Deformation behavior of weakly segregated block copolymers. 2. Correlation between phase behavior and deformation mechanisms of diblock copolymers

The deformation behavior of poly(styrene-b-butyl methacrylate) diblock copolymers, PS-b-PBMA, is studied by high-voltage electron microscopy (HVEM) with an in-situ tensile device. While in the first part the phase behavior of PS-b-PBMA diblock copolymers is investigated via small-angle neutron scattering (SANS), in the second part the deformation behavior depending on composition and molecular weight is discussed. Disordered block copolymers have the same deformation mechanism as the corresponding homopolymers, while microphase-separated block copolymers undergo a cavitation mechanism. At the order−disorder transition, ODT, a transition from crazing to cavitation mechanism is found via HVEM. Moreover, a sharp increase of the diameter of craze fibrils occurs at the ODT, demonstrating that the craze microstructure is strongly influenced by phase behavior. As the incompatibility increases with increasing molecular weight, deformation mechanisms such as diversion and termination of crazes are observed for intermediately segregated block copolymers. The discussed correlation between phase behavior and deformation mechanisms indicates the existence of a unified scheme for deformation behavior of diblock copolymers depending on the strength of segregation, χN.