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.

The sessile drop contact angle measurement is a useful and reliable method for surface energy determination and cleanliness verification. A review of the available methods, commercial instruments, patents, and literature describing the state of the art in contact angle measurement is followed by a description of contact angle measurement techniques that have been modified for use on large surfaces. The negative effects of these changes on accuracy and precision are discussed, and remedies are proposed including the use of standard reference objects that mimic the size and shape of sessile drops. The combination of these validation tools and the modified contact angle measuring techniques fills a need for robust, production-line capable cleanliness verification methods.