Role of electrostatic forces in cluster formation in a dry ionomer

TL;DR

This simulation study explores how electrostatic interactions influence the formation of structures in dry Nafion-like ionomers, revealing morphology dependence on electrostatic component ratios and supporting differing proposed morphologies.

Contribution

It introduces a novel simulation approach to analyze the impact of electrostatic forces on ionomer morphology, highlighting the importance of dipole interactions.

Findings

Morphology depends on electrostatic interaction ratios.

Different morphologies align with Gierke and Gebel models.

Electrostatic parameters significantly influence cluster formation.

Abstract

This simulation study investigates the dependence of the structure of dry Nafion$^{\tiny\textregistered}$-like ionomers on the electrostatic interactions between the components of the molecules. In order to speed equilibration, a procedure was adopted which involved detaching the side chains from the backbone and cutting the backbone into segments, and then reassembling the macromolecule by means of a strong imposed attractive force between the cut ends of the backbone, and between the non-ionic ends of the side chains and the midpoints of the backbone segments. Parameters varied in this study include the dielectric constant, the free volume, side-chain length, and strength of head-group interactions. A series of coarse-grained mesoscale simulations shows the morphlogy to depend sensitively on the ratio of the strength of the dipole-dipole interactions between the side-chain acidic end groups to the strength of the other electrostatic components of the Hamiltonian. Examples of the two differing morphologies proposed by Gierke and by Gebel emerge from our simulations.