By comparing the number of degrees of freedom obtained from the phase rule for capillary systems, the Fowkes surface tension component approach for interfacial tensions is shown to require more degrees of freedom than are available for a two-component solid—liquid—vapour system. Only in a special case has the Fowkes approach two degrees of freedom: a dispersive liquid on a dispersive solid, suggesting that there are no surface tension components. Experimental results suggest that the Fowkes component approach does not describe physical reality; only the liquid and solid surface tensions, γ_1v and γ_sv, are operative in the two-component solid—liquid—vapour system. Generalization of the Fowkes component approach, of course, will increase the number of independent variables and hence definitely require more degrees of freedom than are available.

The number of degrees of freedom of the equation of state for interfacial tensions is shown to agree with that predicted from the phase rule for capillary systems as well as with experimental results. By using the empirical form of the equation of state, essentially constant solid tensions, γ_sv, are obtained from a variety of dispersive and non-dispersive liquids for three solid surfaces: fluorocarbon (FC721), Teflon (FEP) and poly(ethylene terephthalate) (PET).

It is shown that Axisymmetric Drop Shape Analysis (ADSA) is well-suited for the study of polymer melt surface tensions. The technique is not restricted to equilibrium surface (interfacial) tensions; it is also suitable for measuring the time dependence (or kinetics) of surface tension of polymer melts. Results for three polymers, polypropylene, polyethylene, and polystyrene, at temperatures above 170°C are reported. Contrary to the well-known decrease of surface tension in low molecular weight surfactant solutions as a result of equilibration, an increase in the melt surface tension is observed under isothermal conditions.

Low-rate dynamic contact angles of a large number of liquids were measured on a poly(ethyl methacrylate) (PEMA) polymer using an automated axisymmetric drop shape analysis profile (ADSA-P). The results suggested that not all experimental contact angles can be used for the interpretation in terms of solid surface tensions: eight liquids yielded non-constant contact angles and/or dissolved the polymer on contact. From the experimental contact angles of the remaining four liquids, we found that the liquid-vapor surface tension times the cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γlv cos ζ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is again in harmony with those from other methacrylate polymer surfaces of different compositions and side-chains. The solid-vapor surface tension of PEMA calculated from the equation-of-state approach for solid-liquid interfacial tensions was found to be 33.6 ± 0.5 mJ/m2 from the experimental contact angles of the four liquids. The experimental results also suggested that surface tension component approaches do not reflect physical reality. In particular, experimental contact angles of polar and nonpolar liquids on polar methacrylate polymers were employed to determine solid surface tension and solid surface tension components. Contrary to the results obtained from the equation-of-state approach, we obtained inconsistent values from the Lifshitz-van der Waals/acid-base (van Oss and Good) approach using the same sets of experimental contact angles.

A study was conducted which showed that the Lifshitz-van der Waals / acid-base approach yielded liquid-liquid interfacial tensions which were incompatible with experimental results. The approach allowed correct prediction of interfacial tensions for only four completely miscible liquid/liquid pairs. This result calls into question traditionally held interfacial tension theories, and points up the need for caution in the application to solid/liquid contact angle systems if an approach should fail the liquid/liquid test.

Recent progress in the correlation of contact angles with solid surface tensions are summarized. The measurements of meaningful contact angles in terms of surface energetics are also discussed. It is shown that the controversy with respect to measurement and interpretation of contact angles are due to the fact that some (or all) of the assumptions made in all energetic approaches are violated when contact angles are measured and processed. For a large number of polar and non-polar liquids on different solid surfaces, the liquid–vapor surface tension times cosine of the contact angle, γ_lvcosθ, is shown to depend only on the liquid–vapor surface tension γ_lv, and the solid–vapor surface tension γ_sv when the appropriate experimental techniques and procedures are used. Equations which follow these experimental patterns and which allow the determination of solid surface tensions from contact angles are discussed. Universality of these experimental contact angle patterns is illustrated; other reasons which may cause data to deviate from the patterns slightly are discussed. It is found that surface tension component approaches do not reflect physical reality. Assuming the fact that solid surface tension is constant for one and the same solid surface, experimental contact angle patterns are employed to deduce a functional relationship to be used in conjunction with Young's equation for determining solid surface tensions. The explicit form of such a relation is obtained by modifying Berthelot's rule together with experimental data; essentially constant solid surface tension values are obtained, independent of liquid surface tension and molecular structure. A new combining rule is also derived based on an expression similar to one used in molecular theory; such a combining rule should allow a better understanding of the molecular interactions between unlike solid–liquid pairs from like pairs. Existing static contact angles for 34 different types of solid surfaces from Zisman et al. are evaluated in terms of their solid surface tensions using experimental contact angle patterns. A FORTRAN computer program has been implemented to automate these procedures. It is found that literature contact angles do not have to be discarded completely; they can be used to determine solid surface tensions, with caution. The surface tensions for the 34 solid surfaces from Zisman et al. are also reported.

