Polyolefins are well-known and the most commonly used polymers worldwide. Advantages like outstanding mechanical properties, chemical resistance, low cost, and processability are neighboring with some drawbacks like relatively high gas and vapor permeability, low surface energy. This chapter introduces surface plasma modification as an environmentally friendly, fast, and versatile technique. Details regarding different plasma reactor designs, generation methods, working parameters suitable for treating polyolefins are presented. Furthermore, plasma activation, grafting, and etching are described as the most commonly used techniques for surface energy modification to enhance polyolefins' biocompatibility, printability, adhesion to materials, and other parameters. For instance, plasma activation cross-linking of the polymer chains can be achieved, which leads to gas and vapor permeability improvement. Choice of working conditions allows controlling the degree of cross-linking, the type, and the concentration of the incorporated functional groups on the surface. Plasma polymerization is introduced as a technique for coating deposition with different properties and functionality depending on the operating parameters and monomer selection. Improvement of barrier layer performance and modification of the surface energy are the main applications of plasma polymerization of polyolefins.

Atmospheric pressure non-thermal plasma is of interest for industrial applications. In this study, polypropylene (PP) films are modified by a dielectric barrier discharge (DBD) with a non-uniform magnetic field in air at atmospheric pressure. The surface properties of the PP films before and after a DBD treatment are studied by using contact angle measurement, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The effect of treatment time on the surface modification with and without a magnetic field is investigated. It is found that the hydrophilic improvement depends on the treatment time and magnetic field. It is also found that surface roughness and oxygen-containing groups are introduced onto the PP film surface after the DBD treatment. Surface roughness and oxygen-containing polar functional groups of the PP films increase with the magnetic induction density. The functional groups are identified as C-O, C=O and O-C=O by using XPS analysis. It is concluded that the hydrophilic improvement of PP films treated with a magnetic field is due to a greater surface roughness and more oxygen-containing groups.

This book describes the fundamentals and applicability of the atmospheric-pressure non-thermal plasma surface modification of materials. Non-thermal plasma modification is an effective procedure for chemical activation. In this book, the principles of non-thermal plasma surface modification and its application to various machine parts are described. By reading this book, technologists from a variety of fields can learn about plasma generation and surface treatment technology, which will assist them in performing advanced procedures. This book also explains the basics of atmospheric-pressure plasma and the principle of plasma treatment in an easy-to -understand manner and also provides examples of the application of atmospheric-pressure plasma surface modification technologies to plastics, glass, polymers, and metals. After reading this book, readers can get the knowledge that researchers need to apply the methodology to meet their own research goals. T he book is self-contained in the sense that it spans the divide between the fundamentals and more advanced content regarding applications. Many engineers and graduate students working in this field get many helps.

Capillarity is the study of the interfaces between two immiscible liquids, or between a liquid and air. The interfaces are deformable: they are free to change their shape in order to minimize their surface energy. The field was created in the early part of the 19th century by Pierre Simon de Laplace (1749–1827) and Thomas Young (1773–1829). Henri Bouasse wrote a wonderful account of developments in capillarity in a book he published in 1924.1 This discipline enables us to understand the games water can play to break the monotony of a rainy day or the tricks it performs while washing dishes. On a more serious note, capillarity plays a major role in numerous scientific endeavors (soil science, climate, plant biology, surface physics, and more), as well as in the chemical industry (product formulation in pharmacology and domestics, the glass industry, automobile manufacturing, textile production, etc.).

When we place a liquid drop on a clean, planar, solid surface, we can observe a contact angle θ _E , which is precisely the angle contained in Young’s formula. Quite often, though, the surface is marred by defects that are

• either chemical (stains, blotches, blemishes)

• or physical (surface irregularities).

The effect of air dielectric barrier discharge plasma treatment on the chemical structure and morphology of polypropylene (PP)film was studied using UV-VIS (ultraviolet-visible),FT-IR,(Fourier transform infrared),SEM (scanning electron microscopy)and AFM (atomic force microscopy).Polypropylene samples were printed using solvent-based gravure ink.An evaluation of the print quality criteria of the treated PP films included measurement of print density and print gloss.SEM investigated the ink laydown on the modified PP film.The results showed that after a few seconds of plasma treatment,both the surface energy and the surface roughness of the treated PP film increased.There was an increase in the absorbance at the almost-visible range,and C=C and C=O bands were found after the air discharge plasma treatment.A short plasma treatment of 15 seconds was found to bring about a dramatic increase in the print density readings,but a decrease in print gloss.The time of the air discharge plasma treatment was found to have no effect on the print density or print gloss at a high ink film thickness.The results showed that air dielectric barrier discharge plasma treatment,for a few seconds,is effective in printing and is economical for industrial use (this will be studied in detail in future work).

