Effect of Extrusional Shear Flow on Lamellar Polystyrene-Polyisoprene Diblock Copolymers

Abstract

Block copolymers are made of sequences of chemically distinct repeat units connected covalently into chains. They are widely used as adhesives, compatibilizers, additives and a variety of automobile parts. Due to the interplay between enthalpic and entropic driving forces block copolymers self organize into periodic microstructures on a length scale of 10–100 nm and exhibit a rich equilibrium phase behavior which has been elucidated with the help of numerous experimental and theoretical studies in the past1.2. The ordered phases can be controlled through the block copolymer molecular weight and composition. At a specific temperature the microphases undergo a phase transition, the so-called order-disorder transition (ODT). The associated temperature is referred to as the order-disorder transition temperature (T odt ). Above T odt block copolymers exist in a spatially homogenous state. Figure la depicts schematically what happens at the ODT for a lamellar diblock copolymer. Initially block copolymers below T odt are macroscopically isotrop exhibiting a grain structure on a μm length scale. Under the influence of shear the microstructure can be macroscopically aligned (Fig. 1b).