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

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

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

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

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

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

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

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

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

Ultra-high strength polyethylene fibers were treated with excimer laser and high power ion beams (HPIB) to enhance their adhesion to epoxy resins. Laser treatments were carried out in air, argon, and helium environments and HPIB treatments were carried in vacuum. The effects of these treatments on the surface topography and chemistry were characterized using several techniques. It can be seen from the results that both laser and HPIB treatments increased the fiber surface roughness as well as the surface polarity. HPIB treated fibers had a characteristic bumpy surface while the laser treated fibers had deeper striations or a rougher surface. Although the total surface energy did not change after the treatments, the acid-base component increased significantly and the dispersive component decreased by almost the same amount. After the treatments the fiber-epoxy interfacial shear strength (IFSS) increased between 200 to 300%. This enhancement is attributed to the increased roughness of the fiber surface and increased specific interface area, increased polar nature and wettability, as well as improvement in the acid-base component of the surface energy.

The exposure of a polymer to ozone in the presence of ultraviolet light (UV/ozone) is a simple and effective way to improve the wettability of the surface. Using atomic force microscopy (AFM) we were able to examine the changes in morphology and the increase in the adhesion force at the surface of biaxially oriented polypropylene (PP) films after treatment with UV/ozone. It is clearly shown by atomic force microscopy (AFM) that UV/ozone treatment modified the original, fine, fiber-like structure to one displaying the formation of mounds or droplets. These droplets are most likely comprised of short chains of oxidized polymer or low-molecular weight oxidized materials (LMWOM). The size of the mounds increased with increasing treatment time. More interestingly, lateral force imaging AFM were capable of distinguishing these mounds from the surrounding surface, indicating that the mounds were formed on aggregation of the loose LMWOM during the UV/ozone treatment, while the surrounding surface was covered by bound moderately oxidized materials. The adhesion force was estimated from measurements made on the amount of force required to retract the tip from the surface after the two had made contact. A clear increase in adhesion force was observed on the modified PP film surface, which indicates an increase in the surface energy. We have demonstrated that mechanical scratching can alter the surface morphology and increase the surface energy of a polymer on a micrometer scale. The mechanically-scratched areas are more susceptible to modification than the surrounding unscratched surface when exposed to UV/ozone.

High surface energy (60–70 mJ/m2) polymers, i.e., totally wettable by water, from polypropylene to fluoropolymers have been obtained by ion-assisted reaction (IAR), in which the polymer surface was irradiated by energetic ions in a reactive gas environment. The ion energy was 1000 eV and the ion dose was varied in the range of 5 × 1014 – 1 × 1017 ions/cm2. Oxygen gas was introduced near the polymer surfaces during ion irradiation. The change in wettability was critically dependent on the ion dose and on the flux of oxygen gas. The surface energy was mainly increased due to the polar component related to the hydrophilic groups generated such as carbonyl and carboxyl, etc. The reaction generating the hydrophilic groups on the polymer surface modified by ion assisted reaction (IAR) was explained according to a two-step mechanism. The improvement in adhesion between the IAR-modified polymers and other materials was also explained in terms of the increased surface energy as well as surface roughness of the polymers modified by IAR.

Wettability of polyimide (PI) films modified by atomic oxygen (AO) was investigated by contact angle measurements. The PI films with/without being covered by a metal mesh were exposed to the AO beam with fluences from 1.4x 1016 to 9x 1018 atoms/cm2. The atomic force microscopy (AFM) and the X-ray photoelectron spectroscopy (XPS) were used to characterize the PI film surfaces. Both the roughness and the oxygen concentration at the PI surface increased by the AO exposure. The advancing and the receding contact angles of water on the PI films were measured both by the sessile drop method and by the Wilhelmy method. The contact angles measured by these two methods were identical for the PI samples both with/without AO exposures. In the case of the AO-exposed PI films being covered by the metal mesh, the contact angles were evaluated by the Wilhelmy method. A difference in contact angles on the exposed and the covered areas was clearly observed. It was also found that the wettability of the AO-exposed PI films was related to the amount of oxygen detected by the XPS.

