What is Rheological Chaos?
Prof. Michael E. Cates (Universität Edinburgh/GB)

Recent experiments give strong evidence for deterministic chaos in bulk viscoelastic fluid flows at low Reynolds number. Inertia is negligible: the behaviour stems from the intrinsic relation between stress and strain rate in the material, called the `constitutive equation'. This combines nonlinearity (shear-thickening or shear-thinning) with a finite memory time for stress relaxation. (In some cases, it also involves a longer timescale connected with `structural memory'.) Although, thanks to Edwards and others, reliable microscopic constitutive equations now exist for some classes of material (including polymers) these are generally too complicated to analyse precisely in unsteady flows. Some grossly simplified constitutive models will therefore be introduced, and used to discuss several unresolved issues concerning the physical nature of rheological chaos.