4. Adhesion Behavior of Soft Materials

Adhesion is defined as the strength of an interface. The study of adhesion involves understanding the development of interfacial properties when two materials come into contact. Thus, it is a field that has relevance in nearly every aspect of our lives ranging from biological adhesion to microelectronics. In most instances, it is the control of adhesion that is important to the specific application. Additionally, adhesion is important to a diverse set of materials that ranges from soft tissues to hard inorganic materials. Therefore, it is important to discuss the general concepts and key materials properties that are involved in the adhesion and separation of an interface. As the scope of this book addresses properties of biomaterials, this chapter will focus on the adhesion of soft materials. To aid in this understanding, the theories of Hertz and JKR will be discussed as these theories address the coupling between contact geometry of the interfacial and materials properties. We will also discuss examples of the applications of these theories for characterization adhesion of different soft material applications. With the recent interests in biomimetic adhesion, i.e. gecko adhesion, we will also use these theories as foundation for understanding how patterned surfaces can tune interfacial properties and impact macroscopic performance.