Inherent Structure Energy is a Good Indicator of Molecular Mobility in Glasses

TL;DR

This study demonstrates that inherent structure energy accurately reflects local molecular mobility in glasses, showing vapor-deposited glasses are more stable and that energy measures align with dynamic stability.

Contribution

The paper establishes inherent structure energy as a reliable indicator of molecular mobility and stability in glasses, linking energy and dynamics across different preparation methods.

Findings

Vapor-deposited glasses exhibit slower dynamics than liquid-cooled glasses.

Inherent structure energy correlates with local molecular mobility.

Similar stability behaviors are observed in aged and slow-cooled glasses with the same inherent structure energy.

Abstract

Glasses produced via physical vapor deposition can display greater kinetic stability and lower enthalpy than glasses prepared by liquid cooling. While the reduced enthalpy has often been used as a measure of the stability, it is not obvious whether dynamic measures of stability provide the same view. Here, we study dynamics in vapor-deposited and liquid-cooled glass films using molecular simulations of a bead-spring polymer model as well as a Lennard-Jones binary mixture in two and three dimensions. We confirm that the dynamics in vapor-deposited glasses is indeed slower than in ordinary glasses. We further show that the inherent structure energy is a good reporter of local dynamics, and that aged systems and glasses prepared by cooling at progressively slower rates exhibit the same behavior as vapor-deposited materials when they both have the same inherent structure energy. These findings suggest that the stability inferred from measurements of the energy is also manifested in dynamic observables, and they strengthen the view that vapor deposition processes provide an effective strategy for creation of stable glasses.