The effect of activation of the surface of polypropylene sheet, by a corona discharge, upon the contact angles of liquids and on the surface free energy parameters γ^LW, γ^⊕ and γ^⊖, was determined. Both advancing and retreating contact angles were measured. The “acid/base” theory of the components of surface free energy was employed.

The contact angles of water and glycerol were initially lower by as much as 30°, after treatment, and that of diiodomethane was lower by about 5°. With time, the advancing angles rose, and the γ^⊕ and γ^⊖ parameters fell, towards the values on the untreated solids, and attained more or less steady values after 5 to 10 days. The basic component, γ^⊖, was the most strongly affected by the corona treatment; it rose, typically, from 2.2 to as high as 25 mJ/m². The acidic component, γ^⊕, rose from zero to as high as 1.9 mJ/m². Its decay with time was only qualitatively the same as that of γ^⊖. The retreating angles, and the corresponding energy components, were changed in the same direction, and somewhat more strongly, than were the “advancing” data.

The well-known improvement in the property of forming strong joints or adherent coatings, after corona treatment, is no doubt due to the formation of sites or areas on the polymers where hydrogen bonds can be formed. The decay of the strength of adhesion with time is, no doubt, due to the decay of these sites or areas.

The present investigation studys the effects of different electrodes such as copper, nickel, and stainless steel under low-pressure plasma on physicochemical and adhesion characteristics of high-density polyethylene (HDPE). To estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to low-pressure plasmas have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that the surface energy and its polar component increase with increasing exposure time, attain a maximum, and then decrease. The increase in surface energy and its polar component is relatively more important when the polymer is exposed under a stainless-steel electrode followed by a nickel and then a copper electrode. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by optical microscopy and electron spectroscopy for chemical analysis (ESCA). It is observed that when the HDPE is exposed under these electrodes, single crystals of shish kebab structure form, and the extent of formation of crystals is higher under a stainless-steel electrode followed by nickel and then copper electrodes. Exposure of the polymer under low-pressure plasma has essentially incorporated oxygen functionalities on the polymer surface as detected by ESCA. Furthermore the ESCA studies strongly emphasize that higher incorporation of oxygen functionalities are obtained when the polymer is exposed to low-pressure plasma under a stainless-steel electrode followed by nickel and then copper electrodes. These oxygen functionalities have been transformed into various polar functional groups, which have been attributed to increases in the polar component of surface energy as well as the total surface energy of the polymer. Therefore, the maximum increase in surface energy results in stronger adhesion of the polymer when the polymer is exposed under a stainless-steel electrode rather than nickel and copper electrodes.

In the absence of weak boundary layers, surface energy can be an excellent indicator of the suitability of a fiber-reinforced composite surface for adhesive bonding. Mechanical surface treatments such as grit blasting are effective and commonly used to prepare composite surfaces, but the roughness introduced by these treatments makes quantification of the surface energy by contact angle methods difficult. This paper shows that the diameter of a small drop of a low-viscosity fluid chosen to have surface tension characteristics very similar to the adhesive can be used as an effective predictor of adhesive bond fracture energy. This technique could form the basis of a sensitive quality assurance tool for manufacturing.

The theoretical analysis of electrostatic interactions and ion redistribution in the close vicinity of the three-phase contact line shows their important role in the Langmuir wetting process. To provide a sufficient rate for the ion transfer, which is intended to neutralize the interfacial charge, the concentration and potential distributions deviate from the equilibrium. As a consequence, during the deposition process the adhesion work, and hence the contact angle, are defined by the local ionic concentrations near the three-phase contact line. The concentration profiles and the electro-diffusion ion fluxes induced during the Langmuir wetting process are strongly dependent on the subphase composition and on the monolayer properties. The results of the analysis are in a good agreement with the experiments.

Accurate surface tension of Teflon^® AF 1600 was determined using contact angles of liquids with bulky molecules. For one group of liquids, the contact angle data fall quite perfectly on a smooth curve corresponding to γ_sv = 13.61 mJ/m², with a mean deviation of only ±0.24 degrees from this curve. Results suggest that these liquids do not interact with the solid in a specific fashion. However, contact angles of a second group of liquids with fairly bulky molecules containing oxygen atoms, nitrogen atoms, or both deviate somewhat from this curve, up to approximately 3 degrees. Specific interactions between solid and liquid molecules and reorientation of liquid molecules in the close vicinity of the solid surface are the most likely causes of the deviations. It is speculated that such processes induce a change in the solid–liquid interfacial tension, causing the contact angle deviations mentioned above. Criteria are established for determination of accurate solid surface tensions.

