Microstructural changes of a binary polymer blend in simple shear flow across the phase boundary

We explore the dynamic response of a marginally entangled poly(dimethyl siloxane)/poly(ethyl methyl siloxane) blend in simple shear flow using rheology and small angle light scattering in situ. Data are collected in both the flow/gradient and flow/vorticity planes. We find that for this model binary blend, exhibiting upper critical solution temperature behavior, shear suppresses the large pretransitional concentration fluctuations and eventually yields homogenization. The simple modified Cahn–Hilliard–Cook phenomenological model of Lai and Fuller [J. Polym. Sci. Part B: Polym. Phys. 32, 2461–2474 (1994)] describes semiquantitatively the time evolution of the structure factor and orientation angle well, supporting the experimental observations of enhanced orientation with flow. In the phase separated region, when the late stages of spinodal decomposition are reached, the shear-induced anisotropic distortion of the spinodal ring, orienting in the flow direction, and its relaxation upon flow cessation are pr...