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.