Multilayer films were prepared from poly(tetrafluoroethylene) (PTFE) and poly(ethylene terephthalate) (PET) films together with using an adhesion promoting layer (tie-layer) consisting of ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) terpolymer and low density polyethylene (LDPE) blend. Na/naphthalene treatment and subsequent acrylic acid grafting were applied on the surfaces of PTFE for chemical modification. FT-IR spectroscopy, XPS analysis and surface energy measurements were performed to characterize the modified PTFE films. The analyses showed defluorination and oxidation of PTFE surface, and supported the acrylic acid grafting. The surface energy of modified surfaces enhanced with respect to unmodified one, which promoted adhesion. The multilayers were subjected to T-peel tests to measure the adhesion strength between PET and modified PTFE. Peel strength between the films increased with increasing E-MA-GMA amount in the tie-layer. A proportional dependence of peel strength on Na/naphthalene treatment time was observed for multilayers containing acrylic acid grafted or ungrafted PTFE. From SEM analysis, it was observed that the texture of the PTFE surface after modifications became rougher when compared to untreated PTFE. The peeled surfaces were also analyzed by SEM. The micrographs evidence that the energy absorbing mechanism is the plastic deformation of the tie-layer, which is responsible for obtaining high peel strengths.

One of the main differences between low-pressure and atmospheric-pressure plasma treatments is that there is little moisture involved in the low-pressure plasma treatment, although moisture could exist at the wall of the vacuum chamber or react with the substrate after plasma treatment, while in the atmospheric-pressure plasma treatment moisture exists not only in the environment but also in any hygroscopic substrate. In order to investigate the influence of environmental moisture on the effect of atmospheric pressure plasma treatment, ultra-high-modulus polyethylene (UHMPE) fibers were treated using an atmospheric-pressure plasma jet (APPJ) with 10 l/min helium gas-flow rate, treatment nozzle temperature of 100°C and 5 W output power. The plasma treatments were carried out at three different relative humidity levels, namely 5, 59 and 100%. After the plasma treatments, the surface roughness increased while the water-contact angle decreased with increasing relative humidity. The number of oxygen containing groups increased as the environmental moisture content increased. The interfacial shear strength of the UHMPE fiber/epoxy system was significantly increased after the plasma treatments, but the moisture level in the APPJ environment did not have a significant influence on the adhesion properties. In addition, no significant difference in single fiber tensile strength was observed after the plasma treatments at all moisture levels. Therefore, it was concluded that the environmental moisture did not significantly influence the effect of atmospheric-pressure plasma treatment in improving interfacial bonding between the fiber and epoxy. The improvement of the interfacial shear strength for the plasma-treated samples at all moisture levels was mainly due to the increased surface roughness and increased surface oxygen and nitrogen contents due to the plasma etching and surface modification effect.

In this paper, we present a simple, yet novel, method, utilizing scraping to obtain continuous rough microstructures over large areas, leading to a tunable wettability conversion from hydrophilicity to superhydrophobicity on polymer surfaces. A series of polymers ranging from hydrophobic to hydrophilic were used, and we found that the wettability of these polymer surfaces could be modified by the scraping process, irrespective of their hydrophobicity or hydrophilicity. More importantly, those polymers with contact angle ranging from 65° to 90° on their smooth surfaces also exhibit enhanced hydrophobicity after scraping. Our results indicate that 65° is the critical value which is more suitable to define hydrophobicity and hydrophilicity for polymer materials.

Measurements of the surface tension (γ_LV) and advancing contact angle () on poly(tetrafluoroethylene) (PTFE) were carried out for aqueous solutions of cetyltrimethylammonium bromide (CTAB), cetylpyridynium bromide (CPyB), sodium decylsulfate (SDS), sodium dodecylsulfate (SDDS), p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycol)s, Triton X-100 (TX100) and Triton X-165 (TX165) and their mixtures. The results obtained indicate that the values of the surface tension and wettability of PTFE depend on the concentration and composition of the surfactants mixture. In contrast to Zisman finding, there was no linear dependence between cos and the surface tension of aqueous solutions of surfactants and their mixtures for all studied systems, but a linear dependence existed between the adhesional tension and solution surface tension for PTFE in the whole concentration range, the slope of which was –1, indicating that the surface excess concentration of surfactant at the PTFE–solution interface was the same as that at the solution–air interface for a given bulk concentration. It was also found that the work of adhesion of aqueous solutions of surfactants and their mixtures to PTFE surface did not depend on the type of surfactant, its concentration and composition of the mixture. This means that for the studied systems the interaction across PTFE–solution interface was constant, and it was largely of Lifshitz–van der Waals type. On the basis of the surface tension of PTFE and the Young equation and thermodynamic analysis of the work of adhesion of aqueous solutions of surfactants to the polymer surface it was found that in the case of PTFE the changes of the contact angle as a function of the total mixture concentration in the bulk phase resulted only from changes of the polar component of the solution surface tension.

