No abstract

High ionic conductivities of 10-4 to 10-2 S/cm are achieved with Li+-form perfluorosulfonate ionomers over a wide temperature range by swelling in nonaqueous organic solvents. The dependence of ionic conductivity on temperature, solvent absorption, and membrane equivalent weight is examined for Nafion perfluorinated ionomer membranes. These results are compared with other ionomer membranes, including those having hydrocarbon backbones and weaker acid groups, to correlate ionic conductivity with ionomer structure. The most important factors determining ionic conductivity in membranes swollen with polar nonaqueous solvents, beyond the solvent properties such as viscosity and molecular weight, are the basicity of the fixed anion group and the solvent uptake by the membrane. Ionic conductivity is generally limited by dissociation of the cation from the fixed anion site. Several means for increasing conductivity are demonstrated including the use of cation complexing agents to increase ionic dissociation.

High intensity ultrasound causes the formation of cavitation bubbles which collapse in a manner that, in the presence of a solid surface, form high velocity fluid microjets directed toward the surface. The intense fluid agitation at surfaces in a focused ultrasound field enhances transport of momentum, heat, and mass and influences the behavior and integrity of surface films on metal electrodes. A mathematical model is proposed to determine the reaction and transport between liquid microjets and a reactive solid surface. The conditions were estimated under which oxide depassivation and repassivation occur as a function of ultrasonic intensity, surface film thickness, and fluid microjet surface coverage. The model was based on the concept that cavitation induces sufficient momentum and mass transfer rates (water hammer pressures) at a surface to create oxide film stresses leading to depassivation. The model was used in a companion paper (1) to evaluate experimental data on the corrosion behavior of iron in sulfuric acid.Collapse of cavitation bubbles near solid surfaces causes the formation of local fluid microjets which create intense pressure fields and vigorous local fluid motion. For passive metals immersed in corrosive solutions, such cavitation phenomena can influence passive films as well as depassivation and repassivation events. In Part I of the present investigation, a mathematical model of cavitation-induced effects on passivity and transport processes near surfaces is developed. In Part II (1), experimental data are reported and evaluated with use of the model.

The transport properties of lithiated perfluorinated ionomers imbibed with nonaqueous solvents and solvent mixtures were studied. Polymeric ion‐exchange membranes have potential use in the next generation single‐ion secondary lithium polymer batteries, where the lithiated form of the membrane is used as a polymer electrolyte. The novelty of the approach for lithium battery applications lies in the advantage offered by a transference number of unity, no additional salt (e.g., LiPF6) is needed, and the excellent physical and chemical stability of the fluoropolymers. Ion‐exchange membranes were converted to the Li+ salt form and analyzed for total conversion using FT‐IR. Nonaqueous solvents and solvent mixtures were imbibed into the membranes in a glove box, and the uptake was measured over time. A four‐point probe was used to determine the ionic conductivity based on impedance measurements performed over a frequency range of 10 to 35,000 Hz. Conductivities exceeding 10−4 S/cm with transference numbers of unity were achieved making these ionomeric membranes potentially useful in rechargeable lithium polymer batteries.

Perfluorocarboxylate polymers in the carboxylic methyl ester, potassium salt, and carboxylic acid forms have been analyzed by Fourier transform infrared (FT-IR) transmission and attenuated total reflectance (ATR) spectroscopy. Band assignments were made for most of the dominant peaks. An absorbance band ratio, comparing the 555 cm -1 C-F band to the 982 cm -1 C-O-C ether band, was found to be a direct measure of the equivalent weight of the polymers. In addition, the transition from the methyl ester form to the acid form was determined by examining the 2969 cm -1 methyl ester band versus the broad ∼3200 cm -1 acid band. Quantitative expressions are presented to enable the computation of equivalent weight and acid content based on FT-IR thin-film absorbance measurements.