Theoretical studies on the structure of hydration in perfluorinated lithium salt membranes

Using an ab initio molecular orbital (MO) method, the normal frequencies are calculated for perfluorinated lithium sulfonate and carboxylate membranes by construction of a cluster model, which severs the ion core from the polymer chain, and then analysis of the experimentally observed infrared (IR) spectra is carried out. During the process of dehydration, small sharp peaks at about 3650 and 3700 cm(-1) appeared on the shoulder of the broad band at about 3500 cm(-1). These sharp peaks are identified as the symmetric and asymmetric stretching modes of the free water molecule. Furthermore, by estimation of the evaporation ratio based on thermochemical analysis, it can be assumed that the first hydration shells are naked in some part of the ion core, thereby allowing evaporation to take place within the external hydration shell during the dehydration process.