The formation of the interface between aluminium and O₂ or CO₂ plasma-modified poly(ethylene terephthalate) (PET) has been investigated by X-ray photoelectron spectroscopy (XPS). As demonstrated by the changes in the C 1s, O 1s, and A1 2p core level spectra upon A1 deposition, the metal was found to react preferentially with the original ester, with the plasma-induced carboxyl and carbonyl groups to form interfacial complexes. The phenyl ring at the modified PET surface was seen to be involved in the formation of the interface, but to a lesser extent. This confirms the high reactivity of the oxygen-containing groups towards the deposited A1 atoms. The adhesion between A1 and the plasma-modified PET films was evaluated by means of a 180° peel test. A considerable (up to ten times) improvement in adhesion was achieved by plasma treatment of the PET substrate, but for either plasma gas the adhesion strength was found to depend strongly on the plasma power and treatment time. The results are discussed in terms of the concentration of oxygen-containing groups at the polymer surface, the surface topography, and the possible presence of low-molecular-weight materials at the metal-polymer interface.

Ethylene-propylene diene monomer (EPDM) containing dicyclopentadiene (DCPD) and ethylidene norbornene (ENB) as the termonomers, styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR) have been surface-modified by 10% methyl ethyl ketone (MEK) solutions of trimethylol propane triacrylate (TMPTA) at an irradiation dose of 100 kGy. The irradiation dose and TMPTA concentration were optimized using samples treated with 2, 5, 10, 20, and 50% TMPTA and 50, 100, 200, and 500 kGy doses. Two per cent solutions of acrylate rubber having diene, chloro, and epoxy groups at the reactive sites and tripropyleneglycol diacrylate (TPGDA) and tetramethylol methane tetracrylate (TMMT) were also employed as the surface modifiers. The level and nature of the vulcanization system were varied. The modified rubbers were characterized by attenuated total reflection infrared (ATR-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. IR and XPS studies confirmed the generation of polar groups such as CO and COC on the surfaces. The contact angles and the surface energy change with the nature of the modifiers, rubbers, diene monomers, the crosslinking system and the level of the curing agent. The total surface energy and the thermodynamic work of adhesion of the different systems have been correlated with the amount and the nature of the polar groups generated.

Ultra-high molecular weight polyethylene (UHMWPE) fibers were subjected to oxygen plasma treatment in order to improve interfacial adhesion. The treated fibers were characterized by contact angle analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and mercury porosimetry. The surface free energy, O 1s/C 1s ratio, and surface area increased dramatically with 1 min treatment. However, as the treatment time increased further, these parameters either increased slowly at 30, 60, and 100 W, or decreased at 150 W. The increased surface free energy is attributed to the polar component, while the increased O 1s/C 1s ratio is explained by the oxygen-containing moieties introduced by the plasma treatment. The oxygen plasma treatment also roughened the initially smooth surface of the UHMWPE fibers by forming micro-pores and thus increased the surface area. The interfacial shear strength of UHMWPE fibers to vinylester resin was measured by micro-droplet tests and exhibited an increasing trend, believed to result from the increased surface area, the surface free energy, and the oxygen-containing moieties due to the plasma treatment.

One of the causes leading to low bond strength between a coating and a substrate (adhesion strength) - if coatings are formed at elevated temperatures in air - is assumed to be a weak boundary layer generated in the region of adhesional contact: the boundary layer consisting mostly of low-molecular-weight products resulting from thermal oxidative degradation of the polymer. It has been verified experimentally that products of oxidation diffuse from the coating surface layer to the contact area. The oxidation process is supposed to be localized within that surface layer. A method has been devised to determine the thickness of the layer, and model experiments have been conducted to show that low-molecular-weight products of oxidation deteriorate the adhesion strength. Ways have been found to increase the adhesion strength of coatings by means of modification of the coating applied in a layer-by-layer manner. The idea is to introduce separately such modifiers as antioxidants, inorganic fillers possessing high adsorption capacities, and crosslinking agents into the coating surface layer. This method of coating modification allows one to eliminate the negative effects of the low-molecular-weight products generated in the surface layers during the formation.

