Nanochannels and nanodroplets in polymer membranes controlling ionic transport

TL;DR

This paper explores how nanostructures like water droplets and channels within polymer membranes influence ionic transport, emphasizing the importance of molecular details for optimizing membrane selectivity.

Contribution

It provides new insights from computer simulations on how water cluster structures affect ionic diffusion and permeability in low water uptake polymer membranes.

Findings

Water cluster structure significantly impacts ion diffusion.

Water droplet interface potentials influence transport mechanisms.

Transient water channels enable hopping diffusion.

Abstract

Polymer materials with low water uptake exhibit a highly heterogeneous interior, characterized by water clusters in the form of nanodroplets and nanochannels. Here, based on our recent insights from computer simulations, we argue that water cluster structure has large implications for ionic transport and selective permeability in polymer membranes. Importantly, we demonstrate that the two key quantities for transport, the ion diffusion and the solvation free energy inside the polymer, are extremely sensitive to molecular details of the water clusters. In particular, we highlight the significance of water droplet interface potentials and the nature of hopping diffusion through transient water channels. These mechanisms can be harvested and fine-tuned to optimize selectivity in ionic transport in a wide range of applications.