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Self-motion in glass-forming polymers: a molecular dynamics study
1Department of Applied Physics, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
Summary
Molecular dynamics simulations validate mode-coupling theory (MCT) for polymer melts. The study confirms MCT
Area of Science:
- Polymer Physics
- Computational Materials Science
- Statistical Mechanics
Background:
- Mode-coupling theory (MCT) provides a theoretical framework for understanding the dynamics of supercooled liquids.
- Its applicability to realistic polymer melts requires rigorous validation through computational methods.
Purpose of the Study:
- To investigate the validity of mode-coupling theory (MCT) for undercooled polymer melts.
- To analyze polymer dynamics, including diffusion and relaxation processes, using molecular dynamics simulations.
Main Methods:
- Performing molecular dynamics simulations of an undercooled polymer melt.
- Computing mean square displacements of chain segments to determine diffusion constants.
- Analyzing the incoherent intermediate scattering function and relaxation times.
Main Results:
- Diffusion constants exhibit power-law behavior with temperature, consistent with MCT predictions.
- Incoherent scattering functions obey the second scaling law of MCT.
- Alpha-relaxation times follow the same power law as the diffusion constant (gamma=2.9).
- Beta-relaxation regime is accurately described by Von Schweidler relaxation at long times.
Conclusions:
- Molecular dynamics simulations support the validity of mode-coupling theory for realistic polymer melts.
- The study quantifies key parameters (a=0.27, b=0.46) governing beta-relaxation.
- No critical decay was observed in the short-time beta-relaxation regime.