Atmospheric plasmas have traditionally been used as a non-chemical etching process for polymers, but the characteristics of these plasmas could very well be exploited for metals for purposes more than surface cleaning that is presently employed. This paper focuses on how the corona discharge process modifies aluminium AA 1050 surface, the oxide growth and resulting corrosion properties. The corona treatment is carried out in atmospheric air. Treated surfaces are characterized using XPS, SEM/EDS, and FIB-FESEM and results suggest that an oxide layer is grown, consisting of mixture of oxide and hydroxide. The thickness of the oxide layer extends to 150–300 nm after prolonged treatment. Potentiodynamic polarization experiments show that the corona treatment reduces anodic reactivity of the surface significantly and a moderate reduction of the cathodic reactivity.

Continued innovations in the polymer industry have made polymer surface modification methods a subject of intense research. The importance and necessity of surface modification of plastics are explained, and the advantages of physical surface treatments over the less-sophisticated chemical methods are outlined. Currently available physical surface modification methods for food packaging polymers are reviewed from the food packaging perspective. These physical surface modification methods include flame, corona discharge, UV, gamma-ray, electron beam, ion beam, plasma, and laser treatments. The principle of operation of each method is briefly described, and the advantages and disadvantages of each technique are cited. The extent to which each of these methods can produce the specific modifications desired is discussed. Furthermore, the effects of each treatment on barrier, mechanical, and adhesion properties of food packaging polymers are also examined. Finally, an overview of economic aspects of sophisticated surface modification techniques, including ion beam, plasma, and laser treatments, is presented.

This article reviews the various theoretical approaches that have been developed for determination of the surface tension of solids, and the applications to food industrial products. The surface tension of a solid is a characteristic of surface properties and interfacial interactions such as adsorption, wetting or adhesion. The knowledge of surface tension is thus of great interest for every domain involved in understanding these mechanisms, which recover a lot of industrial investigations. Indeed, it is the case for the packaging industry, the food materials science, the biomedical applications and the pharmaceutical products, cleaning, adhesive technology, painting, coating and more generally all fields in relation with wettability of their systems. There is however no direct method for measurements of surface tension of solids, except the contact angle measurements combined with an appropriate theoretical approach are indirect methods for estimation of surface tension of solids. Moreover, since the publication by Young (1805) who developed the basis of the theory of contact angle some two hundred years ago, measurements and interpretations are still discussed in scientific literature, pointing out the need to better understand the fundamental mechanisms of solid-liquid interfacial interactions. Applications of surface tension characterization in the field of food materials science are detailed, especially for packaging and coating applications, which recover different actual orientations in order to improve process and quality.

The low temperature plasma produced by a surface barrier discharge generated in nitrogen at atmospheric pressure has been used for the treatment of polyester nonwoven (PET NW) fabrics. Surface modifications of three types of PET NW with different square weights (25, 50 and 80 g/m(2)) have been investigated. To determine the treated PET NW hydrophilicity, the strike-through time was measured. The optimum treatment time acceptable for technological applications was looked out with respect to the ageing phenomena. The obtained results show significant improvement in the wettability of PET NW. The effect of increasing wettability is considerably reduced with the increase of material square weight. The method has the potential to be suitable for industrial technologies, especially for thin materials.

The plasmochemical and/or electrocatalytical reactions of carbon monoxide with water vapour were studied. Dc corona discharge of both polarities at room temperature and temperatures enhanced up to 70°C was applied at pressures close to atmospheric.

The reaction products were analysed by IR absorption spectrometry. The main products in the gas phase were CO₂ and CH₄. The reactions are influenced by the formation of a catalytically active surface layer on electrodes. The composition of this layer depends on the polarity of electrode.

In atmospheric pressure corona systems, the densities of electrons and ions determine the level of treatments. Here, the electron and ion densities in a corona plasma are evaluated for a DC positive-polarity wire discharge in dry air at atmospheric pressure, in the coaxial wire-cylinder geometry. We use a new numerical iterative approach to solve the coupled equations for the electric field and charge densities. The role of electron diffusivity is discussed and the influence of the charge distribution between electrodes on the electric field strength and on the plasma region is analyzed.

