1 - Introduction and Adhesion Theories

Abstract

An adhesive is a material that is applied to the surfaces of articles to join them permanently by an adhesive bonding process. The basic requirements for a good adhesive bond are proper choice of adhesive, good joint design, cleanliness of surfaces, wetting, and proper adhesive bonding. Adhesion, on the other hand, refers to the state in which two dissimilar bodies are held together by intimate interfacial contact such that mechanical force or work can be transferred across the interface. The interfacial forces holding the two phases together may arise from van der Waals forces, chemical bonding, or electrostatic attraction. Generally, mechanical interlocking, electrostatic, diffusion, and adsorption/surface reaction theories have been proposed to describe mechanisms of adhesion. In mechanical theory, adhesion occurs by the penetration of adhesives into pores, cavities, and other surface irregularities on the surface of the substrate. Electrostatic (electronic) theory states that adhesion takes place due to electrostatic effects between the adhesive and the adherend. Diffusion theory suggests that adhesion is developed through the interdiffusion of molecules in between the adhesive and the adherend. The diffusion theory is primarily applicable when both the adhesive and the adherend are polymers with relatively long-chain molecules capable of movement. This theory proposes that adhesion results from molecular contact between two materials and the surface forces that develop.