This paper reviews recent studies on the mechanism of corona treatment of polyolefin films, specifically the chemical and physical changes of this process and the self-adhesion mechanism. Corona discharge of polymeric films introduces polar groups into the surfaces, which increases the surface energy and, as a consequence, improves substrate wettability and adhesion. The main chemical mechanism of corona treatment is oxidation. In addition, corona treatment can crosslink surface regions and increase the film cohesive strength.

This chapter presents after a short reminder of thermodynamic definitions, the most commonly used techniques for surface tension measurements with some details of the most interesting of them for high temperature applications. Some recent results on the evaluation of the influence of external factors, like the surrounding atmosphere, on the determination of the surface tension of molten systems are also presented. ASTRA is an experimental methodology and an integrated software to get and process data of drop shape profiles to determine surface and interfacial tension and contact-angle values. Due to its high performances in terms of time of acquisition and reliability, it is particularly suitable for both static and dynamic measurements. Indeed, by using ASTRA it is possible to reach up to two interfacial tension measurements per second, having access to dynamic measurements over very large time scale. ASTRA is currently used both for liquid metals and for liquid systems at room temperature.

This chapter discusses the physico-chemical hydrodynamics of rising bubble. At small Reynolds numbers effective approximate analytical methods allow to characterize different states of dynamic adsorption layers quantitatively: weak retardation of the motion of bubble surfaces, almost complete retardation of bubble surface motion, transient state at a bubble surface between an almost completely retarded and an almost completely free bubble surface. The measurement of bubble terminal velocity in water cannot be used for the experimental verification of these theories because uncontrolled impurities in water immobilize a small bubble surface almost completely without any addition of surfactant. The rising bubble velocity relaxation caused by the dynamic adsorption layer (DAL) formation can be measured. The DAL study is more realistic for large bubbles and large Reynolds numbers (Re) because trace concentrations of surface active impurities cannot retard the bubble surface movement completely.

This chapter focuses on the maximum bubble pressure method (MBPM) and deals with the physico-chemical and hydrodynamic processes taking place at various stages of the growth of a bubble and its separation from a capillary. Particular emphasis is made on theoretical problems like surface tension calculation from the measured excess pressure, surface tension calculation from the measured excess pressure, splitting of time interval between consecutive bubbles into lifetime and deadtime, and calculation of these characteristic times involving inertial and viscous properties of liquid and gas, non-stationarity of flows, etc. Emphasis is also made on experimental details like measurements of pressure and bubble formation frequency and optimisation of the geometry of capillary and measuring system related to the application of the MBPM. The results presented in this chapter contribute both to an improvement of the commercially available devices, and to a better understanding of the method by the users, helping them in the application of the MBPM and in a correct interpretation of the results.

The CPT has consequently been employed with several configurations and with different methodologies to measure the interfacial tension of pure liquids and for studying the dynamics of adsorption on different time scales both on earth and in microgravity. Some of these methodologies are described in detail, discussing the critical aspects and the main experimental results. Capillary Pressure (CP) tensiometry is especially helpful for studying liquid/liquid interfaces. Microgravity represents an ideal tool for studying the dynamic aspects of adsorption of soluble surfactants and the CP tensiometry is the most suitable technique for these kind of studies in this environment, both for liquid-liquid and liquid-vapor interfaces. However, provided that the Bond number is sufficiently small, CP tensiometry can also be used in normal laboratory conditions.

The spinning drop technique (SDT) has been developed to measure extremely low interfacial tensions (from 10 ^-6 mNm ^-1 to 10 mNm ^-1). It uses profile analysis of deformed droplets similar to the pendent drop method. Unlike in pendent drop experiments, where the droplets are deformed by the gravitational force, SDT is based on the balance of centrifugal and interracial forces in rapidly rotating systems. Apart from purely tensiometric applications SDT has been found to be a versatile tool for surface and interface science. It allows the study of adsorption phenomena and even permits the “simulation” of spontaneous structure formation processes, e.g., the break-up of liquid threads and the coalescence of droplets. This chapter reviews both standard and non-standard SDT applications. After a brief description of basic principles and properties, the equilibrium properties of a rotating drop, i.e., its shape and its stability, are considered in detail. Experimental aspects of SDT: Both commercial and laboratory SDT set-ups are introduced. Problems arising from sample preparation (particularly in the case of highly viscous polymers) and the determination of the droplet dimensions are discussed.