The retention of chemical structure and functional groups during plasma polymerisation was investigated. Usually plasma polymer layers, prepared by continuous wave radio-frequency plasma, are often chemically irregular in their structures and chemical compositions. To minimise these irregularities, low wattages and the pulsed plasma technique were applied to avoid fragmentations. The polymerisation of vinyl and acryl-type monomers was strongly enhanced in the dark phase (plasma-off) of a pulsed rf plasma caused by the reactivity of the vinyl or acryl-type double bonds. Bifunctional monomers with acryl or allyl double bonds and also polar groups such as OH, NH2, and COOH were used to produce plasma polymers with defined (regular) structures and a high density of a single type of functional groups. The maximum yields were 30 OH, 18 NH2, 24 COOH groups per 100 C atoms. To vary the density of functional groups a chemical copolymerisation with “chain-extending” comonomers such as butadiene and ethylene was initiated in the pulsed plasma. The composition of these copolymers was investigated by XPS and IR spectroscopy. Homopolymers and copolymer layers were deposited on polypropylene (PP) foils and then aluminium was thermally evaporated. The peel force increased considerably and showed a dependence on the density of functional groups. The plasma polymer deposition was also monitored in situ by the Self-Exciting Electron Resonance Spectroscopy (SEERS) to show correlations between plasma parameters and properties of the deposited plasma polymer layers measured “quasi-in situ” by coupling the plasma chamber with an XPS spectrometer.

Oxygen mixed with nitrogen trifluoride (NF3) was used as the gas source for the plasma etching to increase the etching rate of the polyimide (PI) film. In order to investigate the effects of NF3 addition, surfaces of the etched PI films were analyzed with various methods. From the results of x-ray photoelectron spectroscopy (XPS), the chemical bonding state of the etched PI surface with 30% NF3/70% 02 plasma was similar to that of the surface prepared using 100% 02 plasma. The results of FT-IR analyses showed that a part of materials deposited on the etched PI film was soluble in chloroform and it contained carbonyl and ether compounds. Furthermore, the etching products were analyzed using quadrupole mass spectrometry (QMS) and gas chromatography. The main products were found to be H20, HF, CO and C02. In addition, CO/C02 ratio was found to be related to the etching rate which depended on the NF3 concentration.

The adhesion strength of a perfluorinated dielectric adhesive to polyphenylene sulfide (PPS) was investigated. The effect of different fillers in the PPS as a function of plasma treatment conditions was evaluated. The change in adhesion as a result of thermal baking was also addressed. The surface composition and surface energy were monitored and systematically quantified by X-ray Photoelectron Spectroscopy (XPS) and contact angle measurements, respectively. The correlations between the presence of certain functional groups, change in surface energy and polarity, and variation in adhesion properties indicate that the adhesion mechanism is mainly due to van der Waals forces. Enhanced wetting at the adhesive/substrate interface and a deeper interfacial diffusion zone are found to be necessary conditions to achieve the optimal adhesion.

Abstract Application of a pulsed high negative voltage (approx. 10 us pulse width, 300-900 pulses per second (pps)) to a substrate is found to induce discharge and thereby increase the ion current of an inductively coupled plasma. This plasma source ion implantation (PSII) technique is investigated as a surface modification method for poly (ethylene terephthalate)(PET) films using Ar, N2 and CZHZ gases. PSII treatment of PET with N2 and Ar gases is found to change the color of the PET film, effectively increasing the near-ultraviolet absorption. The effects of the treatment using N2 and Ar gases on the chemical bonding of C, H and O are examined by X-ray photoelectron spectroscopy (XPS). PSII treatment with CZHQ gas is shown to produce a thin diamond-like carbon film on the PET surface. The layer is shown to be smooth by scanning electron microscopy, and the structure is analyzed by XPS and laser Raman spectroscopy. The treatment using CZHZ gas effectively reduces the oxygen transmission rate by up to 100 times that of unmodified PET film at a carbon film thickness of only 70-300 mm.

