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The structures of a semidilute polymer solution, comprised of ultrahigh molecular weight polystyrene as a solute and dioctyl phthalate as a solvent, under oscillatory shear flow were investigated by means of small-angle light scattering. The system exhibited a double-winged anisotropic scattering pattern called “butterfly”, characteristic of shear-induced phase separation known to occur under a continuous shear flow. Under oscillatory shear flow the phase separation strongly depended on both a strain amplitude γ 0 and an angular frequency ω, being observed inside a quasi-parabolic line in the space of γ 0 vs log ω. The system was brought to a dynamically stationary state in about 20 min after applying the shear flow, and the shear-induced structures changed with a strain phase φ of the oscillatory shear. At a given φ and γ 0, the shear-induced structures strongly depended on ω:  the characteristic wavelength of the structures decreased with increasing ω, and the mean square of the concentration fluctuations was a maximum at a certain ω.

Oscillatory-shear-flow-induced structures of a semidilute polymer solution of ultrahigh molecular weight deuterated polystyrene in dioctyl phthalate were investigated by using the small-angle light scattering (SALS) and the small-angle neutron scattering (SANS). Under a fixed strain amplitude of oscillatory shear flow at 4.8, we observed the shear-induced structures as a function of the angular frequency (ω) and the strain-phase. At low ω, butterfly patterns, which are the scattering patterns unique to the shear-induced structures formed in semidilute polymer solution, were observed by SALS and isotropic patterns with weak scattered intensities were obtained by SANS. At high ω, on the other hand, SANS showed butterfly patterns and SALS showed almost isotropic patterns. These results indicate that the anisotropic structures developed under oscillatory shear flow become smaller with increasing ω. From the SALS and SANS patterns, we obtained scattering profiles parallel and perpendicular to the flow direction. At ω 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) function, which reflects the scattering from the random two-phase structures, and the Ornstein−Zernike (OZ) function, which gives the scattering from concentration fluctuations in a single phase. This analysis suggests that the shear-induced structures are not just the concentration fluctuations in a single phase but kind of phase-separated structures having well-defined interfaces between two phases.

A new apparatus which makes it possible to measure flow small-angle light scattering ("flow-SALS") and to observe the development of the supramolecular structure by an optical microscope ("shear microscopy") has been developed in our laboratory. It simultaneously provides information on reciprocal space from SALS and on real space from optical microscopy. Therefore, the development of the supramolecular structure in systems such as polymer solutions and polymer mixtures as well as liquid crystals and colloidal systems under shear can be investigated in depth. Shear-induced phase separation and shear-induced homogenization of some polymer solution systems were investigated using this apparatus.