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.

Six solid surfaces were compared with respect to their surface quality, by measuring advancing contact angles along the solid surfaces (in the vertical and horizontal directions) at constant immersion rate. It was found that surfaces of mica, dip coated in FC-721, Teflon (FEP) heat pressed against mica, and siliconized glass yield essentially constant advancing contact angles at different locations of the solid surfaces and, thus, are well suited to dynamic contact angle measurements. Static and low rate dynamic contact angles of a number of pure liquids were therefore measured on these solid surfaces. Low rate dynamic contact angles were found to be identical with the static contact angles and independent of the velocity of the three-phase contact line (up to 0.5 mm/min).

Paper, although ubiquitous, is a complex material. We can classify paper as a basic network of self bonding cellulosic fibers; the chemical and physical characteristics of its surface are controlled by the raw materials, papermaking and converting processes used to produce it. Paper sometimes contains non-cellulosic fibers such as non-wood and synthetic fibers, chemical additives, fillers, and bonding agents. Other chemical additives used in the papermaking process, e.g., formation, drainage, and retention aids or coating materials may also change the physical and chemical characteristics of the paper's surface. With the greater use of recycled fibers we may expect additional changes in surface chemistry and structure.

Adhesion between two substrates is a complex phenomenon which at present is still not well understood. The important existing adhesion models (electrical, diffusion, thermodynamic adsorption, chemical, etc.) are reviewed in order to try to explain their mechanisms. Thermodynamic adsorption is now believed to be one of the most importnat mechanisms by which adhesion is achieved. Difusion and wetting are kinetic means in attaining good adsorption of a polymer at the interface. In the case of this model (thermodynamic adsorption), the notion of surface energy is developed and the importance of this property in the understanding of adhesion phenomena is emphasized. The methods of determining the surface characteristics of low and high energy solids are presented. The role played by acid-base interactions in adhesion is also mentioned.

Tightly integrated composite products are obtained by treating a fluoropolymer member on its surface with atmospheric pressure glow discharge plasma in a helium gas atmosphere containing 97% by volume or more of helium gas, and joining another member of rubber compositions, resins, metals, ceramics, or semiconductors to the surface treated fluoropolymer member. By using a fluoropolymer sheet as the fluoropolymer member and a metal or synthetic resin layer as the other member, there are obtained weather-resistant composite sheets in which the layer is firmly bonded to the fluoropolymer sheet.

A steady-state, glow discharge plasma is generated at one atmosphere of pressure within the volume between a pair of insulated metal plate electrodes spaced up to 5 cm apart and R.F. energized with an rms potential of 1 to 5 KV at 1 to 100 KHz. Space between the electrodes is occupied by air, nitrous oxide, a noble gas such as helium, neon, argon, etc. or mixtures thereof. The electrodes are charged by an impedance matching network adjusted to produce the most stable, uniform glow discharge.

The technique of inverse gas chromatography (IGC) is used to investigate and compare the surface chemical properties of chlorine dioxide-bleached pulps with peroxide- and ozone-bleached pulps and to study the influence of a latex binder (with dispersant) on the properties of calcium carbonate coating particles. IGC measurements with a series of alkane probes yield the dispersive component of the surface energy of the test solid and show only small differences between the various bleached pulps. The use of acid and base probes shows all pulps tested to be predominantly acidic. The presence of latex binder together with a poly (acrylic acid)/carboxymethyl cellulose dispersant decreases the dispersive component, but increases both the acidic and basic components, of the surface free energy of calcium carbonate.

Polymer materials such as film and fabrics, woven, non-woven and meltblown, may be non-destructively surface treated to improve water wettability, wickability, and other characteristics by exposure to a glow discharge plasma sustained at substantially atmospheric pressure in air or modified gas atmospheres comprising helium or argon.

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

A meat product package including an enclosing film having an EVA-containing inside surface and an in situ aqueous medium-cooked meat product in adhering relation to the film inside surface as the meat contacting and adhering surface. Starch particles are preferably dispersed across the meat contacting surface which has been both irradiated and subjected to corona treatment. A method for corona treating a thermoplastic tube inside surface in which small particles within the flat tube separate opposite surfaces providing voids, and the electric discharge crosses the flat tube through the voids.

