Mechanics of Solid Interfaces

Chapter 4

Interface Adherence

4.1. Adhesion and adherence

French scientists make a distinction between two ideas, adhesion and adherence, which also make up the title of a book on the subject [DAR 03]. Adhesion is defined by the NF AFNOR T30-010 standard as “all of the physical and chemical phenomena that arise when two surfaces are put in close contact, thus creating an interface”.

Adhesion is therefore characteristic of the links that form between the atoms, molecules or ions constituting the two bodies in contact. These can be “strong” bonds (ionic, metallic or covalent atomic bonds) or “weak” bonds (Van der Waals, hydrogen or electrostatic bonds). Some also include mechanical anchoring [DAR 03, WEI 95] resulting from the interpenetration of rough surfaces.

The idea of adhesion is therefore related to the creation of an interface, and from a thermodynamic perspective it corresponds to the energy gain resulting from the replacement of the free surfaces of two materials, A and B, by the interface AB, which is given by the Dupré equation [CHE 11, DUP 04]:

[4.1]

where γ_A and γ_B are the free energies of the respective surfaces of the materials A and B, and is the energy spent to create the interface between A and B. This adhesion energy is in the order of a few Joules per m² and is by definition reversible. It is also very difficult to measure directly¹ because, in reality, the separation ...