Prediction of the Structural Relaxation Time from Vibrational Dynamics in Thin Films

The structural relaxation time of glass forming liquids correlates with the cage vibrational dynamics at the picosecond, making it possible to predict one from the other despite a separation of more than ten orders of magnitude in the time scales.
This result, found in computer simulations, has been extended over the years to all kind of glassformers in bulk systems.
Thin films, though, present additional complications due to finite size effects and complex surface interactions, causing shifts in the glass transition temperature and strong gradients in mobility across the film for reasons that are not fully understood yet.
In spite of that, we show that the particle-sized layers of a thin supported film comply without any adjustment with the same scaling observed in bulks, by varying temperature, film thickness and distance from the substrate in a coarse grained molecular dynamics simulation.
This result provides new predicting tools for both simulations and experiments and its implications shed light on the physics of confined liquids approaching the glass transition.