Mathematikgebäude, Seminarraum M614/616 (6. Etage)

I discuss the combination of a microscopic theory for the rheological behavior of glass-forming fluids and glasses with lattice Boltzmann (LB) simulations of the macroscopic flow fields. Glass-forming fluids are characterized by slow structural relaxation. Macroscopic flow interrupts this relaxation, and pronounced nonlinear-rheology phenomena (such as shear thinning) arise. Starting from a formally exact equation of motion for microscopic density fluctuations, the mode-coupling theory of the glass transition derives a constitutive relation for non-Newtonian stresses that takes the form of a set of nonlinear integral equations. We solve (a simplified version of) these integral constitutive equations with a hybrid-LB method. I discuss exemplary results for the transient flows after startup and cessation of pressure-driven flow. In particular, after cessation of the flow, long-lived residual stresses arise that are predicted to persist indefinitely in the glass.

Prof. Dr. Thomas Voigtmann

DLR Köln / Heinrich-Heine-Universität Düsseldorf