The effect of film thickness and surface preparation techniques on contact angles of water, 1-bromonaphtalene, and n-hexadecane on Teflon^® AF 1600 polymeric surfaces is studied. It was found that contact angles of water on different thicknesses of spin-coated films ranging from 27 nm to 420 nm are essentially constant. This is due to the homogeneity and smoothness of the coating layers as shown by the scanning force microscopy of the samples. Furthermore, the contact angle measurements with these three liquids on both dip-coated and spin-coated films suggested that the film preparation technique does not affect contact angles dramatically. Interestingly, slightly higher contact angles on dip-coated surfaces were measured. It is also argued that the anomaly of the water contact angle—in the sense that the measured contact angle is much higher than the expected ideal value—is due to specific interactions between water and Teflon^®.

Low-rate dynamic contact angles of 12 liquids on a poly(methyl methacrylate/n-butyl methacrylate) P(MMA/nBMA) copolymer are measured by an automated axisymmetric drop shape analysis-profile (ADSA-P). It is found that 6 liquids yield non-constant contact angles, and/or dissolve the polymer on contact. From the experimental contact angles of the remaining 6 liquids, it is found that the liquid- vapour surface tension times the cosine of the contact angle changes smoothly with the liquid-vapour surface tension, i.e., γ_iv cos θ depends only on γ_iv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and noninert (polar and non-polar) surfaces [34-42, 51 -53]. The solid-vapour surface tension calculated from the equation-of-state approach for solid -liquid interfacial tensions [14] is found to be 34.4 mJ/m², with a 95% confidence limit of \pm 0.8mJ/m², from the experimental contact angles of the 6 liquids.

The nature of low-pressure glow-discharge plasma, plasma equipment, and the effect of plasma on materials is reviewed. Examples are given of the improved adhesive bonding of polymers after plasma treatment (2–10 times improvement in lap-shear) and of the surface cleaning and chemical modification that occurs during plasma treatment.

Atmospheric pressure plasma processing has attracted significant interests over decades due to its usefulness and a variety of applications. Adhesion improvement of polymer surfaces is among the most important applications of atmospheric pressure plasma treatment. Reflecting recent significant development of the atmospheric pressure plasma processing, this work presents its fundamental aspects, applications, and characterization techniques relevant to adhesion.

In the present study the mechanisms and effectiveness of various pretreatments for fluoropolymers were studied. The pretreatments were “Tetra-Etch,” various plasmas, flame and potassium hydroxide. “Tetra-Etch” was found to be much more reactive than potassium hydroxide (KOH) towards fluoropolymers. The plasma treatment of PTFE showed that it was possible to get substantial increases in adhesion with little or no chemical change to the polymer. However, to obtain large increases in adhesion it may be necessary to modify PTFE chemically as with “Tetra-Etch.” Consideration of the bonding of these fluoropolymers shows that sharp interfaces between these substrates and adhesives do not exist.

A comparative study of the treatment of polytetrafluoroethylene (PTFE) and poly(vinyl fluoride) (PVF) with “Tetra-Etch” has been carried out. The treatment of PTFE resulted in extensive changes in surface chemistry and topography, whereas with PVF there was no significant change in topography and the chemical changes were much less marked. However, treatment of both polymers resulted in large increases in bond strength.

Multiple bonding experiments in which samples are repeatedly fractured and re-bonded were carried out with untreated PTFE and PVF. These resulted in moderate increases in bond strength with PTFE and large increases with PVF. The results indicate that weak boundary layer (WBL) removal is a key element in adhesion improvement by “Tetra-Etch” on PVF. With PTFE, WBL removal also improves adhesion, but the chemical and/or topographical changes introduced by the “Tetra-Etch” are required for optimum performance.