In extrusion coating, the inadequate adhesion between the polymer coating and the fiber-based paper substrate (paper and paperboard) is both a common and a constant problem. The lack of adhesion between the printing ink, or glue, and the polymer coating is another area where adhesion improvement is needed. The common means of improving adhesion are flame, corona, and ozone treatments. A modem extrusion coating line is equipped with both a pretreatment and a post-treatment unit. From the work presented here, the following observations were made. The higher the applied corona power and the thicker the coating, the higher the surface energy and polarity of the low density polyethylene (PE-LD) surface. When a high corona power was applied to the coating, only the polar component of the surface energy was increased. The surface energy decreased sharply as a function of aging, but remained more or less constant after about 2 weeks' storage time. The contact angles of water on paper correlated well with the oxygen contents (determined by ESCA) and with the applied corona power. The polarities of both paper and paperboard increased as a function of the applied corona power. Corona pretreatment of paper and paperboard improved their adhesion to PE-LD remarkably. The adhesion of the polypropylene (PP) homopolymer is based more on mechanical interlocking than on interfacial bonding. On the other hand, the oxidizing pretreatments of the paper substrates significantly promoted the adhesion of the PP copolymer.

Surface modification of Kapton polyimide film (325 nm thick) by means of chromic acid and perchloric acid at different times and temperatures has been carried out. The contact angle of water decreased from 82 to 55° and the surface energy increased accordingly from 26 to 45 mJ/m² with times of etching by chromic acid up to 45 min at 33°C. Etching at higher temperatures increased the surface energy. Chromic acid was more effective than perchloric acid. IR and XPS studies indicated multiple bonding and generation of poler groups on the surface. The peak at 1778 cm^-1 due to the imide group decreased on acid etching. The O/C ratio increased and the N/C ratio decreased. The peel strength of the joint polyimide film/copper film/epoxy adhesive/aluminium sheet increased about two-fold on modification of the polyimide (PI) film at 33°C for 45 min, although the changes were marginal for the PI film/silicone rubber/PI film joint. The peel strength is a function of the time and temperature of etching.

Chemical modification of the PET surface by carbon dioxide plasma treatment has been studied using X-ray photoelectron spectroscopy (XPS). The plasma process results mainly in the formation of carbonyl, carboxyl, and carbonate groups at the PET surface. Under rather mild treatment conditions (low plasma power combined with a short treatment time), the formation of CO bonds was found to be dominant, whereas the formation of highly oxidized carbon or double-bonded oxygen-containing groups required a high plasma power or a relatively long treatment time. The treatments performed under excessive conditions frequently led to degradation at the polymer surface. Angle-resolved XPS analyses performed on a freshly modified PET film showed a slight decrease in the O/C atomic ratio when the take-off angle (TOA) increased, indicating a relatively uniform distribution of oxygen within the sampling depth (estimated to be about 8 nm at 80° TOA). The chemical composition of the plasma-modified surface was found to be relatively stable on extended storage in air under ambient conditions. The decrease in oxygen-containing groups at the carbon dioxide-plasma-treated PET surface upon ageing is mainly ascribed to the surface rearrangement of macromolecular segments, the loss of oxygen-containing moieties introduced by the plasma treatment, and the possible migration of non-affected PET chains from the bulk to the surface region.

