Theoretical and experimental infrared spectra of hydrated and dehydrated Nafion

Abstract

ABSTRACT The time‐dependent IR spectra during dehydration of fully hydrated Nafion show the reversible disappearance of the 1061 cm −1 and 969 cm −1 concurrent with the emergence of peaks at ∼928 cm −1 and ∼1408 cm −1 . The first pair of group modes is associated with a dissociated exchange group (sulfonate) with a local C 3V symmetry. The C 3V group modes shift with state‐of‐hydration: The 969 cm −1 peak completely vanishes and the 1061 cm −1 is reduced to a small shoulder at 1070 cm −1 at end of dehydration. The C 3 V group modes are replaced by the pair of group modes of an associated exchange group (sulfonic acid) with C 1 local symmetry. The density functional theory normal mode analysis confirms that the sulfonic acid/sulfonate site plays a dominant role in the C 1 and C 3V group modes, respectively. This work clarifies the importance of assigning fluoropolymers peaks as group modes rather than traditional single functional group assignments as is often the case with the ∼1061 cm −1 and ∼969 cm −1 C 3 V group modes. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51 , 1329–1334