We developed a new plasma treating method, incorporating the use of microwaves generated by an electronic cooking range. Using this method, polytetrafluorethylene (PTFE) and a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP) were treated. Dialkylphthalates (DAP) were used as the standard liquids of contact angle measurements for evaluation of the wetting properties of plasma treated polymers. The components of surface tension (γ_L) due to the dispersion force (γ^d _L) and the polar force (γ^P _L) of DAP were calculated by Fowkes' equation from the contact angles (θ) on polypropylene. After plasma treatment cos θ of several standard liquids on PTFE and FEP increased. The linear relationship between γ_L(1 + cos θ)/(γ^d _L)^½ and (γ^P _L/γ^P _L)^½ was verified. γ_s and γ^d _s and γ^d _s of the plasma treated PTFE and FEP also increased. From the results of ESCA analysis, it was found that a significant amount of oxygen was introduced to the polymer surface by the plasma treatment. Peel strengths of a pressure sensitive adhesive bonded to PTFE and FEP increased approximately two-to threefold if the plasma treatment was used prior to bonding.

Low density polyethylene (PE) and polyethylene terephthalate (PET) films were treated in air plasma of a low pressure (500 mTorr) large area microwave (2.45 GHz) discharge, or in a corona discharge at atmospheric pressure. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS) for their oxygen content [O] and surface chemical structure, which were related to the corresponding peel strength of PE/PE and PE/PET laminates. Although the oxygen concentration at the surface increased monotonically with the degree of treatment, the peel force reached a maximum and then sharply decreased. Regardless of the treatment type, the maximum peel force occurred for [O] values between 10-15 at.%. The highest peel force has been found to occur when the concentration of CO (hydroxyl, ether, epoxy,…) groups is highest and that of OCO (carboxyl) groups is lowest, which corresponds to the situation when the effect of a weak boundary layer, due to low molecular weight materials, is minimal (low OCO concentration).

In this investigation the fracture surface between bovine dentine and bovine enamel and a dental cement was observed using the scanning electron microscope at magnifications up to 10,000 ×. The results indicated that the topography of the adherend plays an important role in the formation of an adhesive bond and in the fracture pattern of an adhesive joint, even when cohesive failure is involved.

The contact angle of CH₂I₂, α-bromonaphthalene and aniline on crosslinked polystyrene has been measured. The polymer was swollen for as long as 60 days in the liquid whose contact angle was to be measured. The surface free energy, γ_s, of unswelled polystyrene was estimated from the contact angles and the swelling results, using an equation which had previously been proposed by Good. The value of γ_s is estimated to be 42±2 ergs/cm².

The strength of fibre-reinforced materials depends heavily on the adhesion between the fibre and the resin. To predict the bond strength of the adhesion, it is desirable for the surface tension of the fibre to be known. Two independent methods, the Wilhelmy balance method and the solidification front method, were investigated. The fibres used for this investigation included a carbon fibre, Thornel 300®, and an aromatic poiyamide fibre, Kevlar.

In the Wilhelmy experiments three liquids, ethylene glycol, glycerol and distilled water were employed to measure the surface tensions of the test fibres. They were found to be 42.4 mJ/m² and 43.7 mJ/m² for the carbon fibre and Kevlar, respectively. These values agreed very well with the results obtained from the solidification front method, from which the carbon fibre was found to have a surface tension value of 41.8 mJ/m² while that for Kevlar was 46.4 mJ/m². Furthermore, error analysis has shown that the error limits of the experiments are within 5% of the resulting values. The reproducibility and accuracy of these two techniques indicate that they are viable for determining the surface tension of small diameter fibres.

A new method to detect surface oxidation of an otherwise untreated, cross-linked and filled silicone rubber is described. Our method is established on the principle that surface wettability increases during the progress of oxidation. Surface wettability is determined in terms of critical surface tension.

Abhesive polymers, of which silicone rubber is a typical example, are characterized by low surface energy, low friction coefficient and low release value. The problem associated with silicone rubber is its poor adhesion to other polymers. Its adhesional ability, however, can be improved by surface modification, e.g. oxidation, treatment with corona discharge, or ionic bombardment with inert gases.

By our method we found that the oxidation of silicone rubber is comparatively mild below 260°C, but is intensified at 287°C. Excessive oxidation at 316°C results in the formation of low molecular weight siloxanes which lower the wettability of the oxidized surface. Mechanisms of thermal oxidation are discussed.

