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.

The morphology of a polyimide film surface is modified from a semicrystalline state to an amorphous state without altering the bulk properties. The outer layer (0.5-25 nm) of fully cured poly(pyromellitic anhydride-oxydianiline) (PMDA-ODA) and poly(biphenyl dianhydride-p-phenylene diamine) (BPDA-PDA) polyimides is chemically modified to polyamic acid, which is subsequently imidized at 230-250°C for 30 min to give a disordered polyimide surface. This disordered layer seems amorphous since it swells well in 1-methyl-2-pyrrolidinone (NMP) and the ions in the modified layer can be easily removed with a solvent such as water or ethanol. The modified surfaces are analyzed by surface-sensitive techniques such as contact angle measurement, X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), secondary ion mass spectroscopy (SIMS), and external reflectance infrared spectroscopy (ERIR). The adhesion of polyimide layers onto the amorphous polyimides is greatly enhanced. Interdiffusion and subsequent mechanical interlocking are the major contributors to the polyimide-polyimide adhesion. The relationship between the depth of modification and the peel strength is studied. The deeper the modification depth, the greater is the peel strength.

Since the earliest systematic research during the 1960s, the field of materials surface modification by 'cold', low-pressure plasma treatment has undergone an enormous expansion. Much of this expansion has taken place in recent years, particularly in the surface modification of polymeric materials, for which there now exist numerous industrial applications (enhancement of paint adhesion, improved bonding in polymer matrix composites, etc.). In this paper, we provide a critical review of the development and trends in this field; reference is also made to other surface modification techniques, particularly to corona treatment, and comparisons are made wherever appropriate. We begin with a brief overview of adhesion theory, and of the physics and chemistry of 'cold' plasmas. Next, interaction mechanisms between a plasma and a polymer surface are examined; these include physical bombardment by energetic particles and by ultraviolet photons, and chemical reactions at or near the surface. The resulting four main effects, namely cleaning, ablation, crosslinking, and surface chemical modification, occur together in a complex synergy, which depends on many parameters controlled by the operator. In spite of this complexity, for there are still many unanswered questions, it is nevertheless possible to optimize the main set of parameters governing a given process, and then to reliably reproduce the process outcome. Three industrially important systems, for which many research results exist, are then separately examined, namely: (i) polymer-polymer bonding, (ii) polymer-matrix composites, and (iii) metal-polymer bonding. Finally, we present a brief overview of commercial plasma reactors for industrial (non-semiconductor) purposes, and of process considerations for efficient use of such equipment. We foresee that the use of plasma processes will continue to expand, because they have unique capabilities, are economically attractive, and are 'friendly' towards the environment.

X-ray photoelectron spectroscopy (XPS) has been used to study the chemical effects of both inert (argon) and reactive (oxygen, nitrogen, and mixed gas) plasma treatments done in situ on a variety of polymer surfaces. Inert gas plasma treatments introduce no new detectable chemical species onto the polymer surface but can induce degradation and rearrangement of the polymer surface. However, plasma treatments with reactive gases create new chemical species which drastically alter the chemical reactivity of the polymer surface. These studies have also shown that the surface population of chemical species formed after plasma treatment is dependent on both the chemical structure of the polymer and the plasma gas. The effects of direct and radiative energy-transfer processes in a plasma have also been studied. Polymers containing certain functional groups were found to be more susceptible to damage via radiative energy transfer. Ageing studies of plasma-modified polymer surfaces exposed to the atmosphere have shown that the ageing process consists of two distinct phases. The initial phase, which occurs rapidly, involves adsorption of atmospheric contaminants and, in some cases, specific chemical reactions. The second phase, which occurs slowly, is due to surface reorganization.

Hexatriacontane (C₃₆H₇₄) has been used as a model molecule for the study of the surface modifications of high-density polyethylene (HDPE) in argon and oxygen radio-frequency (RF) plasmas. The combination of static secondary ion mass spectrometry (SIMS), ion scattering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS), and contact angle measurements has constituted a powerful method for the investigation of the surface modifications induced by the plasma treatments. The surface degradation and functionalization are shown to depend on both the nature of the treated material and the nature of the plasma atmosphere. The SSIMS results obtained on plasma-modified hexatriacontane and HDPE are compared in order to identify the nature of the functionalities present at the plasma-treated surfaces. Finally, plasma treatment ¹⁸O atmosphere was performed on HDPE, C₃₆H₇₄, and polystyrene (PS). In that case, the isotopic specificity of both ISS and SIMS allowed the determination of the relative concentrations of ¹⁶O and ¹⁸O in relation to the probed depth and plasma atmosphere.

