Molecular layers in thin supported films exhibit the same scaling as the bulk between slow relaxation and vibrational dynamics

TL;DR

This study uses molecular dynamics simulations to show that thin supported molecular films exhibit layer-specific dynamics that follow the same bulk scaling between relaxation time and vibrational motion, revealing layer-by-layer solidification insights.

Contribution

It demonstrates that the scaling between relaxation time and vibrational motion applies locally within layers of supported films, not just in the bulk, providing new understanding of layer-specific dynamics.

Findings

Layer-specific dynamics follow bulk scaling laws.

Vibrational properties can predict layer solidification.

Gradients of dynamics are consistent with bulk behavior.

Abstract

We perform molecular dynamics simulations of a supported molecular thin film. By varying thickness and temperature, we observe anisotropic mobility as well as strong gradients of both the vibrational motion and the structural relaxation through film layers with monomer size thickness. We show that the gradients of the fast and the slow dynamics across the layers (except the adherent layer to the substrate) comply, without any adjustment, with the same scaling between the structural relaxation time and the Debye Waller factor originally observed in the bulk [Larini et al., Nat. Phys., 2008, 4, 42]. The scaling is not observed if the average dynamics of the film is inspected. Our results suggest that the solidification process of each layer may be tracked by knowing solely the vibrational properties of the layer and the bulk.