Broadband Dielectric Spectroscopic Studies of Annealed Nation~? Membranes

摘要

The dynamics of macromolecular motions as coupled to proton migration in annealed Nation~? membranes was explored using broadband dielectric spectroscopy. These fundamental molecular processes are of interest at temperatures above 100℃; in particular, spectral changes were investigated in real-time at 140℃. Loss permittivity vs. frequency spectra of both β and α relaxations showed increased relaxation times with annealing and that water de-sorption was mainly responsible for these behaviors. Spectra were analyzed using the Havriliak-Negami equation and relaxation/conductivity parameters were obtained from equation fitting to experimental data to understand the nature and coupling of conduction and relaxations as annealing progressed in the instrument. A parameter N, reflecting the connectedness of charge hopping pathways, indicated tortuous random pathways. As N decreased with increased annealing time, the conductivity network appears to accumulate more charge traps.