Chapter 5

Controlling Adherence

5.1. Introduction

Controlling adherence is crucial in a wide range of applications in terms of life span, safety of structures, and/or simply proper operation. High adherence is most often sought in order to ensure the durability of interfaces. In some cases, however, low adherence is desired; for example, to ensure reversibility when we want to stick films together and pull them apart easily. Plastic food bags designed to contain chips, candy or other foods are an example of a case in which intermediate adherence is desired — enough to avoid accidental opening during transport, but low enough to allow the bag to be opened manually.

Two routes are possible for controlling adherence. The first route consists of modifying the nature of the links that form at an interface, i.e. modifying adhesion. The second route involves the dissipative phenomena that accompany the propagation of an interfacial crack; particularly in the case of ductile films and (visco)plasticity. Adherence, Gc, can be resolved into two terms:

[5.1]1 images

where Γo is the adhesion or interface energy directly linked to the fracture mechanisms, and Γp corresponds to the different sources of energy dissipation caused by the high level of stress in the areas surrounding the interface near the crack tip; see Figure 5.1, which shows a case of plastic dissipation in the two materials surrounding ...

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