Modification of polymer surfaces by changing the chemical structure, surface energy, and bonding characteristics has considerable technological importance in the area of adhesion. Reactive ion etching (RIE) and ion beam (IB) bombardment were employed to modify the surfaces of fully imidized 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride-p-diaminophenyl (BPDA-PDA)-based polyimide (PI) films. These modification techniques affect only a shallow surface region, approximately 10-20 nm, and the bulk properties of the polymer are unaffected. The angle-resolved X-ray photoelectron spectroscopy (XPS) technique was used to characterize the PI surfaces modified by argon IB bombardment or oxygen RIE treatment. On the argon ion-bombarded surfaces, the XPS spectra indicate that the carbonyl and imide groups are decreased. Oxygen RIE treatment resulted in an increase in the atomic concentration of oxygen. To understand the surface aging effect, the freshly modified PI surfaces were exposed to laboratory air for 1 and 2 days. The changes in composition as a function of the depth of the modified surface region right after treatment and after aging were determined by the angle-resolved XPS technique (ARXPS). Contact angle measurements were used to determine the polar and dispersion components, the sum of which is the surface free energy. The polar component of the surface free energy shows the greatest change, with an increase of 8.0-9.4 times for both the oxygen RIE and ion beam treatments as compared with the as-cured PI surface. Aging of these modified surfaces resulted in a decrease of surface free energy as compared with the just-modified surfaces. In the case of oxygen RIE treatment, the dispersion component of the surface free energy showed little or no change from the as-cured sample. Adhesion of chromium/copper/chromium (Cr/Cu/Cr) films on PI was determined by peel strength measurements. Significant increases in peel strength, by a factor of 10-80, were shown for the modified surfaces. A good correlation between the peel strength and the experimentally determined polar component of surface energy was shown.

The O₂ and O₂-N₂ ([N₂] < 15%) post-discharge microwave plasma modifications of high-density polyethylene (HDPE) and hexatriacontane (HTC) surfaces have been studied as a function of the distance from the discharge and the gas composition. They are compared in terms of the in-situ XPS O/C ratios and C 1s components, and the ex-situ ToF-SIMS O^-/CH^- ratios and relative intensities of series of peaks. The results on the effect of the distance from the discharge showed a clear correlation between the in-situ XPS results and the O₂ post-discharge modeling, exhibiting the double role of oxygen atoms: functionalization initialization by creating radicals (which react with molecular oxygen) and degradation due to the energy released by the oxygen atom recombination process. Specific in-situ XPS and ex-situ ToF-SIMS signatures of this in-situ degradation related to the oxygen atom recombination process were exhibited. When N₂ was introduced in the plasma gas, the in-situ XPS results and the ex-situ ToF-SIMS results were very different. The in-situ functionalization decreased as a function of the N₂ addition and the ex-situ functionalization exhibited a high maximum for the 5% N₂-95% O₂ post-discharge plasma and then decreased. Despite the absence of a complete O₂-N₂ post-discharge modeling, it can be assumed that there is also a maximum of the oxygen atom content for the 5% N₂-95% O₂ post-discharge. Thanks to the in-situ XPS and ex-situ ToF-SIMS specific signatures, it was also shown that this maximum corresponds to a low in-situ degradation effect. Nitrogen introduction could influence the role of oxygen atoms in such a way that there is a decrease in oxygen atom recombination processes (thus in degradation) for small N₂ addition and even a decrease in oxygen functionalization initialization for further N₂ incorporation in the plasma gas. No nitrogen was observed in the in-situ XPS results, whereas some ex-situ ToF-SIMS nitrogen-containing ions were observed for the O₂ and O₂-N₂ post-discharge. However, their relative intensities followed the variation in oxidation and not the variation in N₂ concentration in the plasma gas. They could be related to a post-treatment functionalization effect. Differences observed between HDPE and HTC are explained in terms of their structural differences (desorption of low molecular weight oxygen-containing fragments for HTC).

This paper describes two methods of modifying the surface energy of a plasma-polymerized film. One method is to use diphenylamine (DPA) to stabilize the surface energy increase of the polymer caused on exposure to air or a polar liquid. Another method is to use heptafluorobutyric anhydride (HFBA) to reduce the surface energy of aged (oxidized) film. The HFBA-treated film displays the same surface energy (20 mJ/m²) as the freshly prepared film. It is, however, much more stable than the as-polymerized film in propylene glycol. Other silylation and fluorinated esterification reagents were found to be much less effective. The changes in surface energy were caused by changes in the chemical structure. The chemical changes were analyzed by infrared (IR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). These changes were either caused by oxidation of the film in air, water, and propylene glycol or were induced by fluorination of the oxidized film. The polymer used in this study is a copolymer of perfluoropropane (PFP) and 3,3,3-trifluoropropylmethyldimethoxysilane (TFPS). Other physical properties, such as solubility, thickness, coefficient of friction, adhesion, and thermal transitions of the polymer, have also been studied.

