Influence of Rigidity-Hydration Coupling on Size-Dependent Diffusion in Hydrated Polymer Membranes

Area of Science:

• Materials Science
• Polymer Physics
• Chemical Engineering

Background:

• Selective ion transport in polymer membranes is vital for applications like batteries and separations.
• Understanding the interplay between polymer dynamics, hydration, and penetrant diffusion is crucial but complex.
• Existing models struggle to explain transport in regimes where penetrant size, polymer chain flexibility, and water content are comparable.

Purpose of the Study:

• To systematically investigate penetrant diffusion in hydrated polymer networks.
• To elucidate the mechanistic interplay between polymer rigidity, water content, and penetrant size.
• To develop an improved model for predicting penetrant transport across diverse conditions.

Main Methods:

• Coarse-grained molecular dynamics simulations were employed.
• Simulations covered a wide range of water volume fractions, polymer chain rigidities, and penetrant sizes.
• A modified Yasuda model incorporating polymer rigidity was developed and validated.

Main Results:

• A transition was observed from decoupled diffusion (small penetrants) to coupled diffusion (large penetrants requiring polymer motion).
• Increased polymer rigidity significantly impacts diffusivity, especially at low hydration, deviating from standard scaling laws.
• The extended Yasuda model successfully unified diffusivity data across all simulated conditions.

Conclusions:

• Polymer rigidity is a key tunable parameter governing penetrant diffusion in hydrated polymer matrices.
• The developed model provides a unified framework for understanding size-dependent transport in ion-selective membranes.
• Findings offer insights for designing advanced polymer membranes with tailored transport properties.