An RTV silicone and high density polyethylene are exposed in an activated gas plasma for varying times and varying conditions. Both oxygen and argon are used. Changes in critical surface tension of wetting as determined by contact angle measurements are reported. Bondability of the treated surfaces is evaluated with both the aged bonds and aged surfaces prior to bonding being evaluated. In contradiction to some of the recent work reported in the literature on the effect of activated inert gas on surface characteristics, contact angles always decreased on the materials studied indicating an increase in surface energy. The significance of the results on present adhesion theories is discussed.

The relationship between adhesion and surface energy is well established for systems where specific chemical interactions are unlikely, such as pressure sensitive adhesives. However, the relationship of wetting to adhesion in chemically reactive systems is not well understood. This work used atmospheric pressure plasma treatment in air of high density polyethylene to obtain surfaces with a range of electron donor and acceptor character prior to bonding with an amine cured epoxy. Adhesion correlated strongly with the electron donating character of surface energy, and the likely functional groups responsible for this adhesion were amines created by the plasma treatment process. These results indicate that wetting measurements may be useful in detecting the specific chemical interactions important to adhesion in reactive systems.

The effect of forced air-plasma pre-treatment, Lectro-treat (TM), on polypropylene has been investigated using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS (AR-XPS), and atomic force microscopy (AFM). The pre-treatment process is found to induce both surface chemistry changes and topographical changes. The parameters of the pre-treatment process can be optimised from these observations. The Lectro-treat pre-treatment process has been used for adhesive bonding of a demonstrator component: a bumper assembly. The adhesively bonded bumpers performed successfully in standard automotive tests.

We report on the preparation of amphiphilic diblock copolymers containing a hydrophilic segment, poly(acrylic acid)(PAA), and a polystyrene hydrophobic part. We analysed, by means of contact-angle measurements, how the hydrophilic segments usually bury themselves under the hydrophobic when exposed to air to reduce the surface free energy of the system. In contrast, in contact with water, the hydrophilic blocks have a tendency to segregate to the interface. We first describe the parameters that control the surface reconstruction when the environmental conditions are inversed from dry air to water vapour. Then, annealing time, temperature, composition and size of the diblock copolymers, and size of the matrix that influenced the surface migration process are the main parameters also considered. Finally, the density of the carboxylic functions placed at the surface was determined using the methylene blue method.

The effect of ultraviolet (UV) radiation in the presence of ozone as a surface treatment for polycarbonate is examined in regards to changes in the wettability, adhesion, and surface mechanical properties. Standalone, 175-µm-thick films of a commercially available polycarbonate were exposed to UV radiation from sources of different power with various treatment times in the presence of supplemental ozone. Significant decreases in the water contact angle were observed after exposure to UV radiation in the presence of ozone. After several variations in the experimental setup, it was determined that the change in water contact angle is a function of the UV irradiance and the work of adhesion follows a master curve versus UV irradiance. Nanoindentation experiments revealed that the modulus of the top 500 nm of the surface is increased following UV exposure, attributable to surface cross-linking. Adhesion tests to the surface (conducted by a pneumatic adhesion tensile test instrument) showed little change as a function of UV exposure. Analysis of adhesion test failure surfaces with X-ray Photoelectron Spectroscopy (XPS) showed the locus of bond failure lay within the bulk polycarbonate and the measured bond strength is limited by the bulk properties of the polycarbonate and/or the creation of a weak boundary layer within the polymer.

A review is presented of the adhesion between polymers with particular emphasis on the processes that occur during failure at the level of polymer chains and how these processes relate to the macroscopic interface toughness. The same processes at the chain level, pull-out and scission, occur in both glassy polymers and elastomers, but the two classes of material are considered separately because their deformation processes around a crack tip are so different. Emphasis is placed on the work in which the author has participated and so the review makes no attempt to be an unbiased survey of the field.

