We discuss plasma surface modifications applied to perfluorinated polymers and polyolefins to achieve structural adhesive bonding or for biomedical purposes such as adhesion and proliferation of cells, and interfacial immobilization of biologically active molecules. We compare the properties of surface modifications performed in non-depositing plasma treatments with those of thin coatings produced in depositing plasma vapours (plasma polymerization), with particular emphasis on changes, on subsequent storage, to the properties and composition of the surface layers (‘ageing’). Such changes usually proceed for extended periods of time after plasma processing. Polymer surfaces treated in non-depositing plasmas generally are unstable, showing an increase in the air/water contact angles over days and weeks due to surface reorientation motions. Concurrently, the composition of the surface layers is also affected by post-plasma chemical reactions: originating from trapped radicals, oxidative chain reactions lead to the production of substantial amounts of oxygen-containing groups. These reactions also convert some of the groups originally incorporated into the surface layers by the plasma treatment; for instance, amine groups are converted to amide groups as evidenced by shifts in the XPS N 1s binding energy. Plasma polymer coatings analogously undergo oxidative compositional changes with time, and are capable of some surface reorganization. Thus, the nature and densities of the chemical groups on plasma-treated surfaces and plasma polymer coatings can change considerably with time. The relative contributions by concurrent reorientation motions and oxidative reactions to the compositional changes vary markedly between different plasma-prepared surfaces, but usually both processes contribute to the ageing of a surface. The generally long time constants of the reorientation of plasma polymer surfaces suggest that their limited, slow mobility may be neglected when interpreting interactions with adsorbing proteins.

The physicochemical modifications of ammonia-treated polypropylene (PP) films have been studied and characterized in terms of acid-b ase properties using the contact angle titration method and X-ray photoelectron spectroscopy in conjunction with a molecular probe technique using chloroform as a reference Lewis acid. These techniques have shown that PP surfaces that have been treated for between 0.7-1 s are basic in character. For longer treatment times, the basic character of the surfaces decreases, as shown by the above techniques and confirmed by time of flight-secondary ion mass spectroscopy (ToF-S IMS). On the other hand, for such treatment times, a degradation of the adhesion and mechanical properties was observed. The ageing of an ammonia-plasma-treated PP was limited by a helium (He) plasma pretreatment known to crosslink the surface, stabilizing in this way the wettability, adhesion and mechanical properties. ToF-S IMS was performed on helium treated High Density Polyethylene (HDPE) in order to point out the structural modifications.

The acid-base theory of surfaces, as proposed by van Oss, Chaudhury and Good, comнmonly suffers from a series of problems (apparent too high basicity of surfaces, results depending on the choice of liquid triplets, etc.). These problems can be solved if and only if a great attention is paid to the mathematical properties of the equations on which the theory is based. Two of these problems are analysed in detail in the present paper: the choice of the acid-base scale using water as a reference, and the use of the 'equilibrium' contact angle instead of the adнvancing contact angle.

The effects of 1, 2, 3, 4-tetrahydronaphthalene (tetralin) solvent and ammonia plasma treatments on surface characteristics and adhesion of ultra-high-strength polyethylene (UHSPE) fiнbers to epoxy resin were studied. Spectra™ 1000 (UHSPE) fibers were treated with either tetralin solvent or in combination with ammonia plasma, under various conditions. The changes in the fiber surface topography were characterized using scanning electron microscopy (SEM). Dynamic wetнtability measurements were made using the Wilhelmy technique. The fiber/epoxy resin interfacial shear strength (IFSS) was evaluated by the single fiber pull-out test. The fiber surfaces after the pull-out test were characterized by SEM. The SEM photomicrographs and wettability data showed that the surface roughness of the fibers increased after the tetralin solvent treatment and the fiber surface became more polar after the ammonia plasma treatment. The IFSS results indicated that combined tetralin and ammonia plasma treatments resulted in significant improvement in the adheнsion strength of UHSPE fibers with epoxy resin. This is attributed to the chemical, mechanical and topographical changes of the fibers resulting from the treatments.

The two methods used for contact angle determination in this study are based on liquid porosimetry (LP). The LP measures volumes of different size pores when the liquid advances and then when the liquid drains from a porous structure. The LP provides pore volume distribution (PVD) and numerous other pore structure characteristics. The experimental data for this study were obtained with an automated TRI/Autoporosimeterо. The first method for contact angle measurement uses two liquids. One liquid has a known contact angle with the sample solid and the second is the liquid of interest. A comparison of the capillary pressures in different size pores for the two liquids provides the contact angle data for different size pores in the sample.