Surface modification by corona discharge plasma is one of the most interesting industrial applications for surface modification compared with other techniques which require vacuum conditions. In this work, we have used the corona discharge plasma technique to modify the wettability properties of low density polyethylene (LDPE) film. The effects of this treatment on the surface of LDPE film have been quantified by contact angle measurements, Fourier-transform Infrared Spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. With these methods, we have determined how the treatment modifies, activates and functionalizes the surface of LDPE film, increasing its hydrophilic behavior, and how the process parameters influence the uniformity and homogeneity of the treated surface. The results obtained show good treatment homogeneity and an improvement of adhesion properties by the functionalization and etching of the film surface.

A superhydrophobic polyurethane-based film is described, on which the water advancing and receding contact angles are 150° and 82°, respectively. The film was prepared from surface-fluorinated polyurethane (PU), obtained from a well-defined fluorinated isocyanate, with silica particles incorporated within the film. In the absence of the silica particles, smooth fluorinated PU films with about 2 wt% fluorine demonstrate water advancing and receding contact angles of 110° and 63°, respectively. A major cause for the large contact angle hysteresis, similar to the so-called 'sticky' superhydrophobic behavior, on the roughened PU films is believed to originate from the surface reorganization of the fluorinated PU upon contact with water, which is characteristic for the partially fluorinated PU film. When a similar poly(dimethylsiloxane) (PDMS)-based roughened film was made, the water contact angle hysteresis could be reduced significantly, since the long PDMS chain can effectively suppress the surface reorganization upon contact with water.

The effects of acid oxidation on the surface properties of gel-spun ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers were investigated. Three acid-assisted reactions with CrO₃ (I), K₂Cr₂O, (II), and one base-catalyzed reaction with K₂Cr₂O₇ (III) were studied. In reaction II, two levels of sulfuric acid were used for IIa and IIb, with reaction IIa containing the higher concentration. Under the reaction conditions chosen, i.e. 1 min at 23°C, the effects of these oxidations were restricted to the fiber surfaces. All oxidation reactions either significantly reduced or eliminated the axially oriented macrofibril striations and changed the lamellae perpendicular to the fiber axis to irregular hairline surface structures. The oxidative attacks on the fiber surfaces appeared to have occurred in the fibrillar structure and likely at the disorder regions along the fibrils. The epoxy resin wettability and the interfacial adhesion to the epoxy resin were both improved with reactions I and IIa, whereas reaction III did not affect either of these properties. A positive relationship between surface wettability and interfacial adhesion on single fibers was observed on the untreated and acid oxidized gel-spun UHMWPE fibers.

The solid surface tension γsv of hydrophobic polymer powders has been determined using the capillary penetration technique. By plotting Kγlv cos ζ, where K is a geometric factor, versus the liquid surface tension γlv, the following values of γsv were directly derived from the curves: poly(tetrafluoroethylene) γsv = 20.4 mJ/m², polypropylene γsv = 30.2 mJ/m², polyethylene γsv = 34.4 mJ/m², and polystyrene γsv = 27.5 mJ/m². These values are in good agreement with the γsv values obtained from contact angle measurements on flat and smooth solid surfaces of the same materials. If the contact angles were first calculated from the capillary penetration experiments, which is the usual procedure applied in the literature, distinctly higher contact angles were obtained. Obviously these angles are affected by the powder morphology and are therefore meaningless contact angles in terms of a surface energetic interpretation.

The strength of an adhesive bond depends on the thermodynamic work of adhesion, among other properties. In this paper, we report the direct measurement of the thermodynamic work of cohesion and adhesion between poly(ethylene terephthalate) (PET) and polyethylene (PE) films. The pull-off force between polymer surfaces was measured using the surface forces apparatus (SFA). Thermodynamic work of adhesion was determined from pull-off force measurements using the theory of contact mechanics developed by Johnson, Kendall, and Roberts (JKR theory). The values of the surface energies of PET and PE, and the interfacial energy between PET and PE were obtained from these measurements. The dependence of the measured values of the work of adhesion on the rate of separation, time in contact, and other variables that could reflect an irreversible contribution to the measured adhesion was found to be negligible. The critical surface tensions of PET and PE were determined from contact angle measurements. The critical surface tension of wetting depends on the characteristics of the probe liquids. The surface energy of PET determined by the direct force measurements is higher than the critical surface tension of wetting. These values are 61.2 mJ/m² and about 43 mJ/m , respectively. However, in the case of PE the surface energy determined using the SFA and the critical surface tension of wetting are about the same, 33 mJ/m². The interfacial energy between PET and PE, obtained from direct measurements, is about 17.1 mJ/m².

