Deformation of Oriented Lamellar Block Copolymer Films

Highly ordered, near-single-crystal lamellar films of a triblock copolymer (polystyrene−polybutadiene−polystyrene, PS/PB/PS) were used to study the deformation mechanism of a structure of alternating glassy−rubbery layers, at different orientations of the deformation axis relative to the layer normal. Synchrotron radiation was used for simultaneous in-situ deformation and small-angle X-ray scattering measurements. These were augmented with direct imaging of the structure by transmission electron microscopy. The deformation mechanism depends on the orientation of the force with respect to the structure. Loading parallel to the lamellae results in yielding by propagation of a stable macroscopic neck. The glassy PS layers break up at the neck front, releasing the rubbery layers to achieve high strain. The morphology that develops by deformation of the structure in other directions is an ensemble of new tilt boundaries oriented along the deformation axis. The lamellar normals tilt away from the deformation ax...