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

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 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[<Tc(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+[qy(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.

Effect of Shear Flow on the Phase Behavior of an Aqueous Gelatin−Dextran Emulsion

“…For low molecular weight polymer blends (deuterated polystyrene and polybutadiene), Hobbie et al 14 established that shear inhibits phase separation at the critical molecular composition: flow disrupts the long-range critical fluctuations when the inverse of the shear rate becomes comparable to the relaxation rate of these fluctuations. Changes in the phase state of a synthetic polymer system, consisting of polystyrene and polybutadiene in a common solvent DOP, have also been observed by Hashimoto and co-workers [15][16][17] using small-angle light scattering. These studies show a complex behavior with several regimes depending on the magnitude of the shear rate.…”

Scattering from interfaces and its finite curvature corrections

“…For example, domains are elongated in the direction of gravity in very late stages of spinodal decornposition[9]. It is also known that, when a shear flow is applied to a phase-separating fluid, a stationary domain structure can be produced as a result of dynamical balance between the thermodynamic instability and the break-up mechanism by shear[10]. We stress that the Porod tail can be detected even after the spinodal ring has collapsed in very late stages.…”

Phase Behavior and Morphology of Poly(Methyl Methacrylate)/Poly(α‐Methyl Styrene‐co‐Acrylonitrile) Blends Under Quiescent and Shear Flow

“…The theory predicted that the larger the characteristic time (t j ) for the concentration fluctuations are the larger the change of the cloud point will be. This general principle can be applied also to polymeric system (polymer solution (98), low and high molecular weight polymer blends (72,73), since the relaxation time decreases from high molecular weight polymer blends to becomes very short in the case of simple liquid mixture. Therefore, the large difference in the prefactor values, which reflects the sensitivity of the different systems to shear rate, is not surprising at all.…”