Re-examining the procedure for simulating polymer T_g using molecular dynamics.

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• The glass transition temperature (T_g) is a critical parameter for polymers, influencing their mechanical and thermal properties.
• Understanding the impact of thermal history on T_g is essential for accurate material characterization and prediction.

Purpose of the Study:

• To investigate the influence of thermal history on the simulated glass transition temperature (T_g) of poly(ethylene oxide).
• To rationalize the standard procedure for simulating polymer T_g using molecular dynamics (MD) and provide guidance for reliable results.

Main Methods:

• Iterative heating and cooling cycles of poly(ethylene oxide) using MD simulations.
• Analysis of volumetric and density data to determine T_g.
• Calculation of time-dependent dynamical T_g from monomer vector reorientation functions.

Main Results:

• Simulated T_g, density, and volumetric expansion coefficients show minimal systematic shifts with thermal history when using volumetric or density data.
• Continuous and stepwise heating/cooling processes yield comparable T_g values.
• Dynamical T_g values derived from reorientation functions exhibit greater differences with increasing observation time.

Conclusions:

• The standard MD simulation procedure for determining polymer T_g is validated.
• Volumetric/density-based T_g is less sensitive to thermal history compared to dynamical T_g.
• Observation time is a crucial factor for dynamical T_g determination in MD simulations.