Hydrophobic solid surfaces with controlled roughness were prepared by coating glass slides with an amorphous fluoropolymer (Teflon^® AF1600, DuPont) containing varying amounts of silica spheres (diameter 48 μm). Quasi-static advancing, θ_A, and receding, θ_R, contact angles were measured with the Wilhelmy technique. The contact angle hysteresis was significant but could be eliminated by subjecting the system to acoustic vibrations. Surface roughness affects all contact angles, but only the vibrated ones, θ_V, agree with the Wenzel equation. The contact angle obtained by averaging the cosines of θ_A and θ_R is a good approximation for θ_V, provided that roughness is not too large or the angles too small. Zisman's approach was employed to obtain the critical surface tension of wetting (CST) of the solid surfaces. The CST increases with roughness in accordance with Wenzel equation. Advancing, receding, and vibrated angles yield different results. The θ_A is known to be characteristic of the main hydrophobic component (the fluoropolymer). The θ_V is a better representation of the average wettability of the surface (including the presence of defects).

This work deals with the study of the durability, in a hot/wet environment, of structural adhesively bonded polyetherimide (PEI) assemblies used in power electronics packaging technology. An overall approach is proposed, for which the epoxy joint-PEI substrates assembly on the one hand, and the adhesive system components (substrate surface and bulk adhesive) on the other hand, are studied separately with different analytical techniques. The first part of this work was devoted to the substrate surface state and to its modification using a cold plasma treatment of the PEI surface. Then for chosen parameters (power, duration) contact angle measurements indicated an increased surface tension resulting from surface decontamination (removal of release agent and carbon contaminants) and from the creation of polar species, such as esters or carboxylic acid groups, on the PEI surface (XPS analyses). The second part of this study concerned the bulk adhesive ageing in an ethylene glycol-water solution at 70°C. Mass uptake measurements versus time showed the liquid diffusion in the bulk adhesive associated with a microscopic damage of the epoxy system. An overall plasticizing of the adhesive with a considerable decay of the α-transition temperature of one of the two adhesive epoxy-amine networks (TGDDM-BAPP) was also highlighted using rheometry. However, in these ageing conditions, the adhesive glassy modulus decreases slighty because of the thermomechanical stability of the other epoxy network. In the third part, the asymmetric wedge test showed the beneficial effect of the cold plasma treatment on the epoxy/PEI interface durability in the aggressive medium.

The surface of polyether ether ketone (PEEK) films was modified using plasma treatment, corona, or surface etching to improve their adhesion with regard to glued copper foils and copper layers generated by physical vapor deposition. After the pretreatments, surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The wetting behavior was qualitatively investigated by contact angle measurements. Surface topography was monitored by laser scanning microscopy (LSM). After coating, the adhesion strength of the copper layer was measured by a peel force test. Plasma treatment, corona discharge, or etching lead to a significant increase in adhesion. This increase is caused by a change in surface topography as well as by the incorporation of polar groups into the surface.

The increased use of polyphenylene sulphide (PPS) and polyetheretherketone based composites for aircraft structures has highlighted the need for reliable methods of bonding these materials to metallic components such as titanium. Both composite and titanium adhesive bonds exhibit poor long-term durability when exposed to hot/wet conditions, aerospace fluids and solvents. As a result, surface treatments are employed to enhance surface energy, surface roughness and alter surface chemistry to provide better long-term durability. In this initial study the adhesive bonding of glass fibre reinforced GFR-PPS and commercially pure titanium was investigated. Prior to bonding, both materials were plasma treated using argon and oxygen gases in a RF discharge. Surface characterisation was carried out to optimise these treatments. Surface energy and wettability were examined using contact angle analysis, surface roughness was examined using scanning electron microscopy and atomic force microscopy, while X-ray photo-electron spectroscopy (XPS) was employed to study the surface chemistry. Bond strengths were determined using lap shear tests. Initial results reveal that these optimum plasma treatments produce a significant increase in bond strength.

The interfacial adhesive behavior between acrylic pressure sensitive adhesive-like networks (PSA-LNs) and poly(vinyl N-alkyl carbamate) release coatings was studied using a contact mechanical method and peel tests. Surface energy and interfacial energy were directly measured in JKR tests using a novel sample construction. The surface energy of the poly(vinyl N-alkyl carbamates) was found to be around 20 mJ/m². Interfacial energies between PSA-LNs and the release coatings were found to be quite high – between 7 and 24 mJ/m². Changes in adhesion dynamics were governed by acid-base interactions between the carbamate in the release coating and the acid groups in the PSA-LN. The length of the alkyl chain in the release coating moderated this effect. We also found a correlation between fundamental adhesion energy and peel strength. Examination of this phenomenon provides a basis for understanding the poor storage stability of PSA tapes made using alkyl carbamates and acid-containing PSAs.