A remote plasma reactor, with air as the plasma gas, has been used for in-line surface modification of linear low-density polyethylene tape (LLDPE) passing 10 cm below the main plasma zone. Line speeds of up to 0.70 m/s were tested, allowing the study of 0.014 s exposure times to the plasma. Oxygen to carbon (O/C) ratios averaging 0.11 were observed on a reproducible basis. The reactor was also used for static plasma treatment under similar experiment onditions. This allowed a comparative study of short-term (milliseconds) vs. long-term (several seconds) plasma treatment. High-resolution X-ray photoelectron spectroscopy (XPS) analysis of the treated polymer surface suggested the formation of hydroxyl (C-OH), carbonyl (C=O) and carboxyl (O-C=O) groups, even after short plasma treatment. The intensities of these components were seen to increase in approximately equal quantities with increasing O/C ratio. Water washing of polyethylene surfaces with high O/C ratios showed a loss of oxygen, apparent as a decrease in O-C=O groups in the C 1s spectra. A smaller loss in oxygen was observed when washing samples that had been plasma-treated for milliseconds. A surface ageing study revealed that polyethylene surfaces that had been plasma-treated for short time periods showed only a negligible loss of oxygen on prolonged exposure to air. Surfaces treated for longer time periods showed a loss of up to 50% of the total oxygen on the surface within a few days of treatment. Static secondary ion mass spectrometry has provided some supporting evidence for surface damage of the treated films.

Oxygen plasma treatment as a surface functionalization technique is discussed. Oxygen-containing functionalities were introduced on the surface of high- (HDPE) and low-density polyethylene (LDPE) by glow discharge. The number of surface hydroxyl groups was increased by a post-discharge wet treatment in a reducing solution. The effects of the substrate nature, the discharge parameters, and the post-discharge wet treatment on the surface functional groups are discussed, and the effectiveness of functionalized surfaces on the yield of coupling reactions is shown.

A study of the sticking coefficient of Mg vapour on in situ Ar and N₂ plasma-treated polypropylene (PP) is presented. After exposure of the pretreated sample to a determined amount of Mg vapour, X-ray photoelectron spectroscopy (XPS) allows measurement of the adhered Mg amount at the polymer surface and the chemical nature of the interface. The sticking coefficient on an as-received sample is zero and is increased to several tenths depending on the pretreatment conditions, namely the nature and the pressure of the neutral gas, the treatment time, and the applied RF-bias. Relations between the plasma parameters, the XPS measured surface state before the metallization, and the sticking coefficient are investigated.

A method has been developed to measure the surface acidity of solids using the contact angles of seven probe liquids. The geometric mean model was used to calculate the surface free energy. Then the value of the solid polarity, from the geometric mean, was compared with the polarity values calculated using the geometric mean dispersive component and the contact angles of two Lewis acids (liquefied phenol and glycerol) and two Lewis bases (formamide and aniline.) The deviation between these values was used to determine a value for the acidity, referred to as D. D was measured for a series of polymeric and metallic materials. Lap shear joints were fabricated and tested using these substrates and two adhesives, a urethane and an epoxy. The acidity of the substrate surfaces was found to affect the lap shear joint strength.

The role of Lewis acid-base interactions at the fiber-matrix interface in composites is studied with both glass and Teflon fibers. In the glass fiber case, surface chemistry is modified with amino-, methacryloxy- and glycidoxy-silane coupling agents (A-1100, A-174 and A-187, respectively). Silane adsorption mechanisms as well as the properties of filament-wound, unidirectional epoxy and polyester composites are explained by a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and flow microcalorimetry. The heats of adsorption of pyridine and phenol prove that the coupling agents add acidic sites to the glass fiber surface as well as stronger basic sites. The subsequent adhesion of the matrix polymers and the short beam shear strengths of composites are explained on this basis. The Teflon fibers are first etched with sodium naphthalene solutions, and then sequentially hydroborated and acetylated, producing approximately monofunctional hydroxyl (acidic) and ester (basic) groups on the surfaces, as determined by XPS, FTIR, and electrophoretic mobility analyses. Composites prepared with the acetylated fibers and a chlorinated polyvinyl chloride (acidic) matrix are superior in tensile properties, and SEM fractography shows PTFE fibrillation, indicative of good fiber-matrix adhesion and stress transfer, in this case only.

