Adhesive bonding is the process of securing two similar or dissimilar materials together. In adhesive bonding, as the name implies, an adhesive, usually some kind of glue, is used to bond two surfaces. In the adhesive bonding process, both cohesive and cohesive forces are involved. Depending on the magnitude of these forces, adhesive failure can be cohesive, cohesive, or substrate failure.
Cohesion and cohesion are involved in the bonding process
When a glue is applied to a surface, the importance of its ability to wet the surface for good adhesion cannot be overemphasized. Good wetting properties ensure that the glue can penetrate the surface structure, resulting in better mechanical interlocking at the interface. The bond between the glue and the substrate and the cohesion in the glue determine the ability of the glue to wet the surface. If the cohesion inside the glue (or any other paint formulation) is high, the glue prefers to stay together rather than interact with the surface. However, if the bond between the substrate and the glue is high enough, the glue may spread. Once the glue has hardened and formed an interface, these same forces determine whether the bond is permanent or whether bond failure is likely to occur.
Adhesive Failure Mechanism
To understand why binding fails, we need to first define how the failure occurs. These can be divided into three categories:
adhesive failure
cohesive failure
Substrate failure
Adhesive failure or delamination is one of the common types of failure mechanisms. There, two different materials are separated from each other. A failure can occur between the adhesive and either of the two substrates it is bonding together. Cohesive failure occurs in the adhesive itself or within the coating. Substrate failure has nothing to do with the bonding process itself, as it is a problem in the substrate.
As you might have guessed, cohesive failure occurs if the cohesive forces inside the adhesive are not strong enough. Then, on the other hand, adhesive failure can occur if the glue is not applied properly to the substrate. To ensure that the glue (or other coating formulation) spreads adequately, contact angle measurements can be used.
