On the diffusivity of ring polymers.

Area of Science:

• Polymer Physics
• Materials Science
• Computational Chemistry

Background:

• Understanding polymer dynamics is crucial for materials science.
• The relationship between polymer size and diffusion is complex.
• Previous models struggled to fully capture the behavior of ring polymer melts.

Purpose of the Study:

• To apply a free volume theory to explain the diffusion crossover in ring polyethylene (PE) melts.
• To compare theoretical predictions with simulation data for polymer diffusion.
• To investigate the size dependence of center-of-mass diffusion coefficients (Dcm).

Main Methods:

• Utilized a free volume theory framework.
• Employed polymer reference interaction site model (PRISM) theory for parameter determination.
• Incorporated molecular dynamics (MD) simulation data for parameter validation and temperature dependence analysis.
• Analyzed the crossover in Dcm ~ N scaling at Nc ≈ 100.

Main Results:

• The free volume theory successfully described the crossover in Dcm scaling from Dcm ~ N-1.03±0.15 to Dcm ~ N-1.88±0.14 at Nc ≈ 100.
• PRISM theory provided a computationally efficient method for parameter estimation.
• MD simulations offered higher accuracy, especially for temperature-dependent diffusion, by including explicit potentials.

Conclusions:

• The free volume theory, parameterized by either PRISM or MD, accurately models the diffusion dynamics of ring PE melts across different size regimes.
• Both theoretical and simulation approaches confirm the observed crossover in diffusion behavior.
• This work provides a robust theoretical framework for understanding ring polymer dynamics.