X-Ray Beam Damage of Nafion (perfluorosulfonate ionomer)

XPS spectra were obtained from a Nafion (perfluorosulfonate ionomer) membrane over a period of 15 h in order to measure the effects of x-ray beam exposure on the Nafion surface. This polymer has an aliphatic fluorocarbon backbone, fluoroalkoxy side chains, and sulfonic acid endgroups. Under the conditions used, 10% each of the S 2p, perfluoroether O 1s, and F 1s intensities are lost in 23, 98, and 656 min, respectively. The data also show the sulfonate O 1s loses intensity faster than the perfluoroether O 1s. This suggests that the perfluorosulfonate side chain, particularly the sulfonate endgroup, is susceptible to x-ray damage. In contrast, the perfluoroalkyl backbone of the Nafion is relatively immune from volatilization, although some bond-breaking and rearrangement may be occurring.