The effects of the unit corona-treatment energy on the contact angle of various liquids, on the surface free energy, on the extent of oxidation of a surface layer, and on the adhesion of acrylic adhesive were studied using a biaxially-oriented polypropylene (BOPP) film. The surface free energy was determined with the van Oss-Chaudhury-Good (VCG) approach as well as with the wettability method. The extent of oxidation of the surface layer of the corona-treated BOPP film was evaluated with X-ray photoelectron spectroscopy. The adhesion strength of joints between the BOPP film and the acrylic adhesive was measured using the 180°

In the range of the unit corona-treatment energy up to 1.2 kJ/m², a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.In the range of the unit corona-treatment energy up to 1.2 kJ/m², a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.In the range of the unit corona-treatment energy up to 1.2 kJ/m², a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.

The surface energy and adhesion dynamics of pressure sensitive adhesives-like networks (PSA-LNs) as mimics for PSAs were studied using JKR-based contact mechanics and peel tests. Acrylic acid (AA) was co-polymerized with 2-ethyl hexyl acrylate (2-EHA) and 1,6-hexane diol diacrylate (HDDA) to create PSA-LNs. The measured surface energy (27 to 31 mJ/m²) was sensible as surmised from their structure. Acrylic acid content increases the surface energy, threshold adhesion energy and adhesion hysteresis of PSA-LNs. Measurements of adhesion dynamics showed a dependence of adhesion energy to the 0.6–0.8 power of crack speed, depending upon the model chosen for analysis of the data. When compared with actual pressure-sensitive adhesive tape peel tests, the adhesion dynamics data predicted the peel strength. This study shows a direct relationship between threshold adhesion energy, crack propagation mechanics and peel strength measurements.

We present our unified Lewis acid–base approach to adhesion and solvation at the liquid-polymer interface. This approach is to complement the original methodologies proposed by Fowkes and by van Oss, Chaudhury and Good (VCG). Intermolecular interactions are primarily dominated by dispersion, d, hydrogen bonding, h, and secondarily affected by orientation, o, and induction, i. Generally, the polarization component, p, represents both i and o interactions. Fowkes suggested that the acid–base component, γ^ab, of the surface tension should consist of both h and p interactions. However, VCG proposed that the acid–base components, γ^ab, result solely from hydrogen bonding, γ^h, that is equivalent to 2(γ⁺ γ⁻)^1/2, where γ⁺ and γ⁻ are the two hydrogen bonding parameters. VCG defined γ^LW as the Lifshitz-van der Waals component consisting of d, o and i contributions, thus, surface tension, γ, equals γ^ab(VCG)+γ^LW. Both Fowkes and VCG assumed that the polar interactions for a liquid on a low energy surface are negligible.

Now, we assume otherwise, and we treat the specific acid-base interaction to be hydrogen bonding. In addition, we also take into account the nonspecific polarization, p, interaction in terms of the equilibrium spreading pressure, π_e, resulting from the adsorption of a liquid vapor on the polymer surface. Thus, our unified approach uses the dispersion component, γ^d, of Fowkes, the hydrogen bonding, h, of VCG and the polarization, p, in terms of π_e. The difference between the initial (theoretical) and equilibrium (experimental) surface tensions is π_e, and others have observed that π_e on some polymers is substantial. The determination of several initial surface tensions of polymers by considering the effect of polarization is discussed.

In the Appendix, we shall illustrate that this polar component, π_e, is equivalent to the LESR polarity-dipolarity parameter, π^e, (represented by the same symbol but in different context) for the solvatochromic treatment. Furthermore, the surface tension components, π^d, γ⁺, γ⁻ and π_e, are now somewhat comparable with the four parameters in the original Taft-Kamlet relationship, δ, α, B, and π^e. Thus, our proposed unified approach may finally help elucidate the long-debated Lewis acid–base theories pertaining to adhesion and solvation of polymers.