In this paper we describe the preparation and preliminary characterization of diblock copolymers with a low surface energy block. These polymers were prepared by modifying the isoprene block in styreneisoprene-based block copolymers with either short perfluoroalkyl or dimethyl siloxy ‘fingers’. Specifically, the diene block of a styrene-isoprene block copolymer containing a large proportion of pendent vinyl groups (1,2- and 3,4-isoprene) was reacted with the appropriate hydrosilane in the presence of non-acidic Pt catalyst. The degree of attachment of hydrosilane was as high as 50% of the pendent unsaturations. Pendent vinyl groups were converted more efficiently than pendent methyl vinyl groups. These block copolymers, when mixed with the styrene homopolymer, exhibited surface segregation behaviour which depended on both polymer molecular weight and processing conditions. The surface segregation properties of the resulting block copolymers were studied by a variety of techniques which include contact angle measurements, and either X-ray photoelectron spectroscopy or Rutherford backscattering spectrometry. Contact angles as high as 110° were measured for both the siloxane- and perfluoroalkane-modified materials.

Laser-induced surface modification of different polymers is presented as a suitable pretreatment of surfaces in a two-step metallization process. Materials such as polyamide (PA), polypropylene (PP), polystyrene (PS), polycarbonate (PC), acrylbutadienestyrene (ABS), styreneacrylnitrile (SAN), polybutadieneterephthalate (PBT), and polyoxymethylene (POM) were treated by excimer-laser radiation at 248 nm in air. The aim of this study is to investigate different processing regimes of surface modification and ablation to increase surface roughness. Therefore, the laser-processing variables fluence F, repetition rate v and pulse number N are varied and the ablation depth, optical penetration depth, absorption coefficient and ablation threshold are determined. The metallization of pretreated (laser, wet chemical and plasma etching) polymers is investigated for different surface morphologies. The used metallization processes were electroplating and physical vapour deposition (PVD). The adhesion of the deposited films is measured with scratch and tape test methods in order to determine the regimes of suitable surface modification for metallization.

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.

The possibility of characterizing dispersion forces and acid-base interactions by means of physico-chemical measurements is demonstrated by the examples of contact angle and zeta potential measurements, with special attention being given to the latter. This method has been applied, to characterize the effect of plasma and flame treatment on the adhesion behaviour of injection moulded poly(propylene) specimens. The results with respect to acidic or basic functional surface sites, as obtained by zeta potential measurements, correlate with the elemental surface compositions determined by XPS. There is no general interrelation between acidic and basic parameters determined by contact angle measurements and the results of zeta potential and XPS measurements.

Unprinted, unsized, and sized security papers (SP) were treated under SiCl₄−, O₂−, and CF₄-cold plasma conditions. The plasma treatments were carried out in a stainless steel, parallel plate RF (30 kHz) reactor. The influence of plasma parameters, such as RF power, pressure, and treatment time, on the surface properties of plasma-modified security paper was examined. The newly gained surface characteristics were evaluated by Wilhelmy wettability measurements, x-ray photoelectron spectroscopy (ESCA), and scanning electron microscopy (SEM). Statistical experimental designs were used to understand the interactive effects of the plasma parameters. It was found that short treatment times and low RF power values produced the highest wettability with both SiCl₄ and O₂ plasmas regardless of the sizing. Printing and durability characteristics of the plasma-treated substrates were equivalent or superior to the standard samples. Mechanisms of plasma-induced surface modifications are discussed for the paper substrates.