Recently receding contact angles have increasingly attracted attention in studies of wetting phenomena. The difference between the advancing and receding contact angles of the same liqнid on the same solid surface is termed 'contact angle hysteresis'. The hysteresis is usually ascribed to the solid surface roughness and/or its chemical heterogeneity. These possible mechanisms of the hysteresis appearance do not exclude another interpretation of the receding contact angle origin (E. Chibowski et al., in: Surfactants in Solution, A.K. Chattopadhyay and K.L. Mittal (Eds.), pp. 31-53, Marcel Dekker, 1996). In this approach, the presence of liquid film behind the drop is considered to be the cause for the ovbserved hysteresis, except, of course, for cases of rough and/or macro-chemically heterogeneous solid surfaces. In this paper, a new approach is presented and then verified using experimental advancing and receding contact angles taken from the literature. This approach allows an evaluation of the total surface free energy of a solid if the advancing and receding contact angles for a probe liquid are known. It does not require values of the solid surface free energy components for estimation of the value of total surface free energy.

The objective of this study was to determine the surface free energy components of celнlulose ethers films. The surface free energy parameters were calculated from the contact angles of sessile drops of apolar and polar liquids on cellulose ether films cast on glass slides using the Lifshitz-van der Waals/acid-base (LW/AB) approach according to the method of van Oss, Chaudhury and Good (Chem. Rev. 88, 927-941, 1988). The cellulose ethers studied were hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), hydroxypropylcellulose (HPC) and hydroxyethylcellulose (HEC) and ethylcellulose (EC). The total surface free energy of these cellulose ethers ranged from 29-50 mJ/m2. The overall trend in the values of the thermodynamic terms derived from the surface free energy parameters as indicators of hydrophilicity was in good agreement with the relaнtive bulk solubility and hydration behavior of the polymers. Calculation of the work of adhesion with substrates of varying surface free energy parameters indicated that acid-base interactions made a major contribution to the total work of adhesion between cellulose ethers and bipolar surfaces. Changes in surface free energy as a result of the presence of plasticizer or change in solvent compoнsition for EC films were resolvable with the LW/AB approach. Although no direct correlation could be established between the surface free energy parameters and the type of substitution on the celluнlose backbone for the cellulose ethers, the values of the terms derived from the LW/AB approach were consistent with those of cellulose. The LW/AB approach provides a reasonably consistent method for estimating the surface properties of cellulose ethers and the resulting surface free energy parameters are shown to relate to the interfacial properties of the polymers.

The behavior of a silicone sealant during its application, from its extrusion from the carнtridge to the completion of the joint, has been identified as a key feature for professional applicators. This feature called “ease of use’* is very complex and includes many different criteria such as the ease of extrusion and joint smoothing, the aesthetic of surface finish, the stringing, and the action of a tooling aid (aqueous solution of surfactant) during the smoothing operation. Several of these criteнria seem directly linked to surface properties of the uncured sealant. In an attempt to translate these subjective properties into quantitative measurements in the laboratory and to understand the underнlying parameters that can be used to control these features, the surface energy of uncured sealants was measured using the solid-liquid contact angle technique. The surface energy data were further correlated with ratings collected from professional applicators with regards to ease-of-use criteria. A correlation was also built between the contact angle values obtained with various tooling aid soluнtions against the surface of the sealant and the ease of smoothing obtained by using these tooling aids at the application stage. The evolution of the contact angle of a water droplet at the surface of uncured sealant with time provided some insights in the understanding of the migration and/or reнorientation of polar entities from the sealant bulk to the sealant surface.

The surface energies of poly (methyl methacrylate), polycarbonate and poly (tetrafluoroethylene) which have been exposed to UV radiation in an ambient ozone-air atmosphere have been elucidated from surface tension and contact angle data using these test liquids: ethylene glycol, formamide, glycerol, methylene iodide and water. Comparisons of surface energy values obtained using Kaelble’s two-liquid method, Good’s three-liquid method and Neumann’s macroscopic apнproach are reported. It is tentatively suggested that atmospheric moisture may play a role in producнing discordant values since the test liquids ethylene glycol, formamide and glycerol are highly hyнgroscopic in nature. It has been demonstrated that UV/ozone irradiation produces changes in surface roughness. Poly (tetrafluoroethylene) shows three distinct regions: first, where at low irradiation times the surface roughness is enhanced and following this, the roughness decreases before increasнing finally to a terminal value. The behavior is somewhat similar for polycarbonate although the dramatic increase in roughness exhibited by poly (tetrafluoroethylene) is absent. The roughness characteristics are quite different for poly (methyl methacrylate) where a large change in roughness is observed at only one specific irradiation time. Thus presently it is not possible to predict surface roughness changes for a particular polymer and more studies on the morphological changes occurнring at different surfaces are being carried out.

