TEM FRACTURE STUDIES OF POLYMER INTERFACES

A new transmission electron microscopic technique is described with which it is possible to observe and make quantitative measurements of deformation and fracture mechanisms at planar interfaces between two immiscible homopolymers. Utilizing this technique, we have studied the fracture of interfaces between polystyrene (PS) and poly(2-vinylpyridine) (PVP) homopolymers reinforced with a series of PS-PVP block copolymers. Typically a craze was observed ahead of the crack tip. The craze was formed on the PS side of the interface, as expected, since the crazing stress of PS is lower than that of PVP. Craze breakdown occurred exclusively at the PVP/PS craze interface, showing that the block copolymer reinforced interface was still the weakest link in the material. It was also found that the values of the critical energy release rate of the crack (G(c)) calculated from TEM micrographs are comparable to those obtained from conventional fracture toughness tests over a wide range of G(c), indicating that crazing is the dominant energy dissipation mechanism in this system and governs the fracture toughness of the interface.