Oxidation is the most common surface modification of polymers. This paper presents a comparison of five gas-phase surface oxidation processes: corona discharge, flame, remote air plasma, ozone, and combined UV/ozone treatments. Well-characterized biaxially oriented films of polypropylene and poly(ethylene terephthalate) were treated by each of the five techniques. The surface-treated films were then analyzed by X-ray photoelectron spectroscopy (XPS or ESCA), contact-angle measurements, and Fourier-transform IR (FTIR) spectroscopy. Corona, flame, and remote-plasma processes rapidly oxidize polymer surfaces, attaining XPS O/C atomic ratios on polypropylene of greater than 0.10 in less than 0.5 s. In contrast, the various UV/ozone treatments require orders of magnitude greater exposure time to reach the same levels of surface oxidation. While corona treatment and flame treatment are well known as efficient means of oxidizing polymer surfaces, the ability of plasma treatments to rapidly oxidize polymers is not as widely appreciated. Of the treatments studied, flame treatment appears to be the ‘shallowest’; that is, the oxygen incorporated by the treatment is most concentrated near the outer surface of the film. Corona and plasma treatments appear to penetrate somewhat deeper into the polymers. At the other extreme, the UV/ozone treatments reach farther into the bulk of the polymers.

COF groups are formed by electron irradiation of PTFE [poly(tetrafluoroethylene)] powders in air, especially at the surface and in near-surface regions which can be easily hydrolysed to carboxyl groups by air humidity. The application of special additives during irradiation leads to modified micropowders. Fourier transform infrared (FTIR) spectroscopy enables the detection of carboxyl and COF groups. γ-Irradiation of PTFE mainly causes degradation of the polymer; the concentration of carboxyl groups is much lower. Carboxylated micropowders created via radiation treatment retain the essential properties of PTFE. With increasing radiation dose, the increasing concentration of functional groups in the micropowders causes an increase in the surface free energy. This diminishes the strong water and oil repellency of PTFE in such a way that homogeneous incorporation into aqueous and organic liquids or other polymers is possible. So, the special properties of PTFE can be made effective in these media. Modified PTFE micropowders have been successfully tested in many application areas. The aim of our present work was to increase the concentration and vary the nature of functional groups by radiation-chemical methods or chemical conversion of COF groups (polymer-analogous reactions). A highly modified PTFE powder was used to reduce the repellent properties of PTFE diaphragms for application in brine electrolysis. The COF groups of the micropowders were modified by γ-aminopropyltriethoxysilane. The irradiation of FEP [poly(tetrafluoroethylene-co-hexafluoropropylene)] and PFA [poly(tetrafluoroethylene-co-perfluoroalkylvinylether)] yields products which contain a higher content of carboxyl groups than PTFE.

Polyethylene, polypropylene, polyisobutylene, and polystyrene films have been exposed to high- and low-pressure non-equilibrium electrical air discharges. The modified surfaces have been characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Atmospheric silent discharge treatment causes a greater level of topographical disruption, whereas surface oxygenation is dependent on the chemical nature of the polymer substrate and its reactivity towards the electrical discharge medium. Oxygen incorporation occurs much more readily for the unsaturated polystyrene surface than for the saturated polyethylene, polypropylene, and polyisobutylene substrates.

Contact angle, electrokinetic, and X-ray photoelectron spectroscopic (XPS) measurements have been used to study the surface properties of flame- and oxygen plasma-pretreated polypropylene/ ethylenepropylene-diene monomer rubber (PP-EPDM) blends and of ethylene vinyl acetate (EVA) copolymers grafted with carboxyl group-containing monomers. The contact angles of pure test liquids (water, methylene iodide, and ethylene glycol) were used to calculate the dispersive and polar components of the surface free energy according to Owens and Wendt, and the acid-base parameters according to Van Oss and co-workers. In addition, the acid-base properties of the differently pretreated polymers could be evaluated quantitatively by measuring the zeta potential vs. the pH in a 10^-3 mol/l KCI solution. The zeta potential measurements show that oxygen plasma-treated PP-EPDM and grafted EVA indicate an acidic surface character, whereas the flame-treated PP-EPDM blends possess both acidic and basic surface groups. The basic surface character of flame-treated PP-EPDM injection-moulded sheets could be enhanced by the presence of sterically hindered amine light stabilizers in the blend. This increase in the basic surface character was not only proved by zeta potential measurements, but also by the contact angle method according to Van Oss and co-workers. These results correlate with an increase of the oxygen content in the surface region and the occurrence of nitrogen-containing functional groups detected by XPS. The plasma-treated surface region of PP-EPDM blends contained an increased amount of carboxyl group-containing species (O=C-O). Flame-treated surfaces with additional light stabilizers in the blend indicated an increased concentration C-OH groups together with protonated nitrogen in the surface region. It was found that the adhesion strength of water-based primers was higher at these surfaces. A general interrelation between the acidic and basic parameters determined by zeta potential measurements, on the one hand, and the acidic and basic parameters determined by contact angle measurements, on the other hand, could not be found. A direct correlation was found between the increasing acidic character of EVA grafted with different amounts of carboxyl group-containing monomers and the decrease in the receding contact angle.