Lifshitz-van der Waals (LW) and Lewis acid-base (AB), together with electrostatic (EL) forces are the non-covalent forces acting in adhesion in condensed phase media, such that the work of adhesion, VEadh= WLW+ WAB+ WEL. In the case of serum albumin (SA) and glass surfaces or silica particles, on a macroscopic scale, WEW> 0, WAB< 0 and WEL< 0, so that W'ddh is negative, ie repulsive. Nonetheless, in aqueous media, at neutral pH, SA adheres to glass surfaces, as well as to silica particles. It may be hypothesized that on a microscopic level, negatively charged, electron-donating SA moieties, located on prominent sites with a small radius of curvature, can penetrate the macroscopic repulsion field and bind to electron-accepting cations imbedded in the glass surfaces (Ca ions) or in silica particles (Si ions). The correctness of the hypothesis is supported by the fact that all adhering SA can be desorbed from, say, silica particles with Na2-EDTA. Furthermore, energy vs. distance diagrams demonstrate that the more prominently located SA sites with a small radius of curvature should indeed be able to overcome the macroscopic repulsion field and to adhere locally to microscopic cationic sites in the glass or silica. Thus, energy vs. distance balances of the extended DLVO type (including AB as well as LW and EL forces), combining macroscopic and microscopic interactions, can be used to predict adhesion in complex systems.

Acid–base interactions across interfaces are shown to have predictable influences on adhesion. The history of this development, and methods to assay the acid–base character of solvents, polymers and a variety of powders and fibers are reviewed briefly. Recent studies are described that demonstrate directly how acid–base interactions influence both ‘fundamental’ and ‘practical’ adhesion.

Synthetic and analytical procedures for the preparation of surface-functionalized polyolefins are described within the general context of polymer surface functionalization. Chemistry leading to simple functionalization of both polyolefins in general and polyethylene in particular is described. Selected examples of further chemistry leading to graft copolymers attached to these surfaces are described. The effects of such graft chemistry leading to various sorts of chemically modified surfaces with different solvent-polymer interactions specific to the graft microstructure and to temperature are discussed.

Joining of thermoplastic composite primary structures is an area of great importance in the aerospace industry. In order to achieve a strong and durable joint, an effective surface treatment is needed. Preadhesion surface treatment of thermoplastic composites is limited due to their chemical inertness to aggressive chemicals or mechanical treatments. The feasibility of using a new technique of ArF UV (193 nm) excimer laser irradiation as a preadhesion treatment of PEEK (polyaryletheretherketone) reinforced with carbon fibers is demonstrated. This method presents an alternative to other limited and polluting conventional surface treatment methods, such as sand blasting, etching or welding. Experimental results indicated that laser preadhesion treatment significantly improved the shear and tensile adhesion strength of various structural epoxy adhesives FM 300 2K and AF 163-2 bonded to PEEK composite adherends compared with untreated and SiC blasted substrates. Best results were obtained with laser pulse fluences of 0.18 or 1 J/Pcm2. Shear strength of laser treated PEEK composite joints improved by 450% compared with that of untreated PEEK composite and by 200% compared to SiC blasted adherends, at ambient and at—30 C and 120 C temperatures. An order of magnitude improvement was found in the tensile strength of laser treated PEEK composite in a sandwich structure compared to non-treated or abraded sandwich joints. The mode of failure changed from interfacial to cohesive as the number of pulses or laser energy increased during treatment. A similar improvement was achieved in fracture toughness (Mode I and II) performance of laser treated compared to abraded or non-treated PEEK composite adherends. Surface analysis of laser treated adherends and of the fractured joints revealed surface cleaning (XPS), morphology changes (Scanning Electron Microscopy), chemical modification (FTIR spectroscopy and XPS), changes in crystallinity (X-ray) and in wetting property (contact angle), all correlated with the laser irradiation improving the joint’s performance. The bulk properties of the PEEK composite adherend did not deteriorate by the laser irradiation during treatment, as indicated by the identical flexural strength before and after laser treatment. Durability tests showed no change in performance of joints produced from laser treated adherends compared to untreated and abraded ones, even after exposure of 60 days at 60 C/95% RH. It can be concluded that the excimer laser has a potential as a precise, clean and simple preadhesion surface treatment for PEEK composite.

