Voronoi-based analysis linking microscopic void evolution to macroscopic swelling in supercritical CO₂-saturated...

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• Understanding polymer behavior in supercritical fluids is crucial for material processing and applications.
• Ethylene propylene diene monomer (EPDM) rubber is widely used, but its interaction with supercritical carbon dioxide (scCO2) requires detailed investigation.
• Existing models often lack the resolution to connect microscopic changes to macroscopic material properties.

Purpose of the Study:

• To investigate the expansion behavior of EPDM rubber in scCO2 using molecular dynamics (MD) simulations.
• To correlate microscopic pore evolution with macroscopic swelling using Voronoi analysis.
• To elucidate the influence of CO2 density, temperature, and polymer density on EPDM expansion dynamics.

Main Methods:

• Molecular Dynamics (MD) simulations were employed to model EPDM rubber interacting with scCO2.
• Voronoi analysis was utilized to characterize the free volume and pore structure within the polymer matrix.
• Systematic variation of CO2 density, temperature, and polymer density to study their effects.

Main Results:

• Voronoi analysis revealed that high CO2 densities lead to larger, heterogeneous void volumes, explaining localized accumulation and inhibited expansion.
• Elevated temperatures promote larger, uniform pores, increasing CO2 penetration and potential degradation.
• Lower polymer densities facilitate interconnected channels for faster CO2 diffusion, while higher densities create isolated voids restricting diffusion.

Conclusions:

• Voronoi analysis provides critical insights into the mechanisms of EPDM rubber expansion in scCO2.
• The study links microscopic free volume topology to macroscopic deformation, explaining density-dependent expansion and phase transitions.
• Voronoi analysis is a powerful tool for studying multiscale polymer-fluid interactions under scCO2 conditions.