The degree of roughness and the linear direction of the abrasion process operated over the adherend surface are two important design factors for the adhesive joint. Thus, in the first part of this study, the surface roughness was varied by means of different grades of abrasive paper and its effect on the joint strength was studied. An investigation involving changing the linear direction with respect to the loading direction was also carried out. These experiments were done to determine the effectiveness of the abrasion process for the pretreatment of the adherend. A significant increase in joint strength was found for the abrasion treatment. However, it was shown that different linear directions did not have any significant effect on the joint strength. In the second part of this study, thermodynamic analysis of the bonding of dissimilar polymeric materials using different adhesives in terms of their surface tension, critical surface tension, and joint strength was carried out. The aim of the study was to determine the thermodynamic criteria for maximum joint strength in bonding dissimilar materials. The results showed that the joint strength was dictated by the adherend with the lower critical surface tension. Maximum joint strength for bonding dissimilar materials is attained when the surface tension of the adhesive used is close to that of the adherend with the lower critical surface tension.

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.

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.

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.

Kevlar 149 fibers were surface-modified by NH₃, O₂, and H₂O plasmas to improve the adhesion to epoxy resin. Poly(p-phenylene terephthalamide) (PPTA) film prepared from Kevlar 149 fibers was also modified to estimate the changes in surface energy caused by the plasma treatments. The interfacial shear strength (IFSS) between the fiber and epoxy resin was measured by the microbond pull-out test. The fracture surfaces of microbond pull-out specimens were examined by scanning electron microscopy (SEM) to identify the failure mode of the microcomposites. The results showed that the IFSS of the Kevlar 149 fiber/epoxy resin system was remarkably improved (up to a factor of 2.42) by these plasma treatments and the treatment time was the governing factor in improving the IFSS. After the plasma treatments, the fracture mode of the microcomposites changed from failure at the interface to failure either in the fiber skin or in the epoxy resin. The surface free energy and the work of adhesion of water on the PPTA surface were markedly improved by the plasma treatments. The polar component of the surface free energy and the acid-base (non-dispersion) component of the work of adhesion made an important contribution to the improvement. Some correlations between the IFSS and the surface energies were found.

Kevlar 149 fibers have been surface treated with NH₃-, 0₂-, or H₂O-plasm to modify the fiber surfaces. SEM (scanning electron microscopy) is used to characterize the surface topography of fibers etched by gas plasmas. The chemical compositions and functional groups of the fiber surfaces are identified by ESCA (electron spectroscopy for chemical analysis) and SSIMS (static secondary ion mass spectroscopy), respectively. The contact angle of water on modified PPTA [poly(p-phenylene terepbthalamide)] film prepared from using Kevlar 149 fibers is also used to investigate the wettability. The results show that the etching abilities of gas plasmas are dependent on the type of gas used for plasma treatments. The contact angle data indicate that all the three gas plasma treatments are effective in rendering the surface of PPTA more hydrophilic. The ESCA analysis results show that the surface compositions of plasma-treated fibers are highly dependent on the type of gas used and treatment time. Changes in surface compositions of fibers treated by NH₃-, O₂-, and H₂O-plasma are observed. Increasing nitrogen and oxygen contents are observed for the NH₃-plasma treatment, and the O₂- and H₂O-plasma treatments, respectively. Furthermore, the incorporation of amino groups into fiber surfaces by NH₃-plasma treatment and the extensive damage of the aromatic ring and the polymer backbone by H₂O-plasma and O₂-piasma are evidenced by SSIMS.

The surface chemistry of polystyrene, used as tissue culture ware, subjected to electron beam irradiation was studied. Core-level and valence-band (VB) X-ray photoelectron spectroscopy (XPS) showed that electron beam (EB) treatment resulted in surface oxidation plus sterilization of the polymer material. The extent of oxidation by EB is linear with the dose and, as such, is analogous to gamma-radiation-induced oxidation. The data indicate that EB-radiation treatment alone provides a polystyrene surface analogous to that obtained by corona discharge or plasma plus low gamma sterilization.