Recent experimental (low-rate) dynamic contact angles for 14 solid surfaces are interpreted in terms of their solid surface tensions. Universality of these experimental contact angle patterns is illustrated; other reasons that can cause data to deviate from the patterns are discussed. It is found that surface tension component approaches do not reflect physical reality. Assuming solid surface tension is constant for one and the same solid surface, experimental contact angle patterns are employed to deduce a functional relationship to be used in conjunction with the Young equation to determine solid surface tensions. The explicit form of such a relation is obtained by modifying Berthelot’s rule together with experimental data; essentially constant solid surface tension values are obtained, independent of liquid surface tension and molecular structure. A new combining rule is also derived based on an expression similar to one used in molecular theory; such a combining rule should allow a better understanding of the molecular interactions between unlike solid–liquid pairs.

Recent progress in the correlation of contact angles with solid surface tensions are summarized. The measurements of meaningful contact angles in terms of surface energetics are also discussed. It is shown that the apparent controversy with respect to measurement and interpretation of contact angles are due to the fact that some (or all) of the assumptions made in all energetic approaches [7–14] are violated when contact angles are measured and processed. For a large number of polar and non-polar liquids on different solid surfaces, the values of γ _1v cos θ are shown to depend only on γ _1v and γ_sv when the appropriate experimental techniques and procedures are used. An equation which follows these experimental patterns and which allows the determination of solid surface tensions from contact angles is discussed.

After the atmospheric pressure plasma treatment of polypropylene (PP) film surface, we measured the contact angle of the surface by using polar solvent (water) and nonpolar solvent (diiodomethane). We also calculated the surface free energy of PP film by using the measured values of contact angles. And then we analyzed the change of the contact angle and surface free energy with respect to the conditions of atmospheric pressure plasma treatment. Upon each condition of atmospheric pressure plasma treatment, the contact angle and surface free energy showed optimum value or leveled off. Through AFM analysis, we also observed the change of surface morphology and roughness before and after plasma treatment. The surface roughness of PP film showed the highest value when the plasma treatment time was 90 s. Finally, we analyzed the change of chemical compositions on the PP film surface through XPS. As the result of analysis, we observed that polar functional groups, such as –CO, –C=O, and –COO were introduced on the PP film surface after atmospheric pressure plasma treatment.

In an attempt to modify the hydrophobic surface properties of polypropylene (PP) films, this study examined the optimum process parameters of atmospheric pressure plasma (APP) using Ar gas. Under optimized conditions, the effects of a mixed gas (Ar/O2) plasma treatment on the surface-free energy of a PP film were investigated as a function of the O2 content. The polar contribution of the surface-free energy of the PP film increased with increasing O2 content in the gas mixture. However, slightly more oxygen-containing polar functional groups such as CO, CO, and COO were introduced on the PP film surface by the Ar gas only rather than by the Ar/O2 gas mixture. In addition, AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process.

Previously published pull-out adhesion results have been substantiated by more extensive studies of chemical and plasma treatment. Particular attention has been paid to the affect of geometrical variables on the values of adhesion obtained. The effect of strain rate has also been examined. Most of the results can be understood on a semi-quantitative basis by a simple extension of lap joint theory.

Numerous methodologies have been developed for the measurement of contact angles and surface tensions as outlined in Chapter 8 and Refs. 1-4. Liquid surface tension measurements commonly involve the determination of the height of a meniscus in a capillary, or on a fiber or a plate. Contact angles are most commonly measured by aligning a tangent with the profile of a sessile drop at the point of contact with the solid surface. Other notable methods are the Wilhelmy slide (Chapter 8) and the capillary rise technique (Chapter 9). An overview of such techniques reveals that in most instances a balance must be struck between the simplicity, the accuracy, and the flexibility of the methodology.

