Diffusion Coefficients of Variable-Size Amphiphilic Additives in a Glass-Forming Polyethylene Matrix.

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• Diffusion of additives in polymers is crucial for tailoring composite properties.
• Predicting additive diffusion behavior can reduce experimental costs and time.

Purpose of the Study:

• To estimate self-diffusion coefficients (D) of additives in polyethylene (PE) matrices using molecular dynamics simulations.
• To investigate the influence of PE matrix properties and temperature on additive diffusion mechanisms.

Main Methods:

• Microsecond time-scale molecular dynamics simulations utilizing the MARTINI force field.
• Characterization of PE matrix properties, including glass transition temperature (Tg).
• Analysis of diffusion coefficients' dependence on additive molecular mass and temperature.

Main Results:

• Diffusion coefficients are significantly influenced by the PE matrix's glass-forming properties (Tg = 256-260 K).
• Observed Rouse-like diffusion at high temperatures, deviating within the PE metastability region.
• Diffusion coefficients showed insensitivity to the polar head of similar-sized additives.
• Temperature-dependent diffusion followed Arrhenius behavior at high temperatures and super-Arrhenius trends at lower temperatures, explained by energy landscapes.

Conclusions:

• Polymer matrix mobility critically impacts solute self-diffusion.
• Established a time-equivalence between coarse-grained (CG) and all-atom simulations for large additives in PE at high temperatures.
• The study provides a conceptual framework for understanding super-Arrhenius diffusion behavior in polymer matrices.