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A polymer mixture of polystyrene (PS)/poly(vinyl methyl ether) (PVME) has been investigated by using a three-dimensional small-angle neutron scattering (3D-SANS) method. PS and PVME exhibit a large difference in the glass transition temperature Tg. Therefore, dynamical asymmetry is strongly enhanced in an intermediate temperature region between the Tg values of neat PS and PVME. In the intermediate temperature region, a shear deformation was imposed on the polymer mixture to enhance the concentration fluctuations, i.e. shear-induced phase separation. By rotating the film specimen, which was rapidly quenched after deformation, 3D-SANS due to shear-induced phase separation was observed successfully. In the qx = qy plane of the sample coordinate system, where q is a component of scattering vector q, it was possible to observe SANS of `double-lobe' shape, with the minor axes of the lobes inclined towards qx = qy, where qx, qy and qz, denote the shear, velocity gradient and vorticity directions in reciprocal space, respectively. Abnormal `butterfly' scattering was observed in a section cut through the 3D-SANS in the qxqz plane. The 3D-SANS thus obtained is discussed in comparison with a model of dynamical coupling between stress and diffusion.

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