Digital printing is increasingly being used for package printing. One of the major techniques of digital printing is dry-toner electrophotography. This paper evaluates the printability of three different extrusion coatings used for packaging boards: low-density polyethylene (PE-LD), ethylene methyl acrylate (E/MA) and polyethylene terephthalate (PET). Extrusion coatings in general have an impervious, chemically inert, nonporous surface with low surface energies that cause them to be non-receptive to bonding with toners. The most common methods used in improving the adhesion properties of polymer coatings are different surface treatments. These increase the surface energy and also provide the polar molecular groups necessary for good bonds between the toner and polymer molecules. The polymer coatings have been modified with electrical corona discharge treatment. The effects of corona on polymer surfaces and the correlation between surface modification and print quality have been evaluated. Results show that sufficiently high surface energy and surface-charge uniformity are necessary for even print quality and toner adhesion. E/MA and PET have the required surface-energy level without the corona treatment, but PE-LD needs surface modification in order to succeed in the electrophotographic process. E/MA also has exceptional surface-charge properties compared with PET and PE-LD. Polym. Eng. Sci. 44:2052–2060, 2004. © 2004 Society of Plastics Engineers.

The most important function of a packaging material is to shield the product inside the package. Extrusion coated paperboard is generally used in food, medical and cosmetic packages. Extrusion coatings give a barrier against water, water vapour, aroma, grease, oxygen, etc. In addition to barrier properties, heat sealability and printability are important properties in packaging applications. From point of view of printing, the dense and impervious structure of extrusion coatings is challenging: printing inks and toners do not penetrate into the coatings. The durability of the printed image is significant, because the image must withstand various converting operations when the package is constructed. The most common method for obtaining good ink adhesion is to oxidize the surface. Surface treatments are used to change the chemical composition, increase the surface energy, modify the crystalline morphology and surface topography, or remove the contaminants and weak boundary layers. Two widely used methods are electrical corona discharge treatment and flame treatment. These processes generally cause physical or chemical changes in a thin surface layer without affecting the bulk properties. Treatments will increase surface energy and also provide polar molecular groups necessary for good bonds between ink and polymer molecules. In addition to printability, surface treatments also affect the heat sealing properties of extrusion coatings. In this study, the surface chemistry of the extrusion coatings has been modified with corona and flame treatments. The effect of corona and flame treatment on surface energy has been evaluated with contact angle measurements. Surface energy has the habit of decreasing with time after treatment. In this work, the decay of surface energy and surface oxidation is followed for six months. ESCA and FTIR-ATR have been used to analyze oxidation and the surface chemical composition. Furthermore, the heat sealing and hot tack properties of the extrusion coatings are evaluated. The aim of this study is also to evaluate printability of extrusion coatings and to map out the role of surface modification in print quality formation. This study has concentrated on digital printing, particularly on dry toner-based electrophotographic printing process.

Surface properties of polycarbonate (PC), polypropylene (PP), polyethylene terephthalate (PET) samples treated by microwave-induced argon plasma have been studied with contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanned electron microscopy (SEM). It is found that plasma treatment modified the surfaces both in composition and roughness. Modification of composition makes polymer surfaces tend to be highly hydrophilic, which mainly depended on the increase of ratio of oxygen-containing group as same as other papers reported. And this experiment further revealed that CO bond is the key factor to the improvement of the hydrophilicity of polymer surfaces. Our SEM observation on PET shown that the roughness of the surface has also been improved in micron scale and it has influence on the surface hydrophilicity.

Recently, there has been increased interest in using atmospheric pressure plasmas for materials processing, since these plasmas do not require expensive vacuum systems. However, APGDs face instabilities. Therefore, special plasma sources have been developed to overcome this obstacle, which make use of DC, pulsed DC and AC ranging from mains frequency to RF. Recently, the APPJ was introduced, which features an α-mode of an RF discharge between two bare metallic electrodes. Basically, three different geometric configurations have been developed. A characterization of the APPJs and their applications is presented.

A basic and affordable experimental apparatus is described that measures the static contact angle of a liquid drop in contact with a solid. The image of the drop is made with a simple digital camera by taking a picture that is magnified by an optical lens. The profile of the drop is then processed with ImageJ free software. The ImageJ contact angle plugin detects the edge of the drop and fits its profile to a circle or an ellipse. The tangent to the triple line contact is calculated and drawn by the ImageJ software, thus, returning the value of the contact angle with acute precision on the measurement.

