Modeling the Slow Arrhenius Process (SAP) in Polymers

TL;DR

This paper extends a theoretical model to unify the description of both the primary alpha relaxation and the slow Arrhenius process in polymers, providing insights into their microscopic origins and temperature-dependent behaviors.

Contribution

The authors develop a unified two-state, two-timescale theory that quantitatively models both alpha and SAP relaxations in polymers without extra parameters.

Findings

The model accurately reproduces experimental relaxation data across multiple polymers.

It explains the Meyer-Neldel compensation behavior observed in relaxation processes.

Predicts a transition of SAP from Arrhenius to Vogel-Fulcher-Tammann-Hesse dynamics at low temperatures.

Abstract

Amorphous glass-forming polymers exhibit multiple relaxation processes, including the structural {\alpha}-relaxation associated with the glass transition and faster secondary relaxations that typically follow Arrhenius behavior. Recently, a distinct slow Arrhenius process (SAP) has been observed at frequencies well below the {\alpha}-process. Although Arrhenian in its temperature dependence, the SAP involves much longer relaxation times and its microscopic origin remains unclear. Here, we extend the two-state, two-timescale (TS2) theory to describe both the {\alpha}-relaxation and the SAP within a unified framework. We propose that the SAP represents the high-temperature limit of an {\alpha}-like process in a coarse-grained fluid of dynamically correlated clusters. With renormalized interaction energies and coordination parameters, the same model quantitatively reproduces both {\alpha} and SAP data across multiple polymers without additional adjustable parameters and explains the observed Meyer-Neldel compensation behavior. The theory further predicts that the SAP should deviate from Arrhenius behavior at sufficiently low temperatures, transitioning to Vogel-Fulcher-Tammann-Hesse-like dynamics, thereby offering a physically transparent interpretation of cluster-scale relaxation in glass-forming polymers.