Fluorescence spectroscopic probing of two distinctive microenvironments inperfluorinated ionomer membranes

Ethidium bromide was used as fluorescent molecular probe in the understandi ng of structural properties of Nafion, Dow Chemical, and sulfonimide ionome r membranes. The fluorescence lifetime results show that the probe is locat ed in the interfacial region of the membrane structure, and that the interf acial region is inhomogeneous, consisting of two distinct subsections of di fferent hydrophilicities. The ionomer membranes under consideration have si milar structural properties with respect to the ethidium cation probing, de spite the fact that their corresponding ionomers have different molecular s tructures. The fluorescence Lifetime results also show that there are consi derable mobilities throughout the interfacial region, which allow diffusion al quenching processes. Finally, results of effects of hydrothermally stres sing Nafion membrane at elevated temperatures on structural properties of t he membrane are discussed. (C) 1999 Elsevier Science S.A. All rights reserv ed.