Hydrophilic polymer surfaces are desirable for many applications, such as adhesion and wettability. In this study, we have developed a tenaciously bound hydrophilic surface coating which can be applied to a hydrophobic polymer using a plasma treatment process. In this process, porous polyethylene (PE) was used and pretreated with the plasma discharge of an oxidizing gas, eg carbon dioxide. The treated surface, containing mainly anionic groups, was then soaked in a polycation solution, eg polyethyleneimine (PEI). A tenaciously bound hydrophilic coating was formed due to multiple anchors (ionic interactions) between PEI and the plasma-treated surface. The coated surface was characterized using water contact angle goniometry and X-ray photoelectron spectroscopy (XPS). Both the stability and the durability of the coating have been evaluated using various storage conditions and repeated washing in water. The coating process developed in this study is useful in many applications which require a permanent and lasting wettable polymer surface.

Modified surfaces of polyethylene terephthalate)(Mylar® or PET film) have been studied by surface energetics, ESCA, atomic force microscopy (AFM), and optical profilometry. For the surface energetics studies, receding contact angle titrations were used to evaluate the surface functional groups in the outer few angstroms of the surface. This sensitive method of determining the contact angle with buffer solutions of different pHs allows one to investigate the nature of the chemical species introduced by the various energetic treatments. The data are consistent with a surface that is covered by a low density of carboxylic acid moieties in the case of corona and flame treatments, applied in a high-speed commercial type of a process at low doses. The high contact angle hysteresis indicates that the coverage is moderately heterogeneous but on a very small length scale, less than a few micrometers. ESCA qualitatively supported this, although this technique is not optimum for the low degrees of surface modification. A comparison is made of the two surface treatments in terms of depth of penetration, roughness, and surface density of chemical moieties introduced. UV laser-treated surfaces showed no indication of surface chemical modification.

As shown from the literature data, plasma treatments of polymer materials create chemical and morphological surface modifications which are strongly dependent on the experimental conditions and on the methods and apparatus configurations employed. In the present work, poly(tetrafluoroethylene) (PTFE) substrates were treated by RF plasma (RIE mode) in various gaseous atmospheres (H2, He, Ar, O2, N2, NH3). The main objective was to compare, under similar experimental conditions, the capabilities of these different gases to modify the morphology of the PTFE surface and to graft specific chemical functionalities for a subsequent metallization through an electroless process. The relevant chemical modifications were characterized by XPS and surface energy measurements while the morphology changes were observed by SEM. Under similar experimental conditions (treatment time, working pressure) and with the reactor operating in the RIE mode, defluorination capabilities of the plasma treatments vary as a function of the gaseous atmosphere according to the following sequence H2 > Ar, NH3 > N2 > He ≫ O2. In addition, O2 and He plasmas are shown to strongly etch the PTFE surface. The very low ability of O2 plasmas to graft oxygenated functionalities is largely due to their strong etching power. A discussion is also focused on the complex interactions between nitrogenated plasmas and PTFE surfaces. Especially, it is shown that nitrogen is not grafted in the same chemical form after an NH3 plasma as after a N2 plasma. Furthermore, after treatment in non-nitrogenated and non-oxygenated plasmas (He, Ar, H2) both nitrogen and oxygen species are grafted on the polymer surface, probably in the molecular form. Such a grafting occurs on venting the reactor with dry nitrogen and on exposing plasma-treated samples to ambient atmosphere.