The effects of exposure to [72 nm ultraviolet (UV) excimer light in ambient air on the wettability and surface free energy of polymer films were investigated from contact angle measurements. The polymer films used were polyethylene (PE), polypropylene (PP), poly (ethylene terephthalate)(PET), nylon 6 (Ny6) and polyimide (Pl). As a measure of the wettability, the water contact angle was determined by the sessile drop and the Wilhelmy methods. For all films, considerable increase in wettability was accomplished by UV exposure within a few tens of seconds. After the UV exposure, a decrease in the wettability, the hydrophobic recovery, was observed over a time period of several days. Even after the recovery, the wettability was sufficiently higher compared to that before the UV exposure. The Lifshitz-van der Waals component and Lewis acid-base parame-ters of the surface free energy of the films were determined by contact angle measurements using certain probe liquids. The base parameter was found to increase considerably by the UV exposure. XPS analysis and AFM observation of the film surfaces showed that such increases in the wettability and the surface free energy were due to the increased atomic oxygen concentration at the film surfaces. The effect of the UV exposure on particle deposition onto PP and PET in water was also examined using spherical polyethylene and nylon 12 particles. The apparent equilibrium number of particles deposited on the polymer substrate decreased drastically after UV exposure. The particle deposition behavior was explained well in terms of the free energy change due to deposition, which was calculated from various surface free energies.

Ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated using pulsed KrF (248 nm) excimer laser in air and in diethylenetriamine (DETA), to improve their adhesion to epoxy resin. The effects of fluence, number of pulses and the treatment environment were explored. Topographical and chemical changes on the fiber surface were characterized using several techniques, including X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic wettability measurements. SEM micrographs and AFM images revealed that the surface roughness of fibers increased after the laser treatment and was a function of the fluence (energy density) of the laser beam and number of pulses. The XPS data indicated that oxygen and nitrogen were incorporated on the fiber surfaces making them more polar. The dynamic wettability data confirmed the presence of polar groups on the fiber surfaces. The UHMWPE fiber/epoxy resin interfacial shear strength (IFSS) increased by up to 600% for some treatment conditions. Introduction of polar groups and increased surface roughness are two main factors that contribute to the increased adhesion (IFSS) of the UHMWPE fiber/epoxy resin system significantly.

The objectives of this work were to identify, develop and compare methods for opti-mized welding of polypropylene using the ultrasonic method. The methods considered include: modification of surface polarity by grafting monomers onto polypropylene backbone, thermal and chemical surface pretreatments and surface pretreatment by excimer laser ablation. The weld joint tensile strength was chosen as the optimization criterion for ultrasonic welding. The thermal properties and weld morphology obtained using Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM), respectively, were correlated to weld strength. It was determined that proper surface modification improved material weldability. The results suggest that increased polarity and roughness and decreased melting temperature and heat of melting increase the weld strength.

The surface chemistry and surface energetics of materials are important to the performance of many products and processes—sometimes in as yet unrecognized ways. This review is written for the researcher interested in exploring the nature of surfaces and their relation to processes involving spreading, wetting, liquid penetration and adhesion. Researchers concerned with many types of products including pharmaceuticals, printing and the making of composite materials should have interest in this topic. More specifically, this work is a review of the literature concerning the surface free energy of solids. Both theoretical approaches for understanding the surface free energy of solids are explored and contrasted, as are experimental methods for measuring surface free energy of solids. Experimental methods that offer insight into the chemical nature of surfaces but do not measure surface free energy are also discussed as these two subjects are intertwined.

An overview is presented of a series of papers published during the last decade which show that the conventional thermodynamic approach to liquid—solid adhesion requires some fundamental changes. It is pointed out that it has been a long-neglected fact that adsorption, as generally measured in adsorption isotherms, is actually surface excess, so that it can, in principle, be negative as well as positive. As a result, the free energy of adsorption, AF, can be positive as well as negative. Small amounts of water vapor adsorbing onto previously evacuated poly (tetrafluoroethylene) could, in principle, therefore be increasing the free energy of the low-energy polymer surface. It is further pointed out that from the strictly thermodynamic point of view, changing the free energy of a surface by adsorption of the vapor of a liquid does not necessarily change the contact angle. Resulting changes in contact angle can, however, theoretically occur from changes in the intermolecular force interaction term (proposed work of adhesion), such as those terms proposed by Good and Girifalco, Fowkes and others, where such changes would be speculative. In addition, it is pointed out that an accurate thermodynamic representation of liquid-solid adhesion should take into account the shape of the drop to be deposited (or drop that has been detached), as well as the resulting contact angle. An equation is presented for the free energy of adhesion of a spherical drop.

