Flow-induced structure and viscoelastic properties of poly(styrene-block-2- vinylpyridine)s solutions near the order-disorder transition

Flow effects on the structure and the related viscoelastic properties of lamellar forming poly(styrene-block-2-vinylpyridine)s (SP) and DP in which S in SP replaced by deutrated chains are studied by small angle neutron scattering (SANS) and viscoelastic measurements under shear flows near the order-disorder transition (ODT). A distinctive feature of this sample is that both components have quite similar viscoelastic properties. In the quiescent ordered states, SANS intensities showed strong anisotropy denoting flow-induced alignment of lamellar structure at high shear rates (γ) in a limited range of concentration. When the lamellae are well aligned, first normal stress difference was proportional to γ² and reduced steady state compliance J_eR became practically the same as those of components. The viscosity behaviors in the quiescent ordered and disordered states were also the same as those of components. In the disordered states, on the other hand, J_eR was higher than those of components. Under steady shear flows, however, SANS intensities are isotropic and became lower and J_eR became almost the same as those of components denoting the suppression of fluctuation effects. Because of the similar viscoelastic properties of components, SPs may flow uniformly compared to other block copolymers such as poly(styrene-block-isoprene)s.