STRAIN-ENERGY EFFECTS ON THE ORDERING PROCESS IN DIBLOCK STYRENE-BUTADIENE COPOLYMER

The technique of time-resolved small-angle x-ray scattering is used to monitor the disorder-order transformation occurring in asymmetric, di block styrene-butadiene. A rapid thermal quench is applied to drive th e system from its initial high-temperature disordered state to a low-t emperature ordered structure, a body-centered cubic lattice of styrene spheres characterized by a series of concentric Debye rings in the tw o-dimensional scattering profile. At relatively late times in the micr odomain ordering process, the uniform Debye rings were seen to rapidly develop nonuniformities indicating the existence of preferred orienta tion with a fiber texture, the [110] axis of the bcc structure definin g the fiber axis. These results are interpreted in the context of a de veloping transformation strain energy during the ordering process and shown to be consistent with accompanying changes in lattice spacing as well as earlier observations of apparent fluctuations in the ordering process.