Through the controlled use of selected pretreatments, significant improvements to adhesion levels can be realised. Pretreatment options include chemical activation, corona discharge treatment, plasma-induced modifications and grafting. Using such methods, adhesion levels that render substrates fit for the intended purpose can be achieved. Such improvements can be realised without compromising the inherent properties of the materials being treated. Various approaches are considered as is the nature of the adhesion process. Several reasonably recent examples of the use of surface activation are presented.

The activation of polymer surfaces in glow discharges and the deposition of metals from organo-metallic vapours, both at low pressure, are standard laboratory processes. The upscaling to industrial mass product applications is, however, hampered by cost and the time consumption needed for establishing a sufficient vacuum. Atmospheric pressure processes based on the same physical surface interactions show great promise as replacements of some steps in galvanic plating. Successful metallizations are reported after treatment of polymers in barrier discharges at atmospheric pressure. These may be applied directly to the surface of the workpiece or indirectly from within large-area monochromatic excimer UV lamps. Comparisons with excimer UV laser treatment are made.

The current broad interest in wetting characterization of solid surfaces is driven by recent advances in the formulation of surfaces and coatings that are superhydrophobic, superhydrophilic, oleophobic, oleophilic and so on. Unfortunately, the contact angle data presented in many publications raise some concerns among the surface chemists and physicists who work with contact angle measurement techniques on a regular basis. In those articles, best practices are often ignored, and the data presented are limited to the static contact angles measured for small droplets, a few times smaller than typically recommended. The reported contact angles are neither advancing nor receding, and their reproducibility in different laboratories is therefore questionable. In this note, guidelines to measurements of reproducible and reliable advancing and receding contact angles are summarized.

The surface characteristics of polymers are important factors determining their interfacial properties and their technological performance. Changes in physical and chemical properties of a polymer film may be induced by subjecting the material to a variety of surface modification techniques, one of which is ion-beam modification. In order to understand the underlying mechanisms X-ray photoelectron spectroscopy (XPS) was used to study the alterations of the polystyrene (PS) surface after Ar-ion treatment under well controlled conditions with low ion doses from 10¹² to 10¹⁶ cm^-2. The ion bombardment leads to surface functionalization, loss of aromaticity, and free radical formation. Induced surface cross-linking and the formation of polar groups raised the surface glass transition temperature of PS film.

Polymers have been applied successfully in fields such as adhesion, biomaterials, protective coatings, friction and wear, composites, microelectronic devices, and thin-film technology. In general, special surface properties with regard to chemical composition, hydrophilicity, roughness, crystallinity, conductivity, lubricity, and cross-linking density are required for the success of these applications. Polymers very often do not possess the surface properties needed for these applications. However, they have excellent bulk physical and chemical properties, are inexpensive, and are easy to process. For these reasons, surface modification techniques which can transform these inexpensive materials into highly valuable finished products have become an important part of the plastics and many other industries. In recent years, many advances have been made in developing surface treatments to alter the chemical and physical properties of polymer surfaces without affecting bulk properties. Common surface modification techniques include treatments by flame, corona, plasmas, photons, electron beams, ion beams, X-rays, and γ-rays.

Plasma treatment is probably the most versatile surface treatment technique. Different types of gases such as argon, oxygen, nitrogen, fluorine, carbon dioxide, and water can produce the unique surface properties required by various applications. For example, oxygen-plasma treatment can increase the surface energy of polymers, whereas fluorine-plasma treatment can decrease the surface energy and improve the chemical inertness. Cross-linking at a polymer surface can be introduced by an inert-gas plasma. Modification by plasma treatment is usually confined to the top several hundred ångströms and does not affect the bulk properties. The main disadvantage of this technique is that it requires a vacuum system, which increases the cost of operation.

Thin polymer films with unique chemical and physical properties are produced by plasma polymerization. This technology is still in its infancy, and the plasma chemical process is not fully understood. The films are prepared by vapor phase deposition and can be formed on practically any substrate with good adhesion between the film and the substrate. These films, which are usually highly cross-linked and pinhole-free, have very good barrier properties. Such films find great potential in biomaterial applications and in the microelectronics industry.

