Three-dimensional small-angle neutron scattering of shear-induced phase separation in a dynamically asymmetric polymer mixture

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 T_g. Therefore, dynamical asymmetry is strongly enhanced in an intermediate temperature region between the T_g 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 q_x = q_y 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 q<sub>x</sub> = q<sub>y</sub>, where q<sub>x</sub>, q<sub>y</sub> and q<sub>z</sub>, 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 q_xq_z plane. The 3D-SANS thus obtained is discussed in comparison with a model of dynamical coupling between stress and diffusion.