Water diffusion within hydrated model grafted polymeric membranes with bimodal side chain length distributions

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• Amphiphilic polymers are crucial for membrane applications.
• Controlling pore morphology and solvent diffusion is key for membrane performance.
• Bimodal side chain distributions offer a tunable approach to membrane design.

Purpose of the Study:

• To investigate the influence of bimodal side chain length distributions on polymeric membrane pore morphology.
• To predict the effect of these distributions on solvent (water) diffusion within the membranes.
• To identify design parameters for optimizing solvent and proton diffusion in membranes.

Main Methods:

• Constructed seven polymeric architectures with varying short (p) and long (q) hydrophobic side chains, end-linked with hydrophilic fragments.
• Utilized dissipative particle dynamics (DPD) to calculate pore morphologies at a 0.16 water volume fraction.
• Employed tracer diffusion calculations and analyzed water bead motion from 140 snapshots to determine diffusion constants.

Main Results:

• Diffusion constants decreased as the difference between side chain lengths (q - p) increased.
• The distance between pores also decreased with increasing (q - p).
• A linear relationship was observed between diffusion constants and the average number of bonds between hydrophobic and hydrophilic fragments, 〈N(bond)〉.

Conclusions:

• Bimodal side chain length distribution significantly affects membrane pore structure and solvent diffusion.
• The average number of bonds 〈N(bond)〉 serves as a valuable design parameter for tuning membrane properties.
• This research provides insights for developing membranes with controlled percolation thresholds for efficient solvent and proton transport.