SELF-ASSEMBLED STRUCTURE OF A SEMIDILUTE SOLUTION OF POLYMER MIXTURES UNDER SHEAR-FLOW

The domain structure self-assembled under a steady Couette now 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 in situ light scattering method. This method permits a quantitative analysis of the scattering profile I(qy) in the plane perpendicular to the shear flow as a function of shear rate S at a given quench depth ΔT(0)=Tc(0)-T. Here, qy is the component of the scattering vector q in the plane concerned, Tc(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(qy) 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(qy) 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 oriented random two-phase structure. At the highest S (regime E), I(qy) followed the OZ scattering, thus suggesting the system to change to the shear-induced homogenized state. © 1990 American Institute of Physics.