In the Flexographic printing of polyethylene films with waterbased flexo inks, the partitioning of the surfactants between film/ink, pigment/ water, ink/air interfaces plays a major role in determining the printability. In addition, in formulations containing nonionic surfactants the equilibrium surface properties are much different from the diffusion limited dynamic properties. Problems associated with the printability are examined from an analysis of the above surface chemical considerations.

Historically, the technologies most interested in the wetting of fibers have been those involved in the processing of textiles.(1, 2) Much of the early scientific literature on wetting was concerned with liquid penetration into fabrics and other porous solids.(3) More recently, the rapid development of fiber reinforced composites, notably carbon fiber and glass fiber reinforced polymers (CFRP, GFRP), has generated a renewed interest in the wetting of fibers. However, in the interim there has been a change in the scientific attitude toward the use of contact angle measurements as a means of characterizing the surface chemical constitution of solids. In the early literature, the contact angle was viewed as a characteristic of the fiber and a parameter in the capillarity equations for liquid penetration. Due in large measure to the studies by W. A Zisman and co-workers, there has been a change in attitude toward the physical significance of contact angle measurements. It is now recognized that the contact angle can be a highly sensitive tool for surface characterization. Consequently, there is a growing body of literature on the wetting of textile fibers and fibers used in composites aimed at surface chemical characterization as well as the processing of these fibers into composite materials.

This chapter summarizes our present understanding of surface preparations for structural adhesive bonding of aluminum, titanium, and steel adherends. Both the initial bond strength and the subsequent bond durability depend critically on the interaction of the adhesive (and/or primer) with a pretreated adherend. There are two mechanisms of adhesion that are prominent in structural adhesive bonding: mechanical interlocking of the polymer adhesive with a microscopically rough adherend surface, and chemical bonding (with either covalent bonds or weaker van der Waals bonds) of adhesive molecules to the (intentional) adherend oxide. The magnitude and relative importance of both of these interactions depend greatly on the nature of the adherend surface prior to bonding and on the rheology and chemistry of the adhesive.

Dynamic Contact Angle Technique offers a unique, non-optical alternative to solid surface energy analysis. The technique provides advancing and receding hysteresis profile scans of a surface recorded in real time as the liquid meniscus traverses the solid surface. Changes in the wetting hysteresis scan can be used to characterize the qualitative effects of surface roughness, surface homogeneity, and surface polarity, as well as measure the quantitative surface energy of the solid. Applications in flexography in which wettability plays a critical role are numerous, and the switch from solvent-based inks to water-based inks gives impetus for future study.

Adhesion involves a detailed understanding of polymer synthesis and characterization, mechanics, and surfaces. This chapter reviews surface analysis and interphase analysis emphasizing polymer/metal systems. The interphase is a thin region between the bulk adherend and the bulk adhesive, as depicted in Figure 1. A surface oxide, either native or one produced by pre-treatment, is present on most metal adherends. A primer is often applied in a production process after pretreatment and before the application of an adhesive. Typical thicknesses for the oxide are 0.003–0.4 µm, for the primer 4 µm (0.16 mil), and for the adhesive 40 µm (1.6 mil). The interphase region is expected to have mechanical properties different from either the adherend or the adhesive. Measurement of these properties is important in understanding adhesion, for example, poorly durable bonds are often a consequence of poor interphase properties.(1,2) Thus, one of the frontier areas in adhesion science today is determining interphase properties.

The theory of the apolar components of interfacial forces was examined in the previous chapter of this volume.(1) It has been possible to develop that theory of apolar components at this time owing to the existence of quantitative, mathematically formulated theories of forces between molecules (e.g., the London theory) together with the Lifshitz electromagnetic theory of the interaction of macroscopic bodies. (See the previous chapter for references.)

The theory of the apolar components of interfacial forces was examined in the previous chapter of this volume.(1) It has been possible to develop that theory of apolar components at this time owing to the existence of quantitative, mathematically formulated theories of forces between molecules (e.g., the London theory) together with the Lifshitz electromagnetic theory of the interaction of macroscopic bodies. (See the previous chapter for references.)

We owe a great debt to W. A. Zisman and his colleagues at the Naval Research Laboratory for their extensive, pioneering work that opened up the field of contact angles and made possible the development of the modern theory of wetting and adhesion. Their data on the wetting of solids by apolar liquids and by hydrogen bonding liquids pointed the way to the recent introduction of a theory of hydrogen bond interactions across interfaces. We will devote this chapter to a review of this new theory.

A detail discussion of the theoretical aspects of surface tension measurements by ring method is provided with special emphasis on the sources of error. The accuracy of the measured data is mainly limited by the correction factor “f”, which compensates for the non-symmetrical shape of the surface. Based on the experimental findings, it is suggested to include the correction factor during the evaluation of the surface tension, especially if an accuracy of less than 0.1mN/m is required. The effect of meniscus shape and size on the surface tension is discussed. In addition to the surface tension measurements, several other physical properties of the coating systems such as settling behavior and hardness of the settlement can be measured by using the dynometer from BYK-Gardner as a measuring device. The results on different coating systems are presented to study the settling and hardness of the settled material.

The coating and printing of polymer films with water-based formulations are relatively difficult as compared to solvent-based formulations. The surface tension of water is higher than that of the solvents. In addition, the surface energy of polymer surfaces is in the range of 25–40 ergs/cm2. In order to understand the wetting and spreading behavior of coating materials, the polar and non-polar surface energies were evaluated by measuring contact angle of water and methylene iodide on various non-porous substrates. These results were utilized to explain the spreading, wettability and adhesion phenomena in order to understand the interactions between water-based coating/printing materials and non-porous substrates.