New approaches for electroless plating of nonconductive polymers or polymer-based materials are described. In this work, polyimide substrates were surface-functionalized (i) in nitrogenated (ammonia at reduced pressure) and oxygenated (air at atmospheric pressure) atmospheres under assistance of vacuum-ultraviolet (VUV) irradiation (use of a xenon silent discharge excimer source) or (ii) directly in air at atmospheric pressure using a dielectric-barrier discharge (DBD) device. After functionalization, the substrates were “activated” by dipping in a dilute acidic PdCl₂ solution or by spin-coating of a thin metal-organic film (from a solution of palladium acetate (PdAc) in chloroform). The catalytic activity of the so-deposited palladium species toward the electroless deposition of nickel was studied before and after a VUV post-irradiation (in air at atmospheric or reduced pressure) with a view to understanding better the role of the reducer (sodium hypophosphite) within the electroless bath.

This work confirms the specific interest of grafting nitrogenated functionalities onto polymer surfaces for attaching covalently the palladium-based catalyst (in particular in the case of the PdCl₂ route), forming thus strong Pd - N - C bonds at the metal/polymer interface. This results from the strong chemical affinity of palladium toward nitrogen. On the other hand, when oxygenated functionalities are surface-grafted, the conventional two-step procedure using SnCl₂ and PdCl₂ solutions can be proposed due to the strong chemical affinity of tin toward oxygen. The Ni deposits obtained under these different conditions pass the standard Scotch^®-tape test and, therefore, exhibit a good practical adhesion. For this same purpose, it is interesting to note that the DBD treatment operating in air at atmospheric pressure causes an increase of the surface roughness and, therefore, an improvement in adhesion of metallic films when their initiation is catalyzed through the PdAc route. In addition, this work demonstrates that extensive research still has to be performed to understand and improve the Ni/polymer adhesion when the PdAc route associated with a VUV irradiation is considered.

The adhesive interaction between oxygen-plasma-treated, polyacrylonitrile-based, high-tensile-strength carbon fibers and a polycarbonate matrix has been studied. Several models have been used to predict the impact of the plasma treatment process on the strength of adhesion between both jointing partners. These approaches have been the thermodynamic work of adhesion which was calculated from the solid surface tensions, based on the results of contact angle measurements versus test liquids, the contact angle which was directly obtained via polycarbonate melt droplets on single carbon fibers and the zeta (ς)-potential data provided by streaming potential measurements. The results have been compared with the interfacial shear strength determined from the single-fiber fragmentation test. Additionally, the single-fiber tensile strength of the oxygen-plasma-treated carbon fibers was determined.

We confirmed that any physico-chemical method on its own fails to describe exactly the measured adhesion. However, for the investigated system, the conscientious interpretation of the data obtained from wetting measurements, in conjunction with the thermodynamic approach, is sufficient to predict the success of a modification technique which has been applied to one component in order to improve adhesion.

In this paper, we briefly discuss several ways to determine the work of adhesion and the requirements for achieving maximum adhesion and spontaneous spreading. Specifically, we will concentrate on the methodology developed by van Oss. Chaudhury and Good [5–7] for the determination of the work of adhesion and interfacial tension. Recently, Good [4] has redefined the surface interaction components γ⁺ and γ⁻ as hydrogen bond acidic and basic parameters. We have related the surface−hydrogen−bond components γ⁺ and γ⁻ to the Taft and Kamlet's [28, 29] linear solvation energy relationship (LSER) solvatochromic α and β parameters. We [8, 9] have found that, for water at ambient temperature, α [hydrogen-bond-donating (HBD) ability] and β [hydrogen-bond-accepting (HBA) ability] are not equal, and the ratio for the normalized α and β is 1.8. This new ratio is assumed to be equal to that of γ⁺ & γ⁻ for water at 20°C. On the basis of the new ratio, we will present our recalculated surface-hydrogen-bond components for several polymers and biomaterials. This change in the ratio did not affect the total surface tension or the sign of the interfacial tension. The net improvement is in the lowering of the γ⁻ values. These data may be useful for predicting the adhesion between an adhesive and an adherend.

Copper films evaporated on argon-oxygen plasma-treated poly(phenylene-vinylene) films have been studied by scratch test, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The adhesion of the metallic film to the polymer substrate was greatly enhanced after treatment and found to increase with the treatment time. SEM observation of the treated samples revealed that the morphology of the polymer surface was gradually changed with the treatment time as compared with that of the bare polymer film. On the other hand, XPS analysis of the polymer-metal interface showed that the bonding between carbon, oxygen and copper were subsequently modified as compared with those obtained in untreated samples. The high adhesion strength observed on these substrates was related to the modification in the surface morphology on the one hand and to the formation of new compounds at the polymer-metal interface on the other. The nature of the interfacial layer and its influence on the adhesion of the copper layer was discussed by comparing the results with those obtained in poly(phenylene-vinylene) (PPV)-Al systems.