This paper deals with the electroless metallization (nickel plating) of poly(tetrafluoroethylene) substrates which were previously submitted to RF glow-discharge plasmas in various gaseous atmospheres (H2, He, Ar, O2, N2, NH3) and subsequently to sensitization/activation or direct activation processes in order to chemisorb palladium which is the catalyst of the plating reaction. As shown in previous works and confirmed in this one, the use of the conventional sensitization/activation treatment (immersion of the plasma-treated samples successively in acidic tin chloride and palladium chloride solutions) is made possible due to the strong chemical affinity of tin to oxygen. On the other hand, when nitrogenated species are grafted on the PTFE surface, the chemisorption of the catalyst can be directly accomplished using only a simple acidic palladium chloride solution. It is shown, in more detail, in this paper that O2 and H2 plasmas cannot be used to deposit electroless Ni films through the conventional sensitization/activation process. This is due to the negligible oxygen content grafted onto the PTFE surface (case of O2 plasma), and to the strong crosslinking of this same surface (case of H2 plasma) even though the amount of oxygen grafted during the post reactions in air is relatively high. On the other hand, bright and adherent Ni deposits are obtained by using either He or N2 plasmas via the conventional two-step process again due to the oxygen species grafted during the post-reactions in air, or by N2 and NH3 plasmas via the direct one-step process due to the nitrogen species grafted during the plasmas themselves.

Polymer surfaces can be covered with functional groups by exposure to a plasma. The species of the plasma gas are attached to surface carbon atoms forming functional groups of different compositions. To produce a modified polymer surface with a high density and homogeneity of functional groups several possibilities such as plasma grafting of intact monomers, selective plasma bromination, plasma oxidation followed by conversion to OH groups as well as introduction of spacers with functional groups were tested. Thus, to produce exclusively OH groups at the polymer surface, the O functional groups formed by an oxygen plasma were chemically reduced by diborane, Vitride™ (Na complex) or LiAlH4. Typical yields were 9 to 14 OH groups per 100 carbon atoms as detected by XPS. The segment lengths of the spacers were varied between 1 to 22 ethylene or ethylene oxide units. At the end of the different spacers OH, NH2, COOH, Br or C=C groups are bound. These specifically functionalized polymer surfaces are used in pharmacy and medicine. Especially C=C or OH group terminated spacers have been found to “preserve” the plasma activation of the polymer surface by converting the unstable radical sites into stable functional groups. On further processing these groups can react with polymer coatings by classic radical mechanisms (C=C) or by polyaddition (OH) with polyurethanes or other polymers forming pure covalent bonds.

Glow discharge plasma is an effective method for treating surfaces, sputtering, etching, plasma-assisted deposition, ashing, and is used in a range of other processes. Sigma Technologies Int’l, Inc., has developed a novel plasma system which can be operated at atmospheric pressure, thereby eliminating the need for vacuum chambers and pumps. This atmospheric plasma system can be effectively used for surface treatment and for plasma-assisted deposition. This plasma system has been tested successfully for the functionalization of various polymer films. The surface energies of the films treated by the newly developed atmospheric plasma system have been shown to increase substantially, thereby enhancing the wettability and adhesion properties of these films. Details of the atmospheric pressure plasma system, and the results from treatment tests are presented.

Ultrahydrophobic polymeric surfaces were prepared using two plasma chemistry approaches: (1) fluorocarbon plasma polymerization, and (2) simultaneous argon plasma etching of polypropylene (PP) surfaces and sputtering of poly(tetrafluoroethylene) (PTFE) onto these rough surfaces. In the first case, several fluorinated monomers were selected to study the effect of the monomer structure on the plasma polymer morphology and wettability. Ultrahydrophobic surfaces were generated for those monomer gases that were capable of forming powders. For fluoromonomers that did not form powders, the wetting characteristics were similar to that of PTFE. Plasma polymerization of perfluorohexane does not lead to powder deposition and the highest advancing water contact angle measured was 118° (the receding contact angle was 74°). Fluorinated acrylates and ethyl heptafluorobutyrate were tested as well and in all cases, the powder formation of the polymer led to highly hydrophobic surfaces (advancing and receding contact angles between 164°–174° and 8°–173°, respectively). In the second technique, argon plasma was used to etch PP surfaces, creating a rough surface (the roughness is controlled by the reaction time). Simultaneously, PTFE was sputtered onto the roughened PP surface to create fluorinated surfaces. The most hydrophobic surface exhibited an advancing contact angle of 172° and a receding contact angle of 169°. AFM and SEM analyses of these samples show that the powder deposition of the polymers and the etching of PP concurrent with the sputtering of PTFE lead to rough surfaces resulting in a highly nonwettable surface.