Very high-power microwave-driven mercury lamps are available, and they are used in UV-hardening of photoresist patterns for image stabilization at high temperatures. Other applications of UV irradiation include surface photo-oxidation, increase of hydrophilicity, and photocuring of paintings.

Pulsed UV-lasers are used in surface modification in many areas. Pulsed UV-laser irradiation can produce submicron periodic linear and dot patterns on polymer surfaces without photomask. These interference patterns can be used to increase surface roughness of inert polymers for improved adhesion. These images can also be transferred to silicon surfaces by reactive ion etching. Pulsed laser beams can be applied to inert polymer surfaces for increased hydrophilicity and wettability. Polymer surfaces treated by pulsed UV-laser irradiation can be positively or negatively charged to enhance chemical reactivity and processability. Pulsed UV-laser exposures with high fluence give rise to photoablation with a clean wall profile. There are many other practical applications of laser photoablation, including via-hole fabrication, and diamond-film deposition. The present review discusses all these current applications, especially in the biomedical and microelectronics areas.

Polymers have been applied successfully in fields such as adhesion, biomaterials, protective coatings, friction and wear, composites, microelectronic devices, and thin-film technology. In general, special surface properties with regard to chemical composition, hydrophilicity, roughness, crystallinity, conductivity, lubricity, and cross-linking density are required for the success of these applications. Polymers very often do not possess the surface properties needed for these applications. However, they have excellent bulk physical and chemical properties, are inexpensive, and are easy to process. For these reasons, surface modification techniques which can transform these inexpensive materials into highly valuable finished products have become an important part of the plastics and many other industries. In recent years, many advances have been made in developing surface treatments to alter the chemical and physical properties of polymer surfaces without affecting bulk properties. Common surface modification techniques include treatments by flame, corona, plasmas, photons, electron beams, ion beams, X-rays, and γ-rays.

Plasma treatment is probably the most versatile surface treatment technique. Different types of gases such as argon, oxygen, nitrogen, fluorine, carbon dioxide, and water can produce the unique surface properties required by various applications. For example, oxygen-plasma treatment can increase the surface energy of polymers, whereas fluorine-plasma treatment can decrease the surface energy and improve the chemical inertness. Cross-linking at a polymer surface can be introduced by an inert-gas plasma. Modification by plasma treatment is usually confined to the top several hundred ångströms and does not affect the bulk properties. The main disadvantage of this technique is that it requires a vacuum system, which increases the cost of operation.

Thin polymer films with unique chemical and physical properties are produced by plasma polymerization. This technology is still in its infancy, and the plasma chemical process is not fully understood. The films are prepared by vapor phase deposition and can be formed on practically any substrate with good adhesion between the film and the substrate. These films, which are usually highly cross-linked and pinhole-free, have very good barrier properties. Such films find great potential in biomaterial applications and in the microelectronics industry.

Very high-power microwave-driven mercury lamps are available, and they are used in UV-hardening of photoresist patterns for image stabilization at high temperatures. Other applications of UV irradiation include surface photo-oxidation, increase of hydrophilicity, and photocuring of paintings.

Pulsed UV-lasers are used in surface modification in many areas. Pulsed UV-laser irradiation can produce submicron periodic linear and dot patterns on polymer surfaces without photomask. These interference patterns can be used to increase surface roughness of inert polymers for improved adhesion. These images can also be transferred to silicon surfaces by reactive ion etching. Pulsed laser beams can be applied to inert polymer surfaces for increased hydrophilicity and wettability. Polymer surfaces treated by pulsed UV-laser irradiation can be positively or negatively charged to enhance chemical reactivity and processability. Pulsed UV-laser exposures with high fluence give rise to photoablation with a clean wall profile. There are many other practical applications of laser photoablation, including via-hole fabrication, and diamond-film deposition. The present review discusses all these current applications, especially in the biomedical and microelectronics areas.

Two engineering thermoplastic polymers (polycarbonate, PC, and acrylonitrile butadiene styrene copolymer, ABS) were treated with atmospheric plasma torch using different treatment rates (1, 5 and 10 m/min). The modifications produced by the treatment were analysed by contact angle measurements, XPS, SEM and ATR-IR spectroscopy. Particular emphasiswas placed on the ageing (up to 30 days) after atmospheric plasma treatment on both polymers. The slower the atmospheric plasma treatment, the greater the wettability of the treated polymers. The decrease in water contact angle was mainly ascribed to a significant increase in oxygen content due to the formation of carboxylic and hydroxyl groups and a decrease in the carbon content on the polymer surfaces. After natural ageing, there was an increase in the water contact angle, although the values of the untreated polymer surface were never reached.

