Dielectric and conductivity relaxation in poly(propylene glycol)–lithium triflate complexes

The electric modulus representation is used to display conductivity and dielectric relaxation occurring in poly(propylene glycol)-4000 (PPG) complexed with LiCF3SO3, as the ether oxygen to lithium (O:Li) ratio is varied from 300:1 to 12:1. The frequency range covered is 10 to 107 Hz. Results are obtained for temperatures above the glass transition temperature appropriate for each PPG–LiCF3SO3 complex. For O:M=300:1, the conductivity peak and the α and α′ relaxation are clearly resolved. As the concentration is increased, there is a coupling between the structural and the conductivity relaxations; the various peaks begin to overlap. The coupling is greatest for an O:Li ratio in the range 30:1 to 12:1, where the highest conductivity is measured. Below room temperature, the 30:1 complex has the highest conductivity, above room temperature the 12:1 complex has the highest. At any particular temperature there is a concentration above which the conductivity drops. This drop is due to reduced ion mobility resulting from a dramatic increase in viscosity to values above ∼100 poise.