Modeling the slow Arrhenius process (SAP) in polymers

Area of Science:

• Materials Science
• Polymer Physics
• Statistical Mechanics

Background:

• Amorphous polymers display complex relaxation dynamics, including structural α-relaxation and faster secondary relaxations.
• A recently identified slow Arrhenius process (SAP) below the α-relaxation has an unclear microscopic origin despite its Arrhenius temperature dependence.

Purpose of the Study:

• To extend the two-state, two-timescale (TS2) theory to encompass both α-relaxation and the slow Arrhenius process (SAP).
• To propose a unified theoretical framework for understanding polymer relaxation dynamics.

Main Methods:

• Extension of the two-state, two-timescale (TS2) theory.
• Modeling dynamically correlated clusters in a coarse-grained fluid.
• Quantitative reproduction of α and SAP data across multiple polymers.

Main Results:

• The extended TS2 theory successfully describes both α-relaxation and SAP within a unified framework.
• The SAP is interpreted as the high-temperature limit of an αβ-like process in dynamically correlated clusters.
• The model quantitatively reproduces experimental data without additional parameters and explains Meyer-Neldel compensation behavior.

Conclusions:

• The proposed theory offers a physically transparent interpretation of cluster-scale relaxation in glass-forming polymers.
• The theory predicts a transition of SAP from Arrhenius to Vogel-Fulcher-Tammann-Hesse-like dynamics at low temperatures.