A Mechanistic Picture for the Slow Arrhenius Process (SAP) in Glass Forming Systems. Part 1: The Collective Small Displacements Model.

This talk is part 1 of a 2 part set. Recent experiments have revealed increasing detail about a route to molecular relaxation, the slow Arrhenius process (SAP), which acts in glassy systems alongside the α-relaxation. Here we propose a mechanistic picture for SAP relaxation, the Collective Small Displacements (CSD) model, wherein local amorphous packing is reshaped by molecular movements that are small compared to the α-modes. The model captures numerous SAP characteristics, including its connection to shear flow, physical aging, and kinetic energy-entropy compensation. In part 1, we cover the model assumptions which lead to a simple temperature dependent rate equation. We show that the CSD model is able to predict the SAP's activation energies a priori, based solely on statistical thermodynamic analysis of material properties. In part 2, we compare to SAP data for multiple systems, demonstrating that the CSD model predictions hew closely to experimental results. The other model parameters are all shown to be reasonably material-independent. Thus the CSD model is able to predict SAP relaxation rates, and SAP-driven equilibration rates (e.g. adsorption) without using any data on the SAP at all.