This work concerns the ageing effect of the atmospheric plasma and corona treatments when used to treat paper substrates. Pigment coated and surface sized papers were modified using two types of atmospheric plasma equipment; one at the pilot scale and one at the laboratory scale. In addition, the plasma treatments were compared to conventional corona treatment. Surface energy was estimated by contact angle measurements and surface chemistry by X-ray photoelectron spectroscopy (XPS) as a function of the time during three months. The treatments increased surface energy and oxidation level of surface for both papers. The ageing effect could be detected only in the surface energy, whereas the oxidation level remained stable during the twelve weeks. The decay in surface energy was faster during the first weeks of storage and subsequently leveled off leading to a permanent change. The permanent change was explained as a contribution of oxygen containing polar molecular groups, which were detected by XPS. The ageing effect was suggested to originate from already existing polar molecular groups, which have rotated on the surface by plasma-related process and then rotate back into the material in time. A part of the decay was also explained by the plasma cleaning model, in which the ageing effect occurred through re-contamination. Paper is a multicomponent system, where the constituents that have the lowest surface energy were suggested to migrate to paper surfaces.

Different types of plasma, irradiative and chemical activation were compared in terms of surface functionalization. Corona and spark jet plasmas are characterized by low gas temperatures and high rates in surface modification. UV irradiation in the presence of ozone does not involve any particle bombardment and acts only by enhanced photooxidative processes. Although ion implantation can be avoided, this method is not free of radiative damage in both the surface-near region and the bulk of polymers. Furthermore, its functionalization rate is low. In relation to low-pressure O₂ plasma modification, all treatments mentioned here have a low efficiency in adhesion promotion due to oxidative degradation of macromolecules and formation of molecular debris known as the “weak boundary layer”.

The treatment of surfaces by corona discharges is a well-established method to improve surface properties. The surface to be treated is moved continuously and is exposed to transient gas discharges, known as microdischarges, in air at atmospheric pressure between electrodes, where at least one electrode is covered with a dielectric barrier. Because of the short duration, only some 10 ns, the current through the microdischarges is predominantly carried by electrons. The ion temperature remains close to room temperature. Owing to these properties such discharges are qualified to treat surfaces which are sensitive to higher temperatures. For a large number of applications this treatment is adequate, but the adhesion of aqueous glues and inks to some plastic materials is insufficient if the surfaces are treated in this way. Furthermore, it is difficult to meet the requirements of surface properties of, for instance, polyolefine film (e.g. surface tension, adhesion). This material is not based on monomers containing chlorine or fluorine and is preferred for ecological reasons. This paper presents the results of experiments which demonstrate that in comparison to a common corona treatment significant improvements in surface properties of plastic materials can be achieved if repetitively generated pulse trains and reactive gases are used instead of air. If, for instance, the microdischarges are established in acetylene, thin films with a thickness of several namometres are formed on surfaces, which increase and stabilize the surface tension up to a level of 72 mN m⁻¹. The state of the art of this new technology is discussed.

Surface modifications of polyetheretherketone (PEEK) made by chemical etching or oxygen plasma treatment were examined in this study. Chemical etching caused surface topography to become irregular with higher roughness values R_a and R_q. Oxygen plasma treatment also affected surface topography, unveiling the spherulitic structure of PEEK. R_a, R_q and surface area significantly increased after plasma treatment; topographical modifications were, nonetheless, moderate. Wetting angle measurements and surface energy calculations revealed an increase of wettability and surface polarity due to both treatments. XPS measurements showed an increase of surface oxygen concentration after both treatments. An O:C ratio of 3.10 for the plasma-treated PEEK surface and 4.41 for the chemically-etched surface were determined. The results indicate that surface activation by oxygen plasma treatment for subsequent coating processes in supersaturated physiological solutions to manufacture PEEK for biomedical appiications is preferable over the chemical etching treatment.

For vacuum web coating for permeation barrier coatings in flexible packaging, the final functionality of the packaging media is extremely dependent on the whole chain of processing steps up to the final laminated packaging film. The most sensitive sector appears to be, on the one hand the hand-shake between substrate film pretreatment–substrate surface properties and the coating process with its characteristics on the other. The influence of different surface pretreatment processes (Corona activation, oxygen and ammonia plasma treatment) on active surface groups of BOPP (biaxial-orientated polypropylene) substrates is shown together with: (1) specifities of the thermal deposition (electron beam source); (2) the reactive deposition–microwave plasma process (plasma species, excitation characteristics, kinetic energies, obtained by in situ process monitoring); and (3) structural properties (chemical composition, adhesion and oxygen permeation) of the thin barrier films (Al₂O₃ and SiO_x), in correlation with the achieved functional properties of the barrier coated films.

