Plasma-treated poly-p-xylylene films have been characterized by neutron activation oxygen analysis, internal reflection (IRS) and transmission infrared spectroscopy, transmission electron microscopy (TEM), and surface contact angle measurements. The results indicate that an oxygen plasma roughens the surface and that oxygen is incorporated into the surface. Oxygen is not detected in the bulk of the sample. The infrared transmission spectra exhibited no carbonyl band, but the relative band intensities changed, indicating a change in ring substitution by a loss of chlorine in the chlorinated poly-p-xylylenes. The IRS spectra of the surface of films treated with oxygen plasma did contain carbonyl bands at 1730 and 1640 cm⁻¹. Argon and helium plasmas generally decreased the water contact angle measured on plasma-treated poly-p-xylylene surfaces more than oxygen or nitrogen plasma treatments. Regardless of the plasma utilized, the water contact angles increased with time after the treatment but did not recover to the original level. IRS spectra of the surface of films treated with argon plasma contained carbonyl bands at 1730 and 1695 cm⁻¹. The adhesion of a polyurethane thermosetting material to a poly-p-xylylene surface is greatly improved if a plasma treatment is used prior to the application of the polyurethane. The degree of improvement in adhesion was dependent on the type of plasma and the treatment time.

The relationships between surface energetics and adhesion are critically reviewed. New data that confirm such relationships, for peel tests as well as lap shear tests, are presented. The effect of hydrothermal aging of aluminum surfaces on surface energetics can be used to predict degradation in bond strength. The mechanism of failure for elastic adhesives (such as Scotch^® tape) in peel tests may be essentially the same as for more brittle adhesives (such as epoxies) in lap shear tests. This mechanism may involve brittle fracture that forms a critical flaw at the adherend-adhesive interface (on a microscopic level), followed by crack propagation which then may include considerable elastic and plastic deformation. The locus of propagation (fractography) is generally not (but may be) relevant to the problem of how to remedy mechanical weakness in an adhesive joint, since the local region of critical flaw formation rather than the general surface area determines the joint strength.

Corona treatment of films, mainly polypropylene (PP)-copolymers, was studied at commercial levels in a 2.7 kVA treater. The films were produced on a flat-film extruder with chill rolls. Degree of treatment was characterized by power of the generator divided by web speed and width of film (m Ws/cm²).

The effectiveness of the treatment was measured in terms of the polar and dispersion components of surface-energy, the peel adhesion of pressure sensitive tape (similar to ASTM Adhesion Ratio) and the peel adhesion of polyurethane adhesives.

The polar component of surface energy is a measure of the effectiveness of corona pretreatment. For a given degree of treatment, the polar surface energy component becomes greater as the film cooling rate increases (and the degree of crystallization falls).

A comparison of homopolymers and copolymers does, however, reveal that even where these have the same density or the same degree of crystallization one cannot count on them having equally-sized polar components.

Peel strengths of pressure-sensitive tapes and polyurethane-bonded patches confirm the influence of cooling conditions on wetting properties.

An apparent link between the surface properties of polar group-containing polymers, such as PMMA and Styrene/Acrylic copolymers, and the thermodynamic quality of solvents used in solutions from which the polymers were cast, was described in earlier papers.^1,2 In these polymers, significant variations have been observed in critical surface tensions(γ_c), and in the thermodynamic interaction parameters for selected vapor-polymer pairs, when the configuration of the polymer in solution was varied through the suitable selection of solvents of differing thermodynamic quality. The “solvent history” effect on surface properties of solid film was not detected however for non-polar polymers such as polystyrene (PS).^1,2 Apparently the distinct chain configurations adopted in solution by PMMA are carried over into the solid and result in different proportions of non-polar (backbone) and polar (side chain) moieties being located in the surface layer of the solid. Since only one surface state can correspond to a thermodynamic equilibrium, it may be expected that the film surface properties will change with time, as the thermodynamically preferred state is attained. As a consequence, use properties of these films should also display (initially) the “solvent history” effect, and should vary similarly with time. The present communication is concerned with these points.

Extensive study has been made of the effects of various types of glow discharge plasmas on the changes of the surface properties of some fluorine polymers. The properties were investigated as a function of such factors as the exposing period, aging after exposure, type of plasma, and so on.

