Effect of Interfacial Bonding on the Strength of Adhesion of Elastomers. III. Interlinking by Molecular Entanglements

摘要

Polydimethylsiloxane (PDMS) networks have been formed by endlinking linear PDMS molecules. When second layer is cast on top of a fully-gelled lower-layer, the new molecules diffuse into the surface of the lower layer and form molecular loops ('entanglements') in the course of endlinking with themselves. The two layers are then joined only by the macromolecular loops. Measurements have been made of the work required to separate such layers under threshold conditions, i.e., at low rates, high temperatures, and, in some cases, in the swollen state. Values of the work of detachment have been found to be generally about one-half of the work of fracture of the layers themselves, and consistent with the inferred density of interlinking molecular loops at the interface. The values were higher for higher densities, roughly in proportion, and for interlinking molecular strands of higher molecular weight, in accordance with the theory of Lake and Thomas. In the absence of interlinking the work of detachment was extremely small.