Dynamic mechanical studies of partially ionized and neutralized Nafion polymers

Abstract

The dynamic mechanical properties of Nafion precursor were determined as a function of the degree of conversion to the sodium ionomer, and those of the acid as a function of the degree of conversion to the cesium salt. A run was also made on the barium neutralized material, as well as on a remolded sample of a partly converted precursor. The precursor shows four dispersions which (in order of decreasing temperature) are identified with the glass transition, motions of the ether side chains, CF2 groups in the backbone, and pendant SO2F groups. Four relaxation regions are also seen in the ionomer, which are identified with the glass transition of the ionic regions and of the matrix, as well as with motions of the ether side chains and the backbone CF2 groups. While the polymers in the acid and the salt forms arc compatible, as seen by the gradual movement of the ionic glass transition peak to higher temperatures with increasing degree of neutralization, the salt and the precursor are not compatible. In the barium salt, the ionic glass transition peak occurs at a temperature close to the melting point of the crystalline regions, and most likely contains a contribution from that process also.

Mechanical and Dynamic Mechanical Analysis of Proton‐Conducting Polymers

“…Because of the strong effect of water on the b relaxation, the peak was attributed to a relaxation of the ionic domains, while the a and g relaxations were attributed to the glass transition temperature of the fluorocarbon matrix and short-range motions of the CF2 backbone, respectively. In a later study [24] involving partially ionized and neutralized Nafion, Eisenberg and co-workers [23] reversed the assignments of the a and b relaxations.…”

“…Eisenberg and co-workers [23,24] also studied the effect of ionization and neutralization on the DMA of Nafion polymers. In early studies [24], three relaxation peaks (a > b > g) were observed for the acid form of Nafion in the temperature range from À160 C to about 150 C. Both a and b relaxations were observed to increase by over 100 C when neutralized with alkali salts, while the low-temperature g relaxation remained unaffected by neutralization.…”

Recast Nafion‐117 thin film from water solution

“…The thermal treatment of Nafion in nitrogen, or in air, has shown weight loss curves and mass peaks: this suggests that the presence of oxygen has little effect on the overall stability of Nafion. Other authors, [18,19,20] using dynamic mechanical analysis (DMA) to study the thermal properties of Na + -form Nafion membrane, observed two distinct thermal relaxations at temperatures above 373 K: one was attributed to the glass transition of the matrix, T m , (ca. 413 K), the other to the glass transition of the ionic clusters, T c , (ca.…”

Polybenzimidazole-membrane-based PEM fuel cell in the temperature range of 120–200°C

“…The largest challenge is proton exchange membrane (PEM) materials. Perfluorosulfonic acid (PFSA) membranes (such as Nafion) are the most widely used for conventional PEM fuel cells operated at temperatures below 90 • C. Theoretically, Nafion-based membranes can be operated at temperatures lower than the glass transition value of ∼130 • C [3,4]. However, in the range of 90-130 • C, the structural and chemical degradation of the membrane material * Corresponding author.…”