Fluorescence spectroscopic probing of two distinctive microenvironments in perfluorinated ionomer membranes

Ethidium bromide was used as fluorescent molecular probe in the understanding of structural properties of Nafion, Dow Chemical, and sulfonimide ionomer membranes. The fluorescence lifetime results show that the probe is located in the interfacial region of the membrane structure, and that the interfacial region is inhomogeneous, consisting of two distinct subsections of different hydrophilicities. The ionomer membranes under consideration have similar structural properties with respect to the ethidium cation probing, despite the fact that their corresponding ionomers have different molecular structures. The fluorescence Lifetime results also show that there are considerable mobilities throughout the interfacial region, which allow diffusional quenching processes. Finally, results of effects of hydrothermally stressing Nafion membrane at elevated temperatures on structural properties of the membrane are discussed. (C) 1999 Elsevier Science S.A. All rights reserved.