Two poly(ethylenepropylene)–poly(ethylethylene) (PEP-PEE) diblock copolymer melts, containing 25% and 83% by volume PEP, were investigated using small-angle neutron scattering (SANS) and rheological measurements. The SANS measurements were performed with the aid of an in situ shearing device operated directly in the neutron beam. Each sample was observed to possess three equilibrium phases: two ordered phases at low temperature and a disordered phase at elevated temperatures. The low and high temperature ordered phases have been evaluated to be hexagonally packed (hex) cylinders and body centered cubic (bcc) spheres, respectively. Application of a large amplitude dynamic shear deformation to the hex phase leads to well-aligned cylinders, with a specific crystallographic orientation relative to the shear plane. Upon heating through the cylinder-to-sphere transition, the bcc phase grows epitaxially, with the [111] direction coincident with the original cylinder axis, leading to a well-defined twinned microstructure. SANS measurements performed while the bcc specimens were dynamically sheared revealed a rich compliment of microstructural rearrangements, with the twinned state appearing at low and high shear rates, and two-dimensional disordering at intermediate shear rates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.