In recent years, fluorocarbon plasmas have been extensively used for the treatment of polymer surfaces in an increasing number of applications. A decrease of the surface wettability is observed after exposure of the polymer to the discharge, to a degree depending on the treatment time and discharge parameters. Fluorination of the polymer surface, following exposure of the surface to the discharge, is believed to be the result of functionalization and/or polymerization, depending on the plasma composition. However, due to the complexity of the chemical reactions both in the gas phase and at surfaces, the underlying mechanisms are not yet well understood. The characterization of the reactive species formed in the discharge and the possible correlation of their behaviour to the plasma-induced modification of the surface properties is essential for understanding the role of the species and for the identification of the mechanisms of surface modification. Fluorocarbon radicals can be detected in situ by a number of diagnostic techniques, that include optical emission spectroscopy [1], laser-induced fluorescence (LIF)[2-4], UV absorption [5], infrared diode laser absorption spectroscopy (IRLAS)[6-8], and threshold ionization mass spectrometry [9-11].

The present work focuses on the deposition of fluorocarbon (FC) films on aluminum and SiO2 surfaces, and addresses the issue of selective deposition on Al versus SiO2 in order to obtain surfaces of distinctly different wettability. If this is achieved, hydrophobic/hydrophilic patterning of substrates would be feasible by means of a self-aligned and relatively simple method. The selectivity of the deposition is optimized through proper selection of the deposition conditions, mainly gas-mixture composition and deposition time, and is demonstrated by means of contact-angle measurements on Al and SiO2 surfaces. Chemical (XPS) analysis of the FC films deposited under various conditions is also performed and correlated with the wettability of the plasma-modified Al surfaces.

The changes in the surface properties of oxygen plasma-treated polyethylene films during ageing in various atmospheres (water, dry nitrogen gas, and hexane) were studied from the viewpoint of the interaction of the surface functional groups formed on the films and the ageing media. The XPS (x-ray photoelectron spectroscopy) and the SSIMS (static secondary ion mass spectrometry) spectra indicated the formation of polar groups containing oxygen such as C=O on the film surface. The changes in the critical surface tension (γ_C) of the film with ageing time were largely affected by the ageing atmospheres: the γ_C value of the film aged in water increased, and those of the films aged in nitrogen gas and hexane decreased with an increase in ageing time. These different tendencies among the ageing media could be understood reasonably with examining the surface free energy ratios (the total energy, γ^tot_S, the dispersion force component, γ^d_S/γ^tot_S, the polar component, γ^p_S/γ^tot_S, the hydrogen bonding component, γ^h_S/γ^tot_S) of the films. The ageing in water of which γ_L is large gave the films with higher γ^p_S/γ^tot_S values, suggeting that the overturn and/or the orientation of the polar groups toward the water phase occurred so as to minimize the discrepancy of the surface free energy between the polymer surface and water. On the other hand, the ageing in nitrogen gas and hexane media of which γ_L are small gave the films with lower γ^p_S/γ^tot_S and γ^h_S/γ^tot_S values, suggesting the overturn and/or the orientation of the polar groups into the bulk polymer.

We have been able to generate the wide and stable plasma in open air (discharge distance, 35 cm; discharge-electrode length, 16 m at maximum) using a pulse with a high voltage and narrow wave form. This was applied to treat the surface of rather non-polar plastics intended for the improvement of adhesion of over-coated layers such as coatings, adhesives and printing inks. The treating system (APPS) consists of the apparatus for generating the plasma and the treating process. Polypropylene (PP) and tetrafluoroethylene perfluorovinyl ether copolymer (PFA) have been examined as typical examples of the plastics. The adhesion strength of urethane paint on PP molding and of a PFA film on steel was significantly improved by the APPS treatment. The characteristics of the surface layer were evaluated by means of scanning electron microscopy, electron spectroscopy for chemical analysis, atomic force microscopy, and contact angle measurement, and it was found that hydrophilic functional groups were introduced into the surface layer of the plastics. The level of the improvement changed with time after treatment; this is discussed from the viewpoint of functional group movement from the surface to the interior. Application of paints on PP bumpers by the electrostatic spray method was also accomplished. The use of a small amount of nitrogen-containing compound following APPS treatment decreased the electrical resistance of the PP surface from 10¹⁶ to 10¹¹ Ω, and highly effective electrostatic coatings of PP bumpers could be realized.

