The role of the interface in adhesion phenomena

Abstract The role of the interface in adherend‐adherate combinations and in the strength of adhesive joints has been examined. For the former systems, practical adhesion (as determined experimentally, for example, by peel, tensile, or shear strengths) is a function of basic adhesion (determined by intermolecular, interactions such as van der Waals, electrostatic, or valence type forces) and many other factors. Adhesive joint strength depends pends upon the mechanical response of the various phases involved; however, the data in the literature on such strengths suggest the importance of surface chemical and energetic factors. Various such criteria, including, wetting, thermodynamic work of adhesion W A , and interfacial tension, y SL , for maximum joint strengths and the conditions which optimize these criteria are discussed. The testing of these factors against the literature data on adhesive joint strengths shows that the interfacial tension between the substrate and the adhesive ( y sL ) is the most important criterion; the lower the y SL , the higher the joint strength. In the case of adherend‐adherate systems, (e.g., metallized polymers), basic adhesion can be improved by chemical bonding or electrostatic contributions, and this improvement may or may not be reflected in improved practical adhesion. Examples are cited where an increase in basic adhesion does culminate in improved practical adhesion. On the other hand, practical adhesion does not always correlate with basic adhesion due to the influence of other factors.