Rate-dependent fracture at adhesive interface

Schallamach's theory of rate-dependent bond dissociation is used to underst and the fracture of a polymer-glass interface. The model system consists of an elastomeric film (20 mu m thick) of poly(dimethylsiloxane), chemically bonded to a silanized glass substrate. The fracture energy of the interface varies logarithmically with velocity, which is consistent with Schallamach 's theory of forced bond scission. The activation energy (151 kJ/mol) of si loxane bond scission, as inferred from this study, is similar to that (147- 180 kJ/mol) obtained from thermal de-polymerization and stress relaxation k inetics of the siloxane polymers. It is shown that the equilibrium threshol d toughness of an interface is simply the product of the areal density of t he polymer chains and the energy to dissociate a single bond. The well-know n Lake-Thomas amplification of fracture energy by the number of bonds per c hain can be understood only on the basis of the nonequilibrium aspects of t he bond dissociation phenomena.