Low-pressure plasma treatment has been introduced for the practical pretreatment of automobile bumpers. The differences between the conventional solvent vapor pretreatment and low-pressure plasma or corona treatment, are shown schematically.

Corona, flame, atmospheric plasma, and liquid flame spray (LFS) techniques were used to create highly hydrophilic surfaces for pigment-coated paper and board and machine-glossed paper. All the surface modification techniques were performed continuously in ambient atmosphere. The physical changes on the surfaces were characterized by field emission gun-scanning electron microscopy (FEG-SEM), atomic force microscopy and Parker Print-Surf surface roughness. The chemical changes were analysed by X-ray photoelectron spectroscopy. The superhydrophilic surfaces, i.e. contact angle of water (CAW) <10°, were created mainly by modifying the surface chemistry of the paper and board by argon plasma or SiO2 coating. The nano- and microscale roughness existing on paper and board surfaces enabled the creation of the superhydrophilic surfaces. Furthermore, the benefits and limitations of the surface modification techniques are discussed and compared. For example, the SiO2 coating maintained its extreme hydrophilicity for at least six months, whereas the CAW of argon plasma-treated surface increased to about 20° already in one day.

Polymer and paper structures have been successfully utilized in several fields, especially in the packaging industry. Together with barrier properties, printability is an important property in packaging applications. From the point of view of printing, the dense and impervious structure of extrusion coatings is challenging. Flame, corona and atmospheric plasma treatments were used to modify the surface of low density polyethylene (LDPE) and polypropylene (PP) and the influence of these surface modifications on print quality, i.e., toner adhesion and visual quality was studied. The traditional surface treatment methods, i.e., flame and corona treatments, increased the surface energy by introducing oxygen containing functional groups on the surfaces of LDPE and PP more than helium and argon plasma treatments. Only in the case of flame treatment, the higher surface energy and oxidation level led to better print quality, i.e., toner adhesion and visual quality, than the plasma treatments. The morphological changes observed on LDPE surface after flame treatment are partly responsible for the improved print quality. Atmospheric plasma treatments improved the print quality of LDPE and PP surfaces more than corona treatment. The electret phenomenon observed on LDPE and PP surfaces only after corona treatment is the most likely reason for the high print mottling and low visual quality of corona treated surface.

Nitrogen-containing plasmas are widely used to improve wettability, printability, bondability, and biocompatibility of polymer surfaces. Plasma-treatments fed with NH₃ give rise to N-functionalities, such as amino ( NH₂), imino ( CH NH), cyano ( C N) and others on polymers, plus oxygen-containing groups due to post-plasma atmospheric oxidation. This work deals with NH₃ plasma treatment of PA 6 foils and the evaluation of surface modification as a function of treatment time. The introduced functionalities were observed by streaming potential measurements (surface charge), X-ray photoelectron spectroscopy analysis (nature of introduced functionalities), atomic force microscopy (surface topography), and contact angle measurement (assessment of treatment effect). The results show that the introduction of N-containing groups is increasing with longer treatment time only to a certain extent where the negative effect of surface destruction prevails over the positive effect of introduction of functional groups. The treatment causes a shift of the isoelectric point (IEP) toward pH of 6.2 as compared to 4.2 found for the untreated foil. If the treatment time is longer than 1 min the IEP is shifted to lower pH, the number of amino groups on the surface is reduced and the contact angle is increased.

An attempt to replace a wet-chemical surface modification of styrene-butadiene elastomers (SBS), improving their adhesion to polyurethane adhesives, with a clean low-pressure plasma technique has been undertaken. The plasma has been generated by an RF discharge (13.56 MHz, plate electrode reactor) in various reactive mixtures (eg CHCl3, CCl4, CO2, O2) to create chlorine (C–Cl) and oxygen (> C= O,–OH,–COOH) functionalities on the elastomer surfaces. T-peel tests, contact-angle measurements, and FTIR spectroscopy have been utilized to investigate the surfaces. It has been found that an important role in the plasma-improved adhesion is played by the chemical interaction between the modified SBS surfaces and polyurethanes. The peel strength for plasma-treated samples in many cases is much higher than that for the wetchemical modification. It clearly indicates that the plasma treatment is a very promising method of improving the adhesion properties of SBS