It was found that the wettability and the critical surface tensions were changed considerably with plasma exposure and that periods of several tens of seconds are long enough to cause changes. The extents of change were not so prominent for fluorine polymers as for polyethylene, and this fact may show the important role of the fluorine atom in the surface properties even after the plasma treatments.

Honolulu is a most beautiful place, suitable for all occa­ sions. Its choice as the meeting site for the first Joint Chemical Congress between the American Chemical Society and the Chemical Society of Japan was praised by scientists from both sides. During this Congress, the International Conference on Adhesion and Adsorption of Polymers was held at the Hyatt Regency Hotel between April 2 and 5, 1979. We had speakers from ten nations presenting over forty papers related to the subject matter. It was a memorable event. Unlike our two previous adhesion symposia held in 1971 and 1975, this was the first time in the same conference that we discussed both adhesion and adsorption of polymers simultaneously. These two important phenomena are not only inter-related, but also equally important in adhesive technology as well as biochemical processes. The papers presented to this Conference deal with these two phenomena from both fundamental and practical viewpoints. Furthermore, with the advance of new surface analytical techniques, the actual, microscopic happenings at the interfaces can be pin­ pointed. Thus, characterization of interface became one of the major focuses of this Conference. As a result, a broad coverage of the subject matter includes statistical thermodynamics, surface physics, surface analysis, fracture mechanics, viscoelasticity, failure analysis, surface modification, adsorption kinetics, bio­ polymer adsorption, etc. Thanks to the diligence of our contri­ butors, we are now able to publish the final papers in these two volumes.

The concept of critical surface tension is generalized and reinterpreted in terms of a proposed equation of state. The equation defines a spectrum of critical surface tensions for a given surface, and provides a method by which the surface tension can be accurately determined from the contact angles of a series of testing liquids. The surface tensions obtained for solid polymers, organic solids and monolayers by this method agree remarkably well with those obtained from melt data (temperature dependence), liquid homologs (molecular-weight dependence) and the harmonic-mean equation. In contrast, those obtained by the geometric-mean equation and Zisman’s critical surface tensions are often too low. These results also support the validity of the harmonic-mean equation.

Polymeric films, chiefly polyethylenes, were subjected to corona-discharge treatment in a continuous treater at commercial rates in a program covering wide ranges of the main processing factors (2). Electron-spin-resonance measurements on freshly treated films found no free radicals. Reactions of the treated surfaces with a free-radical compound, diphenyl picryl hydrazyl (DPPH) were studied, focusing mainly on the rate effects. The evidence indicates that corona treatment produces fairly stable peroxide structures of the forms RO₂R and RO₃R on polyethylene surfaces. RO₃R reacts rapidly with DPPH alone, while RO₂R undergoes a slower reaction after addition of the catalyst, triethylene diamine. DPPH is capable of detecting as few as 10¹³ peroxide groups per square centimeter. Activation energies were 12 kcal/mole for the uncatalyzed reaction and 16 kcal/mole for the amine-catalyzed reaction. As with the physical effects reported earlier (2), the production of peroxides is most strongly dependent on the energy delivered to the film during treatment. This energy is proportional to the quotient of corona current and web speed, I/S, Regression analysis showed that air-gap thickness, relative humidity, and number of electrodes used also were significant factors, while dielectric thickness and corona frequency were not. We found that-γ, the polar component of surface energy of the treated film, which is nearly zero for untreated polyethylenes, is exponentially related to the concentrations of both RO₂R and RO₃R with a correlation coefficient for 92 specimens tested of 0.88. We believe this is the first strong evidence linking treatment factors, at commercial levels of treatment, to chemistry of the treated surface and linking both of those to changes in physical behavior of the surface.

Advances in glow discharge excitation for sputtering and surface treatment are reviewed. Conditions for the production of the glow discharges either by using a DC supply with a cold cathode or using an RF supply capacitively coupled to an electrode are discussed. Examples are given of surface treatment processes at present under study including RF magnetron sputtering of silica, a-C film growth in hydrocarbon plasmas and plasma nitriding.

