The presented work comprises a computational study of self-assembly in dilute solution of Nafion-type perfluorosulfonic acid (PFSA) ionomers. We employ coarse-grained molecular dynamics (CGMD) to investigate the formation of ionomer bundles [1] and study the assembly of ionomer bundles into a bundle network upon increasing ionomer concentration. Formation of this supramolecular network is experimentally indicated by a markedly increased viscosity [2]. Evolution of a gel-like structure in the aqueous solutions also studied experimentally by Cirkel et al. [3] and Rubatat et al. [4], revealing more details about transport properties, stability, and water sorption properties of the network structure of interconnected ionomer bundles in Nafion membranes. Simulation of the interconnected, gel-like ionomer state provides opportunities to scrutinize different proposed structural models of ionomer membranes and assess changes in bundle size and network connectivity as functions of backbone hydrophobicity, side chain density, counterion valence, and strength of electrostatic interaction between anionic head groups at ionomer sidechains.

References

[1] M. Ghelichi, K. Malek and M. Eikerling, Ionomer Self-Assembly in Dilute Solution Studied by Coarse-Grained Molecular Dynamics, Macromolecules 49, 1479-1489 (2016).

[2] Private communication.

[3] Peter A. Cirkel, Tatsuhiro Okada, A Comparison of Mechanical and Electrical Percolation during the Gelling of Nafion Solutions, Macromolecules 33, 4921-4925 (2000).

[4] L. Rubatat, G. Gebel, O. Diat, Fibrillar Structure of Nafion: Matching Fourier and Real Space Studies of Corresponding Films and Solutions, Macromolecules 37, 77727783 (2004).