The effects of exposure to ultraviolet (UV) light and ozone, separately and in combination, were investigated with respect to polypropylene (PP) and poly(ethylene terephthalate) (PET) surfaces. Three combinations of UV light and ozone were studied: ozone only, UV light in air (producing ozone), and UV light in air (producing ozone) supplemented by additional ozone in the incoming air. The effect of the exposure time of the PP and PET to each treatment was studied. The samples were analyzed by X-ray photoelectron spectroscopy (XPS) to determine the surface composition, and by dynamic contact angle to determine the water wettability. The results showed that the effect of the treament was dependent on the properties of the exposed polymer, with PET being more sensitive to the UV light and PP being more sensitive to the reactive species in the gas. The exposure times studied ranged from 1 to 90 min. By monitoring the oxygen uptake levels, we were able to determine that surface modification occurred within minutes. The possible reactive species and mechanisms are discussed.

In this study we investigated the stability of poly(ethylene terephthalate) (PET) and polypropylene (PP) surfaces modified using three combinations of UV light and ozone: ozone only, UV light in air (producing ozone), and UV light in air supplemented by additional ozone in the incoming air. Analysis was done using X-ray photoelectron spectroscopy and dynamic contact angle measurements. Our results showed that PET film is oxidized using these treatment conditions and it changes significantly within the first week of aging and after washing with water. These changes are reflected in the decrease in the Δ(O : C) ratio and the increase in the contact angle. Conversely, PP changes very little on aging or washing. Low-molecular-weight oxidized material (LMWOM), produced on the polymer surfaces treated with UV/air or UV/air + ozone, is easily removed with water washing. On aging PET, a number of the oxidized groups at the surface disappear, seeming to migrate into the bulk. The PP, however, does not favour migration as a path to reduce the overall free energy of the system, so the oxidized groups remain at the surface. Treatment with ozone only, in the absence of UV light, is a much different modification process in terms of the mechanism and the functional groups formed on the surface. This is reflected in the aging and washing behaviour of both the PET and the PP treated with ozone only.

Modification of a selective area of a fluororesin surface was accomplished by using ArF excimer laser radiation and a boron complex with oleophilic or hydrophilic functional groups. The chemical stability of fluororesin is attributed to the presence of C-F bonds. The F atoms were abstracted by B atoms selectively from the area irradiated with excimer laser radiation and were replaced with the desired functional groups. In this modification, B(CH₃)₃ and B(OH)₃ were used: a boron compound with methyl groups to generate an oleophilic surface, and one with hydroxyl groups to generate a hydrophilic surface. As a result, the resin surface exposed to ArF laser radiation becomes oleophilic or hydrophilic. Both samples were bonded to stainless steel plates with an epoxy bonding agent and the tensile shear strength was 1.2 x 10⁷ Pa in both cases.

Polypropylene (PP) surface in water was photochemically modified to render it hydrophilic using ArF excimer laser radiation. The chemical stability of PP is attributed to the CH and CH₃ bonds present. Thus, it is considered that H atoms are selectively pulled out from the area irradiated with ArF excimer laser light and are replaced with OH functional groups in the presence of water. In this treatment, the irradiated sample becomes hydrophilic with enhanced adhesion properties. The experimental conditions for this surface treatment were ArF laser fluence of 12.5 mJ/cm² and a shot number of 10000. The treated PP and stainless steel were bonded with epoxy adhesive and the tensile shear strength was 46 kg/cm².