SBS rubbers containing different loadings of calcium carbonate and/or silica fillers were surface treated with UV-ozone to improve their adhesion to polyurethane adhesive. The surface modifications produced on the treated filled SBS rubbers have been analyzed by contact angle measurements, ATR-IR spectroscopy, XPS and SEM. The adhesion properties have been evaluated by T-peel strength tests on treated filled SBS rubber/polyurethane adhesive/leather joints. The UV-ozone treatment improved the wettability of all rubber surfaces, and chemical (oxidation) and morphological modifications (roughness, ablation, surface melting) were produced. The increase in the time of UV-ozone treatment to 30 min led to surface cleaning (removal of silicon-based moieties) due to ablation and/or melting of rubber layers and also incorporation of more oxidized moieties was produced. Although chemical modifications were produced earlier in an unfilled rubber for short time of treatment with UV-ozone, they were more noticeable in filled rubbers for extended length of treatment, mainly for S6S and S6T rubbers containing silica filler. The oxidation process seemed to be inhibited for S6C and S6T rubbers (containing calcium carbonate filler). On the other hand, the S6S rubber containing silica filler and the lowest filler loading showed the higher extent of modification as a consequence of the UV-ozone treatment. The UV-ozone increased the joint strength in all joints, more noticeably in the rubbers containing silica filler, in agreement with the greater extents of chemical and morphological modifications produced by the treatment in these rubbers. Finally, the nature and content of fillers determined the extent of surface modification and adhesion of SBS rubber treated with UV-ozone.

Ink–cellulose interactions were evaluated using a new technique in which the adhesion properties between ink and cellulose were directly measured using a Micro-Adhesion Measurement Apparatus (MAMA). The adhesion properties determined with MAMA were used to estimate the total energy release upon separating ink from cellulose in water. The total energy release was calculated from interfacial energies determined via contact angle measurements and the Lifshitz–van der Waals/acid–base approach. Both methods indicated spontaneous ink release from model cellulose surfaces, although the absolute values differed because of differences in measuring techniques and different ways of evaluation. MAMA measured the dry adhesion between ink and cellulose, whereas the interfacial energies were determined for wet surfaces. The total energy release was linked to ink detachment from model cellulose surfaces, determined using the impinging jet cell. The influences of surface energy and surface roughness were also investigated. Increasing the surface roughness or decreasing the surface energy decreased the ink detachment due to differences in the molecular contact area and differences in the adhesiom properties.

The acid-base theory as developed by van Oss, Chaudury and Good is a powerful tool to analyze the surface free energy of polymeric materials; however, some problems are encountered in its application and some authors have shown that these problems can be theoretically solved considering this theory as an example of the so-called LFER theories. From this point of view, the definition of a well-defined scale of acid-base strength and the use of a wide and well-equilibrated, appropriate set of liquids is very important. In the present paper some recent results are presented which are based on the mathematical approach discussed by Della Volpe and Siboni in previous papers. The treatment is developed as a list of questions, Frequently Asked Questions (FAQs), whose theoretical implications are discussed using numerical examples chosen from the literature. Some literature data, collected by the opponents of the acid-base theory and recently published, are re-analysed using these methods, showing that they constitute a well-defined set to calculate, with a good precision, the acidbase components of the considered materials and the interfacial energies of liquids used. The present paper is the premise of a second one, in which a set of contact angles data collected by the authors and by other researchers will be analysed following the principles discussed here.