The determination of solid surface free energy is still an open problem. The method proposed by van Oss and coworkers gives scattered values for apolar Lifshitz-van der Waals and polar (Lewis acid-base) electron-donor and electron-acceptor components for the investigated solid. The values of the components depend on the kind of three probe liquids used for their determination. In this paper a new alternative approach employing contact angle hysteresis is offered. It is based on three measurable parameters: advancing and receding contact angles (hysteresis of the contact angle) and the liquid surface tension. The equation obtained allows calculation of total surface free energy for the investigated solid. The equation is tested using some literature values, as well as advancing and receding contact angles measured for six probe liquids on microscope glass slides and poly(methyl methacrylate) PMMA, plates. It was found that for the tested solids thus calculated total surface free energy depended, to some extent, on the liquid used. Also, the surface free energy components of these solids determined by van Oss and coworkers' method and then the total surface free energy calculated from them varied depending on for which liquid-set the advancing contact angles were used for the calculations. However, the average values of the surface free energy, both for glass and PMMA, determined from these two approaches were in an excellent agreement. Therefore, it was concluded that using other condensed phase (liquid), thus determined value of solid surface free energy is an apparent one, because it seemingly depends not only on the kind but also on the strength of interactions operating across the solid/liquid interface, which are different for different liquids.

Polyethylene and polystyrene film surfaces have been plasma-oxidized and subsequently characterized by X-ray core level and valence band spectroscopies. The extent of polyethylene surface oxidation was found to be dependent on the power of the oxygen glow discharge employed and the length of time that the treated sample was left exposed to air prior to analysis. In marked contrast to these observations, plasma-oxidized polystyrene surfaces were much less dependent on the oxygen glow discharge power and were also found to retain their oxygenated character over much longer periods of ageing. These differences in oxidative behaviour are explained in terms of the molecular structures of the respective polymers.

The ability of polypropylene (PP) to adhere to mild steel depends to a large extent on the surface characteristics of both PP and steel. The adhesion of PP was improved by treatment in a cold plasma from oxidizing gases (O₂, H₂O, etc.). This surface functionalization was followed ex situ by means of contact angle measurements and XPS (X-ray photelectron spectroscopy) analysis. The polymer/steel assembly was fabricated by hot-pressing in vacuum, or after exposure to ambient air. Adhesion to steel, as determined by the lap-shear test, increased when the PP was treated with Ar-containing plasma gas and joined to steel after exposure to room atmosphere. Correlations between the polarity, the atomic (O/C, N/C) ratio, the dispersive component of the surface energy, and the degree of PP/steel adhesion are discussed.

The dispersive component of the surface free energy, the nondispersive interaction, with polar liquids were determined for cellulose, cellulose acetate and cellulose grafted with alkyl ketene dimer (AKD). and were calculated in the dry state as well as the fully hydrated state by the two liquid contact angle method. was found to be independent of AKD coverage. Iⁿ_sw was found to be highly dependent on AKD coverage and differed significantly between the dry and fully hydrated states. Using the work of adhesion as a criterion, it was postulated that in the dry state, the AKD molecule renders the cellulose hydrophobic, and undergoes surface restructuring in the hydrated state leading to a hydrophilic surface.

The extent of the surface crosslinking of high-density polyethylene (HDPE) under various plasma treatment conditions was investigated. The plasma modification efficiency was studied by surface energy and adhesive bond strength measurements. The results show that the surface crosslinking of HDPE takes place as soon as the HDPE is exposed to the plasma and that the crosslinking rate is a function of the plasma conditions. The surface energy and the adhesion of HDPE are greatly increased by the plasma treatment and these improvements are independent of the depth of surface crosslinking. Based on these results and our previous studies on the surface chemical composition and free radical density on the surface of HDPE after plasma treatment, the relationships among various surface changes and the surface modification efficiency are discussed.

The wettability of aluminum foil is an important concern in many industrial converting processes. X-ray photoelectron spectroscopy (XPS or ESCA) and water contact angle results indicated that relatively mild (i.e. 250 W, 15 s) oxygen plasma treatments efficiently removed residual carbon contamination from cold-rolled foil surfaces. This resulted in a significant improvement in the foil wettability. It was also found that the wettability of plasma-treated foils degraded with time, apparently due to the adsorption of hydrophobic, airborne carbon species and other contaminants. Furthermore, oxygen plasma treatments caused additional aluminum oxide to grow on the metal surface. The composition of this additional oxide was found to be similar to that of the native passivation oxide. The thickness of the aluminum oxide layer increased with both the plasma RF power and the plasma exposure time.

