Elucidating the solvent-modulated self-assembly nanostructures of high ion exchange capacity short-side-chain perfluorosulfonic acid dispersions

Abstract

The self-assembly behavior of short-side-chain perfluorosulfonic acid (SSC-PFSA) dispersions plays a pivotal role in governing the morphology and performance of proton exchange membranes (PEMs). We explored solvent-modulated structural transitions of SSC-PFSA dispersions using combinatory characterization techniques. It is seen that in high-dielectric environment (25 wt% ethanol), the SSC-PFSA chain adopts rigid rod-like assemblies with locally ordered alignment due to electrostatic repulsion and surface polarization. Lowering the dielectric constant (50 wt% ethanol) induces a semi-flexible configuration with approximately 20 % axial compression, and dispersing heterogeneity is observed due to inter-particle association. Upon reaching 75 wt% ethanol conditions, the rod-like assembly is elongated, loosened, and more disordered. The solvent environment plays an important role in determining the dispersion heterogeneity. More ethanol content lowers the dielectric constant, which reduces acidic dissociation and leads to localized assembly association. This work elucidates a fundamental understanding of the dynamic interplay between backbone solubility and electrostatic interactions in governing the PFSA assembly under different solvent environment. These detailed multi-length-scale nanostructures are key in determining the morphology and performance of PEM, which needs to clearly investigated before PEM fabrication.