The purpose of this study was to develop a standard methodology for measuring the surface free energy (SFE), and its component parts, of dental biomaterials. The contact angle of each of four samples of two materials--low density polyethylene and poly(methyl methacrylate)--was measured three times in each of six liquids (1-bromonaphthalene, diiodomethane, ethylene glycol, formamide, glycerol and distilled water). Critical surface tension estimates were obtained from Zisman plots. Data were then analyzed by the least-squares method to estimate the components of SFE. Estimates were also made for each of 12 liquid triplets, and by maximum likelihood and Bayesian analyses. The use of liquid triplets could yield misleading estimates of the components of SFE. A testing protocol is suggested in which multiple test liquids are used, and multiple methods of statistical analyses employed. SFE is important, in that high SFE is desirable when adhesion is required, but undesirable if plaque resistance is needed. Methodology that avoids some of the limitations of existing studies has been proposed.

Tbe relationship of contact angles to surface structure is outlined. The difference between the advancing and receding contact angles is discussed in terms of the modern theory of multimolecular adsorption; this theory indicates that the advancing angle will be unique, whilst the receding one will generally be less than the advancing angle and need not have a unique value.

The vast majority of polymers and composites have low surface energy; this is due to the low presence of functional groups on their surface which results in low adhesive properties. In order to modify this intrinsic property chemical and physical processes are commonly used. These processes present disadvantages, such as the use of products harmful to the environment. An alternative to these processes is the use of plasma technology. The main objective of this study is the improvement of the adhesive properties of the low density polyethylene (LDPE). In order to achieve the target, atmospheric plasma pretreatment has been optimized in order to promote subsequent adhesion processes, as the ones needed in the toy industry or the application of dyes or printing on surfaces. Plasma surface treatment is a clean process from the environmental viewpoint. This process does not emit any residue and it is easy to implement in an industrial process. Moreover the atmospheric plasma treatment is suitable to be applied in a large variety of materials even at high speeds when the treatment lasts less than a few seconds. In the present study it is examined the physical and chemical processes that occur in the LDPE surface as function of speed rate and distance of treatment. An increase both of the polar groups on the surface and the roughness after the treatment may increase its adhesive properties. It has been analyzed the influence of the speed rate and the nozzle distance on the final results. The adhesive properties have been evaluated using the T-peel test. The results show that at low speeds rates and low nozzle/substrate distance there is a greater inclusion of polar molecules at the surface. Consequently the adhesion properties of LDPE are improved.

The effect of varying the chemical constitution of a material on its ability to adhere may be determined to a good first approximation by the nature and packing density of the atoms or molecular radicals in the solid surface. This general conclusion was established by experiments on the wetting of liquids and solids, by the effect of the constitution of polymeric solids on friction, and by the overriding effect of monomolecular adsorbed films on adhesion. The reversible work of adhesion W sub A of a liquid to a low-energy solid can be calculated approximately from the contact angle and liquid surface tension. Both W sub A and the maximum capillary rise in pores and crevices are parabolic functions of the liquid surface tension. The resulting data are discussed in terms of surface constitutive effects, changes in W sub A and in the internal stress concentrations developed as the adhesives solidify.

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.

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.

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.

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.

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.

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 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 physicochemical principles of surface phenomena, and provides an overview of the research regarding surface properties of biopolymers used for the manufacturing of biodegradable films. Surface properties of food packaging polymers, such as wettability, scalability, printability, dye uptake, resistance to glazing, and adhesion to food surfaces or other polymers are of central importance to food packaging designers and engineers with respect to product shelf-life, appearance, and quality control. The most commonly used food packaging polymers are low-density polyethylene, high-density polyethylene, polypropylene, polytetrafluoroethylene, and nylon. In recent years, environmental concerns have increased the interest in preparing biodegradable packaging materials. Proteins and polysaccharides are the biopolymers of prime interest, since they can be used effectively to make edible and biodegradable films to replace short shelf-life plastics. Surface properties of biopolymers provide a supplementary understanding of film behavior, leading to an enhanced design of packaging materials for specific applications.