The critical velocity of engulfing V_c of acetal, nylon-6,6, and nylon-12 particles when encountered by the solidification front of salol is reported as a function of particle size. Using the dimensional analysis derived previously, the free energy of adhesion ΔF^adh for the attachment of these particles to the salol solid/melt interface is determined. These values of ΔF^adh, together with the known surface tension values γ_PV of the particles, are used to determine the salol solid/melt interfacial tension γ_SL to be γ_SL = 0.0053 ± 0.0025 erg/cm². Similarly, the free energies of adhesion ΔF^adh for PMMA particles to the solid/melt interfaces of naphthalene, biphenyl, and salol are determined. As all the γ_SL values for these systems are known—in the case of naphthalene and biphenyl from the temperature dependence of contact angles—γ_PV for the PMMA particles is determined. Using the equation of state for interfaces, the contact angle for the system PMMA/water is predicted. This value is in excellent agreement with the contact angle of water on a film of PMMA obtained by solvent casting. It is concluded that measurement of the critical velocity of engulfing represents a unique method for contact angle determinations on small particles.

“Intrinsic contact angle hysteresis” is defined as hysteresis that cannot be ascribed to roughness, heterogeneity, or penetrability of the solid surface. It can be explained if we postulate that the layer of liquid immediately adjacent to the solid surface has an ordered structure similar to that of a liquid monocrystal. This structure is fluid (zero yield point in shear) in the plane of the solid surface and presents no obstacle to an increase of the solid—liquid interfacial area (advancing of the three-phase boundary line). In planes normal to the solid surface the structure has a positive yield point in shear, which prevents decrease of the solid—liquid interfacial area (receding of the three-phase line) until the yield point is exceeded by the surface pressure π_SL. Mechanical stability of the system at all values of the contact angle between the “advancing” and “receding” angles θ_A and θ_R is ascribed to a continuously changing value of π_SL and of the corresponding specific interfacial free energy γ_SL in this interval. This change reflects the elastic response in shear of the solid—liquid interfacial film in planes normal to the solid surface in this interval.

Process and product-by-process of selectively treating a surface of plastic film to prevent blocking by blanketing the surface with a noble gas and by striking a corona discharge within the noble gas atmosphere, while the other surface of the film is in contact with some other gas or gas composition, such as air.

Films of poly(methyl methacrylate) (PMMA), polystyrene, and a styrene/acrylic terpolymer have been cast from solutions of varying thermodynamic quality and the film properties studied by inverse gas chromatography and by critical surface tension measurements. Surface properties of the non-polar polystyrene were independent of solvent medium, but significant variations in these properties were observed in the case of PMMA and the terpolymer. Solvent balance also appeared to affect the bulk properties of the latter films, as judged by the penetration rates of interacting liquids. The observations indicate the feasibility of controlling film properties of the solid by the appropriate selection of solution media; a time-dependent variation in solid properties is to be expected, however, as the film structure attains an equilibrium state.

Disclosed is a device for the surface treatment of film webs by means of an electrical corona discharge, comprising: at least one grounded counter-electrode comprised of a point electrode; at least one roll electrode rotatably positioned adjacent to said counter-electrode, the roll electrode comprising an outer tube comprised of dielectric material, an inner tube comprised of dielectric material fitted coaxially inside of the outer tube and a plurality of electrodes carried by the inner tube; and a supply of A.C. voltage for the electrodes.

The physical significance of contact angles has been interpreted on the basis of a model derived from known surface energy relationships. The degrees of non-spreading and spreading have been expressed in terms of the magnitude of contact angles. On the basis of the physical picture, hysteresis of contact angle has been calculated from the experimental values of equilibrium contact angle and surface tension of the liquid. It has been suggested that it is not necessary to assume that hysteresis of contact angles is due to surface roughness of solids. The picture also explains why apparent contact angle on a non-flat solid surface is more than that on a flat solid.

Polymeric solid surfaces were prepared by a radiation-induced graft copolymerization technique using various mixtures of 2-hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA). Low-density polyethylene (PE) films were used as graft substrates. Contact angles on these polymeric surfaces were determined in air and under water. The critical surface tension (γ_c) of each polymeric surface in air was estimated by the Zisman method. Geometric mean and harmonic mean approximation methods were utilized to estimate the dispersion force contribution (γ_s^d) and the polar contribution (γ_s^p) to the total surface free energy (γ_s) from contact angle data in air. The geometric mean approximation was also used to estimate γ_s^d′ and γ_s^p′ from contact angles under water. The calculated values of γ_s^d, γ_s^p are strongly dependent on the pair of liquids chosen for the calculation regardless of the approximation adopted. The values of γ_s, calculated as the sum of γ_s^d and γ_s^p, are close to the γ_c values and are less dependent on the pair of liquids used. A comparison of the ratio γ_s^d/γ_s^p for the same surface in air and under water suggests that major polymer chain conformational changes occur, particularly with respect to the hydroxyl side chain, when such surfaces are immersed in water.

