How do intermolecular forces contribute to adhesive bonding?

Intermolecular forces are fundamental to adhesive bonding, as they facilitate the intimate contact required for materials to stick together. According to the adsorption theory, substances adhere primarily because of these forces, which act between molecules in the surface layers of the adhesive and the adherend.1

For an adhesive to form a strong, stable joint, it must first wet and spread across the surface of the adherend. Once this interfacial contact is achieved, intrinsic adhesive forces are generated through several mechanisms, including:1

• Van der Waals forces: These are relatively weak electric forces that attract neutral molecules to one another. They arise from permanent dipoles, induced dipoles, or instantaneous dipoles (London dispersion forces) resulting from electron fluctuations.2
• Hydrogen bonding: A stronger interaction than van der Waals forces, this occurs when a hydrogen atom covalently bonded to a highly electronegative atom (like nitrogen, oxygen, or fluorine) is attracted to another electronegative atom with an unshared electron pair.3

These intermolecular interactions, alongside other mechanisms like mechanical interlocking and chemical reactions, determine the strength and durability of the resulting adhesive joint.1