Dynamics of phase separation in polymer solutions under shear flow

We present a general model for the dynamics of phase separation in polymer-solvent mixtures under shear flow, which unifies previous phenomenological theories. For the dilute case, the model can be derived in the absence of hydrodynamic interactions via the appropriate Smoluchowski equation. Linear analysis shows that the shear flow does not change the equilibrium phase boundary. We then generalize the model to the semidilute case, and find that the phase separation temperature is indeed shifted by the shear flow. The results indicate that a nonlinear concentration dependence of the modulus is necessary for a shift in the phase separation temperature.