Starting from a comparative assessment of the outstanding works on the ring method (du Noüy) for the determination of the surface tension of liquids and its solutions it is shown that the application of this method to surfactant solutions can lead to substantial errors if one follows conventional conditions. These errors are mainly connected with so far unknown phenomena occurring during the raising of the ring and concerning the influence of the hydrophilic vessel wall above the solution level and the stretching of the solution surface. This is demonstrated quantitatively with surfactant solutions of different kind and concentration. These effects can be explained theoretically very simply by introducing certain assumptions on the behaviour of a surfactant adsorption layer on the inner vessel wall. Conditions leading to the elimination of these errors are given, thus enabling the application of the ring method to the determination of the surface tension of surfactant solutions.

A new method of quickly and precisely measuring the surface tension of liquids and solutions is described. Utilizing the fact that the size of the bubbles formed from a gas flowing out of a nozzle is dependent on the nozzle diameter and the surface tension of the liquid used, the surface tension of a liquid can be determined by simply counting the number of bubbles formed from a gas flowing out at a constant flow rate or by measuring the period of bubble formation. The expected accuracy of the method is below 0.1% of variance. An evident correlation between the period of bubble formation and the surface tension was shown with several kinds of liquids which differ in surface tension. Changes in surface tension with varied degree of neutralization were determined in an aqueous solution of polyacrylic acid (PAA), 20-30 points of measurement with an accuracy of about 0.1% could be easily obtained within one hour.

The contact angle of a water droplet on the surface of a solid polymer or hydrogel (water-swollen three-dimensional network) depends on whether a hydrophilic moiety of the polymer molecule is oriented towards the air interface or towards the bulk of the solid, but not on the hydrophilicity of the molecule. Therefore, the short-range rotational mobility of a polymer molecule has a major influence on the apparent hydrophilicity of a polymer surface as measured by the contact angle of water. By the came principle, the abnormally large hysteresis effect observed in advancing and receding contact angles of water on some polymer surfaces can be attributed to the reorientation of hydrophilic moieties of polymer molecules at the surface. These factors are demonstrated by selected polymer surfaces with different degrees of mobility at the polymer-air interface.

The interfaces formed by evaporating copper, nickel, and chromium layers on polystyrene, polyvinyl alcohol, polyethylene oxide, polyvinyl methyl ether, polyvinyl acetate, and polymethyl methacrylate have been studied with x‐ray photoemission spectroscopy (XPS). The adhesion strengths of the metal films to the polymers were measured by a tensile‐pull test. At submonolayer coverages of the metals, the peak positions and widths of the metallic electron core levels measured with XPS vary significantly from one polymer substrate to another. Most of these variations can be accounted for in terms of changes in the atomic and extra‐atomic relaxation energies during the photoemission process. Much of this change is brought about when the metal atom deposited on an oxygen‐containing polymer interacts with the substrate oxygen and forms a metal‐oxygen‐polymer complex. The presence of this complex is verified by changes in the photoemission lineshapes of the substrate carbon and oxygen atoms. The XPS signatures of these various complexes are quite similar and suggest that they are chelate‐like complexes. The adhesion strength of any metal on an oxygen‐containing polymer is greater than on the oxygen‐free polystyrene. In general, the increased adhesion strength correlates with the presence of the metal‐oxygen chelate complexes.

Surface energies of solids can be estimated using contact angles of liquids of known surface tension and susceptibilities for polar or acid-base interactions. Interfacial tensions and work of adhesion can be calculated using these estimated energies. There are three circumstances in which performance or bond strengths are related directly to surface energies: when separation occurs interfacially, when interfaces are not completely wetted, and when third phases are present at the interface.

The paper presents a theory on determining the dynamic surface tension using two methods: the drop volume method and the maximum bubble pressure method.

