The surface properties of three undecyl oxazoline homopolymers and two phenyl/undecyl oxazoline block copolymers (as comparison) were studied. After coating on glass slides and annealing, all films had a low critical surface energy of 21 dynes/cm. Water contact angles were higher than 107° for the most hydrophobic films. The deduction that the polymer surfaces contained close-packed methyl groups was further confirmed by electron spectroscopy chemical analysis (ESCA) angle profiling on an annealed undecyl oxazoline homopolymer film. A model was developed for the variation of elemental ratios as a function of photoelectron take-off angle. This verified that the polymer films had the polymer backbones parallel to the surface with the undecyl tails oriented toward the surface. When these block and homopolymers were coated on copy paper and glass slides, the peel strengths of pressure-sensitive adhesives with these surfaces were very low for short dwell times at room temperature. At long dwell times or at elevated temperatures, the peel strengths remained low for the homopolymers but increased greatly for the block copolymers to values higher than those in the tape on glass. After 24 h at 70°C, ESCA analysis showed that the adhesive diffused into the phenyl block domains of the diblock copolymer, generating high peel strength and cohesive failure. However, under the same annealing conditions, the triblock copolymer showed adhesive failure while peel strength increased. ESCA analysis showed very litle diffusion of the adhesive into the triblock copolymer. The homopolymers were stable toward vinyl acetate type adhesives even at elevated temperature; they were abhesive up to 100°C with no interdiffusion.

An experimental study of the constant velocity displacement of various water/glycerol solutions by air in poly (vinyl chloride)(PVC) capillary tubes is reported. This topic is of particular interest in relation to dewetting processes on surfaces covered by a liquid film. More specifically, variations of the dynamic contact angle with velocity and their relation to the physicochemical properties of the systems studied are investigated. These results and those of other authors are analyzed in the framework of both hydrodynamical and molecular approaches of the dynamic contact-angle problem. These comparisons indicate that either the molecular or the viscous dissipation mechanism may be dominant, depending on the system studied. These results are used to suggest explanations for apparent discrepancies between dewetting velocity measurements in different systems previously reported by the authors.

Remote argon plasma (RP) and ozone in the presence of ultraviolet light (UV–O₃) were used to render polystyrene (PS) surfaces hydrophilic in a controlled manner for eventual application in cell‐surface interaction studies. X‐ray photoelectron spectroscopy (XPS) was used to characterize both methods of modification. The degree of modification on PS was measured by an increase in surface oxygen and concomitant change in C 1s binding energies as a function of time. Both remote plasma and UV–O₃ are shown to be partially surface destructive, producing polymer fragments which are easily washed away to leave stable modified surfaces of oxidized polymer comprising of distributions of C–O, C=O and O—C=O type groups. Of the two methods, UV–O₃ is shown to be more versatile and conducive to preparing PS surfaces with controllably varying degrees of modification. UV–O₃ modified polystyrene is shown to be stable in air for at least eight months. Contact angle methods were used in correlation with XPS in characterizing UV–O₃ modified surfaces. It is shown that changes in surface tension and total surface oxygen content were related, however, not directly connected.

The wetting properties of polyamide 6 rods treated with radiofrequency (RF) low-temperature plasma (LTP) using three different non-polymerizing gases (air, nitrogen and water vapour) were determined using the Wilhelmy contact-angle technique. Information on the acidic or basic nature of the ionizable groups generated on the rod surface was obtained using contact-angle titration. The wettability obtained depends on the plasma gas used, and it tends to decrease with time elapsed after the treatment when the samples are kept in an air environment. However, the wettability can be recovered by immersion of the aged samples in water. The degree of recovery depends on the plasma gas used and the highest recovery was obtained with water vapour plasma treated samples. Both ageing and recovery behaviour can be attributed to the reorganisation of hydrophilic groups which tend to reversibly migrate or orient towards the bulk phase depending on the storage conditions, although other factors can also have influence.

An experimental investigation of the surface modification of polytetrafluoroethylene (PTFE) by an Ar and Ar/O₂ plasma created with an atmospheric-pressure radio frequency (r.f.) torch is presented here. The surfaces were analyzed by atomic force microscopy (AFM), XPS and water contact angle (WCA) to get an insight of the surface morphology and chemistry. An increase of roughness is observed with the Ar/O₂ plasma treatment. The WCA analysis shows that these surfaces are more hydrophobic than pristine PTFE; a contact angle of 135° was measured. When a PTFE surface is treated by Ar plasma, no roughening or significant change of the surface morphology and chemistry of PTFE was observed. The effects of the Ar and O₂ fluxes on the PTFE surface treatment were analyzed, as well as the effect of the power and treatment time. The plasma phase was also analyzed by optical emission spectroscopy, and some correlations with the treatment efficiency of the plasma are made. The chemistry on the surface is finally discussed and the competition between etching and re-deposition chemical reactions on the surface is proposed as a possible explanation of the results. Copyright © 2010 John Wiley & Sons, Ltd. https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/sia.3384

