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String-like Cooperative Motion Explains the Influence of Pressure on Relaxation in a Model Glass-Forming Polymer Melt

Published

Author(s)

Jack F. Douglas, Wensheng Xu, Karl Freed

Abstract

Numerous experiments reveal that the dynamics of glass-forming polymer melts is profoundly influenced by the application of pressure, but a fundamental microscopic understanding of these observations remains incomplete. Here, we explore structural relaxation of a model glass-forming polymer melt over a wide range of pressures (P) by molecular dynamics simulations. In accord with experiments for non-associating polymer melts and the generalized entropy theory, our simulation data for the P de- pendence of the structural relaxation time can be described by a pressure analog of the Vogel-Fulcher-Tammann equation, and the determined characteristic temperatures of glass-formation increase with P, while the fragility decreases with P. Further, we demonstrate that relaxation data for various P can quantitatively be described by the string model of glass-formation, where the enthalpy and entropy of activation are found to be proportional, an effect that is also observed in polymer nanocomposites and thin supported polymer films and thus expected to apply to diverse materials under applied fields.
Citation
ACS Macro Letters

Keywords

polymer glass-formation, pressure, fragility, activation energy, string model

Citation

Douglas, J. , Xu, W. and Freed, K. (2016), String-like Cooperative Motion Explains the Influence of Pressure on Relaxation in a Model Glass-Forming Polymer Melt, ACS Macro Letters (Accessed April 17, 2024)
Created December 14, 2016, Updated June 2, 2021