Segmental Dynamics and Ionic Conduction in Poly(vinyl methyl ether)−Lithium Perchlorate Complexes

Abstract

Broadband dielectric spectroscopy was used to investigate the segmental dynamics and ionic conduction in LiClO4/PVME complexes with Li/O from 0.1/100 to 10/100, at temperatures from Tg to approximately Tg + 80 degrees C. Although no microphase separation is observed via DSC, dielectric experiments reveal two segmental relaxations and one localized ion motion process. The fastest process is attributed to relaxations of segments in ion-depleted domains and it slows down with increasing salt content, as does the ion motion. The segmental relaxation of PVME chains in ion-rich domains is even slower than the ion motion process, and about 104 times slower than the fast segmental process in the 0.5/100 complex. This process becomes faster with increasing LiClO4 content, despite the concurrent increase in the bulk Tg. Maximum molar conductivity is obtained in the 2/100 complex and the ionic conduction is about 10-9 S/cm at 30 degrees C. By using the dynamic bond percolation model, it was found that the ions move about 0.8 nm for the 0.5/100 complex at 25 degrees C at the time scale of the slow segmental relaxation, assuming that structural renewal is realized by the latter. This size, together with the strong correlation between the ionic conduction and the slow segmental relaxation, supports the idea that hopping from one segment to another one is probably the effective fundamental step giving rise to macroscopic conduction.