Corona treatment of films, mainly polyethylene, was studied at commercial levels in a small continuous treater. Degree of treatment was characterized by measuring polar and dispersion components of surface energy, ASTM Wipe and ASTM Adhesion Ratio (“peel adhesion”). The chief factors studied were corona current, applied frequency, web speed, dielectric thickness and air-gap thickness between electrode and film. Other factors less intensively investigated were type of film, film additives, aging time after treatment, humidity and corona atmosphere. The polar component of surface energy, γ, is the key to understanding the changes in adhesive behavior of the films during treatment. We found that, for the equipment used, γ is accurately given by the equation

Polymeric films, chiefly polyethylenes, were subjected to corona-discharge treatment in a continuous treater at commercial rates in a program covering wide ranges of the main processing factors (2). Electron-spin-resonance measurements on freshly treated films found no free radicals. Reactions of the treated surfaces with a free-radical compound, diphenyl picryl hydrazyl (DPPH) were studied, focusing mainly on the rate effects. The evidence indicates that corona treatment produces fairly stable peroxide structures of the forms RO₂R and RO₃R on polyethylene surfaces. RO₃R reacts rapidly with DPPH alone, while RO₂R undergoes a slower reaction after addition of the catalyst, triethylene diamine. DPPH is capable of detecting as few as 10¹³ peroxide groups per square centimeter. Activation energies were 12 kcal/mole for the uncatalyzed reaction and 16 kcal/mole for the amine-catalyzed reaction. As with the physical effects reported earlier (2), the production of peroxides is most strongly dependent on the energy delivered to the film during treatment. This energy is proportional to the quotient of corona current and web speed, I/S, Regression analysis showed that air-gap thickness, relative humidity, and number of electrodes used also were significant factors, while dielectric thickness and corona frequency were not. We found that-γ, the polar component of surface energy of the treated film, which is nearly zero for untreated polyethylenes, is exponentially related to the concentrations of both RO₂R and RO₃R with a correlation coefficient for 92 specimens tested of 0.88. We believe this is the first strong evidence linking treatment factors, at commercial levels of treatment, to chemistry of the treated surface and linking both of those to changes in physical behavior of the surface.

Filter paper and greaseproof paper have been exposed to hydrogen or oxygen plasma. The paper surface composition was determined by ESCA measurements. The unmodified and modified papers then were laminated with polyethylene and the adhesive strength was measured. The hydrogen plasma treatment reduces the cellulose surface and forms low-molecular-weight degradation products. It is shown that the reduction of the cellulose surface has no influence on the adhesion, but the degradation products strongly decrease the adhesion. Oxygen plasma treatment increases adhesion, probably by removing low-molecular-weight wood resin from the surface and by forming covalent bonds across the interface.

Numerous relationships have been proposed in the literature to interpret wettability in terms of solid and liquid surface free energies. In the classical approach based on surface free energy components, the energy of interactions between the liquid and the solid is obtained from the geometric mean of the dispersion and polar contributions of the liquid and solid surface free energies. In this work, it is shown that the surface polarity of polar liquids can be modeled by the interaction of aligned permanent dipoles. A good agreement is found between the surface polarity characterized by polar component of the surface free energy of polar liquids (water, formamide and ethylene glycol) and the dipolar energy of interactions calculated from their dipole moment. At the liquid/polymer interfaces, polar interactions are better described by a simple relationship of proportionality with the polar component of the liquid surface free energy. This observation leads us to evaluate the hypothesis of induced polar interactions at liquid/polymer interfaces, the surface polarity of the solid being induced by the polar liquid in contact with the solid surface. Thus, the variation of the contact angle of a series of polar and non-polar liquids on various polymer substrates appears to be in better agreement when compared to the classical description of permanent polar interactions, so that a surface polarizability is defined for polymers. Using the surface polarizability approach rather than the polar component for the solid surface, we find also that the dispersion (non-polar) component of the polymer surface free energy is obtained with a better confidence, especially by taking into account the contact angles of both non-polar and polar liquid probes, or even by considering only polar liquid probes.

The surface free energy of a polymer can be easily calculated by the Group Contribution Method developed by the authors. After having briefly recalled the method and illustrated it with new examples, the latest developments including the Weighted Group Contribution Method and the study of the molecular weight dependence of surface free energy are also expounded.

Finally, very simple means to determine the dispersive contribution to the surface energy are described. The dispersive component values calculated from the Lifshitz theory, and from the solubility parameters, are in good agreement with those obtained from wettability measurements.

