Effect of block number on multiblock copolymer lamellae alignment under oscillatory shear

The effect of block number on the alignment behavior was systematically studied for lamellae forming poly(styrene- b -isoprene) (SI) diblock to SISISISISIS undecablock copolymers under oscillatory shear. For SI and SIS, both perpendicular and parallel orientations were induced at low strain amplitudes, while only the parallel orientation was produced at large strain amplitudes. For SISI, SISIS, and SISISIS, the perpendicular orientation was induced at low strain amplitudes or high frequencies, whereas the parallel orientation was obtained at large strains and low frequencies. Only the perpendicular alignment was generated with SISISISISIS. The viscoelastic properties of these oriented materials are correlated with the alignment behavior. The parallel configuration in SISI, SISIS, and SISISIS multiblock copolymers is speculated to derive from predominantly looping block conformations, which permit layer-by-layer sliding. Structural evolution during alignment was investigated for SIS and SISIS at low strains using an in situ rheo-small-angle x-ray scattering instrument.