Course 3: Structural Relaxation and Rheology of Soft Condensed Matter

Abstract.

These lectures address the relation between structural dynamics and macroscopic flow behaviour (rheology) in soft condensed matter. After a brief introductions to soft condensed matter, various types of observed rheological behaviour are introduced and classified. I then move on to discuss the flow of entangled polymers. These exhibit slow dynamics, but nevertheless remain close to equilibrium locally at all times. I outline a simple version of the tube model as developed for nonlinear flows by Doi and Edwards in the late 1970s, and also outline an even simpler “dumbell” model. The success of these polymer models is hard to emulate, especially in systems which are nonergodic at rest. Those include many kinds of pastes, dense emulsions, liquid crystal textures etc., and recent attempts are described to develop rheological constitutive equations for these “soft glasses”. This is followed by a discussion of rheological aging, in which the flow properties of a sample depend on the time since its preparation. I then discuss some simple models of “shear thickening”, which attempt to connect jamming phenomena, seen in colloids and some other materials, with a stress-induced glass transition. Finally, I point to ongoing work on two further topics: chaotic dynamics in the flow of soft materials (rheochaos) and fundamental approaches to glasses under flow (based on mode-coupling theory).