Phase Separation in Polymer Solutions Induced by Shear

We numerically investigate nonlinear regimes of shear-induced phase separation in entangled polymer solutions. Use is made of a time-dependent Ginzburg-Landau model describing two fluid dynamics of polymer and solvent. As a new dynamic variable a conformation tensor is introduced to represent chain deformations. Above the coexistence curve a dynamical steady states is attained, where fluctuations are enhanced on various spatial scales. At relatively large shear elongated polymer-rich regions form a transient network supporting most of the stress. Because such a network is continuously deformed in shear flow, the shear stress and the normal stress difference exhibit large fluctuations. In two component viscoelastic fluids the network stress can act on the two components asymmetrically. Then there arises dynamical coupling between stress and diffusion