Ethylene-co-tetrafluoroethylene copolymer (ETFE) films were modified by four plasmas: direct and remote H2 plasmas and direct and remote O2 plasmas; and the hydrophobic recovery process of these plasma-modified surfaces was investigated using water contact angle measurements and angular XPS. The water contact angle measurements showed important aspects for the hydrophobic recovery process. (1) All plasma-modified ETFE surfaces, regardless of the kind and mode of plasmas, showed increases in the contact angle with increasing aging time. The increase continued for 5 days after finishing the plasma modification, and stopped after 5 days. (2) The plasmamodified surfaces after the aging process never reverted back to the same level of the contact angle as for the unmodified (original ETFE) surfaces. (3) The contact angle after the aging process was strongly dependent on to what plasma the ETFE surfaces were exposed in the modification. (4) The aging temperature influenced the contact angle value after the aging process. The angular XPS measurements also provided a detailed description of the chemical composition of the topmost layer. (1) The chemical composition at the topmost layer of the surfaces altered during the aging process. (2) CH₂-CH₂-CHF, and CH₂-CHF-CH₂ and CH₂-CH(OH)-CF₂ groups disappeared from the topmost layer during the aging process; and CH₂-CH₂-CH₂, and CH₂-CH₂-CF2 and CH₂-CH(OH)-CHF groups appeared at the topmost layer. (3) Such disappearance and appearance occurred on all plasma-modified surfaces regardless of the kind (H₂ or O₂ plasma) or mode (direct or remote plasma) of plasmas used for the modification. This may be due to segmental mobility of CH₂-CH₂-CH₂ sequences rather than of CF₂-CF₂-CF₂ sequences.

One of technologically imminent problems related to the use of pressure sensitive adhesives (PSAs) in the LCD industry is how to properly control the surface properties of various polymeric films used in devices to obtain sufficient bond strength with PSAs. To provide practical solutions to this issue, we used two types of surface treatments, NaOH and corona, to control the surface properties of polymeric films that are widely used in the LCD industry. Here we report a significant increase in surface tension in triacetyl cellulose (TAC) and discotic liquid crystal (D-LC) films along with a remarkable enhancement of bond strength in TAC/PSA and D-LC/PSA systems. The major portion of surface tension increase, in both types of films, was found to be due to an increase of polar component. The continuous increase of OH functionality in TAC with NaOH treatment time supported this observation. Furthermore, we established a map of surface treatment by studying the sequential effects of the two treatments, and based on this, we clearly demonstrated that each treatment had its own limiting value that could not be altered regardless of the sequence of surface treatment.

The effectiveness of the treatment with ultraviolet light (UV) on several polymeric surfaces has previously been established. In this study, a low pressure mercury vapour lamp was used as a source of UV radiation for the surface treatment of a difficult-to-bond block styrenebutadiene-styrene rubber (S6), the treatment time ranging from 10 s to 30 min. The UV-treated S6 rubber surfaces were characterized by contact angle measurements (ethylene glycol, 25°C), ATR-IR spectroscopy, XPS, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). T-peel tests on UV-treated S6 rubber/polyurethane (PU) adhesive/ leather joints (before and after ageing) were carried out to quantify adhesion strengths. The UV treatment of S6 rubber produced improved wettability, the formation of CO, CO and COO moieties, and ablation (removal of a thin rubber layer from the surface). The extent of these modifications increased with increasing treatment time. The extended UV treatment produced greater surface modifications, as well as the incorporation of nitrogen moieties at the surface. Furthermore, noticeable ablation of S6 rubber surface occurred. Peel strength values increased with increased treatment time of UV treatment of S6 rubber. Also, with increasing treatment time, the adhesive joints showed different loci of failure: adhesional failure for the as-received and 2 min-UV treated S6 rubber/polyurethane adhesive/leather joints changed to mixed failure (cohesive in the treated S6 rubber + adhesional failure) for the 30 min-UV treated S6 rubber/polyurethane adhesive/leather joint.

The effects of intense pulsed high power ion beam (HPIB) treatment of ultra-high strength polyethylene (UHSPE) fibers on the fiber/epoxy resin interface strength were studied. For this study, argon ions were used to treat Spectra^™ 1000 (UHSPE) fibers in vacuum. Chemical and topographical changes of the fiber surfaces were characterized using Fourier transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), dynamic wettability measurements, and scanning electron microscopy (SEM). The fiber/epoxy resin interfacial shear strength (IFSS) was evaluated by the single fiber pull-out test. The FTIR-ATR and XPS data indicate that oxygen was incorporated onto the fiber surface as a result of the HPIB treatment. The wettability data indicate that the fibers became more polar after HPIB treatment and also more wettable. Although the total surface energy increased only slightly after treatment, the dispersive component decreased significantly while the acid-base component increased by a similar amount. SEM photomicrographs revealed that the surface roughness of the fibers increased following the HPIB treatment. The single fiber pull-out test results indicate that HPIB treatment significantly improved the IFSS of UHSPE fibers with epoxy resin. This enhancement in IFSS is attributed to increased roughness of the fiber surface resulting in mechanical bonding and in increased interface area, increased polar nature and wettability, and an improvement in the acid-base component of the surface energy after the HPIB treatment.

