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What is the adsorption theory of adhesion?

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Why does glue stick? — adhesive Overview of how glue and other adhesives work.

The adsorption theory is the primary mechanism used to explain how adhesives function. It states that substances stick together primarily because of intimate intermolecular contact between the adhesive and the adherend (the component being joined).1

To achieve this, the adhesive must be able to wet and spread across the surface of the adherend, ensuring interfacial molecular contact. Once this contact is established, the bond is maintained by intermolecular or valence forces exerted by the molecules located in the surface layers of both the adhesive and the adherend. These forces can include van der Waals forces, which are weak, short-range attractions caused by quantum fluctuations in electron distribution.12

Some researchers also include chemical reactions within the scope of the adsorption theory. In this context, bonding occurs when adhesive molecules adsorb onto a solid surface and undergo a chemical reaction with it. While some classify this as a distinct mechanism, others view it as a component of the total adsorption process.1