Low-pressure plasma generated in a typical parallel plate reactor and atmospheric pressure plasma produced by a plasma needle were utilized to modify the surface of poly(styrene–butadiene–styrene) (SBS) elastomers. An RF discharge (13.56 MHz) in helium was used in the both cases. The SBS surfaces were investigated by T-peel tests, contact-angle measurements, and IRS–FTIR spectroscopy. It has been found that such plasma treatments drastically improve the strength of adhesive-bonded joints between the SBS surfaces and polyurethane adhesives, however, the plasma needle operation has turned out to be more effective. The molecular processes proceeding on the SBS surfaces have been briefly discussed.

The two methods used for contact angle determination in this study are based on liquid porosimetry (LP). The LP measures volumes of different size pores when the liquid advances and then when the liquid drains from a porous structure. The LP provides pore volume distribution (PVD) and numerous other pore structure characteristics. The experimental data for this study were obtained with an automated TRI/Autoporosimeterо. The first method for contact angle measurement uses two liquids. One liquid has a known contact angle with the sample solid and the second is the liquid of interest. A comparison of the capillary pressures in different size pores for the two liquids provides the contact angle data for different size pores in the sample.

The three states of matter are solid, liquid, and gas. A plasma state exists as its fourth state. A plasma consists of positively charged particles and negatively charged electrons existing at almost the same electrical density, it is overall electrically neutral, and it was named plasma by Langmuir in 1928. The easiest way to obtain a plasma state is to induce an electrical discharge in a gas. A corona discharge treatment is a kind of plasma treatment. Plasmas are classified roughly into two categories: equilibrium plasmas and nonequilibrium plasmas. In equilibrium plasmas, the temperatures of electrons and of the gas are the same. Mainly equilibrium plasmas have been studied, and temperatures of approximately 10,000 C have been reported. In nonequilibrium plasmas the gas is at ambient temperature, but the temperature of electrons is very high (about 10,000 C). These nonequilibrium plasmas are used in chemical applications and are called low-temperature plasmas or cold plasmas. The low-temperature plasmas are classified roughly into two categories:(1) ordinary low-temperature plasmas at low pressure and (2) corona discharges at atmospheric pressure. Ordinary low-temperature plasmas are widely used in chemical modification of the surfaces of materials, especially in semiconductor industries [1] as well as for polymers [2].

Excitation with low temperature helium or helium/water plasma and subsequent exposure to air of polyacrylonitrile (PAN) ultrafiltration membranes was used to hydrophilize the surface of these materials. We analyzed the effectiveness of this approach as a function of plasma operating variables including gas phase composition, plasma power, treatment time, and system pressure. Following the changes in physical and chemical composition of the PAN surface resulting from these modifications was a major aspect of this work. Techniques such as the captive bubble contact angle method, ellipsometry, ESCA, and FTIR-ATR were all used. In addition, the formation and lifetime of peroxides during these processes were determined. At low powers (≤ 25 W) and short treatment periods (≤ 30 s), the main chemical conversion of PAN surfaces was simultaneous hydrophilization and stabilization via PAN cyclization. Relatively small water permeability changes were observed as a result of such treatment. © 1995 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1995.070560304

The adhension between aluminum and poly(ethylene-co-vinyltrimethoxysilane) (EVS) and poly(ethylene-co-butylacrylate-co-vinyltrimethoxysilane) (EVSBA), respectively, have been studied. For comparison an ordinary low density polyethylene (LDPE), a poly(ethylene-co-butylacrylate) (EBA), and an ionomer regarded as a bonding polymer were studied as well. The peel strength of laminates obtained by pressing were measured by a T-peel test. The structure of the fracture surfaces were investigated by reflection-IR, ESCA, and SEM. The peel strength of the LDPE and the EBA samples were 100 and 700 N/m, respectively. Although the amount of vinylsilane was low, about 0.2–0.3 mol %, its presence had a pronounced influence on the adhesion: 1800 and 3000 N/m for EVS and EVSBA, respectively. This is even higher than the value observed for the ionomer, 1560 N/m. Although there was a marked difference in surface topology, the SEM and ESCA analysis showed that the fracture was cohesive for both EVS and EVSBA. Immersion in water at 85°C increased the peel strength even more, especially in the case of EVSBA (up to 9000 N/m), in contrast to what is normally observed with aluminum polyethylene laminates. The results suggest that strong and nonhydrolyzable bonds, e.g., covalent bonds, have been formed across the polymer-metal interface for the ethylene copolymers containing vinylsilane.