Wetting on ambient, heterogeneous surfaces is characterized by contact angle hysteresis. Quantitative models of contact angle hysteresis are essential in order to design surfaces with specific wetting behavior or to interpret experiments seeking to characterize a surface through its wetting properties. We focus on the successes and failures of theoretical models as well as experiments on model surfaces in describing contact angle hysteresis on ambient surfaces. We describe experimental observations of contact line structure and dynamics as well as contact angle hysteresis on laboratory surfaces. We discuss three general classes of models treating one-dimensional periodic heterogeneity, two-dimensional periodic heterogeneity, and random heterogeneity. We show where these models succeed and where they fail to agree quantitatively and qualitatively with experimental observations. New models treating strong, dense heterogeneity as well as temporal relaxation of contact angles in experimental environments need to be developed to provide quantitative descriptions of contact angle hysteresis on ambient surfaces.

A method has been devised to determine the acid/base parameters of reference liquids as absolute numbers, and not as values relative to a conventional set of parameters for water. Contact angle measurements are employed, using three liquids on three solids. The theory calls for the solution of nine simultaneous, nonlinear equations in nine variables–and unreasonably formidable task.

A preliminary set of solutions has been computed, for one set of polar liquids on five solids. These results must be rejected on grounds of physical reasonableness. They also fail the test of predicting liquid-liquid interfacial tension, which for miscible liquids must be negative or zero.

Careful measurements of the surface tension of solid polymers, y_s°, based on the data on contact angles for wetting liquids with various surface tension, y_L°, allows one to establish the functional dependence of y_s° = f(y_L°). This dependence is divided into three zones: one zone, where there is no dependence of y_s° on y_L° and two zones where y_s° changes linearly with y_L°.

Such polymers are commonly used as release coatings for pressure sensitive adhesive tapes. In this paper the bulk, surface, and interfacial structures of polyvinyl N-alkyl carbamates having either decyl or octadecyl side chains are examined. The bulk structures and thermal transitions were characterized using X-ray scattering and differential scanning calorimetry. Dynamic mechanical thermal analysis was used to investigate thermal transitions and rheology (i.e., segmental mobility) of the polyvinyl N-alkyl carbamates. The surface energies of polyvinyl N-alkyl carbamate coatings were determined using contact angle methods, while X-ray photoelectron spectroscopy and static secondary ion mass spectrometry were employed to characterize the near-surface compositional profiles of the coatings. The peel force provided by the polyvinyl N-alkyl carbamate coatings, as a function of aging time and temperature, was measured for a tape having an acrylic acid containing alkyl acrylate based pressure sensitive adhesive. The changes in peel force with aging time and temperature were related to the ability to maintain a stable interfacial structure between the PSA and polyvinyl N-alkyl carbamate coatings. Changes in the interfacial composition upon aging were characterized by comparing the surface compositions of the PSA and polyvinyl N-alkyl carbamate coatings initially, prior to contact, as well as after aging and peeling them apart. The increase in peel force upon aging can be attributed, in large part, to a restructuring at the PSA/polyvinyl alkyl carbamate interface. Energetically favorable acid-base interactions between the basic urethane and acetate groups in the polyvinyl alkyl carbamates and the acrylic acid groups in the PSA provide a driving force for the restructuring. If the segmental mobility within the polyvinyl alkyl carbamate is sufficient, restructuring can occur, leading to increased concentrations of these groups at the PSA/polyvinyl alkyl carbamate interface, resulting in higher attractive forces and greater adhesion. The propensity for the polyvinyl N-alkyl carbamate coatings to restructure upon contact with a polar medium was also characterized by monitoring the receding contact angle of water, as a function of water contact time and temperature. A good correlation is seen between the ability of the polyvinyl alkyl carbamate coatings to provide a low peel force for the acrylate PSA tape and the ability of the coatings to maintain a high water receding contact angle.