To improve the adhesion between poly(p-phenylene terephthalamide), PPTA, fiber and silicone rubber, the surface modification of PPTA was investigated. Combining plasma treatment and coupling agent treatment with the silicone adhesive was found to be effective in improving adhesion. The combination process made the pull-out force of the PPTA yarn/silicone rubber composite 2.5 times higher, compared with the plasma treatment or the coupling agent treatment alone. The plasma treatment led to the elimination of carbonized layer from the PPTA yarn surface and the formation of oxygen functionalities including CO and CO groups. The elimination of the carbonaceous deposits from the PPTA surface and the interaction between the silicone adhesive and the oxygen functionalities created by the plasma treatment contribute to the improvement of adhesion with silicone rubber.

Polyolefin films were surface-modified by different methods to improve the wetting and adhesion of water-borne printing inks. Polyethylene (PE) films were treated with corona at various energy levels. Surface-modified PE films were characterized by contact angle measurements and electron spectroscopy for chemical analysis (ESCA). Good wetting was already achieved with treatment at a lower energy level. Various degrees of adhesion were obtained at various degrees of treatment. A hydrophilic monomer, 2-hydroxyethylmethacrylate (HEMA), was polymerized onto the surfaces of polypropylene (PP) with radiation-induced grafting, which was carried out at two different radiation doses. In both cases, a thick, visible layer of polyHEMA was formed on the surface of PP, and satisfactory wetting was already achieved at lower radiation doses. Scanning electron microscopy (SEM) showed that different degrees of roughness were achieved at various radiation doses. Like the case of corona-treated PE, different degrees of adhesion were obtained at different degrees of surface treatment. This study shows that improved wetting alone is not satisfactory for good practical adhesion', regardless of the surface modification method used.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Wetting hysteresis due to isolated surface heterogeneities is now fairly well understood but when the solid presents a population of defects, complex cooperative effects between neighbours may exist. One such effect is that of ‘shadowing’, in which a proportion of the flaws near the triple line, and which would otherwise contribute to hysteresis, are masked by already existing deformations to the wetting front caused by neighbouring heterogeneities. This renders them inactive and, as a result, the hysteretic wetting force is only expected to be a linear function of density for sparse populations. Theoretical predictions are compared with experimental results obtained with model heterogeneous surfaces consisting of overhead projector transparencies bestrewn with circular ink spots - the defects. Agreement is found to be satisfactory when intrinsic angles on both the homogeneous solid and the flaws are finite, whereas the concordance is less satisfactory when the contact angle of the liquid on the homogeneous solid is zero.

Photochemical dry etching and surface modification of various polymers, e.g. polymethylmethacrylate (PMMA), polyimide (PI), polyethyleneterephthalate (PET) and polytetrafluoroethylene (PTFE) were investigated with coherent and incoherent excimer UV sources. Ablation rates of PMMA were measured as a function of laser fluence and laser pulse at the wavelength λ = 248 nm (KrF*). Decomposition and etch rates of PMMA and PI were determined as a function of UV intensity and exposure time at three different wavelengths λ = 172 nm (Xe*₂), λ = 222 nm (KrCl*) and λ = 308 nm (XeCl*). The transmittance of the polymeric films was determined with a UV-spectrophotometer after different exposure times. The morphology of the exposed polymers was investigated with scanning electron microscopy (SEM). The gaseous products occurring during UV exposure were measured using mass spectrometry (MS). Chemical surface changes of the photoetched PMMA were determined by X-ray photoelectron spectroscopy (XPS). The mechanism of the photo-oxidation process of PMMA is discussed. The etching of PMMA can be explained as a result of extensive photo-oxidation. The results are compared with those obtained from mercury lamp and excimer laser experiments. Good adhesion of electrolessly deposited metal layers was achieved by irradiation of the polymeric surfaces from incoherent UV source before depositing the metal layer.