DEHYDRATION OF PROTONATED NAFION(R) COATINGS INDUCED BY CATION-EXCHANGE AND MONITORED BY QUARTZ-CRYSTAL MICROGRAVIMETRY

A quartz crystal microbalance was employed to monitor the changes in m ass of thin protonated Nafion(R) coatings during the replacement of th e protons by other cations. In almost every case the mass of the coati ngs decreased during the cation exchange, despite the replacement of t he protons in the coatings with much more massive cations. The expulsi on of water from the coatings, induced by the cation exchange, was res ponsible for the decreases in mass. With simple aqua cations the quant ities of water expelled per cation exchanged were relatively small. Ho wever, for multiply charged hexaammine and 2,2'-bipyridine complexes a s many as 50 water molecules were shown to be ejected from the coating s for each incorporated cation. Data for the cation exchange of 18 cat ions are presented and some possible reasons for the accompanying dehy dration of the coatings are suggested.