The Nature of an Adhesion Bond between Two High-Molecular Weight Compounds
Abstract 1. The nature of the adhesion bonds in different cases can be determined by investigations of the mechanical characteristics of adhesion, of electrical effects observed on destruction of the bond, and microscopical investigation of the separation boundaries in various systems consisting of polymer pairs, and polymer-metal and polymer-glass systems held together by forces of adhesion. 2. The adhesion bonds between polymer and metal and polymer and glass are electrical in character, as shown by the form of the adhesiogram, the occurrence of electron emission on separation, and the existence of electric charges on the separated surfaces. 3. After separation, the polymer film continues to emit electrons and carries a negative residual charge. The substrate (glass, metal) does not emit electrons and has a positive charge. 4. The breakdown of the adhesion bond between two polar polymers of different structure, or a polar and nonpolar polymer, is accompanied by the same characteristic effects as the separation of a polymer from glass or metal. A sharp boundary is observed in microscopic specimens. 5. Determinations of the velocities of electrons emitted during separation show that breakdown of a firm adhesion bond is accompanied by emission of electrons with higher velocities than those emitted in the breakdown of a weak bond. These results arc in good agreement with the electrical theory of adhesion. 6. The reaction of the substrate (glass) has a strong influence on the adhesion of a polymer (chlorinated polyvinyl chloride) to it. The maximum adhesion is found in the neutral region. The detached polymer film shows a reversal of residual charge in the strongly acid and strongly alkaline regions, accompanied by a sharp decrease of the work of adhesion; this can only be attributed to a decrease of the surface electrification density of the layers of the electric double layer in the charge reversal region. 7. Mechanical treatment of the metal surface increases the adhesion of polymers to it and intensifies electron emission from the regions of the polymer film which were attached to the treated regions of the metal surface. 8. The formation of an adhesion bond between two nonpolar polymers of similar structure is caused by diffusion processes in the contact zone. In such cases no electrical effects are observed during separation, the boundary in microscopic specimens is diffuse, and the work of separation depends relatively little on the rate of separation. 9. The systems studied can be subdivided into two groups: the adhesion bond in systems of the first group is the result of formation of an electric double layer at the boundary; in systems of the second group the adhesion bond is produced by diffusion processes at the boundary.