This chapter focuses on the drop volume technique. The stalagmometer is the most primitive version of the drop volume method. It allows only a very rough estimate of the surface tension of a liquid. With the drop volume technique an accurate determination of the volume of a drop formed at the tip of a given capillary is obtained. The measuring procedure is realized by means of a precise dosing system, which forms drops continuously at the capillary. The method has restrictions for example with respect to the drop formation time. If drops are formed too fast the measured drop volumes are no longer a measure of the surface tension alone but are in addition governed by chaotic effects leading to so-called drop volume bifurcations. A drop volume experiment is described is this chapter.

This chapter discusses axisymmetric drop shape analysis (ADSA) and its application. It provides an account of these ADSA methodologies. It contains a description of the numerical algorithms and their implementation. The applicability of ADSA is illustrated extensively for the investigation of surface tension measurements with pendant and sessile drops and contact angle experiments with sessile drops using both axisymmetric drop shape analysis - profile (ADSA-P) and axisymmetric drop shape analysis - diameter (ADSA-D). The advantages of pendant and sessile drop methods are numerous. In comparison with a method such as the Wilhelmy plate technique, only small amounts of the liquid are required. Drop shape methods easily facilitate the study of both liquid-vapor and liquid-liquid interfacial tensions. Also, the methods have been applied to materials ranging from organic liquids to molten metals and from pure solvents to concentrated solutions. There is no limitation to the magnitude of surface or interracial tension that can be measured: The methodology presented in this chapter works as well at 10³ mJ/m ² as at 10 ^-3 mJ/m ².

The plasma source ion implantation (PSII) was utilized to improve the wettability and the stability of surface layer formed in the modification of polymeric materials. Polystyrene was treated with different kinds of plasma ions to render the surface more hydrophilic or hydrophobic. Hydrophobic recovery of PSII-treated polystyrene was also observed as a function of aging time, aging temperature, and treatment parameters. Treatment parameters involve kinds of gases, pressure, plasma power, pulse frequency, pulse voltage, etc. To study the effect of inert gas on hydrophobic recovery, polystyrene samples were prepared by helium, argon, or gas-mixture treatment. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to interpret the PSII-treated polystyrene surface and its hydrophobic recovery, with the assistance of x-ray photoelectron spectroscopy and water contact angle measurements. TOF-SIMS spectra of O218 PSII-treated samples showed the presence of O18-containing peaks from the modified surfaces. PSII modifications provide more stable surfaces of polystyrene as a function of aging time than plasma treatments. The comparison of aging behavior data allowed for examination of the differences in the stability of the functionality introduced by the two different treatment techniques.

A detailed X-ray photoelectron spectroscopy study of a plasma-modified polystyrene (PS) surface was carried out after N₂ plasma treatment. PS surfaces were found to be highly hydrophilic and reactive as it readily picks up oxygen giving rise to oxyfunctionalities on the surface. The plasma treatment also led to a slow chain scission with carboxyl, forming carbonate linkage.

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.

Plasma-induced low-density polyethylene (LDPE) radicals were studied in detail by electron spin resonance (ESR) by its comparison with ESR of high-density polyethylene (HDPE). The observed ESR spectra of plasma-irradiated LDPE are largely different in pattern from those of HDPE. The systematic computer simulation disclosed that such observed spectra consist of three kinds of radicals, midchain alkyl radical (1), allylic radical (2) as discrete radical species, and a large amount of dangling bond sites (DBS) (3) at an intra- and intersegmental cross-linked region. All these component radicals are essentially identical to those of HDPE. One of the most special features unique to plasma-irradiated LDPE, however, is the fact that thermally stable DBS (3) is a major component radical instead of a midchain alkyl radical in HDPE. This can be ascribed to the difference in polymer morphology between LDPE and HDPE:  branched structure with a large amount of amorphous region for LDPE and linear structure with a large amount of crystalline region for HDPE. Since one of the characteristics of plasma irradiation is the fact that it is surface-limited, LDPE would undergo the radical formation preferentially on the surface-branched structural moiety followed by facile cross-link reactions resulting in the formation of DBS. Thus, the nature of radical formation of PE was found to be affected by the polymer morphology in a very sensitive manner.

