THE MOLAR CONDUCTIVITY BEHAVIOR IN POLYMER ELECTROLYTES AT LOW-SALT CONCENTRATIONS - A RAMAN-STUDY OF POLY(PROPYLENE GLYCOL) COMPLEXED WITHLICF3SO3

Raman scattering measurements have been carried out on poly(propylene glycol) complexed with LiCF3SO3 salt over a wide salt concentration ra nge, the ether oxygen to alkali metal cation ratios (O:M) ranging from 4820:1 to 12:1. The relative concentrations of solvated anions, anion -cation pairs and ionic aggregates have been calculated from an analys is of the symmetric anion stretch. The degree of association is found to be almost constant in the O:M range 4820:1-40:1 whereafter it incre ases with increasing salt concentration. The results show that the dra matic increase reported for the molar conductivity in the O:M range 10 00:1-40:1 cannot be explained by the redissociation of contact ion pai rs or the formation of conducting triplets. Instead the major contribu tion to the conductivity increase seems to be a concentration dependen t enhancement of the ionic mobility. A percolation based ionic hopping process involving exchange between ions in pairs and dissolved ions, either free or coordinated to ether oxygen sites, is advanced as a pos sible microscopic mechanism.