From heterogeneous probe rotation to the hydrodynamic limit

The recognition of heterogeneous dynamics in single component supercooled liquids has greatly advanced our understanding of the dynamics in glass-forming materials. However, details such as persistence times and length scales associated with dynamically distinct domains remain to be resolved. The rotational correlation function of probe molecules in viscous liquids is used as a tool for exploring the rate exchange or the time a domain memorizes its initial relaxation rate. With high precision dielectric experiments, the dynamics of probe molecules is observed to slow down with increasing size of the guest relative to the host molecules. For the case of di-n-butylether in 3-methylpentane, the situation of purely exponential probe dynamics within dispersive host relaxation is achieved as a result of time averaging. The results suggest that rate exchange occurs on a time scale which is equal to the longest structural relaxation time of the system.