Adhesion to polyethylene and polypropylene is a complex subject requiring understanding of (a) the poor adhesive characteristics of these polymers; (b) the superior performance following certain pretreatments and (c) the nature of the changes brought about by these pretreatments and the mechanisms involved. This review discusses work on these topics and examines the impact of recent data resulting from the application of surface analytical techniques. The roles of ‘weak boundary layers’, surface energy and wettability and specific interactions are discussed in some detail.

The influence of substrate roughness on wettability has been investigated at room and high temperatures using sixteen material combinations, mostly liquid metals and solid ceramics but also water, glycerol and solid nickel. The contact angles assumed by both wetting and non-wetting drops of all but two material combinations increased linearly with the relative steepness of the surface features, the effect being less for experiments conducted at high temperatures. In contrast, the contact angles of good wetting drops of glycerol and exceptionally good wetting drops of Easy-flo decreased when their silica and nickel substrates were roughened. Similarly, contact angles of both wetting and non-wetting drops were decreased by ultrasonic vibration. The experimental data can best be interpreted in terms of the metastable equilibrium configuration models in which an advancing liquid front has to overcome energy barriers associated with surface features. This occurs more readily if these barriers are small relative to the energy of the liquid which our data suggest can be equated with the enthalpy of the liquid. This interpretation enables the effects of substrate roughness at one temperature or with one liquid to be used to predict behaviour at other temperatures and with other liquids.

This paper presents and discusses particle behavior at solidification fronts from a thermodynamic point of view. Engulfing or rejection of particles embedded in a melt by solidification fronts depends on whether such quantities as the free energy of adhesion or of engulfing are positive or negative. As the relevant energy balances contain solid‐liquid interfacial tensions which are difficult to determine, these studies may also be viewed as tests for the validity of such data and the underlying theories used to determine them. In this paper, solid‐liquid interfacial tensions are derived from contact angle data and the equation of state approach for interfacial tensions [Neumann et al., J. Colloid Interface Sci. 49, 291 (1974)]. The thermodynamic predictions obtained in this way for approximately 60 systems agree very well with microscopic observations with particles in the range of 10–200 mm in diameter.

Compounds based on polyolefins may find further use in the footwear industry as solings. However, a significant problem is the poor adhesion obtained with the urethane adhesives currently used. SATRA has recently attempted to develop practical bonding systems for commercial olefinic compounds. The use of flame treatments for polyethylene appeared to be a possible method of improving compatibility between the adhesive and substrate if an isocyanate is present at the interface. Polypropylene does not respond to the flame treatment but reasonable bonds have been obtained after surface oxidation or by using a sensitiser in conjunction with UV irradiation. The use of dual compound moulding is described as a possible alternative means of obtaining adequate adhesion to difficult surfaces.

A new approach to qualitatively predicting adhesion at a solid/solid interface is described. It is based on thermodynamic compatibility of the two adhering surfaces, but it overcomes the weaknesses of existing methods by using a full set of contact angle data and by assembling the data to reveal the main features of the set without loss of information. Adhesive performance data to support this approach are presented.

Plastic surfaces are treated with electrical corona discharge in an atmosphere of nitrogen and carbon dioxide. Oxygen is substantially excluded, and is kept at less than 0.1% by volume.

The London dispersive component of surface free energy γ_s^d and the nondispersive interactions with polar liquids W I_swⁿ were determined for hydrophilic polymers S, that is, cellulose, poly(vinyl alcohol) (PVA), and poly(methylmethacrylate) (PMMA). On applying the geometric-mean relation $\text{2(γ}{}_{\mathrm{s}}{}^{\mathrm{d}}\text{γ}{}_{\mathrm{w}}{}^{\mathrm{d}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ to the dispersive interaction with W I_sw^d, the γ_s^d values were found to be 30, 29, and 37 erg·cm⁻² for cellulose, PVA, and PMMA, respectively. Each of them is completely independent of the nature of the testing liquids W, indicating that the geometric-mean equation is appropriate for representing the dispersive interaction. On the contrary, such a geometricmean expression is shown to be inapplicable to the nondispersive interactions. It is suggested that Fowkes' approach, in which intermolecular forces are regarded to be dominated by dispersion force interactions and electron donor-acceptor interactions, is more reasonable than the popular approach.