A review of studies of polymer-paper adhesion illustrates the thermodynamic nature of the bondability of polymers to plain, uncoated paper surfaces. The bond strength depends strongly on the chemical nature of the polymer surface and on that of the fibrous paper surface. Adhesion to paper may be characterized indirectly through thermodynamic analysis of the paper substrate, or directly through paper laminate or adhesion tape peel testing. The need for adequate paper adhesion is emphasized, particularly for some of the newer printing processes (electrophotographic and thermal imaging). It is concluded that some of the indirect methods of adhesion characterization (surface energetics analysis via contact angle measurements or the inverse gas chromatography technique) may serve to characterize paper adhesion in these processes.

This work demonstrates the usefulness of flow microcalorimetry for surface characterization of metal foils (aluminum) and polymer [poly (ethylene-co-acrylic acid)] fibers. It shows that the polymer to aluminum adhesion is dominated by Lewis acid/Lewis base type interactions. These interactions are predictable from the measured heats of surface adsorption and desorption of probe molecules from dilute solution. The heats of interaction are a measure of the strengths of these sites. Adhesion between basic aluminum foil and acidic polymer resin increases with increasing numbers of either acidic sites on the polymer or basic sites on the foil. The calorimetry and adhesion results are in good agreement. This study supports recent observations vide infra that wettability of the aluminum is much less important for polymer/aluminum adhesion than chemical bonding.

The water vapor permeability of glass-bead-filled phenoxy films was shown to depend strongly on the degree of interfacial interaction between the filler and matrix; the greater the adhesion, the lower the permeability. Scanning electron microscopy (SEM) was used to characterize the glass surface and the corresponding degree of adhesion between the filler and polymer matrix. Maximum interaction between the acidic phenoxy and glass filler was obtained when the glass had been treated with an aminopropyltriethoxysilane, which yielded a basic surface overall. Retention of the cellosolve acetate solvent was also reduced by the glass filler, especially by the more basic glass. The dynamic mechanical properties were affected primarily by the presence of residual solvent.

Improvement of the paint adhesion to a polypropylene (PP) bumper has been investigated without using a primer by treating the bumper surface with O₂, H₂O, and acetylene plasmas. All the plasma treatments resulted in an increase of the adhesion strength in dry conditions. The adhesion strength could be increased up to a value comparable to that obtained by applying a primer. The treated surfaces were quite stable for 7 days in air. After exposure to wet conditions, however, the adhesion strengths for both O₂ and H₂O plasma-treated samples decreased significantly, while the adhesion strength for the acetylene plasma-treated sample did not change much.

The effects of aging temperature and time on the adhesion properties of oxygen plasmatreated low-density polyethylene (LDPE) were investigated. As the aging temperature and time increased, surface rearrangement and the migration of molecules containing polar functional groups into the bulk were accelerated to the surface to form a hydrophobic surface. The adhesion strength of oxygen plasma-treated LDPE/aluminum joints was measured using a 90° peel test by varying the plasma treatment time and aging temperature. The adhesion strength was constant, regardless of the plasma treatment time. As the aging temperature increased, the adhesion strength of the LDPE/aluminum joints decreased and the locus of failure changed from cohesive to interfacial failure. It was also found that the polar functional groups buried in the bulk could be reoriented to the surface in a polar environment. This study also investigated whether repeated oxygen plasma treatment would increase the concentration of polar functional groups at the surface and reduce the surface rearrangement and the migration of molecules containing polar functional groups during aging. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) showed that repeated oxygen plasma treatments increased the concentration of polar functional groups at the surface. However, the aging time between plasma treatments had a negligible effect on the concentration of polar functional groups at the surface.

