Multifrequency electron spin resonance and electron nuclear double resonance studies of metal cations in perfluorinated ionomers

✍ Scribed by Shulamith Schlick1; M.G. Alonso-Amigo; Janusz Bednarek

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 642 KB
• Volume: 72
• Category: Article
• ISSN: 0927-7757
• DOI: 10.1016/0927-7757(93)80445-k

✦ Synopsis

Multifrequency electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) have been applied to the study of cation solvation and to the formation of cation dimers and larger aggregates. The spectra indicated that the paramagnetic cation can be a probe for the process of membrane solvation by one solvent or by a mixture of solvents. The results present conclusive proof for the formation of cation dimers and larger cation aggregates only in perfluorinated ionomers swollen by water. For methanol, dimethylformamide (DMF), and tetrahydrofuran (THF) there is no indication of cation aggregation, even in membranes that have been fully neutralized by cupric ions. Detection of a small amount of cation dimers, and determination by ENDOR of a distance of 8 A between Ti 3 + and fluorine, indicate that the size of the solvent clusters in these solvents is less than about 20 A. A model for the cation dimer is proposed, and appears to explain the increase of the glass transition temperature Tg due to ionic cross-links. An ESR probe for the solvation of ionomer membranes by various solvents has been developed, and has been used to study preferential solvation of Sephadex and silica gel by various solvents.