Low-pressure gas plasma treatments were proposed as an alternative to the chemical surface treatments (e.g. halogenation, cyclization) of vulcanized styrene-butadiene (SBR) rubber. The effectiveness of low-pressure oxygen plasmas has been already shown. In this study the influence of the oxygen/nitrogen ratio on the adhesion performance of rubber/polyurethane adhesive joints was considered. Different mixtures of oxygen (20–40 vol%) and nitrogen (80–60 vol%) were used for the plasma treatment of an SBR rubber between 1 and 15 minutes, using a power of 50 watts and a residual pressure of 1 Torr. The modifications produced on the rubber surface by the plasma treatment were assessed using advancing and receding contact angle measurements, ATR-IR spectroscopy and scanning electron microscopy. Adhesion was determined from T-peel tests on plasma treated rubber/polyurethane adhesive joints. The treatment of rubber with oxygen-nitrogen mixture plasmas decreased the advancing and receding contact angle values and increased the T-peel strength (a cohesive failure in the rubber was produced). This increase was due to the partial removal of hydrocarbon moieties from the rubber surface and to the creation of oxygen containing species. The increase in the time of treatment decreased the peel strength and made the locus of failure mainly cohesive in the rubber. The higher the percentage of oxygen in the gas mixture, the greater the degree of oxidation on the rubber surface, the higher the degree of roughness and the more effective the treatment. A minimum percentage of 20 % oxygen in the gas composition was required to achieve good adhesion. Nitrogen plasma produced a different effect than the oxygen-nitrogen mixture plasma due to crosslinking reactions on the treated rubber surface which directed the failure to be cohesive in the adhesive.

Polycarbonate surfaces have been treated with radiofrequency plasmas of oxygen, air and argon to hydrophilise the surfaces and to provide good cell culture properties. Surfaces treated at high RF power/gas flow ratios were highly hydrophilic and stable towards washing in 70% ethanol, while those treated at lower ratios were not wash-stable. Cell growth properties as good as on commercial tissue-culture polystyrene could be obtained down to 20° water contact angle (measured after ethanol washing) on the treated surfaces for three different human cell lines (HeLa cervix carcinoma cells, MRC-5 lung fibroblasts and Chang hepatoma cells). The HeLa cells were most sensitive to the treatment conditions, while the Chang cells showed the most robust behaviour. Cells grown on surfaces with around 20° water contact angle were assessed by immunofluorescence staining methods and phase contrast microscopy. The cells showed normal behaviour with respect to morphology, spreading, cytoskeleton structure, cell-surface contacts and DNA synthesis.

The chemical and morphological influences of SF6 and Ar plasmas on bisphenol-A-polycarbonate (PC) and the influence of plasma treatments on Al metallisation were investigated. The treatment of the sample, X-ray photoelectron spectroscopic (XPS) and scanning force microscopic (SFM) analyses were made in an ultrahigh vacuum (UHV) chamber without breaking the vacuum. Using SF6 for the etching process, a significant inclusion of fluorine (C-F, C-F2) takes place. After argon plasma treatment of the PC surface a reduction in the carboxylic carbon was observed in the C1s spectrum. Both kinds of plasma treatments reduce the double and single bonded oxygen. During the metallisation process on an Ar-plasma treated PC surface aluminum couples via oxygen to the aromatic carbon. Al-metallisation on the SF6 pre-etched surface leads to the formation of an Al-F interlayer. With the SFM, the roughening effects on the nm scale after the two plasma treatments is observable. On the virgin PC, Al layers can be seen as slightly bound clusters. On both plasma pre-treated PC surfaces the Al grows as a film.

Poly(vinylidene fluoride) (PVDF) samples were treated in plasma atmospheres of ammonia, pure N2 and N2/H2 mixtures in order to enhance their adhesion to evaporated copper. The chemical and physical modifications occurring on the plasma treated PVDF films were studied by XPS measurements. The main effects resulting from these treatments were a substantial defluorination and the grafting of oxygen- and nitrogen-containing groups. The adhesion of 20 nm thick copper layers was evaluated by peel test measurements. XPS depth profiles of the samples with Cu overlayers were used to identify chemical bonds at the Cu-PVDF interface.

Aramid cords and fibers and polyester tire cords were treated in a continuous or pulsed DC plasma containing organic monomers such as pyrrole or acetylene in a custom-built reactor. For the treated cords the rubber adhesion was measured in a standard pull-out test. It was found that the plasma polymer coating significantly increased the pull-out forces. The effect of the power-to-pressure ratio and the pulsing of DC power on the performance of the treated cords or fibers were investigated. It was found that, in general, low power / high pressure conditions gave better results than high power / low pressure conditions. Coatings obtained under these conditions were thoroughly characterized by a range of analytical tools. Based on these data and on failure analysis, models were developed to explain the experimental findings.