A Monte Carlo simulation of tracer diffusion in amorphous polymers.

Area of Science:

• Polymer Science
• Materials Science
• Statistical Mechanics

Background:

• Tracer diffusion in amorphous polymers is crucial for technological applications.
• Understanding the decoupling of viscosity and diffusion coefficients into a fractional relationship is challenging.

Purpose of the Study:

• To investigate the fractional exponent's impact on tracer diffusion coefficients in polymers near the glass transition.
• To develop a simulation framework linking tracer diffusion to polymer dynamics.

Main Methods:

• Employed a 3D Monte Carlo simulation framework.
• Utilized a continuous-time random walk model for tracer diffusion.
• Computed waiting time distributions based on polymer rotational correlation times.

Main Results:

• Established a relationship where the fractional exponent links tracer waiting time to polymer rotational time.
• Achieved reasonable agreement with experimental diffusivities using a fractional exponent based on molar volumes.
• Observed normal Brownian dynamics for tracer diffusion above the glass transition temperature.

Conclusions:

• The proposed method effectively connects microscopic dynamics (rotational times) to macroscopic transport (diffusion).
• The fractional exponent plays a key role in describing tracer diffusion in supercooled polymers.
• Simulation results align with experimental data, validating the approach.