Morphology and proton diffusion in a coarse-grained model of sulfonated poly(phenylenes)

Area of Science:

• Computational materials science
• Polymer physics
• Proton transport mechanisms

Background:

• Sulfonated Diels-Alder poly(phenylene) (SDAPP) polymers are crucial for fuel cell membranes.
• Accurate simulation of their complex nanostructure and ion transport is challenging.
• Previous models often lack detailed proton hopping mechanisms and accurate parameterization.

Purpose of the Study:

• To modify a coarse-grained dissipative particle dynamics (DPD) model for simulating SDAPP polymers.
• To incorporate a proton-hopping mechanism analogous to the Grotthuss mechanism.
• To investigate the relationship between polymer morphology, sulfonation, hydration, and proton transport.

Main Methods:

• Adapted a DPD model previously used for Nafion to simulate SDAPP.
• Derived intramolecular parameters using atomistic molecular dynamics (MD) and iterative Boltzmann inversion.
• Simulated polymer radii of gyration, domain morphologies, cluster distributions, and diffusion constants.

Main Results:

• DPD simulations accurately reproduced polymer radii of gyration, domain morphologies, and cluster distributions compared to atomistic MD.
• Predicted nanophase separation into hydrophobic and hydrophilic domains, with percolation at high sulfonation/hydration.
• Observed increased proton and water diffusion constants with higher sulfonation and hydration, consistent with experiments.

Conclusions:

• The modified DPD model effectively simulates SDAPP polymer behavior and proton transport.
• Proton hopping (Grotthuss mechanism) becomes significant with increased sulfonation and hydration.
• Morphology, specifically percolated hydrophilic domains, plays a critical role in enhancing proton transport.