Model for the rheology and nonlinear response of layered materials

We outline a model to describe the rheology and the nonlinear response of l ayered materials. Explicitly, the focus is on cases wherein the system poss esses internal states whose relative populations undergo a change upon the application of a stress. The objective of the model is to describe the mutu al interplay between stress-induced transformations and the macroscopic rhe ological response of the materials. We focus on the specific case of multib lock copolymers, wherein the bridge and loop conformations of the chain con stitute the internal states. The numerical results of our model for differe nt polymeric architectures and different rheological constraints indicate a rich variety of phenomena including strain localization and shear banding. We derive an explicit constitutive equation that explains the origin of th e inhomogeneous rheological response of the model. (C) 2001 The Society of Rheology.