Corona discharge (CD) treated polyethylene films were examined using X-ray photoelectron spectroscopy (XPS) and a variety of chemical derivatization techniques. The composition of the CD-treated surfaces were found to be relatively unaffected by aging at temperatures between 70 and 80°F. Ink adhesion testing of films treated under progressively more serve conditions indicated the efficiency of adhesion varied directly with the severity of treatment. Derivatization of CDtreated polyethylene films with pentaflurophenylhydrazine (PFPH) resulted in the formation of a stable hydrazone complex. The PFPH complex extends the detection limit for enolizable carbonyl groups ca. eight-fold and provides relative quantitation of the number of these groups on variously treated polyethylenes. Formation of the hydrazone complex destroyed ink adhesion, indicating that the complex had blocked the site responsible for chemical bonding to the ink. Adhesion of water-soluble printing inks to CD-treated polyethylene is a direct consequence of hydrogen bonding between enolic hydroxyls on the polymer surface and carbonyl groups of the ink.

The adhesion between a polyurethane (PU) adhesive and four foams containing different low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) blends was improved by using different surface treatments. UV-ozone, corona discharge, and low-pressure oxygen plasma treatments for different times were used to increase the surface energy of the foams. The low-pressure oxygen plasma was the most successful surface treatment to promote the adhesion of the foams. A reduced length of treatment was needed to improve the adhesion of the foams containing higher EVA content. The surface treatments produced a noticeable decrease in contact angle values due mainly to the creation of different carbon–oxygen moieties and to the formation of cracks/heterogeneities on the foams surfaces. After oxygen plasma, removal of non-polar material from EVA surfaces allowed to expose acetate groups which are likely to be important for increasing the adhesion of the foams.

The barrier solutions presently available on the market all have their drawbacks, e.g. cost, water-sensitivity, opacity or perceived environmental bad-will. At the same time there is a trend to use more plastic-based packaging materials for different applications, e.g. as replacements for metal and glass containers. This situation has stimulated the industry to provide new, more efficient barrier solutions. The innovations go along five major lines: (a) thin, transparent vacuum-deposited coatings; (b) new barrier polymers as discrete layers; (c) blends of barrier polymers and standard polymers; (d) organic barrier coatings; and (e) nanocomposite materials. This paper provides a comprehensive review of the different approaches, outlining the principle behind each barrier technology, its performance, its potential and the companies developing and producing the materials. Copyright © 2003 John Wiley & Sons, Ltd.
https://onlinelibrary.wiley.com/doi/abs/10.1002/pts.621

Plasma treatment and vacuum Al deposition on films from biaxially oriented polypropylene is a multistep large scale industrial process, mainly ending up in packaging film laminates. As atmospheric plasma treatment processes suffer from lack of reproducibility, low pressure plasma treatment processes that can be operated in-line with the metal deposition are being developed. Process development is difficult, because the final packaging film laminate has to deliver optimum properties of adhesion as well as of the barrier against oxygen and water vapor permeation. As a typical production run involves tens of thousands to up to one hundred thousand square meters of film, experiments on an industrial scale are expensive, so smaller scale experimental processes are needed, which so far do not match well enough with industrial process characteristics. Moreover, bonding mechanisms between the treated substrate film and the deposited Al layer are not sufficiently understood. This paper describes the sequence in development and optimization of substrate films and plasma treatment that has been performed on an experimental as well as on an industrial scale. A sufficient correlation between experimental and industrial scales was achieved, which helps to perform development and optimization on a small scale before scaling up to industrial processes. However, improvement is still needed both in fundamental understanding of the aluminum–polypropylene interface as well as in experimental equipment and methodology.

Non-thermal atmospheric pressure plasma jets/plumes are playing an increasingly important role in various plasma processing applications. This is because of their practical capability to provide plasmas that are not spatially bound or confined by electrodes. This capability is very desirable in many situations such as in biomedical applications. Various types of ‘cold’ plasma jets have, therefore, been developed to better suit specific uses. In this paper a review of the different cold plasma jets developed to date is presented. The jets are classified according to their power sources, which cover a wide frequency spectrum from DC to microwaves. Each jet is characterized by providing its operational parameters such as its electrodes system, plasma temperature, jet/plume geometrical size (length, radius), power consumption, and gas mixtures used. Applications of each jet are also briefly covered.