The surface of polypropylene (PP) films was activated by RF plasma method with the use different gases: argon, air, water vapor, and acetic acid vapor. Plasma was diagnosed based on spectra emitted by gas plasma using the method of optical emission spectroscopy. The effectiveness of these processing gases during plasma treatment was analyzed. The effects of PP activation were assessed with the use of IR-ATR absorption spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and the analysis of the surface free energy components based on liquid contact angle. The activation of PP surface by plasma treatment resulted in the increased energy of PP surface layer to the extent being dependent on the type of processing gases and in the formation of new chemical groups on it. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011. https://onlinelibrary.wiley.com/doi/abs/10.1002/app.34486

The contact angle of water on several polymer films was determined by three different methods; telescopic sessile drop, laser beam goniometry, and the Wilhelmy plate technique. The telescopic sessile drop method is the simplest, but the least accurate; whereas the laser beam goniometry compares favorably with the Wilhelmy plate in terms of accuracy, but cannot easily provide information on contact angle hysteresis.

Plasma treatment is often used to modify the surface properties of polymer films, since it offers numerous advantages over the conventional surface modification techniques. However, plasma-treated polymer films have a tendency to revert back to the untreated state (aging process). Therefore, the stability of plasma-induced changes on polymer surfaces over a desired period of time is a very important issue. The objective of this study is to examine the effect of storage conditions (relative humidity and temperature) on the aging behavior in air of plasma-treated low density polyethylene (LDPE) films. Plasma treatment is performed using a dielectric barrier discharge (DBD) operating in different argon/water vapor mixtures at medium pressure (5.0 kPa). Results show that the aging process can be suppressed by storing the plasma-modified LDPE films at low temperature and by decreasing the relative humidity of the surrounding air. Adding water vapor in the plasma discharge has a positive influence on the aging process: lower plateau WCA values are found for plasmas containing a higher water vapor concentration and it takes a longer time to reach these plateau values. In this paper, it is also shown that storage first at a lower temperature and then aging at a higher temperature is not able to slow down the aging effect.

Polytetrafluoroethylene (PTFE) surfaces were treated by oxygen and nitrogen species generated either in a remote (filtered) RF plasma or in an ion gun. In the first case, the majority of the species reaching the surface are neutral molecules, whereas in the second case, ions are the reactive agent. In this paper, we show that ions alone do not lead to a significant grafting of new functions on the PTFE surface. The XPS analysis of the treated surface show identical behaviour with oxygen and nitrogen ion treatment, and the evolution of the C1s peak shape suggest a progressive sputtering, leading to defluorination of the surface. The nitrogen plasma treatment lead to a subsequent grafting that is attributed mostly to the “excited neutrals”, but we suggest here that the ions could play a significant role in the activation process of the surface. The exposure of PTFE to an oxygen plasma lead to chemical etching of the surface, different from the physical sputtering induced by the ion treatment, that lead to a super-hydrophobic behavior of the surface attributed to an increase in the surface roughness.

Recent work in our laboratories has fully characterized the surface region of a segmented poly(ether-urethane) (PEU) extending from the air/polymer interfacial region through bulk depths in the micron range. This characterization utilized energy and angle dependent Electron Spectroscopy for Chemical Analysis (ESCA), Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR–FTIR), and Comprehensive Wettability Profiling (contact angle using a homologous series of liquids) as defined by Zisman. In this study this same multi-analytical-technique approach is used to elucidate changes in these PEU surfaces induced through an H₂O Radio Frequency Glow Discharge (RFGD) plasma. This investigation reports both qualitative and quantitative changes due to the modification treatments as well as the permanency of the changes effected on these surfaces through the plasma treatment. From our analyses, the amount of surface residing polyurethane (hard segment) is observed to increase due to a proposed plasma etching mechanism. Further, the addition of oxygen containing functionality is detected at the modified surfaces unique with respect to the unmodified PEU. These surface modifications which show large increases in wettability, are finally observed to be semi-permanent over a time period of 6 months.