Electroless plating of non-conducting materials needs, prior to the metal deposition itself, to make the sample surface catalytically active. The route involving the chemical reduction of a thin solid metal–organic coating has, for this purpose, a significant potential in reducing the number of steps which are required today in conventional wet chemical metallization processes. In this work, a novel activation process using a dielectric barrier discharge (DBD) is described for the first time. This process is based on the plasma-induced chemical reduction at atmospheric pressure in air of palladium acetate (PdAc) layers resulting in the formation of palladium (Pd) on non-active surfaces. Fast surface activation of polymers like polyimide (PI) was found to occur in only a few seconds using a simple DBD device instead of expensive excimer UV lamps or complicated laser systems. The DBD-induced Pd layers on PI exhibit high activity with regard to initiation of the electroless copper plating. Indeed, copper deposition starts immediately after dipping the activated PI samples in the electroless solution without any inhibition time. Homogeneous copper coatings on PI were achieved under optimal plasma treatment conditions. The results are compared to those achieved with excimer UV lamps and excimer UV lasers.

The means by which plasma treatment enhances the adhesion of polymer materials, remains obscure. Thus far, two possible mechanisms have been proposed: an increase in surface energy, and the anchor effects imparted by plasma etching. Independently from these mechanisms, reactions between free radicals, generated by plasma irradiation and adhesives are also likely to affect the adhesive properties of polymer materials. Free radicals generated on polyethylene (PE) by glow-discharge plasma were exposed to air and converted to peroxide. The peroxides were converted back to free radicals with the application of heat, and then graft polymerization was initiated, by adding a hydrophilic monomer such as acrylic acid. The peroxides formed by the reaction between free radicals and the oxygen in air was detected by chemiluminescence (CL). In this work, plasma-treated PE surfaces were bonded to aluminum boards, using epoxy resin as an intermediate adhesive and then subjected to a series of peeling tests. The sample with the highest peeling strength also had the highest level of CL-detected peroxides. These findings suggest that the free radicals generated by plasma treatment influence the adhesive properties of the polymer materials.

The chemical and morphological stabilities of polymer segments in the near-surface layer were investigated by spectroscopic methods such as X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. Model studies were undertaken with Langmuir–Blodgett films, self-assembled monolayers and oligomer films. For thin polymer layers (30 to 500 nm), the changes in molecular-weight distributions of some polymers were investigated systematically by size exclusion chromatography, matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry and thermal-field flow fractionation for oxygen- and helium-plasma exposures. The polymer surfaces were found to be relatively stable at exposure to an oxygen low-pressure plasma up to ca. 2 s. This is important information to get maximum adhesion to metals in composites. In correlation to their redox potentials, potassium, aluminium and chromium react with oxygen functional groups at the polymer/metal interface. In a dedicated study, chromium was found to attack aromatic rings and form different reaction products.

The hydrophobic recovery of oxygen-plasma-treated hydrophilic surfaces of polyethylene and polypropylene films was investigated by measuring the dependence of the contact angle with the water on the vacuum storage time. It could be shown that the rehydrophobation of the polyethylene surface may be retarded by the previous controlled surface cross-linking in a hydrogen plasma and/or by repeated plasma treatment. However, the loss in hydrophilicity cannot be suppressed for ever. After certain individual periods all treatments lead to the same final state. Nevertheless, in particular, controlled cross-linking seems to be a suitable way for improving the long-term stability of plasma-functionalized polymer surfaces for polymers not tending to chain scission during plasma treatment.

o optimize the effects of some discharge parameters on the surface wettability of polypropylene (PP) in atmospheric pressure dielectric barrier discharge, a surface modification model is created based on statistical theory and orthogonal experimental design method. Contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) are used to study the changes in the surface wettability, surface topology and chemical compositions of the samples. The results show that surface wettability has been improved due to roughness increasing and the introduction of oxygen-containing functional groups. High-resolution XPS of C1s peak deconvolution indicates that the types and contents of oxidized functional groups are different in different discharge conditions or plasma energy. Moreover, the model analysis reveals that it has better predictive ability, and different discharge parameters has selective influence on water contact angle and surface O atom percentage.

