Confinement effects in bulk supercooled liquids

Supercooled liquids are known to display heterogeneous dynamics, with slow and fast relaxation modes being independent and even spatially separated in dynamically distinct domains. In such a situation, it is imaginable that the very fast modes are surrounded by material that is practically frozen on the relaxation time scale of that fast mode. Here, we show experimental evidence of such a confinement effect. For the fastest few percent of all modes, equilibration appears to be linked to a common process (e.g. macroscopic softening), while the remaining majority equilibrate on the time scale of their individual time constant, as expected for heterogeneous dynamics.