Projekte

We discuss the concept of a glass-transition line in the temperature-shear-stress plane in the context of recent simulation data for a metallic melt and dense-packed granular systems. Analyzing these data within a schematic model of the mode-coupling theory for dense glass formers under shear, values for the critical dynamic yield stress (the stress resulting in the limit of arbitrarily slow shear, at the glass transition) are estimated. We discuss two possible scenarios, that of a continuous rise in the dynamic yield stress at the transition, and that of a discontinuous transition, and discuss the data range that needs to be covered to decide between the two cases. A connection is made to the two commonly drawn versions of the jamming diagram, one convex and one concave regarding to the shape of the solid region.

Multiple distinct glass states with different dynamic and mechanical properties occur in binary hard-sphere mixtures with constituents of very disparate sizes according to the mode-coupling theory of the glass transition (MCT), distinguished by considering whether small particles remain mobile or not, and whether small particles contribute significantly to perturb the big-particle structure or not. In the idealized case, the four different glasses are separated by well-defined glass- and localization transitions that give rise to higher-order singularities involving logarithmic decay laws, and to anomalous power-law-like diffusion.