Air plasma treatment at low pressure was applied to modify the surface of a cellulose film with the aim to improve its wettability, dyeability and adhesion properties. The contact angles of different polar liquids on the treated films show an exponential decay with treatment time at a given power; the power–time reciprocity is followed. The calculated surface tension values exponentially rise to the same maximum value with a decrease of the polar fraction. ATR-FTIR analyses suggest that a cellulose dehydration takes place rather than a surface oxidation. The plasma treatment improves also the cellophane dyeability with typical dyes for cellulose fibers: the results of dye uptake follow the same trend as the surface energy. The bond strength of lap joints of cellophane with LLDPE film shows a strong improvement of the adhesion depending on the duration and the power of treatment. The whole results are consistent with ablation effects like those observed with air corona treatment rather than oxygen plasma.

To many people, plasma is a laboratory curiosity or limited in scale. Few know that plasma is a commercial process used daily in the treatment of fabrics, non-woven webs and film. This paper reviews applications and processes used to modify materials up to 60 in. in width in a roll-to-roll plasma system. The applications are quite varied. Sometimes, the process is simply to change the surface energy, while at other times, far more sophisticated processes, such as plasma-enhanced chemical vapor deposition (PECVD) processes, are employed to provide a chemical barrier or alter the tribological properties. As will be seen in this review presentation, plasma is extremely versatile and applicable to high-volume web applications.

This paper deals with the plasma surface treatment of polymers in a low frequency bell jar reactor with non-symmetrical configuration of electrodes. The highly energetic character of this discharge due to its low excitation frequency and electrode configuration, as well as its small discharge volume makes it a very efficient and fast functionalization process. Amongst the different plasma gases used for the adhesion improvement of polypropylene to aluminum, ammonia has shown to be the most suitable one for this application. Since the NH and NH ₂ radicals play an important role in the kinetics of nitrogen incorporation in polymers, mixtures of N ₂ and H ₂ were also used as possible substitutes for ammonia. The former are more environmentally friendly and easier to handle in industry than ammonia. The efficiency of nitrogen rich mixtures in the case of the second application, i.e. adhesion improvement of copper to fluoropolymers has been compared to that of ammonia which still shows faster nitrogen incorporation. The last part of this paper is devoted to the study of the energetic character of plasmas of mixtures of He+NH ₃ by OES and electrical measurements in the whole range of composition of the two gases. The results show that an ammonia percentage ranging from 5 to 10% in plasmas of mixtures of He/NH ₃ represents a transition between two different discharge regimes. Plasmas of mixtures of He+2% NH ₃ , characterized by highly energetic electrons, ions and probably metastables of helium give rise to enhanced adhesion of PP to aluminum which remains stable with time.

Atmospheric pressure N₂ cold plasmas are generated with a torch-type generator using 60-Hz AC power. High flow rate N₂ gas is injected into the plasma generator and high voltage of about 2 kV is introduced into the power electrode through transformer. Discharge characteristics of N₂ cold plasma, such as current–voltage profile, gas temperature and radial species in plasma, are measured. As one possible application, the N₂ cold plasma is used to modify the surface of polymer, especially polypropylene, for adhesion improvement. Power dissipation in discharge has the maximum value at optimal power electrode position, z=3 mm, which lead to the generation of more energetic electrons capable of creating N₂* and N₂⁺ excited states in plasmas effectively. These excited species can induce high population of oxygen and nitrogen atoms on polymer surface through creation of polymer excited states. Maximum bonding strength about 10.5 MPa is obtained at optimal power electrode position.

In this paper, polyester (PET) and polypropylene (PP) films are modified by a dielectric barrier discharge in air, helium and argon at medium pressure (5.0 kPa). The plasma-modified surfaces are characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS) as a function of energy density. The polymer films, modified in air, helium and argon, show a remarkable increase in hydrophilicity due to the implantation of oxygen-containing groups, such as C–O, O–CO and CO. Atomic oxygen, OH radicals, UV photons and ions, present in the discharge, create radicals at the polymer surfaces, which are able to react with oxygen species, resulting in the formation of oxygen-containing functionalities on the polymer surfaces. It is shown that an air plasma is more efficient in implanting oxygen functionalities than an argon plasma, which is more efficient than a helium plasma. In an air plasma, most of the created radicals at the polymer surface will quickly react with an oxygen particle, resulting in an efficient implantation of oxygen functionalities. However, in an argon and helium plasma, the created radicals can react with an oxygen particle, but can also recombine with each other resulting in the formation of an oxidized cross-linked structure. This cross-linking process will inhibit the implantation of oxygen, resulting in a lower efficiency. In argon plasma, more ions are present to create radicals, therefore, more radicals are able to react with oxygen species. This can explain the higher efficiency of an argon plasma compared to a helium plasma.