The modifications induced by excimer laser irradiation of poly(ether ether ketone) (PEEK) surfaces have been investigated as a function of the laser process parameters for laser fluences below the material ablation threshold. In the case of 193 nm laser treatment, a significant increase in the adhesion properties of PEEK was obtained due to the formation of new polar and reactive groups on the surface. The extent of these reactive groups has to be controlled since their presence in high concentration may also have a negative effect on the mechanical properties of the treated surface. Laser treatments using 248 nm radiation did not result in a significant increase in the adhesion properties of PEEK. This probably results from thermal degradation of the surface at this laser wavelength.

To analyze various approaches for the determination of surface free energies of solids from liquid-solid contact angles, comb-like polymers with controlled grafting rates and macromolecular structures have been synthesized. The surface free energy parameters were calculated from the contact angles of standard liquids on the solid surfaces. A mathematical approach of the so-called acid-base theory of adhesion was used to characterize the nucleophilic and/or electrophilic behavior of the polymeric solid surfaces. Thus, correlations were established between the macromolecular structures and the dispersive component of the surface free energy, on the one hand, and the acid and base components, on the other. The main conclusion is that the surface free energy components are relevant for the characterization of functional comb-like polymeric materials: the dispersive and base components increase with the number of grafted electron-donating groups, whereas the acid component decreases.

The deposition of plasma polymers on poly(acrylonitrile) (PAN) fibers has been investigated by X-ray photoelectron spectroscopy and dynamic contact angle measurements. Four polymerizable monomers were examined: tetrafluoromethane (TFM), perfluoropropene (PFP), tetramethyldisiloxane (TMS), and hexamethyldisiloxane (HMS). The deposition rate of TFM was undetectable and the treated fibers exhibited some fluorination and an increase of hydrophilicity, due to posttreatment oxidation after exposure to air. The deposition rate of PFP was quite slow and the formation of an incomplete fluorinated layer was observed, with a remarkable increase of the water advancing contact angles. TMS and more so HMS quickly formed continuous and reproducible polysiloxane layers having pronounced hydrophobic properties. The influence of the position of the fibers in the plasma reactor chamber was also investigated. A good uniformity of deposition was found when the fibers were placed at different points between the electrodes.

FEP sheets were modified with a remote hydrogen plasma and the effects of the modification on the adhesion between copper metal and FEP sheets were investigated. The remote hydrogen plasma treatment is able to make FEP surfaces hydrophilic. In the remote hydrogen plasma treatment process, both defluorination and oxidation occur on the FEP surface. The oxidation reactions on the FEP surface form oxygen functional groups such as CO and CO groups. Modification of the FEP surface by the remote hydrogen plasma is effective in improving the adhesion of copper metal. The peel strength of the Cu/FEP system increased form 0 to 195 mN/5 mm, and the failure mode changed from the Cu metal/FEP polymer interface to within the FEP polymer layer. Remote hydrogen plasma treatment may be a preferable pretreatment of the FEP surface for adhesion with copper metal.

The thin-layer wicking technique was used to determine the surface free energy components and the surface character of three celluloses (Sigmaccll 101, Sigmacell 20, and Avicel 101), using an appropriate form of the Washburn equation. For this purpose, the penetration rates of probe liquids into thin porous layers of the celluloses deposited onto horizontal glass plates were measured. It was found that the wicking was a reproducible process and that the thin-layer wicking technique could be used for the determination of the celluloses' surface free energy components. The size of the cellulose particles was characterized with the Galai CIS-100 system and their crystallinity was measured by X-ray diffraction. The three celluloses have high apolar (y^LWS = 50-56 mJ/m²) and electron donor (γs = 42-45 mJ/m²) components, while the electron acceptor component (γS⁺ ) is practically zero. The free energy interactions of cellulose/water/cellulose calculated from the components are positive, regardless of the cellulose crystallinity. This would mean that the cellulose surfaces have a hydrophilic character. However, the work of spreading of water has a small negative value (3-9 mJ/m²), indicating that the surfaces are slightly hydrophobic. It is believed that the work of spreading characterizes better the hydrophobicity of the surface than the free energy of particle/water/particle interaction, because in the latter case, no electrostatic repulsion is taken into account in the calculations.

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.