The interfacial forces which determine the interaction between a liquid and solid surface have been investigated under dynamic conditions of evaporation. The evaporation characteristics of probe liquids and their influence on the droplet of the liquid on a solid substrate have been investigated. The changes in mass, contact angle, solid–liquid contact radius during evaporation of droplets (3-90 mg) of water on glass, polycarbonate and PTFE substrates and droplets of methyl alcohol on polycarbonate, polypropylene, PTFE and high density polyethylene substrates have been examined. The evolution of contact angle and contact radius with the progress of evaporation has been investigated for each droplet-substrate system in order to identify the common trend. In the systems of water droplets on polycarbonate and glass, the contact radius remained constant with the progress of evaporation but such behavior was not observed in the case of methyl alcohol on polycarbonate, polypropylene, PTFE and high density polyethylene.

We summarize here a mean-field representation of fluid free-energy to a lattice Boltzmann scheme recently proposed for interfacial studies. The interfacial behaviors obtained from this new multi-phase lattice Boltzmann model (LBM) were validated by means of the Laplace equation of capillarity and the capillary wave dispersion relation. Applications of this mean-field LBM to various interfacial studies are reviewed, including wettability on heterogeneous surfaces, self-propelled drop movement, contact line dynamics and solid–liquid interfacial slip. The mean-field LBM simulates systems with better physical reality in terms of solid–liquid interactions and could be an alternative for simulating interfacial phenomena.

An experimental study of the constant velocity displacement of various water/glycerol solutions by air in poly (vinyl chloride)(PVC) capillary tubes is reported. This topic is of particular interest in relation to dewetting processes on surfaces covered by a liquid film. More specifically, variations of the dynamic contact angle with velocity and their relation to the physicochemical properties of the systems studied are investigated. These results and those of other authors are analyzed in the framework of both hydrodynamical and molecular approaches of the dynamic contact-angle problem. These comparisons indicate that either the molecular or the viscous dissipation mechanism may be dominant, depending on the system studied. These results are used to suggest explanations for apparent discrepancies between dewetting velocity measurements in different systems previously reported by the authors.

The essential form of an initially straight wetting triple line perturbed by the presence of a (higher surface free energy)“defect” on the solid surface has been recognised for a long time, and it corresponds to a logarithmically decaying form. However, less attention has been paid to the behaviour of the triple line within the domain of the defect. This was actually studied a few years ago from a theoretical viewpoint, leading to the prediction of an inversion of curvature. Recent experimental work has been concerned with the electrochemical treatment of PTFE, leading to small etched areas of higher wettability with typical widths of 100-300 um. Wetting experiments have been carried out on such solids and the results confirm the general conclusion of inverted curvature of the triple line in the treated zones. However, the “excess wettability” in the treated zones, as evaluated experimentally, was found to be greater than predicted theoretically. Possible causes are discussed.

The measurement of contact angles and, thus, determination of solid surface tension has been considered for years as a “comedy of errors”, but in recent years the introduction of more sophisticated techniques and of computer-controlled devices, along with a general better understanding of surface structures, has led to a greater precision and accuracy of measurements. However, it is common to neglect the difference between the advancing contact angle and the Young’s angle or to underestimate the role and significance of receding contact angles. In previous papers an experimental procedure has been developed, called the Vibration Induced Equilibrium Contact Angle (VIECA), applied to a Wilhelmy experiment, which appeared to be able to provide a really stable and equilibrium-like value: this procedure was based on previous, rare literature attempts at providing an operational and satisfactory definition of equilibrium contact angle. The VIECA results seem to be related to the advancing and receding values through simple, but approximate, relations. Moreover, the VIECA appears to be independent of the roughness and heterogeneity of the surfaces analysed in the majority of cases. In the present paper, the VIECA method is extended to the sessile drop technique and comparison is made with the common advancing or “static” estimates of contact angle. A theoretical modelling of the physical situation induced by the application of mechanical vibrations to the meniscus or to the drop is proposed. The main consequence of these results is that the contact angles on common surfaces for common liquids are overestimated; a more subtle consequence is the effect on the evaluation of the surface free energy via the most common semiempirical models.