The influence of the surface modification of pressure-sensitive adhesive tapes on their adhesion behavior has been investigated. PBA [poly(butyl acrylate)] and PIB [poly(isobutylene)] adhesives were chosen as pressure-sensitive adhesives and nitrogen plasma was used for the surface modification of the adhesives. The peel force of PBA or PIB adhesive/stainless steel joints was evaluated. The nitrogen plasma treatment showed large effects on the adhesion behavior of both the PBA and the PIB adhesives. The peel force for the PBA adhesive/stainless steel joint decreased by 57 times as a result of the nitrogen plasma treatment and that for the PIB adhesive/stainless steel joint increased by 2.2 times. There are essential differences in the modification reactions caused by the nitrogen plasma between the PBA and PIB adhesives. For the PBA adhesive, cross-linking reactions occurred among the PBA polymer chains and the surface was hardened. For the PIB adhesive, degradation reactions occurred and products with a low molecular weight were formed on the surface. These differences are due to the different responses of the PBA and PIB adhesives towards the nitrogen plasma. The mechanism of the changes in adhesion behavior caused by the nitrogen plasma is discussed.

In the present work, rubber-toughened polypropylenes (TPOs) with different properties of the rubbery phase, consisting in different degrees of rubber dispersion and different levels of rubber crystallinity, were considered. The flame-treated surfaces of these materials and their interfaces with a commonly used primer were studied by dynamic contact angle (DCA) analysis using seven liquids and by scanning probe microscopy (SPM). The contact angle data were analysed using the concepts and the equations of the surface free energy acid-base component theory. A new approach consisting in the use of a large number of probe liquids and of a proper mathematical method is proposed; it allows higher precision in the determination of the surface energy components and the work of adhesion, the reduction of possible artefacts, and the calculation of standard deviations of obtained quantities. It was found that: (i) the characteristics of the flame-treated surfaces were largely independent of the composition and morphology of the rubbery dispersed phase; (ii) the flaming effect was better shown by receding angles and the observed hysteresis allowed a quantitative evaluation of the surface heterogeneity induced by the flame process; and (iii) the flame treatment induced fragmentation of the macromolecules with the production of fragments, soluble in all the test liquids, depending on their surface tension and their acid-base character, as shown by repeated DCA immersions. A comparison has been made with the ASTM 2578-67 method ('swab'). The SPM analysis, both in contact and in 'force spectroscopy' modes, confirmed the surface model obtained by the DCA data.

The effects of solvents on the surface properties of oxygen plasma-treated polyethylene and polypropylene films have been studied by ESCA, contact angle measurement, and adhesion testing. The results show that oxygen plasma treatment produces some low molecular weight materials (LMWM) on the treated surfaces, which can be removed, to some extent, by solvents. It seems that the LMWM has different solubilities in different solvents. Among the solvents (water, acetone, and 2-propanol) used, acetone has the most significant effect. The removal of LMWM considerably reduces the wettability of the treated materials, but does not impair the adhesion increased by the plasma treatment.

Contact-angle measurements, the ASTM standard wetting test for polyolefin films, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated polypropylene (PP) films. Two combustion models, STANJAN and PREMIX, were then used to determine the chemical and physical properties of the flames used to treat the PP films. Both the flame equivalence ratio and the position of the PP film in the flame are important variables in determining the extent of oxidation and improvement in wettability obtained by flame treating. The optimal equivalence ratio for the flame treatment of PP is 0.93, while the optimal luminous flame-to-film distance is 0-2 mm. Modeling of the combustion processes occurring in the flame provides evidence that the extent of treatment correlates closely with the concentrations of H, O, and OH radicals present in the flame. The extent of surface modification of the flame-treated PP does not appear to correlate with either the flame temperature or the concentraion of oxygen molecules. The mechanism of surface oxidation by flame treatment probably involves polymer-radical formation by O and OH, followed by rapid reaction of the polymer radicals with O, OH, and O₂.

