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.

Many plastics have a poor tendency to bond to other materials because of their inherent inert chemical structure and thus require a pretreatment. Wet chemical methods are expensive because of the disposal of the waste liquids. In this study, the corona treatment (Ional process), the low-pressure plasma process, and the fluorination process were tested and compared with each other. The following plastics were tested: PP (polypropylene), PBT (polybutyleneterephthalate), PBT blends, and a high-temperature thermoplastic, PEEK (polyetheretherketone). In particular, the low-temperature plasma process results in excellent adhesion strength. In addition, we have shown that the stability of freshly plasma-treated surfaces could be maintained for time periods of at least several days.

The surfaces of polymers, namely polypropylene, copolymers and blends, were exposed to low pressure oxygen and atmospheric pressure air plasmas to improve their adhesion to polyurethane adhesives. A correlation is attempted between lap shear strengths of polypropylene-polyurethane composites and the relevant XPS, AFM and NEXAFS data. It was found that plasma functionalization improved the adhesion to maximum values even when the time of exposure was low: 1 to 10 seconds for low pressure plasmas, and 0.1 to 1 seconds in case of atmospheric plasma jet treatments. Thus, high lap shear strengths were obtained at relatively small oxygen contents. The improvement in shear strength at short time plasma exposures seems to be correlated to the complete smoothening of the supermolecular structure of stretched polypropylene foils as shown by AFM. Valence band XPS and derivatization techniques revealed more details of the oxygen functionalization on polypropylene. NEXAFS experiments confirmed a re-orientation of bonds and segments of the macromolecules by plasma exposure which are assumed to be responsible for adhesion improvement.

Plasma treatment changes the solvent absorption and permeation as well as the swelling properties of polymers. Enchanced solvent absorption and swelling are effects of an improved solvent compatibility. The plasma introduces a large number of different groups at the polymer surface depending on the nature of the plasma. Fluorine-containing plasmas can replace hydrogen atoms of the polymer molecule with fluorine atoms. Moreover, fluorine-containing plasma polymer layers can be formed. All these processes reduce the resulting surface free energy, reduce the diffusion length of solvent molecules, and produce a barrier layer. We have studied the formation of solvent barriers by plasma fluorination and by crosslinking by ultraviolet (UV) radiation. Thin foils of polypropylene (PP) and polyethyleneterephthalate (PET) were used as substrates. CF₄, SF₆, and SOF₂ were applied as sources of fluorine atoms. Hexafluoropropene, tetrafluorethylene, and perfluorohexylethylene form plasma polymer layers on the polymer substrates. Test solvents were n-pentane, tetrachloroethylene, dimethylsulfoxide, and mixtures of n-pentane and methanol.Plasma treatment changes the solve The permeation rate of solvents through plasma-modified polymers was measured gravimetrically. Mass spectrometry was applied to analyze the permeating components of the solvent mixtures. Fluorination of surface layers by plasma-chemical (CF₄, SF₆) means considerably reduces the permeation rate of PP (95% barrier effect) and PET (100%). The preferred permeation of one component of the pentane/methanol mixture is influenced by the polarity of plasma-introduced groups at the polymer surface.

It is recognized that the non-dispersive components, γ^ab, of the surface free energies, γ, play an important role in the interactions of a polymer with other substrates. Because of the difficulty in measuring the surface free energy of a solid polymer surface, many methods to estimate γ have been developed. The purpose here is to examine how to characterize a high energy polymer surface using our recently proposed model and the modified two-liquid contact angle technique. First, the dispersion component, γ^d, of surface free energy of polystyrene (PS) is obtained by measuring the contact angles of water on PS surface in a series of n-alkanes. Its γ^ab is then calculated by our three-parameter semi-empirical model using the contact angle data of several key non-alkane liquids on the surface. Given the surface thermodynamic parameters, our model also enables us to calculate the interfacial free energies, γ_SL, between PS and other liquids. An attempt to relate γ_SL to the equilibrium concentrations of crazing solvents in PS is presented.

