Proton Dissociation of Sulfonated Polysulfones: Influence of Molecular Structure and Conformation

Abstract

The counterion condensation behavior of proton conducting sulfonated polysulfones has been investigated by combining electrophoretic NMR, pulsed magnetic field gradient NMR, and conductivity measurements on monomeric and polymeric samples with concentrations of ionic groups in the range where dissociation is not complete (IEC = 4.55–7.04 mequiv g–1). In this regime, counterion condensation is shown to critically depend on details of the molecular structure, and all atom molecular dynamics (MD) simulations reveal the formation of well-defined ionic aggregates (e.g., triple ions). The corresponding global minima of the free energy are suggested to be the result of a delicate balance of the energetics involved in conformational changes, formation of ionic aggregates, and solvation. This goes beyond Manning’s counterion condensation theory and has important implications for the development of membranes with high ionic conductivity as needed for many electrochemical applications such as fuel cells and batteries.

Configuring Anion‐Exchange Membranes for High Conductivity and Alkaline Stability by Using Cationic Polymers with Tailored Side Chains

“…To facilitate phase separation, QA groups have been highly concentrated to segments in statistical and block copolymers . However, this strategy may lead to limitations in ion‐dissociation, and thus conductivity, caused by the close proximity of the ions in the polymer structure …”

Thermal stability of end‐capped and linear sulfonated polyimides, sulfonated polystyrene, and Nafion 117

“…showed that an increase in the IEC (decreasing the average separation distance of sulfonic acid groups) leads to improved proton conductivity. However, this improvement is limited to how close the sulfonic acid groups are to each other to conform to a stable triple ion aggregate (Figure ) thereby lowering conductivity and leading to a minima in free energy (Δ F ) …”

Surface adsorption of sulfonated poly(phenylene sulfone)/C14TAB mixtures and its correlation with foam film stability

“…23 Dissipative particle dynamics (DPD) simulations have shown that the sPSO 2 -220's polyelectrolyte backbone is significantly stiffer as for example the polyethylene backbones of PAMPS or PSS. 24,25 Furthermore, due to the electron withdrawing sulfonyl group (-SO 2 -) the sulfonate group is especially acidic for sPSO 2 -220, which leads to high dissociation degrees of 54-61%, 26,27 in comparison to a dissociation degree of 33-38% for PSS or PAMPS. 28,29 C 14 TAB was chosen as surfactant, as it is the shortest surfactant in the C n TAB series that forms stable films on its own.…”

“…Therefore, the composition, the homogeneity and the structure of the film will be investigated in a further publication using neutron reflectometry (NR). Secondly, the higher dissociation degree of sPSO 2 -220 as of PAMPS, 27 leads to higher ionic strength, which in turn leads to higher surface potentials. The difference in surface potential C 0 also helps to explain the higher foam film stability of sPSO 2 -220/C 14 TAB mixtures in comparison to PAMPS/C 14 TAB mixtures, as higher surface potential leads to more stable foam films.…”