The theory of the contact angle of pure liquids on solids, and of the determination of the surface free energy of solids, γ_s, is reviewed. The basis for the three components γ^LW_s, γ⊕_s, and γ⊖_s is developed, and an algebraic expression for these properties in terms of measured contact angles is presented. The inadequacy of the 'two-liquid' methodology (which yields a parameter, 'γ^p') is demonstrated. Attention is given to contact angle hysteresis and to the film pressure, π_e. Some recommendations are made with regard to contact angle measurements. A new treatment of hydrophilicity, and of the scale of hydrophobic/hydrophilic behavior, is proposed. It is shown that there are two kinds of hydrophilic behavior, one due to Lewis basicity (electron-donating or proton-accepting structures) and the other due to Lewis acidity (electron-accepting or proton-donating structures). The properties γ^⊖ and γ^⊕ are the quantitative measures of these types of behavior and they are structurally independent of each other. A triangular diagram, with γ^LW at the hydrophobic corner, and γ^⊕ and γ^⊖ at the two hydrophillic corners, is suggested.

The surface chemical modification of polypropylene by CF₃Cl plasma treatment was studied by ESCA, wettability measurements, and pressure-sensitive-adhesive performance tests. Improved adhesion was observed on polypropylene treated under CF₃Cl plasma conditions that maximized Cl and minimized F and O incorporation. Polypropylene treated using CF₃Cl plasmas had a high dispersive component of surface energy, as indicated by low diiodomethane contact angles. High dispersive energy is characteristic of chlorinated surfaces, and may contribute to the improved adhesion.

Contact-angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated biaxially oriented polypropylene (PP) films. While the surface of PP treated in a fuel-lean flame is highly oxidized, no watersoluble low-molecular-weight oxidized material (LMWOM) is formed by the flame treatment. A new computational model, SPIN, was used to determine the chemical composition of the impinging flames used to modify the PP. The SPIN model indicates that the species primarily responsible for the surface oxidation of the PP are OH, HO₂, H₂O₂, and O₂. Because the concentration of atomic O in the flame is low, there is little scission of the PP chains and no formation of LMWOM. AFM indicates that a 'nodular' surface topography is generated during the flame oxidation of the PP. The surface topographical features generated by flame treatment are probably the result of the agglomeration of intermediate-molecular-weight materials.

Injection-molded samples of polypropylene were exposed to oxygen plasma and SACO (SAndblasting and COating) treatments. The pretreated surfaces were successively adhesively bonded or lacquered. The adhesion strength and failure mode of these specimens were examined. The surfaces obtained after treatments were characterized by electron spectroscopy for chemical analysis (ESCA), contact angle measurements, and scanning electron microscopy (SEM). Both microroughness and chemical modification of the surface led to an increase in adhesion by up to a factor of 10. The stability of the surface changes generated during the plasma and SACO pretreatments was observed by different kinds of aging experiments in air and water. The aging of SACO-treated surfaces led to no significant change on the surface. In the case of plasma-treated surfaces, hydrophobic recovery during aging in air reduced the polarity of the surface layer. During aging in water, no hydrophobic recovery on the surface was observed.

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.

The effects of cross-linking and crystallinity on the aging of plasma-treated high-density polyethylene (HDPE) have been investigated. In the case of mixed argon and oxygen, aging has been found to be reduced with an increased amount of argon in the mixture owing to an increased degree of cross-linking. A similar decrease in hydrophobic recovery has been achieved by increasing the crystallinity of HDPE. Diffusion of polar functional groups from the surface into the bulk has been observed to be lowered by both increasing the degree of cross-linking and crystallinity. The samples were analyzed by angle-resolved XPS, contact angle measurements and SEM investigations.

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

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

The electron beam-initiated surface modification of films prepared from various blends of low-density polyethylene (LDPE), ethylene vinyl acetate (EVA), and ditrimethylol propane tetraacrylate (DTMPTA) was carried out over a range of radiation doses (20-500 kGy) and concentrations of DTMPTA. The films were characterized by Fourier transform infrared-attenuated total reflectance (FT-ATR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), contact angle measurements, and peel adhesion. The printability of the films was also measured. FT-ATR and XPS revealed that the surface polarity of the films made from a 50 : 50 blend of LDPE and EVA increased up to a radiation dose of 100 kGy, compared with the unirradiated sample. The polarity decreased after 100 kGy radiation. Surface pitting and roughness were observed in the SEM photomicrographs of the same films, irradiated at higher radiation doses. Higher values of the surface energy were obtained at 100 kGy for the samples without DTMPTA and for the samples containing 3 wt% DTMPTA. Excellent printability was observed for all the films irradiated above an irradiation dose of 20 kGy. The data on the printability and peel adhesion of the irradiated films could be explained by surface energy, XPS, and SEM results.

