitution of Ar for O₂ at constant fraction of CF₄ results in the monotonic increase in F atom density toward more oxygenated plasmas. The natures of these phenomena as well as theirs possible impacts on the etching/polymerization kinetics were discussed in details.