The increasing use of polymeric materials in high technological fields, such as automotive, has forced the need to overcome some of their limitations by means of innovative processing. In the automobile industry a complex and critical process is used in order to enhance both wettability and adhesive properties of polypropylene bumper surfaces. Cold plasma treatment represents an efficient, clean and economic alternative to activate polymeric surfaces.

The present work deals with air cold plasma treatment of polypropylene surfaces. Particularly, the influence of AC electrical discharge cold plasma parameters on wettability and adhesion of polymeric surfaces was studied. Also, the nature of the relationship between wettability and adhesion was investigated. Owing to the complexity of plasma–workpiece interaction, an experimental approach was followed. A set of process variables (voltage, time and air flow rate) was identified and used to conduct some experimental tests on the basis of design of experiment techniques. The experimental results show that the proposed plasma process may considerably increase polypropylene wettability and adhesion properties. These outcomes represent the first step in trying to optimise the polymeric adhesion by means of this non-conventional manufacturing process.

Analytical expressions have been derived relating the length, surface area, volume, and Laplace excess pressure of a liquid drop adhering to a cylindrical fiber to linear drop dimensions and the contact angle. Extensive tables of dimensionless forms of these quantities have been computed. The calculations form the basis of a precise and accurate method for measuring contact angle in such systems. A description of experimental technique for contact angle measurement is given, together with results for some well-defined systems.

Compounds based on polyolefins may find further use in the footwear industry as solings. However, a significant problem is the poor adhesion obtained with the urethane adhesives currently used. SATRA has recently attempted to develop practical bonding systems for commercial olefinic compounds. The use of flame treatments for polyethylene appeared to be a possible method of improving compatibility between the adhesive and substrate if an isocyanate is present at the interface. Polypropylene does not respond to the flame treatment but reasonable bonds have been obtained after surface oxidation or by using a sensitiser in conjunction with UV irradiation. The use of dual compound moulding is described as a possible alternative means of obtaining adequate adhesion to difficult surfaces.

X-ray photoelectron spectroscopy (XPS) and contact angle methods were used to examine the surfaces of an homologous series of poly(ether urethane) (PEU) samples before and after cleaning treatments. Four PEU films with Shore hardnesses varying from 45 to 75 D were studied as well as two commercially available intravenous catheters of related PEUs. The four as received PEU films have similar surface compositions (~79% C, ~17% O, ~2% N, and ~ 2% Si) although they differ in bulk composition. Critical surface tension (γ_c) values are all similar and high (45-46 dynes/cm). The similarity in the surfaces of the four PEUs, despite the differences in their mechanical properties, demonstrates that surface properties do not necessarily reflect bulk properties. Soap washing and methanol-acetone extraction of the PEU films resulted in surfaces more representative of the bulk compositions of the PEUs. Analysis of the intravenous catheters confirmed that they are lubricated with PDMS, a common practice in the medical device industry. This study documents the value of detailed surface analysis for an enhanced understanding of the surface zone of PEUs. It also illustrates how cleaning protocols can remove labile surface species.

The main available theories for the dynamics of wetting are brieflysummarized and discussed in reference to experiments. In partial wetting,hydrodynamic and molecular theories are equivalently efficient, even if thephysical meaning of parameters is not so clear in the former ones. Incomplete wetting, hydrodynamic theories are the only ones valid at lowangles, but some care has to be taken in the interpretation of the “slip length” introduced to remove the divergence of thedissipation at the contact line. The situation is less favourable at themolecular scale, where the theoretical description is still at itsbeginning, due to the multiplicity of behaviours.

Polyimide films are currently of great interest for the development of flexible electronics and sensors. In order to ensure a proper integration with other materials and PI itself, some sort of surface modification is required. In this work, microwave oxygen plasma, reactive ion etching oxygen plasma, combination of KOH and HCl solutions, and polyethylenimine solution were used as surface treatments of PI films. Treatments were compared to find the best method to promote the adhesion between two polyimide films. The first selection of the treatment conditions for each method was based on changes in the contact angle with deionized water. Afterward, further qualitative (scratch test) and a quantitative adhesion assessment (peel test) were performed. Both scratch test and peel strength indicated that oxygen plasma treatment using reactive ion etching equipment is the most promising approach for promoting the adhesion between polyimide films.

