This review about bond formation resembles a jigsaw puzzle because we cannot see the overall picture until we put most of the pieces together. There have been many questions about solid adhesion. However, it is surprising to learn how little we do know about this subject matter.
This work outlines the mechanism of interfacial interactions with respect to different types of forces involved, discusses a transition between theoretical considerations and practical applications, e.g., in the area of adhesive bonds, and describes experimental techniques necessary for characterization of surfaces with respect to thermodynamic parameters that are significant for the bond design.
1. The Lifshitz—van der Waals Component of Interaction and Adhesion
Abstract
It is widely recognized that hydrogen bonding, or (more generally) acid—base interaction, across an interface, can make a major contribution to joint strength. It has recently been found(1,2) that, under certain conditions, hydrogen bonding can lead to a negative inter-facial free energy between condensed phases.
2. Interfacial Hydrogen Bonds as Acid—Base Phenomena and as Factors Enhancing Adhesion
Abstract
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.)
Robert J. Good, Manoj K. Chaudhury, Carel J. van Oss
The wetting properties of liquids against a solid surface are important for many adhesion purposes. A vast amount of knowledge on the statics of wetting has been collected by Zisman and his co-workers(1) mainly for the case of partial wetting, where contact angles can be measured, and related to interfacial energies. Situations of complete wetting are equally important, but have suffered from a certain lack of experimental information since there is no macroscopic angle to be measured.
Polymer—polymer interdiffusion has important applications in engineering, such as welding of plastics and of layered structures, preparing bulk thermoplastics from small resin particles via coalescence, crack healing, and creating structures in polymer mixtures.
In recent years, we have considered the problem of strength development at polymer—polymer interfaces in terms of the static and dynamic properties of random-coil chains.(1–4) When two pieces of solid polymer are brought into contact, wetting or close molecular contact (van der Waals) first occurs followed by interdiffusion of chain segments back and forth across the wetted interface.
The phenomenon of adhesion is the attraction of one material to another in either a gaseous or liquid medium. There are many mechanisms which can contribute to the adhesion between materials. The discussion in this chapter is limited to adhesion mechanisms due to electrostatic forces between dissimilar solid materials in a gaseous medium. The effect of electrostatic forces on adhesion is widely known and observed not only today but as early as 500 BC when the Greeks attracted pieces of straw to amber that had been charged by rubbing with another material. In spite of early observations and the ubiquitous nature of adhesion and triboelectric charging between materials, our present understanding is not satisfactory. Our understanding of electrostatic attraction is satisfactory when materials are separated. But when the materials are in intimate contact, the importance of electrostatic effects relative to other adhesion mechanisms becomes uncertain.
A high school teacher invited four men from the community to meet with his class on creativity. He showed them an assortment of rocks on a table and asked for their comments.
The science of adhesion is multidisciplinary in scope. Both chemical and physical forces contribute to adhesion and lack of adhesion. It is impossible to understand adhesive forces without an appreciation of both chemical and physical interactions. It is a goal of adhesion research to separate and measure the individual factors which lead to adhesion. This commendable goal has been attempted by some and achieved by few. Two difficulties have always hampered such a correlation. First, it is difficult to develop physical test methods which scientifically measure adhesive forces. Second, it has required decades for the development of analytical techniques which can begin to provide researchers with information about the nature of the chemical and physical forces at work at an interface or in an interphase.
When two solid surfaces are brought into contact, strong adhesive bonding forces can develop at the interface formed by the solids. The magnitude of the forces will depend on the state of the surfaces, their cleanliness, and the fundamental properties of the two solids, both surface and bulk.
The donor—acceptor interaction(1,2) and the acid—base interaction(3) have been reviewed. On many occasions, the two terms, though different, have been used interchangeably to describe the interactions involving the exchange of electrons between a donor and an acceptor. For polymer adhesion, Fowkes(4,5) and Bolger et al.(6) have pointed out the important role of the acid-base interaction in the formation of an adhesive bond.
Technological demands for good adhesion performance of thin coatings on critical surfaces arise in many applications. Examples include reflective coatings on optical components, chrome plating for corrosion protection, metallic contacts and conducting patterns on semiconductor chips and their packaging substrates, enamel glazing, low-friction coatings, and magnetic thin films for data storage applications.
In microelectronics, the large-scale integration of devices necessitates the use of multi-layered metallization structures on the chip level and for packaging. Such structures are usually fabricated using alternate metal and insulating layers. This incorporates metal—insulator interfaces throughout the structure which, depending on the configuration and dimension of the devices, can have varying degree of complexities. These interfaces have to be designed with certain functional characteristics, particularly good chemical and adhesion properties. For this purpose, it is important to understand these basic properties of the metal—insulator interface.
Paul S. Ho, Richard Haight, Robert C. White, B. D. Silverman, F. Faupel
The joining of substances in wet, salty, biochemically active environments is perforce an event of—at least—water displacement from interfaces. When living cells or tissues are to be intimately mated, or that mating prevented, consideration must be especially given to interaction of the hydrated peripheries of the particles/materials in question.(1) If neither, or only one, of the potentially adherent members easily sheds its bound water layer, prompt practical underwater adhesion is weak to negligible, although it might later become quite secure as excess water is expressed from the joint. Natural mucosal surfaces that resist bioadhesion to most other substances, living or synthetic, provide excellent examples. Witness the inherent resistance to biofouling of the inside of the cheek, the outside of the porpoise and killer whale,(2) and the uncompromised endothelial lining of blood vessels,(3) for instance.