The nature of peroxy radical formation from plasma-induced surface radicals of polyethylene (PE), both low-density polyethylene (LDPE) and high-density polyethylene (HDPE), was studied by electron spin resonance with the aid of systematic computer simulations. It was found that peroxy radical formation varies with the structure of component radicals of plasma-irradiated PE, both LDPE and HDPE:  Among three plasma-induced radicals of PE, dangling bond sites (DBS) undergo an instant conversion into the corresponding peroxy radicals in contact with oxygen, while the midchain alkyl radical is of very low reactivity with oxygen in both LDPE and HDPE. Computer simulations disclosed that ESR spectra of peroxy radicals are similar to each other in LDPE and HDPE, both being composed of two types of spectra, a partial >em>g-averaging anisotropic spectrum and a nearly isotropic single line spectrum due to different molecular motional freedom at the trapping sites of peroxy radicals.

The chemical modification of polystyrene surfaces by low-energy (10−100 eV) SF₅⁺, C₃F₅⁺, and SO₃⁺ ions was studied by X-ray photoelectron spectroscopy and two-laser ion trap mass spectrometry. The mechanism of fluorination was found to be dissimilar for SF₅⁺ and C₃F₅⁺ ions in this energy range at fluences of 10¹⁴−10¹⁶ ions/cm². SF₅⁺ was found to induce fluorination of the polymer surface by grafting reactive F atoms upon dissociation at impact. SF_n fragments were not found to be grafted or implanted into the polymer. Sulfur was detected on the polymer surface only at incident energies above 50 eV and was found to be sulfidic in nature. In contrast, C₃F₅⁺ ions induced grafting of both reactive F atoms and molecular C_mF_n fragments from the dissociation of the incident projectile. Larger proportions of highly fluorinated sites and thicker fluorocarbon layers were found for C₃F₅⁺ at all energies and fluences. A variety of aliphatic and aromatic fluorine bonding environments were detected on both SF₅⁺ and C₃F₅⁺ modified polystyrene surfaces.

Plasma surface treatment of plastics is definitely not new, nor is it commonplace. What is a plasma and what can it do is the subject of the following paper. A plasma is an excited gas, not unlike the aurora borealis. The excited particles that comprise the plasma bombard materials placed within their environment causing permanent change to their surface properties. By the judicious selection of process gas(es) and process parameters, the surface can be reengineered to fit specific needs. This paper presents quantitative analytical data on the chemical changes to the surface of polyethylene subjected to a plasma.

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.

The influence of thermal treatment on the adhesion between isotactic poly(propylene) (iPP) and ethylene-propylene copolymer has been studied. The adhesive force between the polymer films was measured by performing peel tests. It was found that an interface layer has been formed. Its structure and thickness are dependent on the thermal history of the sample: the peel strength increases with annealing temperature and time, and the cooling rate, too, influences the peel strength. The method of preparing the iPP films has an effect on the adhesion of the sandwich sample as well.

The manufacture of polyolefin films by an extrusion process will today almost certainly include as part of the processing line some form of adhesion promoter. For Cast and Blown extrusion this would mean corona as the adhesion promoter. Often overlooked as being an insignificant component on the manufacturing line, the Corona Treater is often purchased in haste and without adequate deliberation. Without this consideration a capital expenditure may arise that may meet current requirements but offers little or no flexibility for the future. When considering a Corona Treater, first and foremost a choice must be made between Bare Roll and Covered Roll. This paper deals with the decision making process leading up to this determination. We will stress that one should not allow any preconceived notions to cloud the issue on the type of treater station required. Both Bare Roll and Covered Roll treater stations serve a particular purpose and play an integral part in the manufacturing process.

Physical and chemical surface modifications of polyethyleneterephthalate (PET) films due to treatment with excimer UV lamps (222 nm) have been studied. Interpretations of the reactions and products were made in comparison to known PET irradiations with excimer UV lasers and broad-band UV sources. In this context the advantages of the excimer UV lamps as a light source, i.e., a quasi monochromatic radiation source with a power density which is sufficient for initiating surface reactions without changing the topography of the substrate, have been shown. Analytical data on treated PET to characterize the surface modifications were obtained by contact-angle measurements, dyeing with cationic dyestuff, scanning electron microscopy (SEM), photoacoustic Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) studies. With regard to possible industrial applications, the relevance for textile finishing and some perspectives for future developments are pointed out.

