(193g) In-Situ Investigation of Shear-Induced Close-Packed Spherical Morphology in an ABA Triblock Copolymer

Linear ABA triblock copolymers find a wide range of applications such as in thermoplastic elastomers, masks for lithography, and membranes for batteries. Block copolymer morphologies formed spontaneously from the melt state lack long range order. Application of external forces, such as shear, electric fields, or magnetic fields, can lead to alignment of microdomains. In this study, a microphase-separated exhibiting a disordered spherical microdomain with randomly oriented spheres, was aligned through the application of large-amplitude oscillatory shear (LAOS) at a temperature below the order−disorder transition temperature of the triblock copolymer, yet above the glass transition temperature of the polystyrene spherical domains. Ex situ small-angle X-ray scattering (SAXS) experiments, conducted in all three shear directions (shear gradient, vorticity, velocity) revealed highly aligned morphologies after application of LAOS. In contrast to prior studies on shear-aligned morphologies in bulk and thin film block copolymers, the coexistence of hexagonal close packed and face centered cubic spherical structures was observed, attributed to the higher dispersity of the poly(lauryl acrylate) matrix of the triblock copolymer. To explore this phenomenon further, in situ time-resolved small-angle X-ray scattering was employed to examine the kinetics of shear induced alignment. The measurements were performed in both the shear gradient and vorticity directions. The effects of temperature, strain and frequency on the kinetics of alignment were investigated.