Polar surface intermolecular forces with adsorbents

The nature of the problem, as well as the solution to it, is represented in Fig. 1. The figure shows the circumstances in which adhesive joints are normally made with the substrate and adhesive surrounded by air. In the making of adhesive joints, the presence of air is seldom even considered, for the perfectly good reason that it does not represent a problem. However, the fact is that aU surfaces are contaminated by the permanent gases, but they are only weakly adsorbed (see Adsorption theory of Adhesion) and are readily displaced by adhesive, which then spreads freely and spontaneously over the substrate surface. In this way, intimate contact is achieved between liquid adhesive and solid substrate and adhesion results. Various Theories of adhesion are discussed elsewhere, but all require that adhesive and adherend are in intimate contact. For example, attractive intermolecular forces (van der Waals, see Dispersion forces. Polar forces) can operate only over short ranges ( 1 nm) and chemical interaction between adhesive and adherend also reqnires the two reactants to be in close contact. 

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