Comparison between flow-induced alignment behaviors of poly(styrene-block- 2-vinylpyridine)s and poly(styrene-block-isoprene)s solutions near ODT

Flow-induced structure of lamellar forming poly(styrene-d ₈-block-isoprene)s (DI) solutions under steady shear flow are examined by small angle neutron scattering and compared with those of poly(styrene-d₈block-2-vinylpyridine)s (DP) solutions based on the experimentally determined interaction parameters, (Chi;^N) _eff. For DI solutions, it is observed that parallel and perpendicular alignments of lamellae coexist at low shear rates and the latter become dominant at high shear rates in the quiescent ordered states and disordered states very close to the quiescent order-disorder transition (ODT). At still lower concentration C below the quiescent ODT, flow-induced ordering with perpendicular alignment is observed. For DP solutions, coexistence of parallel and perpendicular alignments are only observed at low shear rates for relatively high C above the ODT, while only perpendicular alignment was observed at lower C near the ODT. It is concluded that the degree of perpendicular alignment (ratio of sector averaged intensities) is primarily determined by (Χ^N)_eff and reduced shear rates. In addition, concentration and shear rate regions in which parallel alignment coexists become narrower for the DP diblock copolymers consist of components with almost the same viscosities.