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.

The overwhelming basicity of all analysed surfaces strongly dependent on the choice of liquid triplet used for contact angle measurements and the negative values sometimes obtained for the square roots of the acid-base parameters can be summarized as the main problems arising from the application of the Good-van Oss-Chaudhury (GvOC) theory to the calculation of Lewis acid-base properties of polymer surfaces from contact angle data. This paper tries to account for these problems, namely: (1) the Lewis base, or electron donor component, is much greater than the Lewis acid or electron-acceptor component because of the reference values for water chosen in the original GvOC theory. A direct comparison of the acidic component with the basic one of the same materials has no meaning. A new reference scale for water which is able to overcome this problem is suggested. For the calculation of acid-base components, a best-fit approach is proposed which does not require any starting information about the liquids or polymers and can yield estimates of the acid-base parameters for both the liquids and the polymers involved; (2) the strong dependence of the value of the acid-base components on the three liquids employed is due to ill-conditioning of the related set of equations, an intrinsic and purely mathematical feature which cannot be completely cured by any realistic improvement in experimental accuracy. To reduce or eliminate the effect, one only needs a proper set of liquids, representative of all kinds of different solvents; (3) the negative coefficients appear as a simple consequence of measurement uncertainty, combined with the possible ill-conditioning of the equation set. We cannot exclude, however, that in some cases they could have a different origin.

According to the general guidelines presented in the accompanying paper, some relevant examples of common polymer surfaces are analysed and discussed; a number of polymers commercially available or laboratory synthesized have been analysed. In particular, the case of poly(vinyl chloride) (PVC), often considered as peculiar in the literature, is fully analysed on the basis of a new set of well-prepared samples, whose compositions were checked by high-vacuum spectroscopies. 'Equilibrium' contact angles, obtained by a new experimental technique, are presented. The results are, however, preliminary, because the final set of liquids used is not so 'well equilibrated' as possible, from the point of view of acid–base properties. The contact angle data obtained are analysed in a non-linear way to calculate the acid–base components of all the liquids and solids. The results are discussed and compared with those obtained from liquid–liquid interfaces presented in the accompanying paper. The physico-chemical features of these samples have also been compared with the adhesion properties of some bacterial cells, commonly found as infective agents on biomaterials surfaces of medical devices, in order to rationalize these results within the theoretical framework of acid–base theory.

The properties of the fiber/matrix interface in carbon fiber-reinforced composites play a dominant role in governing the overall performance of the composite materials. Understanding the surface characteristics of carbon fibers is a requirement for optimizing the fiber-matrix interfacial bond and for modifying fiber surfaces properly. Therefore, a variety of techniques for the surface treatment of carbon fibers have been developed to improve fiber-matrix adhesion as well as to enhance the processability and handling of these fibers. Many research groups have studied the effects of plasma treatments, correlating changes in surface chemistry with the interfacial shear strength. This article reviews the recent developments relative to the plasma surface modification of carbon fibers.

The interfacial forces between a polyethylene particle and a toner substrate in alkaline aqueous solutions were studied using an atomic force microscope colloidal probe technique. Measurements were taken at pH 9 in water and solutions of 5 × 10^-4 M CaCl₂, 1 × 10^-4 M Na oleate, and 1 × 10^-4 M Na oleate plus 5 × 10^-4 M CaCl₂ in order to mimic the conditions present during de-inking flotation. A polyethylene particle was used to represent the air bubble. The observed interaction forces were described by the extended DLVO theory. An energetic barrier caused by electrical double-layer repulsion was observed in water and Na oleate solutions but was greatly diminished in CaCl₂ solution. A long-range attractive force was found to be present in these systems and was described using a simple exponential function. The long-range attractive force was virtually the same in water and CaCl₂ solution but decreased significantly in Na oleate solution because of the reduced hydrophobicity of the interacting surfaces caused by the adsorbed carboxylate layer. However, in the presence of oleate and calcium ions the observed attraction was even stronger and of longer range than in water and CaCl₂ solutions. Moreover, no energetic barrier was observed. These results can be attributed to the presence of precipitated calcium oleates on the interacting surfaces.