Surface biomedical effects of plasma treatment and plasma polymerization on medical-grade polyetherurethane were studied. N2 and Ar plasma treatments and hexamethyldisiloxane (HMDS) plasma polymerization were performed at a power of 100 W with exposure times ranging from 1 to 15 min. The results showed that the contact angle of water was decreased from 79° to 62° by N2 and Ar plasma treatments, and N2 plasma treatment caused a slight enhancement in anti-coagulability and anti-calcific behavior. HMDS polymerization resulted in a decrease from 79° to 43° in the contact angle and an increase from 30.5 to 37.4 s in the recalcification time. At the same time, the anti-coagulability of polymerized samples for the exposure time of 2-5 min was 2.5 times that of the untreated sample. Results of XPS and ESR analyses showed that HMDS deposited onto the polyetherurethane surface and formed new Si-N bonds, and increased the number of radicals in the sample. XPS analysis also showed that N2 and Ar plasma treatments broke some of the CO and CO bonds at the surface and resulted in oxidation of the surface.

The surface energetics and acid-base character of paper handsheets were investigated using dynamic contact angle analysis. The surface energies were calculated using both geometric and harmonic mean methods. The surface acid-base property was characterized by calculating the work of acid-base interaction according to Fowkes' theory. To evaluate the effect of sizing on the paper surface properties, handsheets with various sizing treatments were studied in comparison with unsized handsheets. It was found that the sizing on the paper handsheets tends to reduce the surface energy and cover the acid-base sites. The results also show that the handsheet surface can be characterized directly using contact angle analysis.

The effect of the addition of clay and TiO₂ pigments on the surface energy and surface chemistry of films made from polymers used in paper coating formulations was evaluated. The polymers were carboxymethyl cellulose, polyvinyl alcohol and a protein-based polymer - all water-soluble - and two styrene-butadiene latexes of different carboxylation levels. The morphology of the surfaces was characterized by SEM examination, gloss measurement and stylus profilometry. Chemical composition was determined by EDS and XPS techniques. Surface energy and its Lifshitz-van der Waals and acid-base components were obtained from contact angle measurements using the van Oss et al. approach. Even though the addition of pigment increasingly upset the planar surface of the films, their surface chemistry and surface energy were only slightly affected over the pigmentation range studied (up to 40% by volume) and were dominated by the characteristics of the binder polymer.

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.

Polypropylene (PP), low-density polyethylene (LDPE), and high-density polyethylene (HDPE) sheets were surface-modified by radio-frequency ammonia plasmas in order to improve the strength and durability of adhesive bonding, particularly under hot and humid conditions. Surface analyses by contact angle measurements, XPS (X-ray photoelectron spectroscopy), and FTIR-ATR (Fourier transform infraredattennuated total reflection) showed incorporation, upon plasma treatment, of both nitrogen- and oxygen-containing functional groups on the polyolefin surfaces, with similar surface compositions on modified LDPE and PP. Plasma-treated polyolefin samples bonded with a cyanoacrylate adhesive possessed a high shear bond strength in ‘dry’ conditions. On exposure to hot and humid conditions (immersion in 60°C water), the bond strength decreased with time in some cases while for other samples the lap shear strength was the same after exposure to the humid environment for 1 month compared with that under 'dry' conditions. Ammonia-plasma-treated HDPE specimens displayed the best strength retention upon water immersion. The excellent durability of the bond strength under humid conditions is indicative of covalent bonding between the cyanoacrylate adhesive and amine groups, which unlike physical bonding (e.g. van der Waals interactions) is not disrupted by the ingress of water molecules. It is also possible that the structure of the interphase is in the form of an interpenetrating network, obtained through penetration of the adhesive into the plasma-modified laycr, followed by covalent bonding and curing of the penetrated adhesive.

Surface pretreatment methods to enhance adhesion to polymers with low surface energies generally either remove a region of low strength from the surface or introduce new surface functional groups. The relative importance of these two mechanisms is examined in the present paper for various combinations of pretreatment and polymer.