An understanding of the surface free energy and surface chemistry of solids is needed for investigation into the nature of processes involving adhesion, wetting and liquid penetration. Frequently the contact angles of several probe liquids on a given solid are used for calculation of solid surface free energy. Models by Fowkes, Kwok and Neumann, van Oss, Chaudhury and Good, as well as by Chang and Chen have been used for such calculations. Each of the above models has been championed in the literature. It has been noted by the present author and others that the use of different models may lead to different qualitative interpretations of the nature of a solid surface. A disinterested comparison of the various available models has not been made. In the present paper, a comparison of the calculations is undertaken in order to better understand the limitations of each model. Particular attention to the assumptions required for contact-angle data to be used for surface free energy calculations is given. The effect of the degree to which the experimental contact-angle data meet the required assumptions have on the calculated surface free energy is addressed in this work. When data meeting the theoretical assumptions common to the various published models are used, all of the published models fit the data, to a good approximation, equally well. A poor fit of the experimental data is an indicator that at least one liquid does not fully meet the assumptions re-quired by the chosen model. Differences in the acid—base character of the solid surface appear to re-sult from the acid—base scale used by the model. The paper is intended to raise the awareness of the difficulties in assigning surface free energy and predicting wetting behavior.

Ammonia plasma treatments were performed on both thermoplastic plates and fabrics made of poly (ethylene terephthalate)(PET). The plates became more hydrophilic with improved adhesion properties as expected, whereas the fabrics became more hydrophobic, yet positively charged. Plasma treatments of PET fabrics using gas mixtures such as NH3/N2 and HZ/NZ were performed in order to simulate pure ammonia plasma treatments since such treatments are not always applicable in industrial applications, due to environmental and safety reasons. It was shown that the recommended and allowed gas compositions, 15% NH; in N2 and 5% H2 in N2, did not show any similarity with pure ammonia plasma treatments with respect to surface charge, wettability and chemical surface composition. At least 80% NH; in N; or 80% H2 in N2 is needed to simulate an ammonia-like plasma treatment of PET fabrics.

Ultra-high-molecular-weight polyethylene (UHMWPE) fibers (Spectra® 1000) were treated using pulsed XeCl excimer laser (308 nm) to improve their adhesion to epoxy resin. The la-ser treatments were carried out in air and in diethylenetriamine (DETA) environments with varying numbers of pulses and fluences. The effects of the laser treatments on the fiber surface topography, chemistry and wettability were investigated. The interfacial shear strength (IFSS) with epoxy resin was measured using a single fiber pull-out test. The surface roughness was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AF M). The laser treatment introduced grooves along the fiber length and increased the fiber surface roughness up to 6-times the control value, as measured by AFM. The X-ray photoelectron spectroscopy (XPS) data indicated that oxygen and/or nitrogen were incorporated on the fiber surface afier the laser treatments depending on the environment in which the treatments were carried out. For some treatments the oxygen/carbon ratio increased by up to 2.5-times the control value. The dynamic wettability data showed that the laser treatments significantly increased the acid-base component of the surface energy and the work of adhesion. The UHMWPE fiber/epoxy resin IFSS increased by up to 400% for certain treatment conditions. The introduction of polar groups and higher surface roughness were found to be the two main factors that contributed to the significant increase in the adhesion of the UHMWPE fiber/epoxy resin system.

Plasma web treatment is a common practice for promoting adhesion, wettability and other surface or interfacial properties in the conversion industry. While the objective of creating new surface functional groups is conceptually simple, it can be difficult to choose the most appropriate kind and configuration of plasma source, the most appropriate feed gas composition and the most appropriate operating pressure for a given application. Such difficulties arise from the variety of species that can be formed in the plasma and the variety of possible plasma-surface interactions that can occur. A brief review of the importance of various plasma parameters (eg, specific energy, species concentrations, and energy distributions) and an example relating nitrogen uptake in poly (ethylene-2, 6-naphthalate) to plasma diagnostic data in a low-radiofrequency capacitivelycoupled nitrogen plasma are presented. The importance of driving frequency and treatment configuration is discussed in detail. Uptake kinetics for samples treated at floating potential at low radiofrequency is compared with that for samples treated in the cathode sheath. Analysis of the treatment kinetics is based on a simple model of surface saturation. This approach can be used not only to compare practical treatment results as a function of process conditions, but also to compare different treatment techniques in a practical manner.

A novel atmospheric pressure plasma jet, that is operated with air, is used for the pretreatmet of different polymers. The resulting adhesive bond strengths and the corresponding changes of the polymer substrate surface are studied. The plasma treatment induces chemical and topographical changes on the polymer surface. It is likely that both types of surface modification contribute to the adhesion improvement. Results for poly (ethylene terephthalate) indicate that surface chemical composition is more influential in adhesion enhancement than surface roughness.