Two ethylene vinyl acetate (EVA) copolymers (12 and 20 wt% of vinyl acetate,VA, content) have been treated with low pressure RF plasmas from non-oxidizing gases (Ar, N₂) and oxidizing gases (air, a mixture of 4N₂: 6O₂ (v/v), O₂ and CO₂). The formation of polar moieties on both EVAs was more noticeable by treatment with plasmas from non-oxidizing gases than from oxidizing ones (the higher the reactivity, the lower the difference with respect to untreated EVA surfaces). The surface etching with the non-oxidizing plasmas, giving rise to a high roughness, depends on the wt% of VA in the composition of the copolymer because of the different resistances of VA (low) and PE (high) to the non-oxidizing plasma particles bombardment. The adhesion properties obtained using a polyurethane adhesive (PU) showed high T-peel strength values and adhesion failure in EVAs treated with plasmas from oxidizing gases, due to roughness produced causing mechanical interlocking of the adhesive. Lower T-peel strength values were obtained with non-oxidizing plasmas: the values for EVA12 being, in general, lower than those obtained for EVA20. The durability of the treated EVAs/PU adhesive joints after ageing in humidity and temperature was quite good.

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.

Surface tension is frequently expressed as the sum of a polar and a nonpolar term. In this paper an empirical approach is proposed for approximating the nonpolar term γ_sd of the surface tension of fluoropolymers. The experimental data were obtained from contact angle measurements employing a series of linear alkanes. These data are plotted by two different methods to evaluate γ_sd. The critical surface tension γ_e obtained from nonpolar contact angle liquids should reasonably approximate the γ_sd of the fluoropolymer surface. This work is based on classical molecular interactions, many concepts of which were established in earlier reports by Fowkes, Good, and Zisman.

It is generally accepted that the surface tension of fluoropolymers is approximately equal to the sum of a polar and nonpolar term. The first paper in this series described an empirical method for approximating the nonpolar term, and this paper proposes a similar approach for determination of the polar term, based upon contact angle measurements of polar liquids. The method is applicable to other solid surfaces provided suitable contact angle liquids are available.

Electron Spectroscopy for Chemical Analysis (ESCA) is generally considered to be a non-destructive analytical technique as compared to e.g., SIMS and Auger spectroscopy. In fact, there have appeared only a few reports in the literature where soft X-ray induced spectral changes were noted. These studies have recently been reviewed by Storp. Several of these studies have been carried out with non-monochromatic X-ray sources which typically expose a sample surface with a flux of high kinetic energy electrons and thermal radiation. As pointed out by Storp, it is not entirely clear whether or not the reported changes can be therefore considered as uniquely caused by X-ray photons. Wheeler and Pepper have published a detailed beam damage study on polytetrafluoroethylene (Teflon) using a non-monochromatic X-ray source. The authors provided convincing evidence that the detected fluorine depletion of the surface is indeed caused by X-rays rather than electron bombardment. We wish to report ESCA experiment on Teflon and several other polymeric materials using a spectrometer with a monochromatic Al Kα X-ray source. Due to the physical separation between source and sample an unambiguous differentiation between X-ray vs. electron induced damage can be obtained.

The recently observed enhancement in adhesion between Cu and Teflon due to a presputtering treatment of Teflon prior to the Cu deposition is analyzed. The sputtering treatment resulted in a morphology change of the Teflon, with the deposited Cu showing similar textures, and changes in chemical bondings between the two. A simple geometric model is used to analyze the contribution from the morphology changes to the observed peel strength. It is shown that, for a finite chemical bonding, an appreciable contribution to the peel strength is possible from the morphology changes observed.

Applications of corona discharge induced plasmas and unipolar ions are reviewed. Corona process applications emphasize one of two aspects of the discharge: the ions produced or the energetic electrons producing the plasma. The ion identities depend on the polarity of the discharge and the characteristics of the gas mixture, specifically on the electron attaching species. The electron energies depend on the gas characteristics and on the method of generating the corona. In general, in an application using ions, the corona induced plasma zone will occupy a small fraction of the total process volume, while a process using the electrons will fill most of the volume with the plasma. Current state-of-the knowledge of ionized environments and the function of corona discharge processes are discussed in detail.

Pyrene time-resolved fluorescence has been applied to correlate the surface tension levels obtained for polyethylene and polypropylene films after exposure to corona-discharge treatment. The surface tension level of the films was validated with surface tension test fluids according to the ASTM D2578 standard test method. Although in direct contact with air, pyrene showed an extremely long lifetime upon deposition on the polymer films, which approached the lifetime of pyrene in freeze/pump/thaw deoxygenated hexane. The I/III ratio of pyrene fluorescence at 373 and 384 nm, designated as bands I and III, was determined at 150-ns delay relative to the time at laser maximum. Prolonged time delay was imposed before fluorescence measurement in order to minimize the background interferences from the blank films. Measurements of the time-resolved pyrene fluorescence I/III ratio from pyrene/ethanol depositions showed averages of 0.63, 0.56, and 0.49 for 42, 35, and 30 dyne/cm treated films. The uncertainty of the measurements was estimated to be 1–2 dyne/cm. Application of the pyrene I/III ratio can be used easily to monitor incorrectly and nonuniformly treated polymer film surfaces.