How do adhesives bond?
Adhesives are ‘bridges’ between two substrate surfaces and bonding depends on two factors: • Adhesion defines the bonding strength at the point of contact between the surfaces. The strength of the intermolecular forces that are needed for bonding is lower if the adhesive material does not come into intimate contact with bonding sites. Such lack of contact is often due to contamination on the materials – and this can prevent the adhesive from penetrating into the surface and wetting the whole area. At any given surface tension of the adhesive, wetting depends on the surface energy of the substrate and the viscosity of the adhesive. • Cohesion refers to the strength within the adhesive – or the force prevailing between the adhesive molecules that keeps the material together. These forces include the intermolecular forces plus the interlocking of the polymer molecules among themselves. Most adhesives are reactive polymers – they change from liquids to solids through chemical polymerisatio
