Adhesion of high polymers. I. Influence of diffusion, adsorption, and physical state on polymer adhesion

It is possible to identify three distinct types of polymer adhesion on the basis of the physical state of adhesive and adherend: ( 1 ) rubbery polymer–rubbery polymer (R–R adhesion); ( 2 ) rubbery polymer–glassy polymer (R–G adhesion); ( 3 ) rubbery polymer–nonpolymer (R–S adhesion). Limitations of the diffusion and adsorption theories and their conflicting results are discussed within the framework of the proposed classification. By defining the physical state of the polymer as an adhesive or as an adherend, it is possible to eliminate many of the discrepancies commonly noted in attempted application of the diffusion and adsorption theories. As predicted by the Bueche‐Cashin‐Debye equation, the diffusion of a polymer into another should be greatly reduced as it changes from the rubbery to the glassy state. For this reason, diffusion, which depends to a great extent on the physical state of the polymer, is actually a limited, selective process. Assuming a 10 13 poise bulk viscosity at glass temperature, self‐diffusion constants of forty polymers were calculated to be 10 −21 cm. 2 /sec. or 10 −5 A. 2 /sec. This slow rate of diffusion is unmeasurable and insignificant. Adsorption, which is less dependent on the physical state of the polymer, is more frequently encountered.