Parallel plates dielectric barrier discharge (DBD) at atmospheric pressure has been investigated to modify and functionalize the surface of different polymer substrates, e.g. polyolefins, poly(ethylene terephtalate), polyamide, in order to enhance their hydrophilic properties. Surface properties have been altered to meet the requirements of specific applications by introducing the appropriate functionalities through the use of either acetic acid or ethyl acetate. The coatings have been characterized through wettability measurements, labeling coupled with X-Ray photoelectron spectroscopy, and IR spectroscopy.

In the present work three common polyolefins: high density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP) have been treated with an atmospheric pressure air plasma torch (APPT) in order to improve their wettability properties. The variations in surface energy (γ_s), as well as the durability of the treatment are determined by means of contact angle measurements for different aging times after plasma exposure (up to 270 days) using five test liquids which cover a wide range of polarities. The introduction of new polar moieties (carbonyl, amine or hydroxyl) is confirmed by Fourier transform infrared spectroscopy in attenuated total multiple reflection mode (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Furthermore, scanning electron microscopy (SEM) provides information on the morphological changes and variation on surface roughness, revealing that smoother, lamellar and semispheric micrometric structures are created on the LDPE, HDPE and PP surfaces, respectively. Results show that APPT treatment enhances both the total and polar components of the γ_s under study, with an unprecedent stability (> 8 months) in time.

The peel strength of aluminium to polypropylene and poly(tetrafluoroethylene) was determined in dependence on the type and the concentration of functional groups on the polymer surface. For this purpose the polymer surface was equipped with monotype functional groups. The first method to produce monotype functionalized surfaces was an introduction of O functional groups using an oxygen plasma treatment and converting these groups to OH groups applying a wet chemical reduction. In result of this two-step treatment the hydroxyl group concentration at the polymer surface could be increased from 3–4 to 10–14 OH groups/100 C atoms. The second method consists in the deposition of a 150 nm adhesion-promoting layer of plasmapolymers or copolymers onto the polymer surface using the pulsed plasma technique. For that purpose functional groups carrying monomers as allyl alcohol, allylamine and acrylic acid were used. Applying the plasma-initiated copolymerization and using neutral “monomers” like ethylene or butadiene the concentration of the functional groups was varied.

A correlation of peel strength with the ability of forming chemical interactions between Al atoms and functional groups was found: COOH > OH >> NH₂ > H(CH₂–CH₂).

In this work particular attention has been paid to the aging behavior of biaxially oriented polypropylene (BOPP) film surfaces modified with the acrylic acid (AAc) corona discharge treatment previously reported. Three different corona energies of 15.3, 38.2 and 76.4 kJ/m² were studied. The surface properties of treated films during 90 days of aging were compared with those of normal air-corona treated films prepared with the same corona energies. The surface chemical compositions of aged films were analyzed by curve-fitting of the ATR-FTIR spectra. The wettabilities of all aged films were monitored by water contact angle and surface free energy measurements. The change of surface topology of air- and AAc-corona treated films was investigated at 1 day, 7 days and 90 days of aging using the technique. In addition, the surface adhesions of aged films were determined with the T-peeling test. The results showed that the amount of polar functional groups on the surface of aged films had changed. However, the aged films of the AAc-corona treated films still showed greater wettability than did the air-corona treated films and could retain high surface hydrophilicity for more than 90 days of aging under ambient condition. The surface topology of both types of aged films changed after aging from a globular structure to a flatter surface, due to mobility of the deposited polymer layer. The AAc-corona treated films showed rougher surfaces due to the influence of poly(acrylic acid) deposition and they could retain the improved surface wettability despite the change in surface topography. The adhesion peel forces of aged films decreased slightly due to the topological changes. A mechanism for the change in surface topography and in chemical functionality of each type of aged film is proposed.

