Self-assembled structure of a semidilute solution of polymer mixtures under shear flow

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Abstract
The domain structure self‐assembled under a steady Couette flow was investigated on a semidilute solution of polymer mixture (polymer A + polymer B + solvent) at a composition near the critical one by use of the i n s i t ulight scattering method. This method permits a quantitative analysis of the scattering profile I(q y ) in the plane perpendicular to the shear flow as a function of shear rateS at a given quench depth ΔT(0)=T c (0)−T. Here, q y is the component of the scattering vector q in the plane concerned, T c (0) the critical temperature at S=0, and T[<T c (0)] the temperature of the experiment. Effects of shear rate on the self‐assembled structure were pronounced, and they were classified into five regimes A to E. At the lowest S (regime A), I(q y ) was expressed by a linear combination of the Porod scattering and the Ornstein–Zernike (OZ) scattering, the former being due to the domain structure and the latter to critical composition fluctuations inside the domains. At higher S (regime B), I(q y ) was complex. However, with increasing S further (regimes C and D), it was universally represented by the squared Lorentzian form {1+[q y(ξ⊥) d ]2}−2, with a shear‐rate‐dependent length parameter (ξ⊥) d which depends on S −n with n=1/4 to 1/3. This fact indicates the self‐assembling of a domain structure which we call o r i e n t e d r a n d o m t w o‐p h a s e s t r u c t u r e. At the highest S (regime E), I(q y ) followed the OZ scattering, thus suggesting the system to change to the shear‐induced homogenized state.

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