Investigating the influence of different thermodynamic paths on the structural relaxation in a glass forming polymer melt

TL;DR

This study uses Molecular Dynamics simulations to explore how different thermodynamic paths affect the structural relaxation in a glass-forming polymer melt, testing predictions of mode coupling theory in the pressure-temperature plane.

Contribution

It investigates the influence of thermodynamic paths on the glass transition and confirms path independence of critical temperature and exponent in the MCT framework.

Findings

Critical line of MCT mapped in (p,T)-plane.

Critical temperature and gamma are path-independent.

Simulation results support MCT predictions.

Abstract

We present results from Molecular Dynamics simulations of the thermal glass transition in a dense polymer melt. In previous work we compared the simulation data with the idealized version of mode coupling theory (MCT) and found that the theory provides a good description of the dynamics above the critical temperature. In order to investigate the influence of different thermodynamic paths on the structural relaxation (alpha-process), we performed simulations for three different pressures and are thus able to give a sketch of the critical line of MCT in the pressure-temperature-plane [(p,T)-plane], where, according to the idealised version of MCT, an ergodic-nonergodic transition should occur. Furthermore, by cooling our system along two different paths (an isobar and an isochor), with the same impact point on the critical line, we demonstrate that neither the critical temperature nor the exponent gamma depend on the chosen path.