| Wed September 25th 2013 9:30 ZH286 | Seminar | Shear-Banding in Polymer Solutions; or "Not so" Simple Shear Flow of Polymer Solutions Gary Leal |
Details:A well-known phenomena exhibited by some complex fluids is shear-banding, namely the observation that the velocity profile in a simple shear device can exhibit two regions at different shear rates but constant total shear stress. The generally accepted understanding is that this is a consequence of a constitutive instability, due to a non-monotonic dependence of the shear stress on the shear rate, including an unstable region where the stress actually decreases with increase of shear rate. One fluid that exhibits this type of behavior is solutions of entangled, worm-like micelles. Polymer solutions, on the other hand, have a monotonic constitutive behavior, and hence it is believed by most researchers that shear banding is impossible in such fluids. In this work, we show that shear banding is possible provided that we include coupling between the stress and polymer concentration fields. The basis for the theory is the well-studied model for polymer migration due to Helfand and Fredrickson, and used previously for studies of flow-induced concentration fluctuations in polymer solutions. Almost all studies of fluid mechanics for complex fluids assume that the fluid remains homogeneous in the presence of flow. The present study challenges that assumption, and in that sense, seems to us to represent an important new direction for fluid mechanics studies of this class of materials. | ||
