Small-angle scattering on soft matter with dynamical asymmetry

By employing small-angle neutron scattering, we investigated the mixing behavior in a quiescent state or under a shear flow on a miscible polymer mixture of deuterated polystyrene and poly(vinylmethylether). This polymer mixture uniquely shows the following behaviors in the intermediate temperature range between the two glass transition temperatures; (i) due to a large difference in glass transition temperatures, dynamical asymmetry or a difference of mobilities is enhanced upon temperature decrease, and (ii) the rheological relaxation becomes much slower than the concentration fluctuations determined by thermodynamics (gel-like limit). These two factors play an important role in the generation of a stress field and suppress small-angle scattering in a quiescent state. Under a shear flow, the stress imbalance enhanced by the dynamical asymmetry causes a butterfly pattern or shear-induced phase separation in the q-range of small-angle neutron scattering.