In this work, air dielectric barrier discharge (DBD) operating at the line frequency (60 Hz) or at frequency of 17 kHz was used to improve the wetting properties of polypropylene (PP). The changes in the surface hydrophilicity were investigated by contact angle measurements. The plasma-induced chemical modifications of PP surface were studied by X-ray photoelectron spectroscopy (XPS) and Fourier-transformed infrared spectroscopy (FTIR). The polymer surface morphology and roughness before and after the DBD treatment were analyzed by atomic force microscopy (AFM). To compare the plasma treatment effect at different frequencies the variation of the contact angle is presented as a function of the deposited energy density. The results show that both DBD treatments leaded to formation of water-soluble low molecular weight oxidized material (LMWOM), which agglomerated into small mounts on the surface producing a complex globular structure. However, the 60 Hz DBD process produced higher amount of LMWOM on the PP surface comparing to the 17 kHz plasma treatment with the same energy dose. The hydrophilic LMWOM is weakly bounded to the surface and can be easily removed by polar solvents. After washing the DBD-treated samples in de-ionized water their surface roughness and oxygen content were reduced and the PP partially recovered its original wetting characteristics. This suggested that oxidation also occurred at deeper and more permanent levels of the PP samples. Comparing both DBD processes the 17 kHz treatment was found to be more efficient in introducing oxygen moieties on the surface and also in improving the PP wetting properties.

We present a new approach for the surface treatment of polymer films at atmospheric pressure. The DC glow discharge is generated by applying a high voltage between two electrodes which are placed in a channel with a high flux of air. The air flow removes charge carriers from the plasma zone which prevents the formation of sparks. In the almost homogeneous plasma a comparably high electrical power is converted forming a high concentration of active species. The flowing air transports them to the polymer surface. We report the results of the first experiments with this set-up. The influence of various process parameters on the discharge properties is shown. The resulting alterations in the surface structure of the polymers are characterised by XPS and contact angle geometry.

After the atmospheric pressure plasma treatment of polypropylene (PP) film surface, we measured the contact angle of the surface by using polar solvent (water) and nonpolar solvent (diiodomethane). We also calculated the surface free energy of PP film by using the measured values of contact angles. And then we analyzed the change of the contact angle and surface free energy with respect to the conditions of atmospheric pressure plasma treatment. Upon each condition of atmospheric pressure plasma treatment, the contact angle and surface free energy showed optimum value or leveled off. Through AFM analysis, we also observed the change of surface morphology and roughness before and after plasma treatment. The surface roughness of PP film showed the highest value when the plasma treatment time was 90 s. Finally, we analyzed the change of chemical compositions on the PP film surface through XPS. As the result of analysis, we observed that polar functional groups, such as –CO, –C=O, and –COO were introduced on the PP film surface after atmospheric pressure plasma treatment.

The surface modification of high density polyethylene by a CO₂ microwave plasma is described with the aim of fixing carboxylic groups. The characterization is discussed in terms of functionalization, degradation, crystallization and cross-linking. The formation of carboxylic acids seems mainly favored by the presence of the CO₂ active species. The degradation leading via chain scissions to the formation of volatile byproducts is shown to be heterogeneous by mainly affecting amorphous zones. The structural modification is associated with a twisting motion of macromolecular chains having defects to more organized conformations. Finally, cross-linking appears weak due to the absence of chromophoric sites and of VUV radiations in the plasma.

In this work, the surface modifications of various polymer films due to helium–oxygen dielectric barrier discharge (DBD) exposure operating under atmospheric pressure are reported. The polymer films studied include ultra high molecular weight polyethylene, polyamide, polytetrafluoroethylene and polyimide. Experimental results reveal increased hydrophilicity and surface energy of the plasma exposed polymers. This is attributed to the presence of oxygen containing groups grafted onto the surface during plasma treatment, as confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Scanning electron microscopy (SEM) data show the appearance of micro depressions, the size of which depends on the chemical structure and the treatment time, suggesting that mild etching occurs in a predicted fashion. Most importantly, this uniform modification occurs within a few seconds of exposure, time comparable to continuous on-line industrial processing.

Polymers such as rubbers generally have low surface energy, thus high hydrophobicity and inherent low bondability. An atmospheric pressure ejected plasma (APEP) source is developed for pre-treatments of polymers to overcome these intractable properties and improve the adhesion ability between polymers as environmental-friendly and simple alternative methods to conventional treatments in spite of several limitations until now. Proper operational conditions are found by T-peel tests performed with various plasma parameters and high peel strength up to 3.5 kgf/cm is achieved at those conditions. Optical emission spectroscopy revealed that the amount of oxygen radicals and gas temperatures are found to be higher at proper conditions in T-peel tests and Fourier transform infrared spectroscopy using attenuated total reflection. Scanning electron microscopy is used for the measurement of surface composition and morphology of pre-treated polymer specimen. These results established the advantage of pre-treatments by APEP source in proper operation conditions when compared to the conventional treatments in terms of improvement of the adhesion ability between polymers.