The treatment of surfaces by corona discharges is a well-established method to improve surface properties. The surface to be treated is moved continuously and is exposed to transient gas discharges, known as microdischarges, in air at atmospheric pressure between electrodes, where at least one electrode is covered with a dielectric barrier. Because of the short duration, only some 10 ns, the current through the microdischarges is predominantly carried by electrons. The ion temperature remains close to room temperature. Owing to these properties such discharges are qualified to treat surfaces which are sensitive to higher temperatures. For a large number of applications this treatment is adequate, but the adhesion of aqueous glues and inks to some plastic materials is insufficient if the surfaces are treated in this way. Furthermore, it is difficult to meet the requirements of surface properties of, for instance, polyolefine film (e.g. surface tension, adhesion). This material is not based on monomers containing chlorine or fluorine and is preferred for ecological reasons. This paper presents the results of experiments which demonstrate that in comparison to a common corona treatment significant improvements in surface properties of plastic materials can be achieved if repetitively generated pulse trains and reactive gases are used instead of air. If, for instance, the microdischarges are established in acetylene, thin films with a thickness of several namometres are formed on surfaces, which increase and stabilize the surface tension up to a level of 72 mN m⁻¹. The state of the art of this new technology is discussed.

Different types of plasma, irradiative and chemical activation were compared in terms of surface functionalization. Corona and spark jet plasmas are characterized by low gas temperatures and high rates in surface modification. UV irradiation in the presence of ozone does not involve any particle bombardment and acts only by enhanced photooxidative processes. Although ion implantation can be avoided, this method is not free of radiative damage in both the surface-near region and the bulk of polymers. Furthermore, its functionalization rate is low. In relation to low-pressure O₂ plasma modification, all treatments mentioned here have a low efficiency in adhesion promotion due to oxidative degradation of macromolecules and formation of molecular debris known as the “weak boundary layer”.

Three different dielectric barrier-controlled discharge regimes in helium at atmospheric pressure under sinusoidal excitation have been obtained by varying the excitation frequency or the gas chemical composition: the filamentary discharge, which is the discharge that is usually obtained; the glow discharge, which is controlled by cathode secondary emission; and the homogeneous discharge, which is of a nature in between those of the filamentary and the glow discharges. All the characteristics that have been studied, such as the discharge current, the emission spectrum, the wettability and the chemical transformations of a polypropylene film, are related to the discharge-regime variation. The glow discharge is clearly more efficient than the others as a means of increasing the polypropylene-surface energy. Values as high as 62 mJm^-2 are obtained with this discharge whereas the maximum value after interaction with the filamentary one is 45 mJm^-2. This improvement in wettability is due to there being more O atoms implanted at the surface as well as to the addition of N atoms. The differences among in surface transformations have been correlated to the characteristics of these different discharges and more specifically to the localization of the electrical energy transfer into the gas and to the nature of the ions created during the discharge.

Surface tensions of polymers can be accurately determined by observing whether droplets of liquids spontaneously spread or not. The polymer surface tension will be higher than the surface tension of a liquid which spreads, and lower than that of a liquid which remains as a droplet.

Ultra-high molecular weight polyethylene (UHMWPE) fibers were subjected to oxygen plasma treatment in order to improve interfacial adhesion. The treated fibers were characterized by contact angle analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and mercury porosimetry. The surface free energy, O 1s/C 1s ratio, and surface area increased dramatically with 1 min treatment. However, as the treatment time increased further, these parameters either increased slowly at 30, 60, and 100 W, or decreased at 150 W. The increased surface free energy is attributed to the polar component, while the increased O 1s/C 1s ratio is explained by the oxygen-containing moieties introduced by the plasma treatment. The oxygen plasma treatment also roughened the initially smooth surface of the UHMWPE fibers by forming micro-pores and thus increased the surface area. The interfacial shear strength of UHMWPE fibers to vinylester resin was measured by micro-droplet tests and exhibited an increasing trend, believed to result from the increased surface area, the surface free energy, and the oxygen-containing moieties due to the plasma treatment.