Interaction, structure and tensile property of swollen Nafion® membranes

Impacts of Organic Sorbates on the Ionic Conductivity and Nanostructure of Perfluorinated Sulfonic-Acid Ionomers

“…Alcohols and acetone have been shown to interact with the perfluoroether side chains, partition across the water−fluoropolymer interface, and impact the fluoropolymer matrix. [22][23][24][27][28][29][30]54 The implications of this modified water− fluoropolymer interface on the structure and transport are qualitatively similar to changes incurred by the cation partitioning processes, which alter the ionic character and local environment. 1,30,38,39,55−58 In the case of organic sorbates, however, the extent of these interfacial modulations changes significantly with the sorbate type and polarity, with broad implications for domain-network morphology.…”

“…Alcohols, while interacting more preferably with the fluoropolymer matrix compared to water, are still not able to dissolve PTFE crystallites, so this loss of scattering is likely due to redistribution (i.e., increasing isotropy) of crystallites within the ionomer's amorphous matrix, which is consistent with observations in acetone-swollen Nafion 23 and with matrix plasticization observed in methanol-and isopropanol-swollen Nafion. 24,27,30 Young et al also reported changes to the intercrystalline morphology of Nafion swollen with ethanol, including quenching of the intercrystalline peak at a high sorbate volume fraction. 30 Changes in nanostructure morphology are also clear when comparing the ionomer nano-domain swelling (d saturated /d ref ) to bulk swelling for the different species (Figure 3a).…”

“…These changes likely arise from the affinity of the sorbate for different moieties in the polymer; highly polar water molecules (ε ∼ 80) strongly solvate sulfonic acid moieties but display minimal affinity for perfluoroether side chains, resulting in a strong phase separation and a relatively sharp fluoropolymer–water interface. Alcohols and acetone have been shown to interact with the perfluoroether side chains, partition across the water–fluoropolymer interface, and impact the fluoropolymer matrix. − ,− , The implications of this modified water–fluoropolymer interface on the structure and transport are qualitatively similar to changes incurred by the cation partitioning processes, which alter the ionic character and local environment. ,,,,− In the case of organic sorbates, however, the extent of these interfacial modulations changes significantly with the sorbate type and polarity, with broad implications for domain-network morphology. Increased mixing of the sorbate and fluoropolymer would have the following impacts on ionomer domain structure and conductivity summarized in Figure : (i) reduced phase separation and redistribution of sorbate across the liquid–fluoropolymer interface, (ii) significant changes in the shape and ordering of ionomer domains accompanied by disruption of the domain-network, and (iii) increased penetration of the fluoropolymer into swollen ionomer channels.…”

“…This reveals a clear need to understand structure–property relationships of ion-conducting membranes in the presence of organic chemical species. Previous studies, primarily driven by the need to improve and tune performance in DMFCs, investigated the effects of ethanol and methanol on diffusion and conductivity in Nafion. − A number of studies have probed the ionomer structure using NMR, permeability, FTIR, and X-ray and neutron scattering. − Some studies also investigated and modeled how the interactions between the ion form and alcohol solution influence membrane properties. ,− However, as most of the studies focused on one alcohol or a specific transport property, the understanding of structure–swelling–conductivity relationships with a wider range of sorbates of varying polarities is limited. With the emergence of new technologies employing ionomers in chemically rich environments, it is even more pertinent to elucidate their impact on ionomers’ local environment and transport functionality.…”

Perspective: Morphology and ion transport in ion-containing polymers from multiscale modeling and simulations

“…More recently, experimental results show that the decrease in the polarity of the solvent increases the swelling of the fluoropolymer resulting in low proton mobility. Alkanes do not change the Nafion structure from its dry state due to the minimal interaction with fluoropolymer backbone and ionic groups (Katzenberg et al, 2021;Shi et al, 2021).…”