Light scattering and small-angle neutron scattering studies of structures in a semidilute polymer solution induced under oscillatory shear flow

Oscillatory-shear-flow-induced structures of a semidilute polymer solution of ultrahigh molecular weight deuterated polystyrene in dioctyl phthalate w ere investigated by using the small-angle light scattering (SALS) and the s mall-angle neutron scattering (SANS). Under a fixed strain amplitude of osc illatory shear flow at 4.8, we observed the shear-induced structures as a f unction of the angular frequency (omega) and the strain-phase. At low w, bu tterfly patterns, which are the scattering patterns unique to the shear-ind uced structures formed in semidilute polymer solution, were observed by SAL S and isotropic patterns with weak scattered intensities were obtained by S ANS. At high omega, on the other hand, SANS showed butterfly patterns and S ALS showed almost isotropic patterns. These results indicate that the aniso tropic structures developed under oscillatory shear flow become smaller wit h increasing omega. From the SALS and SANS patterns, we obtained scattering profiles parallel and perpendicular to the flow direction. At omega higher than 0.6133 rad/s, the SANS profiles parallel to the flow direction could be reproduced by a linear combination of the squared Lorentzian (SQL) funct ion, which reflects the scattering from the random two-phase structures, an d the Ornstein-Zernike (OZ) function, which gives the scattering from conce ntration fluctuations in a single phase. This analysis suggests that the sh ear-induced structures are not just the concentration fluctuations in a sin gle phase but kind of phase-separated structures having well-defined interf aces between two phases.