A new surface modification technique for PET films is proposed. This technique, called VPI modification technique, is a combination of two processes: The first step involves the deposition of vinylphthalimide (VPI) on the PET film surfaces, followed by Ar plasma irradiation of the VPI-covered film surfaces. The VPI modification technique led to large increases in the N/C atom ratio on the PET film surfaces. On the VPI-modified PET film surface, a new N_ls peak containing two components due to amide groups as well as imide groups appeared. The C_ls signal for the VPI-modified PET film surface also showed a new component due to ketone groups. These changes indicate that VPI reacted with the PET film surfaces to form nitrogen-containing groups. VPI modification made PET film surfaces hydrophilic. The VPI-modified film surfaces showed a decrease in water contact angle from 73 degrees to 48–56 degrees.

Surface modification of poly(lactic acid) (PLA) film surface by Ar-plasma was investigated by contact angle measurements and XPS in order to answer the following two questions. (1) Could the Ar-plasma modify the PLA film surfaces? (2) What chemical reactions occurred on the film surfaces during the Ar-plasma treatment? The Ar-plasma treatment did not lead to hydrophilic modification of the PLA film surface, but to degradation reactions of the PLA film. Poor modification may be due to instability of the carbon radicals formed from CO bond scission in the PLA chains by the Ar-plasma.

In order to explore the fundamental mechanism of paint adhesion to polymer substrates the surface of polypropylene- ethylene propylene rubber (PP-EPR) blends was modified by flame or plasma treatments. The changes in surface composition and properties were investigated and discussed in light of the results of simple adhesion tests. The topography and surface properties of the PP-EPR samples were studied by employing various surface sensitive techniques. Additionally, the surface properties of the pre-treated PP-EPR were compared with the model polymers poly(methyl methacrylate) (PMMA) and polycarbonate (PC) displaying a poor and an excellent paint adhesion, respectively. Differential scanning calorimetry (DSC) measurements showed that the miscibility of the polymer substrate with paint components was an essential factor for the understanding of the adhesion mechanism. A general model of paint adhesion to polymer surfaces is proposed, where the degree of interdiffusion of the polymer chains of the substrate and paint in the interphase determines the adhesion strength.

To improve the hydrophilicity and reduce the aging effect, argon and oxygen mixtures were employed in the plasma treatment of low-density polyethylene (LDPE). Argon resulted in producing more oxygen ions and radicals in the plasma than only oxygen and forming cross-linked layers on the LDPE surface. Therefore, the water contact angle on plasma-treated LDPE decreased and the oxygen content measured by X-ray photoelectron spectroscopy (XPS) increased with the increase of argon content. The aging effect was also much reduced with the increase of argon content since argon induced cross-linking.

The effects of the specimen temperature of low-density polyethylene (LDPE) in O₂ plasma treatment were studied to enhance the amount of hydrophilic functional groups introduced and to reduce the aging effect. The specimen temperature was varied from 25°C to 100°C. The smallest water contact angle was obtained with the 45°C specimen and the largest amount of hydrophilic functional groups was introduced with the 100°C specimen, as determined by X-ray photoelectron spectroscopy (XPS). Therefore, a two-step plasma treatment with two different specimen temperatures, i.e. 100°C followed by 45°C, decreased the water contact angle and reduced the aging effect. It appears that the hydrophilic functional groups introduced were located at the specimen surface (about 0.5 nm) at low temperature and that the aging effect was reduced due to the hydrophilic functional groups formed inside (0.5-8 nm) at high specimen temperature. The aging rate and the diffusion coefficient were also estimated, depending on the specimen temperature, using the experimental aging data.

A new surface modification technique, the so-called ion-assisted reaction (IAR), has been developed; such modification of polymer surfaces offers many industrial applications. The addition of new functional groups on polymer surfaces and permanent hydrophilic polymer surfaces (water contact angle below 30° and surface energy 60-70 mJ/m²) have been accomplished by IAR treatment. The formation of functional groups is significantly dependent on the flow rate of the reactive gas, the irradiating ion dose, and the ion beam energy. Improvements in wettability and surface energy are primarily attributed to the increase of polar characteristics due to the formation of functional groups such as (CO), (CO)O, (CO), etc. The characteristics of the IAR treatment have been reviewed, with outstanding results regarding the wettability and adhesion of various polymers such as PMMA, PC, PP, PS, PI, PVDF, and PTFE.